bluuebunny/crossref_metadata_2025 huggingface dataset:
Dream Bizarreness as the Cognitive Correlate of Altered Neuronal Behavior in REM Sleep
Authors: Mamelak Adam N. , Hobson J. Allan
Published: February 2008

Bizarreness is a cognitive feature common to REM sleep dreams, which can be easily measured. Because bizarreness is highly specific to dreaming, we propose that it is most likely brought about by changes in neuronal activity that are specific to REM sleep. At the level of the dream plot, bizarreness can be defined as either discontinuity or incongruity. In addition, the dreamer's thoughts about the plot may be logically deficient.

We propose that dream bizarreness is the cognitive concomitant of two kinds of changes in neuronal dynamics during REM sleep. One is the disinhibition of forebrain networks caused by the withdrawal of the modulatory influences of norepinephrine (NE) and serotonin (5HT) in REM sleep, secondary to cessation of firing of locus coeruleus and dorsal raphe neurons. This aminergic demodulation can be mathematically modeled as a shift toward increased error at the outputs from neural networks, and these errors might be represented cognitively as incongruities and/or discontinuities.

We also consider the possibility that discontinuities are the cognitive concomitant of sudden bifurcations or “jumps” in the responses of forebrain neuronal networks. These bifurcations are caused by phasic discharge of pontogeniculooccipital (PGO) neurons during REM sleep, providing a source of cholinergic modulation to the forebrain which could evoke unpredictable network responses. When phasic PGO activity stops, the resultant activity in the brain may be wholly unrelated to patterns of activity dominant before such phasic stimulation began. Mathematically such sudden shifts from one pattern of activity to a second, unrelated one is called a bifurcation. We propose that the neuronal bifurcations brought about by PGO activity might be represented cognitively as bizarre discontinuities of dream plot.

We regard these proposals as preliminary attempts to model the relationship between dream cognition and REM sleep neurophysiology. This neurophysiological model of dream bizarreness may also prove useful in understanding the contributions of REM sleep to the developmental and experiential plasticity of the cerebral cortex.
A Source Analysis of the Late Human Auditory Evoked Potentials
Authors: Scherg Michael , Vajsar Jiri , Picton Terence W.
Published: February 2008

The intracerebral generators of the human auditory evoked potentials were estimated using dipole source analysis of 14-channel scalp recordings. The response to a 400-msec toneburst presented every 0.9 sec could be explained by three major dipole sources in each temporal lobe. The first was a vertically oriented dipole located on the supratemporal plane in or near the auditory koniocortex. This contributed to the scalp-recorded N1 wave at 100 msec. The second was a vertically oriented dipole source located on the supratemporal plane somewhat anterior to the first. This contributed to both the Nl and the sustained potential (SP). The third was a laterally oriented dipole source that perhaps originated in the magnopyramidal temporal field. This contributed a negative wave to the lateral scalp recordings at the latency of 145 msec. A change in the frequency of the toneburst elicited an additional negativity in the scalp-recording —the mismatch negativity (MMN). When the frequency change was large, the mismatch negativity was composed of two distinct sources with sequential but partially overlapping activities. The earlier corresponded to the Nl dipole sources and the later to a more anteriorly located dipole with an orientation more lateral than Nl. Only the later source was active when the frequency change was small. MMN source activities peaked about 15 msec earlier in the contralateral hemisphere, while this difference was only 4 msec for the sources of the Nl.
Visual Search Performance in the Neglect Syndrome
Authors: Eglin Mirjam , Robertson Lynn C. , Knight Robert T.
Published: February 2008

Patients with hemispatial neglect fail to respond to stimuli on one side of space. We assessed to what extent the complexity and number of visual stimuli on both sides determine the severity of neglect. Patients with neglect were required to find specified targets in a cluttered visual field. Two sets of stimuli were used. One set produced effortless and parallel search performance in normal controls; the other set was more complex and produced serial search performance in normal controls. Both sets of stimuli resulted in a serial performance pattern in the patients. Their baseline search performance on both sides was similar when all stimulus items were restricted to one side. A pronounced difference between the two sides was evident when stimuli appeared on both sides. Search for targets on the intact side of space was unaffected by distractors on the neglected side, whereas search for targets on the neglected side was slowed disproportionately by distractors on the intact side. The slowing on the neglected side was more severe during the more demanding search task and when more items were present on the intact side. The results indicate that neglect is associated with an inability to move attention from objects on the intact side to items on the neglected side.
Neocortical Expansion: An Attempt toward Relating Phylogeny and Ontogeny
Authors: Killackey Herbert P.
Published: February 2008

