title: Working memory

text: Oberauer has extended Cowan's model by adding a third component, a more narrow focus of attention that holds only one chunk at a time. The one-element focus is embedded in the four-element focus and serves to select a single chunk for processing. For example, four digits can be held in mind at the same time in Cowan's "focus of attention". When the individual wishes to perform a process on each of these digits—for example, adding the number two to each digit—separate processing is required for each digit since most individuals cannot perform several mathematical processes in parallel. Oberauer's attentional component selects one of the digits for processing and then shifts the attentional focus to the next digit, continuing until all digits have been processed.


title: Working memory

text: Working memory is widely acknowledged as having limited capacity. An early quantification of the capacity limit associated with short-term memory was the "magical number seven" suggested by Miller in 1956. He claimed that the information-processing capacity of young adults is around seven elements, which he called "chunks", regardless of whether the elements are digits, letters, words, or other units. Later research revealed this number depends on the category of chunks used (e.g., span may be around seven for digits, six for letters, and five for words), and even on features of the chunks within a category. For instance, span is lower for long than short words. In general, memory span for verbal contents (digits, letters, words, etc.) depends on the phonological complexity of the content (i.e., the number of phonemes, the number of syllables), and on the lexical status of the contents (whether the contents are words known to the person or not). Several other factors affect a person's measured span, and therefore it is difficult to pin down the capacity of short-term or working memory to a number of chunks. Nonetheless, Cowan proposed that working memory has a capacity of about four chunks in young adults (and fewer in children and old adults).


title: Working memory

text: In the visual domain, some investigations report no fixed capacity limit with respect to the total number of items that can be held in working memory. Instead, the results argue for a limited resource that can be flexibly shared between items retained in memory (see below in Resource theories), with some items in the focus of attention being allocated more resource and recalled with greater precision.


title: Working memory

text: Whereas most adults can repeat about seven digits in correct order, some individuals have shown impressive enlargements of their digit span—up to 80 digits. This feat is possible by extensive training on an encoding strategy by which the digits in a list are grouped (usually in groups of three to five) and these groups are encoded as a single unit (a chunk). For this to succeed, participants must be able to recognize the groups as some known string of digits. One person studied by Ericsson and his colleagues, for example, used an extensive knowledge of racing times from the history of sports in the process of coding chunks: several such chunks could then be combined into a higher-order chunk, forming a hierarchy of chunks. In this way, only some chunks at the highest level of the hierarchy must be retained in working memory, and for retrieval the chunks are unpacked. That is, the chunks in working memory act as retrieval cues that point to the digits they contain. Practicing memory skills such as these does not expand working memory capacity proper: it is the capacity to transfer (and retrieve) information from long-term memory that is improved, according to Ericsson and Kintsch (1995; see also Gobet & Simon, 2000).


title: Working memory

text: Working memory capacity can be tested by a variety of tasks. A commonly used measure is a dual-task paradigm, combining a memory span measure with a concurrent processing task, sometimes referred to as "complex span". Daneman and Carpenter invented the first version of this kind of task, the "reading span", in 1980. Subjects read a number of sentences (usually between two and six) and tried to remember the last word of each sentence. At the end of the list of sentences, they repeated back the words in their correct order. Other tasks that do not have this dual-task nature have also been shown to be good measures of working memory capacity. Whereas Daneman and Carpenter believed that the combination of "storage" (maintenance) and processing is needed to measure working memory capacity, we know now that the capacity of working memory can be measured with short-term memory tasks that have no additional processing component. Conversely, working memory capacity can also be measured with certain processing tasks that don't involve maintenance of information. The question of what features a task must have to qualify as a good measure of working memory capacity is a topic of ongoing research.


title: Working memory

text: Recently, several studies of visual working memory have used delayed response tasks. These use analogue responses in a continuous space, rather than a binary (correct/incorrect) recall method, as often used in visual change detection tasks. Instead of asking participants to report whether a change occurred between the memory and probe array, delayed reproduction tasks require them to reproduce the precise quality of a visual feature, e.g. an object’s location, orientation or colour.


title: Working memory

text: Measures of working-memory capacity are strongly related to performance in other complex cognitive tasks, such as reading comprehension, problem solving, and with measures of intelligence quotient.


title: Working memory

text: Some researchers have argued that working-memory capacity reflects the efficiency of executive functions, most notably the ability to maintain multiple task-relevant representations in the face of distracting irrelevant information; and that such tasks seem to reflect individual differences in the ability to focus and maintain attention, particularly when other events are serving to capture attention. Both working memory and executive functions rely strongly, though not exclusively, on frontal brain areas.


title: Working memory

text: Other researchers have argued that the capacity of working memory is better characterized as the ability to mentally form relations between elements, or to grasp relations in given information. This idea has been advanced, among others, by Graeme Halford, who illustrated it by our limited ability to understand statistical interactions between variables. These authors asked people to compare written statements about the relations between several variables to graphs illustrating the same or a different relation, as in the following sentence: "If the cake is from France, then it has more sugar if it is made with chocolate than if it is made with cream, but if the cake is from Italy, then it has more sugar if it is made with cream than if it is made of chocolate". This statement describes a relation between three variables (country, ingredient, and amount of sugar), which is the maximum most individuals can understand. The capacity limit apparent here is obviously not a memory limit (all relevant information can be seen continuously) but a limit to how many relationships are discerned simultaneously.


title: Working memory

text: There are several hypotheses about the nature of the capacity limit. One is that a limited pool of cognitive resources is needed to keep representations active and thereby available for processing, and for carrying out processes. Another hypothesis is that memory traces in working memory decay within a few seconds, unless refreshed through rehearsal, and because the speed of rehearsal is limited, we can maintain only a limited amount of information. Yet another idea is that representations held in working memory interfere with each other.


title: Working memory

text: The assumption that the contents of short-term or working memory decay over time, unless decay is prevented by rehearsal, goes back to the early days of experimental research on short-term memory. It is also an important assumption in the multi-component theory of working memory. The most elaborate decay-based theory of working memory to date is the "time-based resource sharing model". This theory assumes that representations in working memory decay unless they are refreshed. Refreshing them requires an attentional mechanism that is also needed for any concurrent processing task. When there are small time intervals in which the processing task does not require attention, this time can be used to refresh memory traces. The theory therefore predicts that the amount of forgetting depends on the temporal density of attentional demands of the processing task—this density is called "cognitive load". The cognitive load depends on two variables, the rate at which the processing task requires individual steps to be carried out, and the duration of each step. For example, if the processing task consists of adding digits, then having to add another digit every half second places a higher cognitive load on the system than having to add another digit every two seconds. In a series of experiments, Barrouillet and colleagues have shown that memory for lists of letters depends neither on the number of processing steps nor the total time of processing but on cognitive load.


title: Working memory

text: Resource theories assume that the capacity of working memory is a limited resource that must be shared between all representations that need to be maintained in working memory simultaneously. Some resource theorists also assume that maintenance and concurrent processing share the same resource; this can explain why maintenance is typically impaired by a concurrent processing demand. Resource theories have been very successful in explaining data from tests of working memory for simple visual features, such as colors or orientations of bars. An ongoing debate is whether the resource is a continuous quantity that can be subdivided among any number of items in working memory, or whether it consists of a small number of discrete "slots", each of which can be assigned to one memory item, so that only a limited number of about 3 items can be maintained in working memory at all.


title: Working memory

text: Several forms of interference have been discussed by theorists. One of the oldest ideas is that new items simply replace older ones in working memory. Another form of interference is retrieval competition. For example, when the task is to remember a list of 7 words in their order, we need to start recall with the first word. While trying to retrieve the first word, the second word, which is represented in proximity, is accidentally retrieved as well, and the two compete for being recalled. Errors in serial recall tasks are often confusions of neighboring items on a memory list (so-called transpositions), showing that retrieval competition plays a role in limiting our ability to recall lists in order, and probably also in other working memory tasks. A third form of interference is the distortion of representations by superposition: When multiple representations are added on top of each other, each of them is blurred by the presence of all the others. A fourth form of interference assumed by some authors is feature overwriting. The idea is that each word, digit, or other item in working memory is represented as a bundle of features, and when two items share some features, one of them steals the features from the other. The more items are held in working memory, and the more their features overlap, the more each of them will be degraded by the loss of some features.


title: Working memory

text: None of these hypotheses can explain the experimental data entirely. The resource hypothesis, for example, was meant to explain the trade-off between maintenance and processing: The more information must be maintained in working memory, the slower and more error prone concurrent processes become, and with a higher demand on concurrent processing memory suffers. This trade-off has been investigated by tasks like the reading-span task described above. It has been found that the amount of trade-off depends on the similarity of the information to be remembered and the information to be processed. For example, remembering numbers while processing spatial information, or remembering spatial information while processing numbers, impair each other much less than when material of the same kind must be remembered and processed. Also, remembering words and processing digits, or remembering digits and processing words, is easier than remembering and processing materials of the same category. These findings are also difficult to explain for the decay hypothesis, because decay of memory representations should depend only on how long the processing task delays rehearsal or recall, not on the content of the processing task. A further problem for the decay hypothesis comes from experiments in which the recall of a list of letters was delayed, either by instructing participants to recall at a slower pace, or by instructing them to say an irrelevant word once or three times in between recall of each letter. Delaying recall had virtually no effect on recall accuracy. The interference theory seems to fare best with explaining why the similarity between memory contents and the contents of concurrent processing tasks affects how much they impair each other. More similar materials are more likely to be confused, leading to retrieval competition.


title: Working memory

text: Measures of performance on tests of working memory increase continuously between early childhood and adolescence, while the structure of correlations between different tests remains largely constant. Starting with work in the Neo-Piagetian tradition, theorists have argued that the growth of working-memory capacity is a major driving force of cognitive development. This hypothesis has received substantial empirical support from studies showing that the capacity of working memory is a strong predictor of cognitive abilities in childhood. Particularly strong evidence for a role of working memory for development comes from a longitudinal study showing that working-memory capacity at one age predicts reasoning ability at a later age. Studies in the Neo-Piagetian tradition have added to this picture by analyzing the complexity of cognitive tasks in terms of the number of items or relations that have to be considered simultaneously for a solution. Across a broad range of tasks, children manage task versions of the same level of complexity at about the same age, consistent with the view that working memory capacity limits the complexity they can handle at a given age. Although neuroscience studies support the notion that children rely on prefrontal cortex for performing various working memory tasks, an fMRI meta-analysis on children compared to adults performing the n back task revealed lack of consistent prefrontal cortex activation in children, while posterior regions including the insular cortex and cerebellum remain intact.


