bluuebunny/crossref_metadata_2025 huggingface dataset:
Scalability Problems of Simple Genetic Algorithms
Authors: Thierens Dirk
Published: February 2008

Scalable evolutionary computation has. become an intensively studied research topic in recent years. The issue of scalability is predominant in any field of algorithmic design, but it became particularly relevant for the design of competent genetic algorithms once the scalability problems of simple genetic algorithms were understood. Here we present some of the work that has aided in getting a clear insight in the scalability problems of simple genetic algorithms. Particularly, we discuss the important issue of building block mixing. We show how the need for mixing places a boundary in the GA parameter space that, together with the boundary from the schema theorem, delimits the region where the GA converges reliably to the optimum in problems of bounded difficulty. This region shrinks rapidly with increasing problem size unless the building blocks are tightly linked in the problem coding structure. In addition, we look at how straightforward extensions of the simple genetic algorithm—namely elitism, niching, and restricted mating are not significantly improving the scalability problems.
Static and Dynamic Aspects of Cortical Somatotopy: A Critical Evaluation
Authors: Killackey Herbert P.
Published: February 2008

The demonstration that functional somatotopic maps within the adult neocortex undergo some degree of reorganization following peripheral injury has aroused considerable interest. The evidence for such reorganization in the rat and monkey is reviewed and it is concluded that in both species there is good evidence for limited functional map reorganization in the adult neocortex following peripheral injury. The significance of such functional map reorganization, particularly in terms of whether or not cortical maps are continuously modifiable throughout life, is discussed. It is concluded that the current evidence for map reorganization is best interpreted in terms of the unmasking of preexisting neuronal circuits rather than as evidence of dynamic cortical selection processes.
Is Word Recognition Automatic? A Cognitive-Anatomical Approach
Authors: Posner Michael I. , Sandson Jennifer , Dhawan Meena , Shulman Gordon L.
Published: February 2008

What are the implications of anatomical localization of component mental operations for cognitive models? In this paper we use the anatomical localizations of visual and auditory word processing that were previously reported from PET studies (Petersen, Fox, Posner, Mintun & Raichle, 1988. We hypothesize that two operations performed simultaneously by the same or heavily interconnected anatomical areas will produce specific interference. One task is repeating back (shadowing) auditory words as quickly as possible. This task is shown to interfere with shifts of visual attention in the direction of peripheral cues. Both tasks are known to require common attentional operations localized to the medial frontal lobe. The shadowing task does not interfere with operations involving priming of a visual word form. This kind of priming involves areas of the ventral occipital lobe not used during shadowing. Finally, both shadowing and semantic priming involve anterior semantic and intentional areas. Accordingly, they can interfere. The conditions under which they produce interference suggest that the interference involves operations performed by the anterior attention system. These experiments support the idea that words automatically activate visual word forms, but involve shared attentional systems for higher level processes.
Derivation of Encoding Characteristics of Layer II Cerebral Cortex
Authors: Granger Richard , Ambros-Ingerson José , Lynch Gary
Published: February 2008

Computer simulations of layers I and II of pirifonn (olfactory) cortex indicate that this biological network can generate a series of distinct output responses to individual stimuli, such that different responses encode different levels of information about a stimulus. In particular, after learning a set of stimuli modeled after distinct groups of odors, the simulated network's initial response to a cue indicates only its group or category, whereas subsequent responses to the same stimulus successively subdivide the group into increasingly specific encoding of the individual cue. These sequences of responses amount to an automated organization of perceptual memories according to both their similarities and differences, facilitating transfer of learned information to novel stimuli without loss of specific information about exceptions. Human recognition performance robustly exhibits such multiple levels: a given object can be identified as a vehicle, as an automobile, or as a Mustang. The findings reported here suggest that a function as apparently complex as hierarchical recognition memory, which seems suggestive of higher ‘cognitive’ processes, may be a fundamental intrinsic property of the operation of this single cortical cell layer in response to naturally-occurring inputs to the structure. We offer the hypothesis that the network function of superficial cerebral conical layers may simultaneously acquire and hierarchically organize information about the similarities and differences among perceived stimuli. Experimental manipulation of the simulation has generated hypotheses of direct links between the values of specific biological features and particular attributes of behavior, generating testable physiological and behavioral predictions.
Brainprints: Computer-Generated Two-Dimensional Maps of the Human Cerebral Cortex in vivo
Authors: Jouandet Marc L. , Tramo Mark Jude , Herron Daniel M. , Hermann Allison , Loftus William C. , Bazell Josh , Gazzaniga Michael S.
Published: February 2008