The neocortex is the most characteristic feature of the human brain. On gross inspection, its convoluted surfaces can be seen to have overgrown and covered most other brain structures. In the functional sphere, it is to the neocortex that we attribute those behaviors assumed to be most uniquely human such as cognition and linguistic behavior. This essay is an attempt to understand how this structure expanded during the course of mammalian evolution. At present, any attempt must be more speculative than definitive, but it is offered in the hope that it will generate more discussion on a topic that is central to all neurobiology, as well as a number of allied disciplines. I will proceed by outlining current views on the evolution of the brain, briefly review the organization of the somatosensory cortex in several mammalian forms, and then discuss in some detail ontogenetic mechanisms that may have some bearing on neocortical phylogeny. The primary proposition put forth is that the mammalian neocortex is relatively unspecified by strict genetic means, and that this allowed the neocortex to expand and adapt to a variety of circumstances during the course of phylogeny.
Modulation of Spontaneous Brain Activity during Mental Imagery
Authors: Kaufman L. , Schwartz B. , Salustri C. , Williamson S. J.
Published: February 2008

Magnetic measurements of average power of human alpha and beta activity over the occipital and parietal areas of the scalp reveal spatially selective suppression of the activity of the occipital cortex when abstract figures are briefly presented visually and subjects simply indicate that they saw the figure. However, the duration of the suppression increases markedly when subjects must indicate whether or not they had previously seen the figure. The reaction time is similarly prolonged during the search of visual memory, and is commensurate with the duration of selective suppression of brain activity. It is also demonstrated that alpha activity is not replaced by beta activity during this suppression, but that power in the beta band is also diminished during memory search. Low correlations between the scalp distributions of power in the beta and alpha bands indicate that partly different neuronal populations give rise to activity of these different frequency bands. Since magnetic fields are negligibly affected by intervening bone tissues, dramatic asymmetries in the distribution of alpha activity across the scalps of individuals and the differences in distribution between individuals cannot be ascribed to differences in skull thickness but are due instead to differences in underlying brain anatomy or function. Nevertheless, a common pattern of suppression of alpha activity is observed across subjects during well-controlled cognitive tasks. This implies that the visual system is involved in mental imagery.
Receptive Field Characteristics That Allow Parietal Lobe Neurons to Encode Spatial Properties of Visual Input: A Computational Analysis
Authors: O'Reilly Randall C. , Kosslyn Stephen M. , Marsolek Chad J. , Chabris Christopher F.
Published: February 2008

A subset of visually sensitive neurons in the parietal lobe apparently can encode the locations of stimuli, whereas visually sensitive neurons in the inferotemporal cortex (area IT) cannot. This finding is puzzling because both sorts of neurons have large receptive fields, and yet location can be encoded in one case, but not in the other. The experiments reported here investigated the hypothesis that a crucial difference between the IT and parietal neurons is the spatial distribution of their response profiles. In particular, IT neurons typically respond maximally when stimuli are presented at the fovea, whereas parietal neurons do not. We found that a parallel-distributed-processing network could map a point in an array to a coordinate representation more easily when a greater proportion of its input units had response peaks off the center of the input array. Furthermore, this result did not depend on potentially implausible assumptions about the regularity of the overlap in receptive fields or the homogeneity of the response profiles of different units. Finally, the internal representations formed within the network had receptive fields resembling those found in area 7a of the parietal lobe.
The Cerebellum and Motor Learning
Authors: Glickstein Mitchell , Yeo Christopher
Published: February 2008

People with profound memory deficits can acquire new motor skills, even though on each day of training they may be unaware of having seen the training apparatus before. Similarly, rabbits can acquire or retain a conditioned nictitating membrane response despite massive lesions of the hippocampus or the cerebral cortex. Both lines of evidence suggest that sub-cortical structures may be sufficient for many forms of motor learning. One possible locus for motor learning is the cerebellum. This article traces the history of our knowledge of structure and function of the cerebellum. The anatomical and physiological evidence demonstrates that the cerebellum has the neural connections necessary to mediate simple forms of motor learning or reflex plasticity. Behavioral studies demonstrate that the cerebellum is involved in modification of the vestibuloocular reflex, recalibration of saccadic eye movements, and acquisition of the conditioned nictitating membrane response. Although the evidence in all three instances suggests that the cerebellum is important, there is no agreement as to whether the cerebellum is always necessary for motor learning or how it might participate. Two views are presented: one supporting the idea of the cerebellum as the locus for motor learning and the other opposing this idea. Some evidence that might resolve these disagreements is discussed.
Cortical Maturation and the Development of Visual Attention in Early Infancy
Authors: Johnson Mark H.
Published: February 2008