title: Working memory

text: Working memory is among the cognitive functions most sensitive to decline in old age. Several explanations for this decline have been offered. One is the processing speed theory of cognitive aging by Tim Salthouse. Drawing on the finding that cognitive processes generally slow as people grow older, Salthouse argues that slower processing leaves more time for working memory content to decay, thus reducing effective capacity. However, the decline of working memory capacity cannot be entirely attributed to slowing because capacity declines more in old age than speed. Another proposal is the inhibition hypothesis advanced by Lynn Hasher and Rose Zacks. This theory assumes a general deficit in old age in the ability to inhibit irrelevant information. Thus, working memory should tend to be cluttered with irrelevant content that reduces effective capacity for relevant content. The assumption of an inhibition deficit in old age has received much empirical support but, so far, it is not clear whether the decline in inhibitory ability fully explains the decline of working memory capacity. An explanation on the neural level of the decline of working memory and other cognitive functions in old age has been proposed by West. She argues that working memory depends to a large degree on the prefrontal cortex, which deteriorates more than other brain regions as we grow old. Age-related decline in working memory can be briefly reversed using low intensity transcranial stimulation to synchronize rhythms in prefrontal and temporal areas.


title: Working memory

text: Some studies in the effects of training on working memory, including the first by Torkel Klingberg, suggest that working memory in those with ADHD can improve by training. This study found that a period of working memory training increases a range of cognitive abilities and increases IQ test scores. Another study by the same group has shown that, after training, measured brain activity related to working memory increased in the prefrontal cortex, an area that many researchers have associated with working memory functions. One study has shown that working memory training increases the density of prefrontal and parietal dopamine receptors (specifically, DRD1) in test subjects. However, subsequent experiments with the same training program have shown mixed results, with some successfully replicating, and others failing to replicate the beneficial effects of training on cognitive performance.


title: Working memory

text: In another influential study, training with a working memory task (the dual n-back task) improved performance on a fluid intelligence test in healthy young adults. The improvement of fluid intelligence by training with the n-back task was replicated in 2010, but two studies published in 2012 failed to reproduce the effect. The combined evidence from about 30 experimental studies on the effectiveness of working-memory training has been evaluated by several meta-analyses. tr The authors of these meta-analyses disagree in their conclusions as to whether or not working-memory training improves intelligence. Yet these meta-analyses agree that, the more distant the outcome measure, the weaker is the causal link–training working memory almost always yields increases in working memory, often in attention, and sometimes in academic performance, but it is still an outstanding question what exact circumstances differs between cases of successful and unsuccessful transfer of effects.


title: Working memory

text: The first insights into the neuronal and neurotransmitter basis of working memory came from animal research. The work of Jacobsen and Fulton in the 1930s first showed that lesions to the PFC impaired spatial working memory performance in monkeys. The later work of Joaquin Fuster recorded the electrical activity of neurons in the PFC of monkeys while they were doing a delayed matching task. In that task, the monkey sees how the experimenter places a bit of food under one of two identical-looking cups. A shutter is then lowered for a variable delay period, screening off the cups from the monkey's view. After the delay, the shutter opens and the monkey is allowed to retrieve the food from under the cups. Successful retrieval in the first attempt – something the animal can achieve after some training on the task – requires holding the location of the food in memory over the delay period. Fuster found neurons in the PFC that fired mostly during the delay period, suggesting that they were involved in representing the food location while it was invisible. Later research has shown similar delay-active neurons also in the posterior parietal cortex, the thalamus, the caudate, and the globus pallidus. The work of Goldman-Rakic and others showed that principal sulcal, dorsolateral PFC interconnects with all of these brain regions, and that neuronal microcircuits within PFC are able to maintain information in working memory through recurrent excitatory glutamate networks of pyramidal cells that continue to fire throughout the delay period. These circuits are tuned by lateral inhibition from GABAergic interneurons. The neuromodulatory arousal systems markedly alter PFC working memory function; for example, either too little or too much dopamine or norepinephrine impairs PFC network firing and working memory performance.


title: Working memory

text: The research described above on persistent firing of certain neurons in the delay period of working memory tasks shows that the brain has a mechanism of keeping representations active without external input. Keeping representations active, however, is not enough if the task demands maintaining more than one chunk of information. In addition, the components and features of each chunk must be bound together to prevent them from being mixed up. For example, if a red triangle and a green square must be remembered at the same time, one must make sure that "red" is bound to "triangle" and "green" is bound to "square". One way of establishing such bindings is by having the neurons that represent features of the same chunk fire in synchrony, and those that represent features belonging to different chunks fire out of sync. In the example, neurons representing redness would fire in synchrony with neurons representing the triangular shape, but out of sync with those representing the square shape. So far, there is no direct evidence that working memory uses this binding mechanism, and other mechanisms have been proposed as well. It has been speculated that synchronous firing of neurons involved in working memory oscillate with frequencies in the theta band (4 to 8 Hz). Indeed, the power of theta frequency in the EEG increases with working memory load, and oscillations in the theta band measured over different parts of the skull become more coordinated when the person tries to remember the binding between two components of information.


title: Working memory

text: Localization of brain functions in humans has become much easier with the advent of brain imaging methods (PET and fMRI). This research has confirmed that areas in the PFC are involved in working memory functions. During the 1990s much debate has centered on the different functions of the ventrolateral (i.e., lower areas) and the dorsolateral (higher) areas of the PFC. A human lesion study provides additional evidence for the role of the dorsolateral prefrontal cortex in working memory. One view was that the dorsolateral areas are responsible for spatial working memory and the ventrolateral areas for non-spatial working memory. Another view proposed a functional distinction, arguing that ventrolateral areas are mostly involved in pure maintenance of information, whereas dorsolateral areas are more involved in tasks requiring some processing of the memorized material. The debate is not entirely resolved but most of the evidence supports the functional distinction.


title: Working memory

text: Brain imaging has revealed that working memory functions are not limited to the PFC. A review of numerous studies shows areas of activation during working memory tasks scattered over a large part of the cortex. There is a tendency for spatial tasks to recruit more right-hemisphere areas, and for verbal and object working memory to recruit more left-hemisphere areas. The activation during verbal working memory tasks can be broken down into one component reflecting maintenance, in the left posterior parietal cortex, and a component reflecting subvocal rehearsal, in the left frontal cortex (Broca's area, known to be involved in speech production).


title: Working memory

text: There is an emerging consensus that most working memory tasks recruit a network of PFC and parietal areas. A study has shown that during a working memory task the connectivity between these areas increases. Another study has demonstrated that these areas are necessary for working memory, and not simply activated accidentally during working memory tasks, by temporarily blocking them through transcranial magnetic stimulation (TMS), thereby producing an impairment in task performance.


title: Working memory

text: A current debate concerns the function of these brain areas. The PFC has been found to be active in a variety of tasks that require executive functions. This has led some researchers to argue that the role of PFC in working memory is in controlling attention, selecting strategies, and manipulating information in working memory, but not in maintenance of information. The maintenance function is attributed to more posterior areas of the brain, including the parietal cortex. Other authors interpret the activity in parietal cortex as reflecting executive functions, because the same area is also activated in other tasks requiring attention but not memory.


title: Working memory

text: A 2003 meta-analysis of 60 neuroimaging studies found left frontal cortex was involved in low-task demand verbal working memory and right frontal cortex for spatial working memory. Brodmann's areas (BAs) 6, 8, and 9, in the superior frontal cortex was involved when working memory must be continuously updated and when memory for temporal order had to be maintained. Right Brodmann 10 and 47 in the ventral frontal cortex were involved more frequently with demand for manipulation such as dual-task requirements or mental operations, and Brodmann 7 in the posterior parietal cortex was also involved in all types of executive function.


title: Working memory

text: Working memory has been suggested to involve two processes with different neuroanatomical locations in the frontal and parietal lobes. First, a selection operation that retrieves the most relevant item, and second an updating operation that changes the focus of attention made upon it. Updating the attentional focus has been found to involve the transient activation in the caudal superior frontal sulcus and posterior parietal cortex, while increasing demands on selection selectively changes activation in the rostral superior frontal sulcus and posterior cingulate/precuneus.


title: Working memory

text: Articulating the differential function of brain regions involved in working memory is dependent on tasks able to distinguish these functions. Most brain imaging studies of working memory have used recognition tasks such as delayed recognition of one or several stimuli, or the n-back task, in which each new stimulus in a long series must be compared to the one presented n steps back in the series. The advantage of recognition tasks is that they require minimal movement (just pressing one of two keys), making fixation of the head in the scanner easier. Experimental research and research on individual differences in working memory, however, has used largely recall tasks (e.g., the reading span task, see below). It is not clear to what degree recognition and recall tasks reflect the same processes and the same capacity limitations.


title: Working memory

text: Brain imaging studies have been conducted with the reading span task or related tasks. Increased activation during these tasks was found in the PFC and, in several studies, also in the anterior cingulate cortex (ACC). People performing better on the task showed larger increase of activation in these areas, and their activation was correlated more over time, suggesting that their neural activity in these two areas was better coordinated, possibly due to stronger connectivity.


title: Working memory

text: One approach to modeling the neurophysiology and the functioning of working memory is prefrontal cortex basal ganglia working memory (PBWM). In this model, the prefrontal cortex works hand-in-hand with the basal ganglia to accomplish the tasks of working memory. Many studies have shown this to be the case. One used ablation techniques in patients who had had seizures and had damage to the prefrontal cortex and basal ganglia. Researchers found that such damage resulted in decreased capacity to carry out the executive function of working memory. Additional research conducted on patients with brain alterations due to methamphetamine use found that training working memory increases volume in the basal ganglia.