We describe an in vivo method for the quantitative analysis of human necrotical anatomy. The technique allows unfolded regions of functional and morphological interest to be measured planimetrically. Two-dimensional cortical maps and surface area determinations derived from magnetic resonance images of monozygotic twins are presented. In addition, reconstructions and measurements of published post-mortem human and rhesus monkey hemispheres are reported. Potential applications for the study of brain organization in relation to cognitive, motor, and perceptual performance in normal and neurological populations are considered.
Timing Functions of The Cerebellum
Authors: Ivry Richard B. , Keele Steven W.
Published: February 2008

This study investigated the effects of different types of neurological deficits on timing functions. The performance of Parkinson, cerebellar, cortical, and peripheral neuropathy patients was compared to age-matched control subjects on two separate measures of timing functions. The first task involved the production of timed intervals in which the subjects attempted to maintain a simple rhythm. The second task measured the subjects' perceptual ability to discriminate between small differences in the duration of two intervals.

The primacy of the cerebellum in timing functions was demonstrated by the finding that these were the only patients who showed a deficit in both the production and perception of timing tasks. The cerebellar group was found to have increased variability in performing rhythmic tapping and they were less accurate than the other groups in making perceptual discriminations regarding small differences in duration. Critically, this perceptual deficit appears to be specific to the perception of time since the cerebellar patients were unaffected in a control task measuring the perception of loudness.

It is argued that the operation of a timing mechanism can be conceptualized as an isolable component of the motor control system. Furthermore, the results suggest that the domain of the cerebellar timing process is not limited to the motor system, but is employed by other perceptual and cognitive systems when temporally predictive computations are needed.
Positron Emission Tomographic Studies of the Processing of Singe Words
Authors: Petersen Steven E. , Fox Peter T. , Posner Michael I. , Mintun Mark , Raichle Marcus E.
Published: February 2008

PET images of blood flow change that were averaged across individuals were used to identify brain areas related to lexical (single-word) processing, A small number of discrete areas were activated during several task conditions including: modality-specific (auditory or visual) areas activated by passive word input, primary motor and premotor areas during speech output, and yet further areas during tasks making semantic or intentional demands.
Why are “What” and “Where” Processed by Separate Cortical Visual Systems? A Computational Investigation
Authors: Rueckl Jay G. , Cave Kyle R. , Kosslyn Stephen M.
Published: February 2008

In the primate visual system, the identification of objects and the processing of spatial information are accomplished by different cortical pathways. The computational properties of this “two-systems” design were explored by constructing simplifying connectionist models. The models were designed to simultaneously classify and locate shapes that could appear in multiple positions in a matrix, and the ease of forming representations of the two kinds of information was measured. Some networks were designed so that all hidden nodes projected to all output nodes, whereas others had the hidden nodes split into two groups, with some projecting to the output nodes that registered shape identity and the remainder projecting to the output nodes that registered location. The simulations revealed that splitting processing into separate streams for identifying and locating a shape led to better performance only under some circumstances. Provided that enough computational resources were available in both streams, split networks were able to develop more efficient internal representations, as revealed by detailed analyses of the patterns of weights between connections.
Regulation of Synaptic Molecular Architecture in a Rat Sympathetic Ganglion and Hippocampus
Authors: Wu K. , Black I.B.
Published: February 2008

Extensive evidence suggests that the synapse, the communicative organelle between neurons, plays a pivotal role in learning and memory. To begin defining epigenetic factors that potentially regulate molecular structure of the synapse, we have been studying a relatively simple model system, the rat sympathetic, superior cervical ganglion. Initially, we focused on the postsynaptic density (PSD), a disc-shaped structure in the postsynaptic neuron (see cover illustration). Previously, we found that trans-synaptic impulse activity regulates the predominant PSD protein molecule (PSDp). We now examine two related questions. Do other factors influence c synaptic structure independent of presynaptic innervation? Conversely, does denervation alter synaptic molecular structure in the hippocampus, as in the ganglion? Our studies indicate that the trophic protein, nerve growth factor, that governs sympathetic development and mature function, regulates the PSDp in normal and denervated ganglia. Consequently, synaptic structure in the periphery is, indeed, regulated by multiple factors. In the brain, fimbria-fornix lesions, which partially denervate the hippocampus, significantly reduce the hippocampal PSDp. We conclude that presynaptic innervation regulates synaptic structure in the hippocampus, as well as the periphery. More generally, epigenetic factors apparently regulate synaptic structure, potentially providing a molecular mechanism for information storage at the synapse.
A Simple Model of Prefrontal Cortex Function in Delayed-Response Tasks
Authors: Dehaene Stanislas , Changeux Jean-Pierre
Published: February 2008

Both psychologists and neurobiologists have used delayed response (DR), AB, and delayed matching-to-sample (DMS) tasks as tools to study the functions of prefrontal cortex in primates and humans. We describe a simulation model that relates behavioral and electrophysiological-data relevant to these tasks into a minimal neural network.