Bronson (1974) reviewed evidence in support of the claim that the development of visually guided behavior in the human infant over the first few months of life represents a shift from subcortical to cortical visual processing. Recently, this view has been brought into question for two reasons; first, evidence revealing apparently sophisticated perceptual abilities in the newborn, and second, increasing evidence for multiple cortica streams of visual processing. The present paper presents a reanalysis of the relation between the maturation of cortical pathways and the development of visually guided behavior, focusing in particular on how the maturational state of the primary visual cortex may constrain the functioning of neural pathways subserving oculomotor control.
The Pyramidal Cell and its Local-Circuit Interneurons: A Hypothetical Unit of the Mammalian Cerebral Cortex
Authors: Marín-Padilla Miguel
Published: February 2008

A pyramidal cell with five of its local-circuit interneurons (Cajal–Retzius, Martinotti, Cajal double-bouquet, basket, and chandelier cells), constitutes a distinct structural/functional assemblage of the mammalian neocortex. This pyramidal/local-circuit neuronal assemblage is proposed herein as a basic neocortical unit. This unit is shared by all mammals, embodies both specific structural as well as functional elements, and constitutes an essential developmental building block of the neocortex. In the model, the pyramidal cell represents a distinct, stable, projective, excitatory neuron that has remained essentially unchanged in the course of mammalian phylogeny. On the other hand, its local-circuit interneurons are more likely to be inhibitory and less stable, designed perhaps to adapt, and modify in response to environmental needs. The proposed model infers that the number of pyramidal cells contacted by each local-circuit interneuron as well as the number of synaptic contacts established with each one are elements acquired post-natally in response to individual needs. Thereby, the overall three-dimensional distribution and extent of these pyramidal/local-circuit neuronal assemblages should be species-specific, variable among individual of the same species, and able to adapt in response to environmental needs. The model introduces a different approach, perhaps a new vantage point, for the study of the basic structural organization of the mammalian cerebral cortex. Relationships of the proposed model to cortical function in general and to learning behavior in particular are discussed.
Hemispheric Mechanisms Controlling Voluntary and Spontaneous Facial Expressions
Authors: Gazzaniga Michael S. , Smylie Charlotte S.
Published: February 2008

The capacity of each disconnected cerebral hemisphere to control a variety of facial postures was examined in three split-brain patients. The dynamics of facial posturing were analyzed in 30-msec optical disc frames that were generated off videotape recordings of each patient's response to lateralized stimuli. The results revealed that commands presented to the left hemisphere effecting postures of the lower facial muscles showed a marked asymmetry, with the right side of the face sometimes responding up to 180 msec before the left side of the face. Commands presented to the right hemisphere elicited a response only if the posture involved moving the upper facial muscles. Spontaneous postures filmed during free conversation were symmetrical. The results suggest that while either hemisphere can generate spontaneous facial expressions only the left hemisphere is efficient at generating voluntaly expressions. This contrasts sharply with the fact that both hemispheres can carry out a wide variety of other voluntary movements with the hand and foot.
Amnesia due to Lesions Confined to the Hippocampus: A Clinical-Pathologic Study
Authors: Victor Maurice , Agamanolis Dimitri
Published: February 2008

Reported here is the case of a 65-year-old man who suffered a burst of severe, repetitive generalized seizures (status epilepticus). On recovery of consciousness he was left with a profound impairment of memory, which remained unchanged for the subsequent 30 months of his life. During this period the cognitive defect was fully documented. Careful neuropathologic examination disclosed the presence of remarkably discrete lesions, confined to the hippocampus on each side. Because of the rarity of well-documented instances of this type and their importance in the study of memory function, we are reporting our case in some detail.
Visual Object Representation: Interpreting Neurophysiological Data within a Computational Framework
Authors: Plaut David C. , Farah Martha J.
Published: February 2008

Significant progress has been made in understanding vision by combining computational and neuroscientific constraints. However, for the most part these integrative approaches have been limited to low-level visual processing. Recent advances in our understanding of high-level vision in the two separate disciplines warrant an attempt to relate and integrate these results to extend our understanding of vision through object representation and recognition. This paper is an attempt to contribute to this goal, by using a computational framework arising out of computer vision research to organize and interpret human and primate neurophysiology and neuropsychology.
Face-Selective Cells in the Temporal Cortex of Monkeys
Authors: Desimone Robert
Published: February 2008

The notion of a neuron that responds selectively to the image of a particular complex object has been controversial ever since Gross and his colleagues reported neurons in the temporal cortex of monkeys that were selective for the sight of a monkey's hand (Gross, Rocha-Miranda, & Bender, 1972). Since that time, evidence has mounted for neurons in the temporal lobe that respond selectively to faces. The present paper presents a critical analysis of the evidence for face neurons and discusses the implications of these neurons for models of object recognition. The paper also presents some possible reasons for the evolution of face neurons and suggests some analogies with the development of language in humans.
Eigenfaces for Recognition
Authors: Turk Matthew , Pentland Alex
Published: February 2008