title: Working memory

text: Working memory is impaired by acute and chronic psychological stress. This phenomenon was first discovered in animal studies by Arnsten and colleagues, who have shown that stress-induced catecholamine release in PFC rapidly decreases PFC neuronal firing and impairs working memory performance through feedforward, intracellular signaling pathways. Exposure to chronic stress leads to more profound working memory deficits and additional architectural changes in PFC, including dendritic atrophy and spine loss, which can be prevented by inhibition of protein kinase C signaling. fMRI research has extended this research to humans, and confirms that reduced working memory caused by acute stress links to reduced activation of the PFC, and stress increased levels of catecholamines. Imaging studies of medical students undergoing stressful exams have also shown weakened PFC functional connectivity, consistent with the animal studies. The marked effects of stress on PFC structure and function may help to explain how stress can cause or exacerbate mental illness.


title: Working memory

text: The more stress in one's life, the lower the efficiency of working memory in performing simple cognitive tasks. Students who performed exercises that reduced the intrusion of negative thoughts showed an increase in their working memory capacity. Mood states (positive or negative) can have an influence on the neurotransmitter dopamine, which in turn can affect problem solving.


title: Working memory

text: Excessive alcohol use can result in brain damage which impairs working memory. Alcohol has an effect on the blood-oxygen-level-dependent (BOLD) response. The BOLD response correlates increased blood oxygenation with brain activity, which makes this response a useful tool for measuring neuronal activity. The BOLD response affects regions of the brain such as the basal ganglia and thalamus when performing a working memory task. Adolescents who start drinking at a young age show a decreased BOLD response in these brain regions. Alcohol dependent young women in particular exhibit less of a BOLD response in parietal and frontal cortices when performing a spatial working memory task. Binge drinking, specifically, can also affect one's performance on working memory tasks, particularly visual working memory. Additionally, there seems to be a gender difference in regards to how alcohol affects working memory. While women perform better on verbal working memory tasks after consuming alcohol compared to men, they appear to perform worse on spatial working memory tasks as indicated by less brain activity. Finally, age seems to be an additional factor. Older adults are more susceptible than others to the effects of alcohol on working memory.


title: Working memory

text: Individual differences in working-memory capacity are to some extent heritable; that is, about half of the variation between individuals is related to differences in their genes. The genetic component of variability of working-memory capacity is largely shared with that of fluid intelligence.


title: Working memory

text: Little is known about which genes are related to the functioning of working memory. Within the theoretical framework of the multi-component model, one candidate gene has been proposed, namely ROBO1 for the hypothetical phonological loop component of working memory.


title: Working memory

text: More recently another gene was found regarding working memory. Looking at genetically diverse mice, Gpr12 was found in promoting a protein necessary for working memory. When they took mice that were performing worse on memory tests than their control mouse counterparts and increased their Gpr12 proteins, those mice improved from 50% to 80%. That brought the low performance mice up to level similar to their control counterparts.


title: Working memory

text: Working memory capacity is correlated with learning outcomes in literacy and numeracy. Initial evidence for this relation comes from the correlation between working-memory capacity and reading comprehension, as first observed by Daneman and Carpenter (1980) and confirmed in a later meta-analytic review of several studies. Subsequent work found that working memory performance in primary school children accurately predicted performance in mathematical problem solving. One longitudinal study showed that a child's working memory at 5 years old is a better predictor of academic success than IQ.


title: Working memory

text: A randomized controlled study of 580 children in Germany indicated that working memory training at age six had a significant positive effect in spatial working memory immediately after training, and that the effect gradually transferred to other areas, with significant and meaningful increases in reading comprehension, mathematics (geometry), and IQ (measured by Raven matrices). Additionally, a marked increase in ability to inhibit impulses was detected in the follow up after one year, measured as a higher score in the Go-No Go task. Four years after the treatment, the effects persisted and was captured as a 16 percentage point higher acceptance rate to the academic track (German Gymnasium), as compared to the control group.


title: Working memory

text: In a large-scale screening study, one in ten children in mainstream classrooms were identified with working memory deficits. The majority of them performed very poorly in academic achievements, independent of their IQ. Similarly, working memory deficits have been identified in national curriculum low-achievers as young as seven years of age. Without appropriate intervention, these children lag behind their peers. A recent study of 37 school-age children with significant learning disabilities has shown that working memory capacity at baseline measurement, but not IQ, predicts learning outcomes two years later. This suggests that working memory impairments are associated with low learning outcomes and constitute a high risk factor for educational underachievement for children. In children with learning disabilities such as dyslexia, ADHD, and developmental coordination disorder, a similar pattern is evident.


title: Working memory

text: There is some evidence that optimal working memory performance links to the neural ability to focus attention on task-relevant information and to ignore distractions, and that practice-related improvement in working memory is due to increasing these abilities. One line of research suggests a link between the working memory capacities of a person and their ability to control the orientation of attention to stimuli in the environment. Such control enables people to attend to information important for their current goals, and to ignore goal-irrelevant stimuli that tend to capture their attention due to their sensory saliency (such as an ambulance siren). The direction of attention according to one's goals is assumed to rely on "top-down" signals from the pre-frontal cortex (PFC) that biases processing in posterior cortical areas. Capture of attention by salient stimuli is assumed to be driven by "bottom-up" signals from subcortical structures and the primary sensory cortices. The ability to override "bottom-up" capture of attention differs between individuals, and this difference has been found to correlate with their performance in a working-memory test for visual information. Another study, however, found no correlation between the ability to override attentional capture and measures of more general working-memory capacity.


title: Working memory

text: ADHD: Several authors have proposed that symptoms of ADHD arise from a primary deficit in a specific executive function (EF) domain such as working memory, response inhibition or a more general weakness in executive control. A meta-analytical review cites several studies that found significant lower group results for ADHD in spatial and verbal working memory tasks, and in several other EF tasks. However, the authors concluded that EF weaknesses neither are necessary nor sufficient to cause all cases of ADHD.


title: Working memory

text: Several neurotransmitters, such as dopamine and glutamate may be involved in both ADHD and working memory. Both are associated with the frontal brain, self-direction and self-regulation, but cause–effect have not been confirmed, so it is unclear whether working memory dysfunction leads to ADHD, or ADHD distractibility leads to poor functionality of working memory, or if there is some other connection.


title: Working memory

text: Parkinson's disease: Patients with Parkinson's show signs of a reduced verbal function of working memory. They wanted to find if the reduction is due to a lack of ability to focus on relevant tasks, or a low amount of memory capacity. Twenty-one patients with Parkinson's were tested in comparison to the control group of 28 participants of the same age. The researchers found that both hypotheses were the reason working memory function is reduced which did not fully agree with their hypothesis that it is either one or the other.


title: Working memory

text: Alzheimer's disease: As Alzheimer's disease becomes more serious, less working memory functions. In addition to deficits in episodic memory, Alzheimer’s disease is associated with impairments in visual short-term memory, assessed using delayed reproduction tasks. These investigations point to a deficit in visual feature binding as an important component of the deficit in Alzheimer’s disease. There is one study that focuses on the neural connections and fluidity of working memory in mice brains. Half of the mice were given an injection that mimicked the effects of Alzheimer's, and the other half were not. Then the mice were expected to go through a maze that is a task to test working memory. The study helps answer questions about how Alzheimer's can deteriorate the working memory and ultimately obliterate memory functions.


title: Working memory

text: Huntington's disease: A group of researchers hosted a study that researched the function and connectivity of working memory over a 30-month longitudinal experiment. It found that there were certain places in the brain where most connectivity was decreased in pre-Huntington diseased patients, in comparison to the control group that remained consistently functional.


title: Working memory

text: A recent study by Li and colleagues showed evidence that the same brain regions responsible for working memory are also responsible for how much humans trust those memories. In the past, studies have shown that individuals can evaluate how much they trust their own memories, but how humans can do this was largely unknown. Using spatial memory tests and fMRI scans, they processed where and when the information was being stored and used this data to determine memory errors. They also asked the participants to express how uncertain they were about their memories. With both sets of information, the researchers could conclude that memory and the trust in that memory are stored within the same brain region.


title: 1972 Miami Dolphins season

text: The 1972 Miami Dolphins season was the franchise's seventh season and third in the National Football League (NFL). The team was led by third-year head coach Don Shula and achieved the only perfect season in NFL history. They also led the league in both points scored and fewest points allowed.


title: 1972 Miami Dolphins season

text: Starting quarterback Bob Griese broke his ankle in Week 5, leaving backup Earl Morrall to start the remainder of the regular season, though Griese relieved Morrall in the second half of the AFC Championship Game and started Super Bowl VII. Morrall, a thirty-eight-year-old who spent much of his career backing up stars including Griese, Johnny Unitas, and Bobby Layne, was named MVP in 1968 under Shula when the pair led the Baltimore Colts to the NFL championship. The Dolphins clinched the AFC East title in Week 10 with Morrall at quarterback.


title: 1972 Miami Dolphins season

text: Running backs Larry Csonka and Mercury Morris became the first teammates to each rush for 1,000 yards in a season. Paul Warfield led the team in receptions and receiving yards. The offensive line included future Hall of Famers Jim Langer and Larry Little.


title: 1972 Miami Dolphins season

text: The Dolphins' early-1970s defensive unit was termed the "No-Name Defense" by Dallas Cowboys coach Tom Landry given its lack of high-profile players (the unit's only Hall of Famer, linebacker Nick Buoniconti, achieved much of his success with the New England Patriots and was not inducted until 2001). The defense was led by Buoniconti, end Bill Stanfill, tackle Manny Fernandez, and safeties Dick Anderson and Jake Scott. In all, nine Dolphins—Csonka, Morris, Warfield, Little, Norm Evans, Buoniconti, Stanfill, Anderson, and Scott—were selected to the Pro Bowl, and Little, Morrall, Stanfill, and Anderson were named first-team All-Pro.