The inputs to the network are two visual objects and a positive or negative reinforcement signal. As the output, the network orients toward one of the two objects. We subdivide the architecture of the network into two levels, both of which embody constraints from neuroanatomy in a simplified form. Level 1 consists of a sensory-motor loop with modifiable synaptic weights and provides a capacity for grasping. Level 2 contains memory and rule-coding units and modulates the lower level 1. When level 1 only is simulated, the network fails to learn the tasks. The errors made by the network resemble those of young monkeys, infants, or adults with prefrontal lesions. In particular, the systematic AB error can be reproduced. With level 2 on top of level 1, the network acquires systematic rules of behavior by mere reinforcement and rapidly adapts to changes in the reinforcement schedule. Learning takes place by selection among a repertoire of possible rules. The properties of the model are discussed in terms of actual behavioral and physiological data, and several critical experimental predictions are presented. In particular, we address the issues of prefrontal functions, “systematicity” in neural networks, and “mental Darwinism.”
Temporal Constraints on Language Processing: Syntactic Priming in Broca's Aphasia
Authors: Friederici Angela D. , Kilborn Kerry
Published: February 2008

This study tests the hypothesis that agrammatic comprehension is due to a computational rather than a structural language deficit. It is claimed that grammatic Broca's aphasics do not meet the temporal constraints in the activation of different types of linguistic information necessary for normal parsing. These temporal constraints are investigated in two experiments using a crossmodal syntactic priming paradigm. Each experiment tests the effect on recognition of grammatical versus ungrammatical links between an auditory sentence fragment (the prime) and a visually presented word (the target). The experiments differ in the interstimulus interval (ISI i.e., the amount of time provided between the offset of the auditory prime and the onset of the visuai target. Experiment 1, with an ISI of 0 msec, reveals that Broca patients — much like the control groups — show a grammaticality effect. In contrast to normal students and age matched controls, however, these patients are in general much slower in making lexical decisions when auditory context is present as compared to when visual targets are presented in isolation. Experiment 2 with an ISI of 200 msec demonstrates that when additional time is given to process the syntactic context, Broca's aphasics in contrast to age matched controls show faster decision times on the target than when the ISI is 0 msec. The results are in accord with the view that agrammatic Broca's aphasics have not lost their syntactic knowledge, but that their a grammatic comprehension behavior is due to the inability to process the linguistic information within a given time frame. More generally, the findings suggest that language processing can break down once activation of different types of linguistic information does not follow the normal time pattern.
Comparisons between Active Properties of Distal Dendritic Branches and Spines: Implications for Neuronal Computations
Authors: Shepherd Gordon M. , Woolf Thomas B. , Carnevale Nicholas T.
Published: February 2008

The specific contributions of distal dendrites to the computational properties of cortical neurons are little understood and are completely ignored in most network simulations of higher brain functions. Compartmental models, based on realistic estimates of morphology and physiology, provide a means for exploring these contributions. We have pursued analysis of a model of synaptic integration in a distal dendrite bearing four spines, using a new general-purpose simulation program called SABER. We have analyzed this model under the assumption that the dendrite contains sites of impulse-generating membrane, and we have compared its responses to synaptic activation with the case of impulse-generating membrane located instead in the spine heads, as previously reported. Both types of models generate basic logic operations, such as AND, OR, and AND-NOT gates. Active spine heads require lower excitatory synaptic conductances, but active branch segments lead to larger responses in the soma. The transients recorded near the soma give no evidence of their origin in either active branch or active spines, indicating that the interpretation of experimental recordings with regard to sites of distal active responses must be viewed with caution. The results suggest the hypothesis that a hierarchy of logic operations is virtually inherent in the branching structure of dendritic trees of cortical pyramidal neurons. Inclusion of these properties in representations of cortical neurons would greatly enhance the computational power of neural networks aimed at simulating higher brain functions.
The Origins of Neocortex: Connections and Lamination as Distinct Events in Evolution
Authors: Karten Harvey J. , Shimizu Toru
Published: February 2008