We have developed a near-real-time computer system that can locate and track a subject's head, and then recognize the person by comparing characteristics of the face to those of known individuals. The computational approach taken in this system is motivated by both physiology and information theory, as well as by the practical requirements of near-real-time performance and accuracy. Our approach treats the face recognition problem as an intrinsically two-dimensional (2-D) recognition problem rather than requiring recovery of three-dimensional geometry, taking advantage of the fact that faces are normally upright and thus may be described by a small set of 2-D characteristic views. The system functions by projecting face images onto a feature space that spans the significant variations among known face images. The significant features are known as "eigenfaces," because they are the eigenvectors (principal components) of the set of faces; they do not necessarily correspond to features such as eyes, ears, and noses. The projection operation characterizes an individual face by a weighted sum of the eigenface features, and so to recognize a particular face it is necessary only to compare these weights to those of known individuals. Some particular advantages of our approach are that it provides for the ability to learn and later recognize new faces in an unsupervised manner, and that it is easy to implement using a neural network architecture.
Visual Processing of Faces in Temporal Cortex: Physiological Evidence for a Modular Organization and Possible Anatomical Correlates
Authors: Harries M. H. , Perrett D. I.
Published: February 2008

Physiological recordings along the length of the upper bank of the superior temporal sulcus (STS) revealed cells each of which was selectively responsive to a particular view of the head and body. Such cells were grouped in large patches 3-4 mm across. The patches were separated by regions of cortex containing cells responsive to other stimuli. The distribution of cells projecting from temporal cortex to the posterior regions of the inferior parietal lobe was studied with retrogradely transported fluorescent dyes. A strong temporoparietal projection was found originating from the upper bank of the STS. Cells projecting to the parietal cortex occurred in large patches or bands. The size and periodicity of modules defined through anatomical connections matched the functional subdivisions of the STS cortex involved in face processing evident in physiological recordings. It is speculated that the temporoparietal projections could provide a route through which temporal lobe analysis of facial signals about the direction of others' attention can be passed to parietal systems concerned with spatial awareness.
Fractionating the Word Repetition Effect with Event-Related Potentials
Authors: Petten Cyma Van , Kutas Marta , Kluender Robert , Mitchiner Mark , McIsaac Heather
Published: February 2008

Word repetition has been a staple paradigm for both psycholinguistic and memory research; several possible loci for changes in behavioral performance have been proposed. These proposals are discussed in light of the event-related brain potential (ERP) data reported here. ERPs were recorded as subjects read nonfiction articles drawn from a popular magazine. The effects of word repetition were examined in this relatively natural context wherein words were repeated as a consequence of normal discourse structure. Three distinct components of the ERP were found to be sensitive to repetition: a positive component peaking at 200 msec poststimulus, a negative one at 400 msec (N400), and a later positivity. The components were differentially sensitive to the temporal lag between repetitions, the number of repetitions, and the normative frequency of the eliciting word. The N400 responded similarly to repetition in text as it has in experimental lists of words, but the late positivity showed a different pattern of results than in list studies.
When Metacognition Fails: Impaired Awareness of Deficit in Alzheimer's Disease
Authors: McGlynn Susan M. , Kaszniak Alfred W.
Published: February 2008

Two new measures were developed to assess quantitatively the degree to which patients with Alzheimer's disease (AD) are aware of their memory deficit, and to evaluate the relation between dementia severity and awareness of deficit. Results of a questionnaire measure indicated that AD patients rated their own difficulties with cognitive activities of daily life significantly lower than relatives rated patients' problems, and this discrepancy was related to patients' dementia severity. On another measure involving task performance predictions, AD patients were inaccurate in predicting their performance on most cognitive tasks when compared to both their actual performance and relatives' predictions, despite generally accurate prediction of their relatives' performance on the same tasks. These results are discussed in terms of a breakdown in metacognitive processes.
“Dead Reckoning,” Landmark Learning, and the Sense of Direction: A Neurophysiological and Computational Hypothesis
Authors: McNaughton B. L. , Chen L. L. , Markus E. J.
Published: February 2008