title: 1972 Miami Dolphins season

text: The Dolphins went 14–0 in the regular season and won all three postseason games to finish 17–0, the only undefeated and untied season in NFL history. Three other teams, the Chicago Bears in 1934 and 1942 and the New England Patriots in 2007, reached the NFL's title game undefeated, but all three lost the championship. Miami led the league in total offense, total defense, scoring offense, and scoring defense, the only team ever to do so. On August 20, 2013, four decades after the perfect season, President Barack Obama hosted the surviving members of the 1972 Dolphins, noting they "never got their White House visit." 50 years later, on October 23, 2022, the 1972 Dolphins were honored at halftime during a Sunday Night Football game featuring the Miami Dolphins and Pittsburgh Steelers, the same matchup that occurred for the 1972 AFC Championship Game. For the 50th anniversary celebration, the Dolphins wore throwback uniforms as well as patches bearing a classic Dolphins logo, the number 50, and the years 1972 and 2022.


title: 1972 Miami Dolphins season

text: The 1972 Dolphins ranked number 1 on the 100 greatest teams of all-time by the NFL on its 100th anniversary.


title: 1972 Miami Dolphins season

text: The Miami Dolphins franchise was founded in 1966 under head coach George Wilson. Wilson led the Dolphins to just fifteen wins in four seasons before being fired and replaced by Baltimore Colts head coach Don Shula. Despite his poor record, many of Wilson's acquisitions contributed to the Dolphins' success in the early 1970s. The team drafted quarterback Bob Griese in 1967, fullback Larry Csonka in 1968, and defensive end Bill Stanfill and running back Mercury Morris in 1969. Wilson also signed Manny Fernandez and traded for Nick Buoniconti, Larry Little, and Paul Warfield. Wilson was initially resentful of the Dolphins' success, believing his firing was premature and Shula had inherited a "ready-made team." However, tension between Wilson and Shula lessened after the team won Super Bowl VII, and Wilson congratulated Shula and invited him to play at his golf course.


title: 1972 Miami Dolphins season

text: After accepting the job in Miami, Shula hired Howard Schnellenberger as offensive coordinator, Bill Arnsparger (who had served as defensive line coach under Shula in Baltimore) as defensive coordinator, Carl Taseff as offensive backs coach, Monte Clark as offensive line coach, and Mike Scarry as defensive line coach, and retained defensive backs coach Tom Keane from Wilson's staff; each of these coaches remained with the team through 1972. In the 1970 draft and ensuing free agency period, Shula added cornerback Tim Foley, safety Jake Scott, guard Bob Kuechenberg, and future Hall of Fame center Jim Langer. In Shula's first season, the Dolphins went 10–4 and reached the playoffs for the first time. Miami returned to the playoffs in 1971 and defeated the Kansas City Chiefs in the longest game in NFL history to secure the franchise's first playoff victory. The Dolphins shut out the Baltimore Colts, Shula's former team, to reach Super Bowl VI, where they lost 24–3 to Dallas.


title: 1972 Miami Dolphins season

text: The Dolphins opened the season against the Chiefs in the first regular season game at Arrowhead Stadium. In the the year prior, Miami defeated Kansas City at Kansas City Municipal Stadium in double overtime, the longest game in NFL history.


title: 1972 Miami Dolphins season

text: On the Chiefs' first drive, Miami safety Dick Anderson recovered an Ed Podolak fumble, leading to a seven-play, 57-yard drive capped by a 14-yard touchdown from Bob Griese to Marlin Briscoe. Lloyd Mumphord blocked a Jan Stenerud field goal attempt on Kansas City's ensuing drive. Late in the second quarter, the Dolphins scored twice in quick succession – a 47-yard Garo Yepremian field goal and a two-yard Larry Csonka run following an interception by Jake Scott. The Chiefs did not score until a 40-yard field goal by Stenerud late in the third quarter, and a touchdown from Len Dawson to Willie Frazier was the only score of the fourth quarter as Miami won 20–10.


title: 1972 Miami Dolphins season

text: The Orange Bowl's new Poly-Turf field and intermittent rains led to slippery conditions for Miami's Week 2 meeting with Houston. Less than two minutes in, Bill Stanfill returned a Hoyle Granger fumble to Houston's one-yard line to set up a Jim Kiick touchdown. Minutes later, Houston quarterback Dan Pastorini muffed the ball in punt formation; the Dolphins recovered again and Mercury Morris scored four plays later. Garo Yepremian's subsequent extra point attempt was blocked, his first miss after seventy-five consecutive successful attempts. Miami engineered another four-play scoring drive on its following possession, using a 30-yard Paul Warfield reception to set up a short Larry Csonka touchdown and give the Dolphins a 20–0 halftime lead. Pastorini completed three of ten passes for minus-ten yards in the first half.


title: 1972 Miami Dolphins season

text: A nine-play, 76-yard drive to open the second half pushed Miami further ahead. A long Charlie Joiner touchdown got Houston on the board and a second score after a Morris fumble cut Miami's lead to 27–13. However, Kiick's second touchdown following a fourteen-play drive in the fourth quarter put the game out of reach, and a Tim Foley interception sealed a 34–13 Dolphins victory.


title: 1972 Miami Dolphins season

text: The first-ever meeting between the Dolphins and Vikings began with a long first-quarter touchdown from Fran Tarkenton to John Gilliam; Minnesota held this 7–0 lead into halftime. Tim Foley intercepted Tarkenton early in the third quarter, setting up a 51-yard Garo Yepremian field goal. A second Yepremian field goal cut Minnesota's lead to one point, but the Vikings responded with thirteen-play drive which ended in a touchdown on the first play of the fourth quarter.


title: 1972 Miami Dolphins season

text: Minnesota quickly regained possession by intercepting Bob Griese, but two sacks of Tarkenton kept Minnesota out of field goal range and the game at 14–6. On Miami's ensuing drive, a 22-yard pass from wide receiver Marlin Briscoe to Jim Mandich set up another 51-yard Yepremian field goal. A short Vikings punt was followed by a six-play Miami drive and a three-yard touchdown pass from Griese to Mandich to give the Dolphins a 16–14 win. The Dolphins sacked Tarkenton five times and intercepted him three times.


title: 1972 Miami Dolphins season

text: The Jets received the opening kickoff and quickly marched 65 yards downfield, taking a 7–0 lead when a Cliff McClain fumble was recovered by guard Randy Rasmussen in the end zone. New York maintained this advantage until early in the second quarter when a 16-yard touchdown pass from Bob Griese to Howard Twilley tied the game. A six-yard Jim Kiick touchdown run gave Miami a 14–7 lead just before halftime.


title: 1972 Miami Dolphins season

text: A field goal early in the third quarter increased Miami's lead to ten points. On New York's subsequent drive, Joe Namath found Jerome Barkum for a 52-yard gain which gave the Jets first-and-goal at the one-yard line. However, two penalties and three failed attempts forced New York to settle for an 18-yard Bobby Howfield field goal, cutting the lead to 17–10. Early in the fourth quarter, Miami capitalized on a long pass interference penalty against Steve Tannen with a second Jim Kiick touchdown run. Miami fumbled a punt deep in its own territory in the fourth quarter and allowed New York cut the lead to 24–17, but a late field goal put the game out of reach as the Dolphins won 27–17.


title: 1972 Miami Dolphins season

text: The Dolphins and Chargers traded first-quarter field goals before Dick Anderson returned a fumble 35 yards for a touchdown to give Miami a 10–3 lead. The Dolphins scored a second touchdown on an 18-yard pass from Earl Morrall to Howard Twilley to take a 17–3 lead into halftime. In the third quarter, Morrall's second touchdown pass increased the lead to 24–3. A late San Diego touchdown made the final score 24–10 as the Dolphins moved to 5–0.


title: 1972 Miami Dolphins season

text: Dolphins quarterback Bob Griese broke his ankle early in the first quarter on a sack by Ron East and Deacon Jones. He did not play again for the remainder of the regular season; Griese was replaced by the thirty-eight-year-old Morrall until returning in the AFC Championship Game.


title: 1972 Miami Dolphins season

text: The Dolphins remained at home during week 6 for a game against the intradivisional rival Buffalo Bills. Miami scored a touchdown on the opening drive, capped off by a 5-yard run by Mercury Morris. After regaining possession later in the first quarter, the Dolphins managed to reach the Bills 7-yard line. However, four failed attempts at reaching the end zone gave the Bills possession again. Then, in the second quarter, Dolphins running back Jim Kiick fumbled the ball, recovered by Alvin Wyatt of the Bills. This ultimately set up a 35-yard field goal by Buffalo's John Leypoldt. Shortly after, Bills linebacker Ken Lee intercepted a pass from Earl Morrall and returned it for a touchdown. Late in the second quarter, Morrall attempted to throw a lateral pass, but fumbled and Buffalo defensive tackle Don Croft secured the ball. Leypoldt then kicked a 34-yard field goal, allowing the Bills to lead 13–7 at halftime.


title: 1972 Miami Dolphins season

text: Dolphins tackle Manny Fernandez strip-sacked Bills quarterback Dennis Shaw at the Buffalo 10-yard line on the first play of the third quarter. Miami fullback Larry Csonka then ran 10 yards into the end zone, allowing the Dolphins to take a 14–13 lead. A few minutes after this transpired, Dolphins cornerback Curtis Johnson blocked a punt by Spike Jones of the Bills. After the Dolphins were penalized four times on that drive (a loss of 33 yards), Garo Yepremian kicked a 54-yard field goal, the longest in franchise history until Pete Stoyanovich's 59-yard field goal in 1989. The fourth quarter began with a 45-yard field goal by Leypoldt, cutting Miami's lead to 17–16. With 9:18 remaining in the final period, the Dolphins scored again with a 15-yard run by Morris, amassing 106 rushing yards in the game. Later, the Bills capped off a touchdown-scoring drive with a 6-yard pass from quarterback Mike Taliaferro to fullback Jim Braxton. However, with only about one minute remaining by then, the Dolphins won the game by a score of 24–23.


title: 1972 Miami Dolphins season

text: The Dolphins then traveled to Memorial Stadium in Baltimore for a match against the Colts on October 29. Miami scored in the first quarter on an 80-yard drive that included a 20-yard pass from quarterback Earl Morrall to wide receiver Howard Twilley, a 32-yard rush by running back Larry Csonka, a 19-yard rush by running back Mercury Morris, and finally a 1-yard rush by Csonka for a touchdown. Garo Yepremian's extra point allowed the Dolphins to take a 7–0 lead. Dolphins cornerback Curtis Johnson blocked a punt by David Lee of the Colts and recovered the football at Baltimore's 22-yard line. A few plays later, at 3rd and 15 on Baltimore's 27-yard line, Morrall threw the ball to wide receiver Marlin Briscoe, who then threw a pass to wide receiver Paul Warfield at the 1-yard line. Csonka then ran 1-yard for a touchdown, but defensive tackle Jim Bailey blocked Yepremian's extra point attempt.


title: 1972 Miami Dolphins season

text: Later in the second quarter, Dolphins defensive back Lloyd Mumphord blocked Boris Shlapak's field goal attempt. The second quarter then ended after Yepremian kicked a 24-yard field goal. The Dolphins led 16-0 after the first half. The game's final score occurred in the third quarter. Bruce Laird of the Colts was returning a punt but fumbled the ball, which was recovered by Hubert Ginn of the Dolphins at Baltimore's 20 yard line. After a few more plays, Morris scored a 7-yard rushing touchdown, followed by a Yepremian extra point. Miami won the game with a score of 23-0 and improved to 7–0 at the halfway point of the regular season.


title: 1972 Miami Dolphins season

text: For week 8, the Dolphins traveled to War Memorial Stadium in Buffalo to take on the Bills on November 5. A Garo Yepremian 33-yard field goal allowed Miami to take an early 3–0 lead. The Bills then overtook the Dolphins on a drive capped off by quarterback Dennis Shaw throwing a 13-yard pass to running back Randy Jackson, although John Leypoldt's extra point attempt would be blocked. Buffalo now led Miami by a score of 6–3. However, the Dolphins reclaimed the lead on a possession culminating in a 22-yard run by running back Mercury Morris, followed by an extra point by Yepremian. Miami increased their lead further early in the second quarter with a pair of Yepremian field goals from 17 yards and 16 yards. Shortly thereafter, Dolphins quarterback Earl Morrall was intercepted by Bills safety Tony Greene and returned for a touchdown, narrowing Miami's lead to 16–13. This would be the final score of the first half, as Miami halted another scoring attempt by Buffalo when cornerback Tim Foley intercepted Shaw at Miami's 20-yard line.


title: 1972 Miami Dolphins season

text: Miami increased their lead again in the third quarter with a 7-yard pass from Morrall to tight end Marv Fleming. The antecedent drive included several long runs and an unsportsmanlike conduct penalty against the Bills. Later in the third quarter, Leypoldt kicked a 28-yard field goal, cutting their deficit to 23–16 at the end of the period. However, in the fourth quarter, the Dolphins put together another scoring drive that included a 26-yard pass from Morrall to Morris and then 4-yard rush by Morris for the touchdown. With neither team able to accumulate more points after that drive, the game ended as a 30-16 win for the Dolphins. Of note, Morris surpassed 100 rushing yards in a game for only the second time in his professional football career.


title: 1972 Miami Dolphins season

text: Following their win against the Buffalo Bills, the Dolphins hosted the New England Patriots at the Orange Bowl for Week 9. Miami annihilated New England both offensively and defensively. On the third play of the game, Dolphins safety Dick Anderson intercepted Patriots quarterback Jim Plunkett at New England's 26-yard line. Anderson returned the ball to the New England 4-yard line before fumbling. Although it appeared that the Patriots may have recovered the fumble, the officiating crew ruled that they did not. Dolphins running back Mercury Morris then scored a touchdown on a 4-yard rush. On just the fifth offensive play for the Dolphins, Morris again scored a 4-yard rushing touchdown. Miami scored on every possession they had during the first half, leading the Patriots 31–0 at intermission.


title: 1972 Miami Dolphins season

text: In the third quarter, Morrall threw a 16-yard pass to Marlin Briscoe, increasing the Dolphins lead to 38–0. By the beginning of the fourth quarter, with little doubt about which team would win, Dolphins quarterback Jim Del Gazio replaced Morrall. Del Gazio threw two touchdown passes in the final quarter – a 51-yard pass to Briscoe and a 39-yard pass to Jim Mandich. The Dolphins did not allow the Patriots to score throughout the game.


title: 1972 Miami Dolphins season

text: The final score of 52–0 in favor of Miami remains the most lopsided win for either team in the history of the Dolphins–Patriots rivalry. Miami totaled 482 yards, far higher than New England's 169 yards. Morrall passed for 162 yards, while Del Gazio passed for 145. The Dolphins defense limited the Patriots to just 77 net passing yards and 92 rushing yards, including four sacks against Plunkett for a loss of 40 yards. Morris, the leading rusher of the game, accumulated 90 rushing yards and 35 receiving yards; he scored 3 rushing touchdowns. With the victory, the Dolphins improved to 9–0. Don Shula became the 9th head coach in NFL history to win at least 100 regular season games, but the first to do so in only 10 seasons.


title: 1972 Miami Dolphins season

text: The Dolphins then returned home in week 10 for their second matchup against the Jets. Near the beginning of the first quarter, Dolphins safety Dick Anderson intercepted Jets quarterback Joe Namath's first pass of that game. After seven more plays, Miami scored on a 9-yard pass from quarterback Earl Morrall to wide receiver Howard Twilley. New York responded with an 80-yard drive that included several short passes from Namath, before eventually ending with a 1-yard rushing touchdown by fullback John Riggins. In the game's second quarter, Morrall fumbled on a lateral pass, with the ball being recovered by cornerback Earlie Thomas of the Jets at the Dolphins 38-yard line. Within a few plays, the Jets scored another touchdown via a 28-yard pass from Namath to wide receiver Rich Caster. New York increased their lead on Miami to 17–7 after Bobby Howfield kicked a 33-yard field goal. However, the Dolphins cut the Jets lead to 17–14 just before halftime on a drive that ended with a 1-yard run by running back Mercury Morris.<ref name="tc-j11/20"> </ref>


title: 1972 Miami Dolphins season

text: Early in the third quarter, Morrall rushed for 31 yards for a touchdown. Miami then led New York by 21–17. The Jets reclaimed the lead later in the third quarter on a drive that ended with a 4-yard pass from Namath to tight end Wayne Stewart. However, in the game's final quarter, Anderson landed on the ball after Jets running back Cliff McClain fumbled it at New York's 27-yard line. On the fourth play after the fumble, Morris managed to run 14 yards to the end zone. Miami would ultimately win the game by a score of 28–24 and improve to 10–0. With the victory, the Dolphins also clinched the AFC East title.


title: 1972 Miami Dolphins season

text: The Dolphins remained at home at the Orange Bowl in Week 11 for a Monday Night Football game against the St. Louis Cardinals. Dolphins safety Dick Anderson intercepted St. Louis quarterback Gary Cuozzo's first pass of the game at the Cardinals' 29-yard line. On the sixth play following the interception, Dolphins running back Jim Kiick reached the end zone on a 2-yard run. Miami led St. Louis 7–0 following the first quarter. Both teams scored a field goal in the second quarter, from 49-yards and 25-yards by Jim Bakken of the Cardinals and Garo Yepremian of the Dolphins, respectively. At half time, Miami led St. Louis by a score of 10–3.


title: 1972 Miami Dolphins season

text: The Dolphins would widen their lead by two touchdowns in the third quarter. First, Miami scored on a 37-yard pass from quarterback Earl Morrall to wide receiver Otto Stowe. Later in the quarter, Dolphins cornerback Lloyd Mumphord intercepted Cardinals quarterback Jim Hart and returned the ball for a touchdown. Miami now led by 24–3 after the third quarter. St. Louis finally responded again in the fourth quarter via a 2-yard rush by running back Leon Burns. However, the Dolphins then scored another touchdown on a drive capped off by a 27-yard pass from Morrall to Stowe. Miami won the game by a score of 31–10.


title: 1972 Miami Dolphins season

text: In Week 12, the Dolphins traveled to Schaefer Stadium for their second matchup of the season against the Patriots. The only score in the first quarter was 36-yard field goal by Miami's Garo Yepremian. The Dolphins increased their lead further in the second quarter, with a 10-yard field goal by Yepremian and a 1-yard rush by running back Jim Kiick on a drive that spanned 89 yards. New England responded late in the second quarter via a 36-yard pass from quarterback Jim Plunkett to wide receiver Tom Reynolds. The Dolphins led by a score of 13–7 at halftime.


title: 1972 Miami Dolphins season

text: Early in the third quarter, Miami defensive Vern Den Herder intercepted a pass by Plunkett and reached New England's 11-yard line before the play ended. The Dolphins soon scored another touchdown when quarterback Earl Morrall threw a 3-yard pass to tight end Jim Mandich. Later in the third quarter, Yepremian kicked a 18-yard field goal. Dolphins linebacker Doug Swift intercepted Plunkett on New England's next possession. On the fifth play following the interception, Miami scored on a 14-yard pass from Morrall to wide receiver Marlin Briscoe. Miami added another touchdown early in the fourth quarter via an 8-yard rush by running back Hubert Ginn. At this point, the Dolphins led by 37–7. The Patriots scored two touchdowns in the fourth quarter, the first being an 8-yard pass from quarterback Brian Dowling to running back John Tarver and the second being a 1-yard rush by Dowling. The game ended with a 37–21 victory for the Dolphins.


title: 1972 Miami Dolphins season

text: With the win, the Dolphins became only the third team in NFL history to win at least 12 consecutive games, after the 1934 Chicago Bears and 1969 Minnesota Vikings. Also of note, running back Larry Csonka surpassed 1,000 rushing yards on the season during this game.