Behavioral and neurophysiological evidence strongly suggests that, within certain limits, rodents and humans can keep track of their directional heading relative to an inertial, and hence allocentric coordinate system. This “sense of direction” appears to involve the integration of angular velocity signals that arise primarily in the vestibular system. A hypothesis is proposed in which the integration process, an operation that may be difficult for neurons to implement, is replaced by a linear associative mapping, an operation that is at least theoretically easy to implement with neurons. The proposed system makes use of a set of linearly independent vectors representing the combination of the current head direction, and head angular velocity representations to “recall” the resulting head direction. It is then proposed that visual landmarks become incorporated into the directional system, enabling both the correction of cumulative error and, ultimately, the computation of novel, optimal trajectories between locations. According to the hypothesis, this occurs through the association of hippo-campal “local-view” cells (i.e., direction selective “place cells”) with “head-direction” cells located downstream in the dorsal presubiculum. The possible neurophysiological and neuroan-atomical bases for the proposed system are discussed.
High Precision Systems Require High Precision “Blueprints”: A New View Regarding the Formation of Connections in the Mammalian Visual System
Authors: Chalupa Leo M. , Dreher Bogdan
Published: February 2008

It is well established that early in development interconnections within the mammalian visual system are often more widespread and less precise than at maturity. The literature dealing with the formation of visual connections has largely ignored differences in developmental specificity among species differing in their phylogenetic status and/or the visual ecological niche that they occupy. Based on a review of the available evidence, we have formulated an hypothesis to account for the varying degrees of developmental specificity that characterize different visual systems. It is suggested that extremely precise systems required for high-acuity binocular vision exhibit fewer presumed developmental errors than do visual systems characterized by poorer acuity and relatively crude depth perception. The developmental implications of the hypothesis are considered, and specific experiments are proposed to further test its validity.
Short-Latency Single Unit Processing in Olfactory Cortex
Authors: McCollum Jonn , Larson John , Otto Tim , Schottler Frank , Granger Richard , Lynch Gary
Published: February 2008

Single-unit recording of layer II—III cells in olfactory (piriform) cortex was performed on awake, unrestrained rats actively engaged in learning novel odors in an olfactory discrimination task. Five of the 67 cells tested had very brief monophasic action potentials and high spontaneous firing rates (30–80 Hz); it is suggested that these units were interneurons. The remainder of the neurons had broader spikes and did not discharge for prolonged periods. Thirty-nine percent of the broad spike cells responded to at least one and usually more of the odors presented to the rats during either of the first two trials on which that odor was present, but, in most cases, these responses occurred only very infrequently over the course of subsequent trials. Six percent of the broad-spike group, how ever, continued firing robustly to a single odor but not to others.

From these results it appears that most cells in piriform cortex do not respond to most odors, i.e., coding is exceedingly sparse. A subgroup of the predominant broad-spike cell type does react to several odors but this response drops out with repeated exposure, perhaps because of training. However, a few members of this class (a small fraction of the total cell population) do go on responding to a particular odor, thus exhibiting a form of odor specificity. The results are discussed with regard to predictions from recently developed models of the olfactory cortex.
Components of Visual Orienting in Early Infancy: Contingency Learning, Anticipatory Looking, and Disengaging
Authors: Johnson Mark H. , Posner Michael I. , Rothbart Mary K.
Published: February 2008

Three aspects of the development of visual orienting in infants of 2, 3, and 4 months of age are examined in this paper. These are the age of onset and sequence of development of (1) the ability to readily disengage gaze from a stimulus, (2) the ability to consistently show “anticipatory” eye movements, and (3) the ability to use a central cue to predict the spatial location of a target. Results indicated that only the 4--month-old group was easily able to disengage from an attractive central stimulus to orient toward a simultaneously presented target. The 4--month-old group also showed more than double the percentage of “anticipatory” looks than did the other age groups. Finally, only the 4--month-old group showed significant evidence of being able to acquire the contingent relationship between a central cue and the spatial location (to the right or to the left) of a target. Measures of anticipatory looking and contingency learning were not correlated. These findings are, in general terms, consistent with the predictions of matura-tional accounts of the development of visual orienting.
Timing and Force Control Deficits in Clumsy Children
Authors: Lundy-Ekman Laurie , Ivry Richard , Keele Steven , Woollacott Marjorie
Published: February 2008

This study investigated the link between cognitive processes and neural structures involved in motor control. Children identified as clumsy through clinical assessment procedures were tested on tasks involving movement timing, perceptual timing, and force control. The clumsy children were divided into two groups: those with soft neurological signs associated with cerebellar dysfunction and those with soft neurological signs associated with dysfunction of the basal ganglia. A control group of age-matched children who did not exhibit evidence of clumsiness or soft neurological signs was also tested. The results showed a double dissociation between the two groups of clumsy children and the tests of timing and force. Clumsy children with cerebellar signs were more variable when attempting to tap a series of equal intervals. They were also more variable on the time perception task, indicating a deficit in motor and perceptual timing. The clumsy children with basal ganglia signs were unimpaired on the timing tasks. However, they were more variable in controlling the amplitude of isometric force pulses. These results support the hypothesis that the control of time and force are separate components of coordination and that these computations are dependent on different neural systems.
N400 to Semantically Anomalous Pictures and Words
Authors: Nigam Arti , Hoffman James E. , Simons Robert F.
Published: February 2008