title: 1972 Miami Dolphins season

text: The Dolphins traveled to Yankee Stadium in New York to face the New York Giants in Week 13. After Joe Orduna of the Giants returned the opening kickoff for 38 yards, New York began a five play, 50-yard drive. New York running back Ron Johnson rushed 1-yard for a touchdown, which was preceded by a 34-yard pass from quarterback Norm Snead to wide receiver Don Herrmann. However, the Dolphins blocked Pete Gogolak's extra point attempt. Miami quickly responded with a 10 play, 82-yard drive capped off by a 12-yard rush by Mercury Morris for a touchdown and a successful extra point attempt by Garo Yepremian. Later in the first quarter, New York's Rocky Thompson fumbled during a kickoff return, with the ball recovered by Miami running back Charles Leigh. The Giants defense forced the Dolphins to kick a 37-yard field goal, increasing their lead to 10–6.


title: 1972 Miami Dolphins season

text: Miami extended their lead further in the second quarter, when wide receiver Paul Warfield caught a 34-yard pass from quarterback Earl Morrall. New York responded with another touchdown, the result of an 81-yard, 12 play drive which again ended with a 1-yard run by Johnson. By the end of the first half, the Dolphins led by a score of 17–13. Neither team scored in the third quarter. In the fourth quarter, Dolphins cornerback Curtis Johnson intercepted a pass from Snead, which eventually led to Yepremian kicking a 31-yard field goal. A turnover by New York's John Mendenhall during a punt return later in the fourth quarter led to another field goal by Yepremian, this time by a distance of 16 yards. The Giants were unable to score after the second quarter, and thus, the game ended with a 23–13 victory for the Dolphins.


title: 1972 Miami Dolphins season

text: In the final week of the regular season, the Dolphins returned home for their second matchup against the Colts. The Dolphins scored first, with a 40-yard field goal by Garo Yepremian in the first quarter. Miami extended their lead further in the second quarter, with a 14-yard pass from quarterback Earl Morrall to wide receiver Paul Warfield. After Colts quarterback Marty Domres sprained his ankle, Baltimore briefly inserted Johnny Unitas at quarterback late in the second quarter for what would be his final game as a Colt. In the second half, the Dolphins added six more points with a pair of third and fourth quarter field goals by Yepremian from 50 yards and 35 yards, respectively. Miami Dolphins quarterback Bob Griese entered the game in the fourth quarter, his first time on the field since his injury against the Chargers in Week 5. With Baltimore unable to score throughout the game, Miami won 16–0.


title: 1972 Miami Dolphins season

text: With the Dolphins defeating the Baltimore Colts, they finished the regular season with a perfect win–loss record of 14–0. The 1972 Dolphins became the third team in the history of the NFL to complete a regular season undefeated and untied, after the 1934 and 1942 Chicago Bears, while the 1948 Cleveland Browns achieved a 14–0 record as a member of the All-America Football Conference. Later, the 2007 New England Patriots also earned an undefeated and untied regular season record.


title: 1972 Miami Dolphins season

text: There is an urban legend that every season, whenever the last remaining undefeated NFL team loses its first game, all the surviving members of the 1972 Miami Dolphins open bottles of champagne in celebration. Coach Don Shula tried to play down the myth by saying that two players, Dick Anderson and Nick Buoniconti, who live near each other, sometimes have a toast together. However, they occasionally had Diet Cokes together, such as in 2005 when Bob Griese and Shula watched the Chargers win over the Colts, the last undefeated team that season.


title: 1972 Miami Dolphins season

text: The NFL capitalized on the legend during a commercial that aired during Super Bowl LIII commemorating the 100th year of the NFL. The commercial featured "44 of the greatest NFL athletes" at a formal dinner event with the attendees dressed in black tie. Cacophony breaks out, and three members of the 1972 Dolphins, Larry Little, Paul Warfield, Larry Csonka, are shown casually sitting at a table together uniquely dressed in aqua-colored formal coats, and all three are drinking champagne, laughing at the chaos happening around them.


title: 1972 Miami Dolphins season

text: The 1972 Miami Dolphins were the first team to execute a perfect regular season in the post-merger NFL. They are the only team in NFL history to go undefeated and untied in the regular season and postseason.


title: 1972 Miami Dolphins season

text: After their loss to the Dallas Cowboys in Super Bowl VI (Miami's only loss during calendar year 1972), Don Shula had vowed to not only reach the Super Bowl again but to win it. He forced the team to watch film of the loss twice while at training camp. Shula would later go on to say:


title: 1972 Miami Dolphins season

text: An enduring controversy is based on the argument that the 1972 Dolphins played a soft schedule not possible under the current scheduling formula. Prior to the implementation of position scheduling in 1978, opponents were set by the NFL on a rotating basis. The Dolphins’ 1972 regular-season opponents posted an aggregate winning percentage of .397, and only two had winning records for that season (both the Kansas City Chiefs and New York Giants finished 8–6). However, this does not constitute any record; the 1975 Minnesota Vikings, who began 10–0 and finished 12–2, played 14 opponents with an average winning percentage of .332, and nine of their games were against teams 4–10 or worse.


title: 1972 Miami Dolphins season

text: The Dolphins were beneficiaries of a weak AFC East that saw the Colts lapse from a perennial contender into a three-year stretch in which they would win only 11 games; a Bills team yet to find its legs with O. J. Simpson and the return of coach Lou Saban; a dysfunctional Patriots organization that had little to no talent to surround former No. 1 overall draft choice Jim Plunkett; and a Jets squad with a porous defense, offsetting the benefits of Joe Namath remaining healthy throughout the season and an emerging John Riggins in the running game. Miami also caught a scheduling break by facing an Oilers team that was in the midst of back-to-back 1–13 seasons, a Chargers team beginning a run of four consecutive seasons in the AFC West cellar, and a Cardinals team that appeared to lack direction by rotating its starting quarterbacks instead of giving the job full-time to Jim Hart. The Dolphins also caught the Vikings in the midst of a massive transformation following the return of Fran Tarkenton, missing the playoffs for the only time between 1968 and 1978, finishing 7–7.


title: 1972 Miami Dolphins season

text: The NFL's rules at the time forced the undefeated Dolphins (14–0) to play the Steelers (11–3) in Pittsburgh for the AFC Championship Game. Subsequent rule changes have since changed the playoff structure so that this would never happen again. Since the 1975 season, teams that have won their division and have had a superior record than their opponent (as was the case with the 1972 Dolphins when they faced the Steelers) would play their postseason games at home.


title: 1972 Miami Dolphins season

text: The 1972 Dolphins consisted mostly of the same core of players that it possessed from 1970 through 1974 and was the most dominant NFL team during that stretch. In those five seasons, the Dolphins reached the playoffs all five years, won three AFC Championships, two Super Bowls and went undefeated and untied while winning the Super Bowl in 1972. They posted a record of 65–15–1, and were also the fastest franchise to win a Super Bowl after franchise inception and joining the NFL (seven years after starting in the AFL, three years after becoming a member of the NFL).


title: 1972 Miami Dolphins season

text: Fans in the Miami area could not view the team's home games on television, as 1972 was the final year in which all NFL home games were blacked out on local television even if the stadium had sold out. To view the team's home games, Dolphins fans in the Miami-Dade area would have to attend home games in person or travel to outside markets such as Orlando and Jacksonville to watch the games on television.


title: 1972 Miami Dolphins season

text: Super Bowl VII was the first game to be televised in the market of origin under new rules that would come into effect the following season requiring games to be sold out within 72 hours of kickoff time to be aired in the market of origin (these blackout rules were lifted in 2015). As all Super Bowls (except Super Bowl I) have sold out, none have been blacked out since.


title: 1972 Miami Dolphins season

text: President Richard Nixon, many of his White House staff, and members of Congress were angered by the blackout rules, as they could not watch the home games of the Dolphins’ eventual Super Bowl opponent, the Redskins, even though all games at RFK Stadium had been sold out since 1966.


title: 1972 Miami Dolphins season

text: Four decades later, on August 20, 2013, the team was invited by President Barack Obama to visit the White House. Obama noted that the team "never got their White House visit." Asked why the team had not been invited by President Richard Nixon in 1973, Larry Csonka stated that he did not feel neglected as it had not been a regular occurrence at the time. However, MSNBC reported that this was a deliberate snub by Nixon, who was a Redskins fan, even though Nixon owned a vacation home in nearby Key Biscayne, Florida and telephoned Shula only hours after the Dolphins defeated the Colts in the 1971 AFC Championship game to suggest a play for Miami to use in Super Bowl VI (a down-and-out pass to Warfield that was broken up by Cowboys safety Cornell Green). Obama had previously invited the 1985 Bears to the White House, as their original visit had been canceled because of the Space Shuttle Challenger disaster. Obama, a Chicago resident and Bears fan, had called the 1985 Bears the greatest team ever, but during the Dolphins' visit, he called his own words into question, also noting that the 1985 Bears' only defeat came at the hands of the Dolphins. Bob Kuechenberg, Jim Langer, and Manny Fernandez all refused to attend because of their political differences with the Obama administration.


title: Diesel locomotive

text: A diesel locomotive is a type of railway locomotive in which the prime mover is a diesel engine. Several types of diesel locomotives have been developed, differing mainly in the means by which mechanical power is conveyed to the driving wheels.


title: Diesel locomotive

text: Early internal combustion locomotives and railcars used kerosene and gasoline as their fuel. Rudolf Diesel patented his first compression-ignition engine in 1898, and steady improvements to the design of diesel engines reduced their physical size and improved their power-to-weight ratios to a point where one could be mounted in a locomotive. Internal combustion engines only operate efficiently within a limited power band, and while low power gasoline engines could be coupled to mechanical transmissions, the more powerful diesel engines required the development of new forms of transmission. This is because clutches would need to be very large at these power levels and would not fit in a standard -wide locomotive frame, or wear too quickly to be useful.


title: Diesel locomotive

text: The first successful diesel engines used diesel–electric transmissions, and by 1925 a small number of diesel locomotives of were in service in the United States. In 1930, Armstrong Whitworth of the United Kingdom delivered two locomotives using Sulzer-designed engines to Buenos Aires Great Southern Railway of Argentina. In 1933, diesel–electric technology developed by Maybach was used to propel the DRG Class SVT 877, a high-speed intercity two-car set, and went into series production with other streamlined car sets in Germany starting in 1935. In the United States, diesel–electric propulsion was brought to high-speed mainline passenger service in late 1934, largely through the research and development efforts of General Motors dating back to the late 1920s and advances in lightweight car body design by the Budd Company.


title: Diesel locomotive

text: The economic recovery from World War II caused the widespread adoption of diesel locomotives in many countries. They offered greater flexibility and performance than steam locomotives, as well as substantially lower operating and maintenance costs.


title: Diesel locomotive

text: The earliest recorded example of the use of an internal combustion engine in a railway locomotive is the prototype designed by William Dent Priestman, which was examined by William Thomson, 1st Baron Kelvin in 1888 who described it as a "[Priestman oil engine] mounted upon a truck which is worked on a temporary line of rails to show the adaptation of a petroleum engine for locomotive purposes." In 1894, a two-axle machine built by Priestman Brothers was used on the Hull Docks. In 1896, an oil-engined railway locomotive was built for the Royal Arsenal in Woolwich, England, using an engine designed by Herbert Akroyd Stuart. It was not a diesel, because it used a hot bulb engine (also known as a semi-diesel), but it was the precursor of the diesel.


title: Diesel locomotive

text: Rudolf Diesel considered using his engine for powering locomotives in his 1893 book "Theorie und Konstruktion eines rationellen Wärmemotors zum Ersatz der Dampfmaschine und der heute bekannten Verbrennungsmotoren". However, the massiveness and poor power-to-weight ratio of early diesel engines made them unsuitable for propelling land-based vehicles. Therefore, the engine's potential as a railroad prime mover was not initially recognized. This changed as development reduced the size and weight of the engine.


title: Diesel locomotive

text: In 1906, Rudolf Diesel, Adolf Klose and the steam and diesel engine manufacturer Gebrüder Sulzer founded Diesel-Sulzer-Klose GmbH to manufacture diesel-powered locomotives. Sulzer had been manufacturing diesel engines since 1898. The Prussian State Railways ordered a diesel locomotive from the company in 1909, and after test runs between Winterthur and Romanshorn, Switzerland, the diesel–mechanical locomotive was delivered in Berlin in September 1912. The world's first diesel-powered locomotive was operated in the summer of 1912 on the same line from Winterthur, but was not a commercial success. During test runs in 1913 several problems were found. The outbreak of World War I in 1914 prevented all further trials. The locomotive weight was 95 tonnes and the power was with a maximum speed of .


title: Diesel locomotive

text: Small numbers of prototype diesel locomotives were produced in a number of countries through the mid-1920s.


title: Diesel locomotive

text: Adolphus Busch purchased the American manufacturing rights for the diesel engine in 1898 but never applied this new form of power to transportation. He founded the Busch-Sulzer company in 1911.


title: Diesel locomotive

text: Only limited success was achieved in the early twentieth century with internal combustion engined railcars, due, in part, to difficulties with mechanical drive systems.


title: Diesel locomotive

text: General Electric (GE) entered the railcar market in the early twentieth century, as Thomas Edison possessed a patent on the electric locomotive, his design actually being a type of electrically propelled railcar. GE built its first electric locomotive prototype in 1895. However, high electrification costs caused GE to turn its attention to internal combustion power to provide electricity for electric railcars. Problems related to co-ordinating the prime mover and electric motor were immediately encountered, primarily due to limitations of the Ward Leonard current control system that had been chosen. GE Rail was formed in 1907 and 112 years later, in 2019, was purchased by and merged with Wabtec.


title: Diesel locomotive

text: A significant breakthrough occurred in 1914, when Hermann Lemp, a GE electrical engineer, developed and patented a reliable control system that controlled the engine and traction motor with a single lever; subsequent improvements were also patented by Lemp. Lemp's design solved the problem of overloading and damaging the traction motors with excessive electrical power at low speeds, and was the prototype for all internal combustion–electric drive control systems.


title: Diesel locomotive

text: In 1917–1918, GE produced three experimental diesel–electric locomotives using Lemp's control design, the first known to be built in the United States. Following this development, the 1923 Kaufman Act banned steam locomotives from New York City, because of severe pollution problems. The response to this law was to electrify high-traffic rail lines. However, electrification was uneconomical to apply to lower-traffic areas.


title: Diesel locomotive

text: The first regular use of diesel–electric locomotives was in switching (shunter) applications, which were more forgiving than mainline applications of the limitations of contemporary diesel technology and where the idling economy of diesel relative to steam would be most beneficial. GE entered a collaboration with the American Locomotive Company (ALCO) and Ingersoll-Rand (the "AGEIR" consortium) in 1924 to produce a prototype "boxcab" locomotive delivered in July 1925. This locomotive demonstrated that the diesel–electric power unit could provide many of the benefits of an electric locomotive without the railroad having to bear the sizeable expense of electrification. The unit successfully demonstrated, in switching and local freight and passenger service, on ten railroads and three industrial lines. Westinghouse Electric and Baldwin collaborated to build switching locomotives starting in 1929. However, the Great Depression curtailed demand for Westinghouse's electrical equipment, and they stopped building locomotives internally, opting to supply electrical parts instead.


title: Diesel locomotive

text: In June 1925, Baldwin Locomotive Works outshopped a prototype diesel–electric locomotive for "special uses" (such as for runs where water for steam locomotives was scarce) using electrical equipment from Westinghouse Electric Company. Its twin-engine design was not successful, and the unit was scrapped after a short testing and demonstration period. Industry sources were beginning to suggest "the outstanding advantages of this new form of motive power". In 1929, the Canadian National Railways became the first North American railway to use diesels in mainline service with two units, 9000 and 9001, from Westinghouse. However, these early diesels proved expensive and unreliable, with their high cost of acquisition relative to steam unable to be realized in operating cost savings as they were frequently out of service. It would be another five years before diesel–electric propulsion would be successfully used in mainline service, and nearly ten years before fully replacing steam became a real prospect with existing diesel technology.


title: Diesel locomotive

text: Before diesel power could make inroads into mainline service, the limitations of diesel engines circa 1930 – low power-to-weight ratios and narrow output range – had to be overcome. A major effort to overcome those limitations was launched by General Motors after they moved into the diesel field with their acquisition of the Winton Engine Company, a major manufacturer of diesel engines for marine and stationary applications, in 1930. Supported by the General Motors Research Division, GM's Winton Engine Corporation sought to develop diesel engines suitable for high-speed mobile use. The first milestone in that effort was delivery in early 1934 of the Winton 201A, a two-stroke, mechanically-aspirated, uniflow-scavenged, unit-injected diesel engine that could deliver the required performance for a fast, lightweight passenger train. The second milestone, and the one that got American railroads moving towards diesel, was the 1938 delivery of GM's Model 567 engine that was designed specifically for locomotive use, bringing a fivefold increase in life of some mechanical parts and showing its potential for meeting the rigors of freight service.


title: Diesel locomotive

text: Diesel–electric railroad locomotion entered mainline service when the Burlington Railroad and Union Pacific used custom-built diesel "streamliners" to haul passengers, starting in late 1934. Burlington's "Zephyr" trainsets evolved from articulated three-car sets with 600 hp power cars in 1934 and early 1935, to the "Denver Zephyr" semi-articulated ten car trainsets pulled by cab-booster power sets introduced in late 1936. Union Pacific started diesel streamliner service between Chicago and Portland Oregon in June 1935, and in the following year would add Los Angeles, CA, Oakland, CA, and Denver, CO to the destinations of diesel streamliners out of Chicago. The Burlington and Union Pacific streamliners were built by the Budd Company and the Pullman-Standard Company, respectively, using the new Winton engines and power train systems designed by GM's Electro-Motive Corporation. EMC's experimental 1800 hp B-B locomotives of 1935 demonstrated the multiple-unit control systems used for the cab/booster sets and the twin-engine format used with the later "Zephyr" power units. Both of those features would be used in EMC's later production model locomotives. The lightweight diesel streamliners of the mid-1930s demonstrated the advantages of diesel for passenger service with breakthrough schedule times, but diesel locomotive power would not fully come of age until regular series production of mainline diesel locomotives commenced and it was shown suitable for full-size passenger and freight service.


title: Diesel locomotive

text: Following their 1925 prototype, the AGEIR consortium produced 25 more units of "60 ton" AGEIR boxcab switching locomotives between 1925 and 1928 for several New York City railroads, making them the first series-produced diesel locomotives. The consortium also produced seven twin-engine "100 ton" boxcabs and one hybrid trolley/battery unit with a diesel-driven charging circuit. ALCO acquired the McIntosh & Seymour Engine Company in 1929 and entered series production of and single-cab switcher units in 1931. ALCO would be the pre-eminent builder of switch engines through the mid-1930s and would adapt the basic switcher design to produce versatile and highly successful, albeit relatively low powered, road locomotives.


title: Diesel locomotive

text: GM, seeing the success of the custom streamliners, sought to expand the market for diesel power by producing standardized locomotives under their Electro-Motive Corporation. In 1936, EMC's new factory started production of switch engines. In 1937, the factory started producing their new E series streamlined passenger locomotives, which would be upgraded with more reliable purpose-built engines in 1938. Seeing the performance and reliability of the new 567 model engine in passenger locomotives, EMC was eager to demonstrate diesel's viability in freight service.


title: Diesel locomotive

text: Following the successful 1939 tour of EMC's FT demonstrator freight locomotive set, the stage was set for dieselization of American railroads. In 1941, ALCO-GE introduced the RS-1 road-switcher that occupied its own market niche while EMD's F series locomotives were sought for mainline freight service. The US entry into World War II slowed conversion to diesel; the War Production Board put a halt to building new passenger equipment and gave naval uses priority for diesel engine production. During the petroleum crisis of 1942–43, coal-fired steam had the advantage of not using fuel that was in critically short supply. EMD was later allowed to increase the production of its FT locomotives and ALCO-GE was allowed to produce a limited number of DL-109 road locomotives, but most in the locomotive business were restricted to making switch engines and steam locomotives.


title: Diesel locomotive

text: In the early postwar era, EMD dominated the market for mainline locomotives with their E and F series locomotives. ALCO-GE in the late 1940s produced switchers and road-switchers that were successful in the short-haul market. However, EMD launched their GP series road-switcher locomotives in 1949, which displaced all other locomotives in the freight market including their own F series locomotives. GE subsequently dissolved its partnership with ALCO and would emerge as EMD's main competitor in the early 1960s, eventually taking the top position in the locomotive market from EMD.