The N400 component of the human event-related brain potential appears to be related to violations of semantic expectancy during language comprehension. The present experiment investigated whether the N400 is related specifically to activity in a language system or is an index of a conceptual system that is accessed by both pictures and words. Sentences were visually presented one word at a time with the last word being replaced in one condition by a line drawing representing the same concept (eg, the word “socks” was replaced by a picture of socks). The N400 recorded in the Pictures Condition was found to be identical to the N400 generated by words in terms of amplitude, scalp distribution, and latency. These results suggest that the N400 is an index of activity in a conceptual memory that is accessed by both pictures and words.
Event-Related Potentials and Recognition Memory for Low- and High-Frequency Words
Authors: Rugg Michael D. , Doyle Michael C.
Published: February 2008

Event-related potentials (ERPs) were recorded while subjects made recognition judgments on high- and low-frequency words, half of which had previously been presented in an incidental study task. Compared to high-frequency items, low-frequency words were associated with superior recognition performance, and attracted a higher proportion of confident judgments. In the case of the low-frequency words only, the region of the ERPs post-500 msec evoked by correctly classified, previously studied (old) words was more positive-going than was the same region of the EWs to nonstudied (new) words. These “old/new” ERP differences were larger from electrodes over the left than over the right hemisphere. This old/new by frequency interaction held when EWs were formed only from words that attracted confident judgments. It is argued that these data are consistent with the ideas that (1) post-500 msec “old/ new” EW differences in recognition memory tasks reflect differences in old and new words' levels of relative familiarity, and (2) the recognition memory advantage for low-frequency words results, at least in part, from the higher level of relative familiarity engendered at test by previously studied low-frequency items. The data are interpreted as providing support for “two-process” models of recognition memory.
Is Cognitive Neuropsychology Possible?
Authors: Caramazza Alfonso
Published: February 2008

Cognitive neuropsychology's domain of inquiry concerns the structure of normal perceptual, motor, and cognitive processes. As such, it constitutes a branch of cognitive science. Cognitive neuropsychology differs from other branches of cognitive science only by the type of observation that it uses in developing and evaluating theories of normal cognition. The data used in cognitive neuropsychology are the patterns of performance produced by brain-damged subjects. Because the basic data used in cognitive neuropsychology are the result of a biological manipulation—a brain lesion—these data will be relevant to claims about the functional organization of the brain. Hence, cognitive neuropsychology may also be considered to be a branch of cognitive neuroscience. However, in this paper I will be concerned with an assessment of research programs whose principal or only aim is to constrain theories of normal cognitive functioning through the analysis of acquired disorders of cognition. Following a brief discussion of the basic assumptions that motivate cognitive neuropsychological research, I consider Kosslyn and Van Kleeks (1990) claim that the study of brain-damaged subjects for the purpose of constraining theories of normal cognitive processing cannot lead to meaningful conclusions unless the theories are directly cast in terms of anatomical and physiological facts. I argue that these authors conflated criticisms that may apply to any empirical science with criticisms that may apply specifically to cognitive neuropsychology. Separate consideration of the criticisms specific to cognitive neuropsychology reveals that these are unfounded. The main point of this discussion is to emphasize the pragmatic character of the motivation for using impaired performance to constrain theories of normal cognition. The usefulness of cognitive neuropsychological research is illustrated through specific examples.
A Neuroethological Framework for the Representation of Minds
Authors: Brothers Leslie , Ring Brian
Published: February 2008

The cognition that constructs mental features such as intention, disposition, and character is an aspect of theory of mind. This aspect of representation of minds, which inherently has valence, is viewed from cognitive, evolutionary, and neural perspectives. It is proposed that this cognition is modular, and that it normally operates in association with a valence-free cognition able to represent mental states such as belief. Examples of neural activity capable of supporting the social representations macaque monkeys are believed to possess (understanding of affective displays, purposeful movement, and elemental social interactions) are presented.
An Event-Related Potential (ERP) Analysis of Semantic Congruity and Repetition Effects in Sentences
Authors: Besson Mireille , Kutas Marta , Petten Cyma Van
Published: February 2008

In two experiments, event-related brain potentials (ERPs) and cued-recall performance measures were used to examine the consequences of semantic congruity and repetition on the processing of words in sentences. A set of sentences, half of which ended with words that rendered them semantically incongruous, was repeated either once (eg, Experiment 1) or twice (e.g., Experiment 2). After each block of sentences, subjects were given all of the sentences and asked to recall the missing final words.

Repetition benefited the recall of both congruous and incongruous endings and reduced the amplitude and shortened the duration of the N400 component of the ERP more for (1) incongruous than congruous words, (2) open class than closed class words, and (3) low-frequency than high-frequency open class words. For incongruous sentence terminations, repetition increased the amplitude of a broad positive component subsequent to the N400.

Assuming additive factors logic and a traditional view of the lexicon, our N400 results indicate that in addition to their singular effects, semantic congruiry, repetition, and word frequency converge to influence a common stage of lexical processing. Within a parallel distributed processing framework, our results argue for substantial temporal and spatial overlap in the activation of codes subserving word recognition so as to yield the observed interactions of repetition with semantic congruity, lexical class, and word frequency effects.
Mnemonic Dissociations: The Power of Parameters
Authors: Olton David S. , Shapiro Matthew L.
Published: February 2008

Memory, as reflected in neural plasticity, is certainly not a functionally homogeneous process. Within the context of the mnemonic functions of the hippocampal system, this paper discusses two issues. The first concerns the appropriate conceptual approach to be taken in a neuropsychological analysis of memory. We conclude that a dimensional approach, emphasizing a quantitative analysis of individual mnemonic processes, has a significant advantage over the dichotomous classification of different types of memory. The second issue concerns the most appropriate way to describe the role of the hippocampus in mnemonic processes. On the basis of electrophysiological, neurochemical, behavioral, and computational analyses of hippocampal function, we suggest that its major role is the reduction of interference.
The Hippocampal System and Declarative Memory in Animals
Authors: Eichenbaum Howard
Published: February 2008

Theoretical arguments and empirical data are presented in favor of the hypothesis that the hippocampal system supports a declarative memory capacity in animals as well as humans. This view is advanced by identifying two prominent characteristics of human declarative memory and by operationalizing and evaluating them using both experimental lesion and single unit recording studies on animals. First, hippocampal processing is not selective to any particular category of learning materials; instead, it supports comparisons among all kinds of information in memory, resulting in a representation of critical relations between items. Conversely, individual representations are supported outside the hippocampal system. Second, hippocampal-dependent, relational memory representations involve a flexible organization that permits inferences from memory in novel situations. Conversely, hippocampal-independent individual representations can support only repetition of procedures acquired during original learning. Correspondences between the neuropsychological and neurophysiological findings presented serve to indicate how these properties of hippocampal representation support declarative memory across behavioral paradigms and across species.
Memory and Working-with-Memory: A Component Process Model Based on Modules and Central Systems
Authors: Moscovitch Morris
Published: February 2008

A neuropsychological model of memory is proposed that incorporates Fodor's (1983) idea of modules and central systems. The model has four essential components: (1) a non-frontal neocortical component that consists of perceptual (and perhaps interpretative semantic) modules that mediate performance on item-specific, implicit tests of memory, (2) a modular medial temporal/hippocampal component that mediates encoding, storage, and retrieval on explicit, episodic tests of memory that are associative/cue dependent, (3) a central system, frontal-lobe component that mediates performance on explicit tests that are strategic and on procedural tests that are rule-bound, and (4) a basal ganglia component that mediates performance on sensorimotor, procedural tests of memory. The usefulness of the modular/central system construct is explored and evidence from studies of normal, amnesic, agnosic, and demented people is provided to support the model.
Computational Consequences of a Bias toward Short Connections
Authors: Jacobs Robert A. , Jordan Michael I.
Published: February 2008

A fundamental observation in the neurosciences is that the brain is a modular system in which different regions perform different tasks. Recent evidence, however, raises questions about the accuracy of this characterization with respect to neo-nates. One possible interpretation of this evidence is that certain aspects of the modular organization of the adult brain arise developmentally. To explore this hypothesis we wish to characterize the computational principles that underlie the development of modular systems. In previous work we have considered computational schemes that allow a learning system to discover the modular structure that is present in the environment (Jacobs, Jordan, & Barto, 1991). In the current paper we present a complementary approach in which the development of modularity is due to an architectural bias in the learner. In particular, we examine the computational consequences of a simple architectural bias toward short-range connections. We present simulations that show that systems that learn under the influence of such a bias have a number of desirable properties, including a tendency to decompose tasks into subtasks, to decouple the dynamics of recurrent subsystems, and to develop location-sensitive internal representations. Furthermore, the system's units develop local receptive and projective fields, and the system develops characteristics that are typically associated with topographic maps.
Brain Potentials during Memory Retrieval Provide Neurophysiological Support for the Distinction between Conscious Recollection and Priming
Authors: Paller Ken A. , Kutas Marta
Published: February 2008