title: Diesel locomotive

text: Early diesel–electric locomotives in the United States used direct current (DC) traction motors, but alternating current (AC) motors came into widespread use in the 1990s, starting with the Electro-Motive SD70MAC in 1993 and followed by General Electric's AC4400CW in 1994 and AC6000CW in 1995.


title: Diesel locomotive

text: In 1914, the world's first functional diesel–electric railcars were produced for the "Königlich-Sächsische Staatseisenbahnen" (Royal Saxon State Railways) by Waggonfabrik Rastatt with electric equipment from Brown, Boveri & Cie and diesel engines from Swiss Sulzer AG. They were classified as DET 1 and DET 2 (). Because of a shortage of petrol products during World War I, they remained unused for regular service in Germany. In 1922, they were sold to Swiss Compagnie du Chemin de fer Régional du Val-de-Travers (), where they were used in regular service up to the electrification of the line in 1944. Afterwards, the company kept them in service as boosters until 1965.


title: Diesel locomotive

text: Fiat claims to have built the first Italian diesel–electric locomotive in 1922, but little detail is available. Several Fiat-TIBB Bo'Bo' diesel–locomotives were built for service on the narrow gauge Ferrovie Calabro Lucane and the Società per le Strade Ferrate del Mediterrano in southern Italy in 1926, following trials in 1924–25. The six-cylinder two-stroke motor produced at 500rpm, driving four DC motors, one for each axle. These locomotives with top speed proved quite successful.


title: Diesel locomotive

text: In 1924, two diesel–electric locomotives were taken in service by the Soviet railways, almost at the same time:


title: Diesel locomotive

text: In 1935, Krauss-Maffei, MAN and Voith built the first diesel–hydraulic locomotive, called V 140, in Germany. Diesel–hydraulics became the mainstream in diesel locomotives in Germany since the German railways (DRG) were pleased with the performance of that engine. Serial production of diesel locomotives in Germany began after World War II.


title: Diesel locomotive

text: In many railway stations and industrial compounds, steam shunters had to be kept hot during many breaks between scattered short tasks. Therefore, diesel traction became economical for shunting before it became economical for hauling trains. The construction of diesel shunters began in 1920 in France, in 1925 in Denmark, in 1926 in the Netherlands, and in 1927 in Germany. After a few years of testing, hundreds of units were produced within a decade.


title: Diesel locomotive

text: Diesel-powered or "oil-engined" railcars, generally diesel–mechanical, were developed by various European manufacturers in the 1930s, e.g. by William Beardmore and Company for the Canadian National Railways (the Beardmore Tornado engine was subsequently used in the R101 airship). Some of those series for regional traffic were begun with gasoline motors and then continued with diesel motors, such as Hungarian BC (The class code doesn't tell anything but "railmotor with 2nd and 3rd class seats".), 128 cars built 1926–1937, or German Wismar railbuses (57 cars 1932–1941). In France, the first diesel railcar was Renault VH, 115 units produced 1933/34.


title: Diesel locomotive

text: In Italy, after six Gasoline cars since 1931, Fiat and Breda built a lot of diesel railmotors, more than 110 from 1933 to 1938 and 390 from 1940 to 1953, Class 772 known as "Littorina", and Class ALn 900.


title: Diesel locomotive

text: In 1945, a batch of 30 Baldwin diesel–electric locomotives, Baldwin 0-6-6-0 1000, was delivered from the United States to the railways of the Soviet Union.


title: Diesel locomotive

text: In 1947, the London, Midland and Scottish Railway (LMS) introduced the first of a pair of Co-Co diesel–electric locomotives (later British Rail Class D16/1) for regular use in the United Kingdom, although British manufacturers such as Armstrong Whitworth had been exporting diesel locomotives since 1930. Fleet deliveries to British Railways, of other designs such as Class 20 and Class 31, began in 1957.


title: Diesel locomotive

text: Series production of diesel locomotives in Italy began in the mid-1950s. Generally, diesel traction in Italy was of less importance than in other countries, as it was amongst the most advanced countries in the electrification of the main lines and as Italian geography makes freight transport by sea cheaper than rail transportation even on many domestic connections.


title: Diesel locomotive

text: In Japan, starting in the 1920s, some petrol–electric railcars were produced. The first diesel–electric traction and the first air-streamed vehicles on Japanese rails were the two DMU3s of class Kiha 43000 (キハ43000系). Japan's first series of diesel locomotives was class DD50 (国鉄DD50形), twin locomotives, developed since 1950 and in service since 1953.


title: Diesel locomotive

text: One of the first domestically-developed Diesel vehicles of China was the DMU Dongfeng (东风), produced in 1958 by CSR Sifang. Series production of China's first Diesel locomotive class, the DFH 1, began in 1964 following the construction of a prototype in 1959.


title: Diesel locomotive

text: The Trans-Australian Railway built 1912 to 1917 by Commonwealth Railways (CR) passes through 2,000 km of waterless (or salt watered) desert terrain unsuitable for steam locomotives. The original engineer Henry Deane envisaged diesel operation to overcome such problems. Some have suggested that the CR worked with the South Australian Railways to trial diesel traction. However, the technology was not developed enough to be reliable.


title: Diesel locomotive

text: As in Europe, the usage of internal combustion engines advanced more readily in self-propelled railcars than in locomotives.


title: Diesel locomotive

text: Unlike steam engines, internal combustion engines require a transmission to power the wheels. The engine must be allowed to continue to run when the locomotive is stopped.


title: Diesel locomotive

text: A diesel–mechanical locomotive uses a mechanical transmission in a fashion similar to that employed in most road vehicles. This type of transmission is generally limited to low-powered, low speed shunting (switching) locomotives, lightweight multiple units and self-propelled railcars.


title: Diesel locomotive

text: The mechanical transmissions used for railroad propulsion are generally more complex and much more robust than standard-road versions. There is usually a fluid coupling interposed between the engine and gearbox, and the gearbox is often of the epicyclic (planetary) type to permit shifting while under load. Various systems have been devised to minimise the break in transmission during gear changing; e.g., the S.S.S. (synchro-self-shifting) gearbox used by Hudswell Clarke.


title: Diesel locomotive

text: Diesel–mechanical propulsion is limited by the difficulty of building a reasonably sized transmission capable of coping with the power and torque required to move a heavy train. A number of attempts to use diesel–mechanical propulsion in high power applications have been made (e.g., the British Rail 10100 locomotive), although none have proved successful in the end.


title: Diesel locomotive

text: In a diesel–electric locomotive, the diesel engine drives either an electrical DC generator (generally, less than net for traction), or an electrical AC alternator-rectifier (generally 3,000hp net or more for traction), the output of which provides power to the traction motors that drive the locomotive. There is no mechanical connection between the diesel engine and the wheels.


title: Diesel locomotive

text: The important components of diesel–electric propulsion are the diesel engine (also known as the prime mover), the main generator/alternator-rectifier, traction motors (usually with four or six axles), and a control system consisting of the engine governor and electrical or electronic components, including switchgear, rectifiers and other components, which control or modify the electrical supply to the traction motors. In the most elementary case, the generator may be directly connected to the motors with only very simple switchgear.


title: Diesel locomotive

text: Originally, the traction motors and generator were DC machines. Following the development of high-capacity silicon rectifiers in the 1960s, the DC generator was replaced by an alternator using a diode bridge to convert its output to DC. This advance greatly improved locomotive reliability and decreased generator maintenance costs by elimination of the commutator and brushes in the generator. Elimination of the brushes and commutator, in turn, eliminated the possibility of a particularly destructive type of event referred to as a flashover (also known as an arc fault), which could result in immediate generator failure and, in some cases, start an engine room fire.


title: Diesel locomotive

text: Current North American practice is for four axles for high-speed passenger or "time" freight, or for six axles for lower-speed or "manifest" freight. The most modern units on "time" freight service tend to have six axles underneath the frame. Unlike those in "manifest" service, "time" freight units will have only four of the axles connected to traction motors, with the other two as idler axles for weight distribution.


title: Diesel locomotive

text: In the late 1980s, the development of high-power variable-voltage/variable-frequency (VVVF) drives, or "traction inverters", allowed the use of polyphase AC traction motors, thereby also eliminating the motor commutator and brushes. The result is a more efficient and reliable drive that requires relatively little maintenance and is better able to cope with overload conditions that often destroyed the older types of motors.


title: Diesel locomotive

text: A diesel–electric locomotive's power output is independent of road speed, as long as the unit's generator current and voltage limits are not exceeded. Therefore, the unit's ability to develop tractive effort (also referred to as drawbar pull or tractive force, which is what actually propels the train) will tend to inversely vary with speed within these limits. (See power curve below). Maintaining acceptable operating parameters was one of the principal design considerations that had to be solved in early diesel–electric locomotive development and, ultimately, led to the complex control systems in place on modern units.


title: Diesel locomotive

text: The prime mover's power output is primarily determined by its rotational speed (RPM) and fuel rate, which are regulated by a governor or similar mechanism. The governor is designed to react to both the throttle setting, as determined by the engine driver and the speed at which the prime mover is running (see Control theory).


title: Diesel locomotive

text: Locomotive power output, and therefore speed, is typically controlled by the engine driver using a stepped or "notched" throttle that produces binary-like electrical signals corresponding to throttle position. This basic design lends itself well to multiple unit (MU) operation by producing discrete conditions that assure that all units in a consist respond in the same way to throttle position. Binary encoding also helps to minimize the number of trainlines (electrical connections) that are required to pass signals from unit to unit. For example, only four trainlines are required to encode all possible throttle positions if there are up to 14 stages of throttling.


title: Diesel locomotive

text: North American locomotives, such as those built by EMD or General Electric, have eight throttle positions or "notches" as well as a "reverser" to allow them to operate bi-directionally. Many UK-built locomotives have a ten-position throttle. The power positions are often referred to by locomotive crews depending upon the throttle setting, such as "run 3" or "notch 3".