Event-related brain potentials were recorded from subjects as they attempted to identify words displayed tachistoscopically. Words that had also been presented a few minutes earlier in a different context were identified more often than were words that had not been presented before. This priming effect was observed for words initially seen in an imagery task requiring size estimations as well as for words initially seen in an orthographic task requiring letter counting. Unlike priming, recall and recognition were much better for words repeated from the imagery task than from the orthographic task. Brain potentials elicited during word identification also differed as a function of task. Based on these differences, a potential from 500 to 800 msec was interpreted as an index of recollection processes. Earlier potentials may have indexed processing related to priming. These effects thus provide measures of the hypothetical processes underlying memory performance and demonstrate that recollection and priming are associated with distinct neural events.
A Neural Network Model of Cortical Activity during Reaching
Authors: Kettner Ronald , Marcario Joanne , Port Nicholas
Published: February 2008

A neural network model that produces many of the directional and spatial response properties that have been observed for cortical neurons in monkeys moving toward targets in space is described. These include motor cortex units with broad tuning in a single preferred direction, approximately linear variation in activity for different hold positions, and approximate invariance in preferred direction for different starting points in space. Association cortex units in the model are sometimes irregular and reminiscent of neurons observed in visually responsive brain areas such as the posterior parietal cortex. The model is also compatible with population analyses performed on motor cortical neurons. Across network units, the distribution of preferred directions is uniformly distributed in directional space, and the degree of tuning and response magnitude vary from unit to unit. A population code used to predict accurately the direction of arm movements from a large population of coarsely tuned individual neurons allows predictions using a simulated population of unit responses obtained from the neural network model. This code works for different starting locations in space using the same parameters.
Distributed Representation of Limb Motor Programs in Arrays of Adjustable Pattern Generators
Authors: Berthier N. E. , Singh S. P. , Barto A. G. , Houk J. C.
Published: February 2008

This paper describes the current state of our exploration of how motor program concepts may be related to neural mechanisms. We have proposed a model of sensorimotor networks with architectures inspired by the anatomy and physiology of the cerebellum and its interconnections with the red nucleus and the motor cortex. We proposed the concept of rubrocerebellar and corticocerebellar information processing modules that function as adjustable pattern generators (APGs) capable of the storage, recall, and execution of motor programs. The APG array model described in this paper extends the single APG model of Houk et al. (1990) to an array of APGs whose collective activity controls movement of a simple two degree-of-freedom simulated limb. Our objective was to examine the APG array theory in a simple computational framework with a plausible relationship to anatomy and physiology. Results of simulation experiments show that the APG array model is capable of learning how to control movement of the simulated limb by adjusting distributed motor programs. Although the model is based on many simplifying assumptions, and the simulated motor control task is much simpler than an actual reaching task, these results suggest that the APG array model may provide a useful step toward a more comprehensive understanding of how neural mechanisms may generate motor programs.
Perseverative and Semantic Influences on Visual Object Naming Errors in Optic Aphasia: A Connectionist Account
Authors: Plaut David C. , Shallice Tim
Published: February 2008

Although perseveration—the inappropriate repetition of previous responses—is quite common among patients with neurological damage, relatively few detailed computational accounts of its various forms have been put forth. A particularly well-documented variety involves the pattern of errors made by “optic aphasic” patients, who have a selective deficit in naming visually presented objects. Based on our previous work in modeling impaired reading via meaning in deep dyslexia, we develop a connectionist simulation of visual object naming. The major extension in the present work is the incorporation of short-term correlational weights that bias the network towards reproducing patterns of activity that have occurred on recently preceding trials. Under damage, the network replicates the complex semantic and perseverative effects found in the optic aphasic error pattern. Further analysis reveals that the perseverative effects are strongest when the lesions are near or within semantics, and are relatively mild when the preceding object evokes no response. Like optic aphasics, the network produces predominantly semantic rather than visual errors because, in contrast to reading, there is some structure in the mapping from visual to semantic representations for objects. Viewed together with the dyslexia simulations, the replication of complex empirical phenomena concerning impaired visual comprehension based on a small set of general connectionist principles strongly suggests that these principles provide important insights into the nature of semantic processing of visual information and its breakdown following brain damage.
Image Segmentation Cues in Motion Processing: Implications for Modularity in Vision
Authors: Stoner Gene R. , Albright Thomas D.
Published: February 2008

The problem of processing visual motion is underconstrained—many possible real world motions are compatible with any given dynamic retinal image. Recent psychophysical and neurophysiological experiments have shown that the primate visual system's normally veridical interpretation of moving patterns is attained through utilization of image segmentation cues unrelated to motion per se. These findings challenge notions of modularity in which it is assumed that the processing of specific scene properties, such as motion, can be studied in isolation from other visual processes. We discuss the implications of these findings with regard to both experimental and computational approaches to the study of visual motion.