In the nonmammalian telencephalon, there are neuronal populations corresponding to cell groups in the neocortex of mammals in terms of connections, single unit-responses, chemical content, and functions. Some of these populations in nonmammals, however, are organized in a nonlaminar, rather than laminar fashion. These observations may prompt a reassessment of the functional roles of lamination and the evolutionary origins of the mammalian neocortex. Thus, the role of neural circuits and laminar organization can be differentiated in order to understand the cognitive functions of the neocortex. Moreover, the origins of neocortex can be separable into the precursors of nonlaminar and laminar regions.
Microstimulation of a Neural-Network Model for Visually Guided Saccades
Authors: Goodman Sabrina J. , Andersen Richard A.
Published: February 2008

Microstimulation of many saccadic centers in the brain produces eye movements that are not consistent with either a strictly retinal or strictly head-centered coordinate coding of eye movements. Rather, stimulation produces some features of both types of coordinate coding. Recently we demonstrated a neural network model that was trained to localize the position of visual stimuli in head-centered coordinates at the output using inputs of eye and retinal position similar to those converging on area 7a of the posterior parietal cortex of monkeys (Zipser & Andersen 1988; Andersen & Zipser 1988). Here we show that microstimulation of this trained network, achieved by fully activating single units in the middle layer, produces “saccades” that are very much like the saccades produced by stimulating the brain. The activity of the middle-layer units can be considered to code the desired location of the eyes in head-centered coordinates; however, stimulation of these units does not produce the saccades predicted by a classical head-centered coordinate coding because the location in space appears to be coded in a distributed fashion among a population of units rather than explicitly at the level of single cells.
Transformation from Head- to Shoulder-Centered Representation of Target Direction in Arm Movements
Authors: Soechting J. F. , Tillery S. I. H. , Flanders M.
Published: February 2008

In a previous study (Soechting and Flanders 1990a) we suggested that subjects used a coordinate system centered at the shoulder while pointing to targets in extrapersonal space. In particular, we suggested that this coordinate system was used to define target location in terms of its distance and the direction from the shoulder. In this paper we examine this suggestion in more detail. We show that when subjects make errors in the distance of a pointing movement, the computed errors in direction will depend on the origin of the coordinate system chosen to measure direction. From an analysis of the computed error, we estimate the origin of each subject's coordinate system. We artificially induced large errors in pointing distance by asking subjects to point half-way to a target on a line from the shoulder or from the head, that is, in directions from two possible centers. The subjects' performance on both these tasks was comparable to the performance of subjects asked to point directly to the target. From this finding we argue that there exists both a head-centered and a shoulder-centered representation of target location within the central nervous system.
Genetics and Epigenetics of Neural Function: A Model
Authors: Kerszberg Michel
Published: February 2008

A neural model for one- or few-trial irreversible behavior learning such as occurs in imprinting is introduced. It is assumed that synaptic connections in the relevant parts of the central nervous system are initially set up in a largely, but not totally random fashion, as a result, for instance, of differential cell–cell adhesion. The behavior to be learned is then sometimes exhibited, but not in a reproducible, mature way. During early neural activity, active postsynaptic neurons may, however, deliver a putative retrograde trophic factor to some of their afferent synaptic boutons. This is taken to occur according to a Hebb-type rule. At a later stage, only those synapses that have accumulated enough trophic factor are stabilized selectively. We show explicitly how this process may lead to a perfectly wired circuit. The calculations indicate that if the connections were relatively well defined from the beginning, then random pulses at the inputs suffice for this refinement process to take place. This is analogous to the maturation of neural circuits under spontaneous electrical activity (unsupervised learning). If the initial connections are “fuzzy,” however, well-defined patterns of activation are needed at the inputs so that selective stabilization leads to a correct functional system (the model now behaves in an instructionist mode). Experiments suggested by the model are discussed, and involve the manipulation of afferent inputs, of the initial synapse distribution, or of the stabilization phase.
Effects of Ibotenic Lesions of Mammillary Bodies on Spontaneous and Rewarded Spatial Alternation in Mice
Authors: Beracochea Daniel J. , Jaffard Robert
Published: February 2008

Previous experiments in our laboratory have shown that lesions of the mammillary bodies (MB) in mice induce memory deficits in spontaneous spatial alternation (SA) tasks. However, it has also been shown that performance on memory tasks by both humans and animals depends on the degree of effort involved in a given task. Thus, we hypothesized that the involvement of MB-damaged subjects in tasks that require more effortful processing than does SA might reduce their memory deficits. Accordingly, in the first experiment, the effects of MB lesions were studied in both an SA and a rewarded alternation (RA) task. Daily test sessions consisted of six successive trials separated by a short intertrial interval (ITI) of 30 sec, which allowed us to study interference (i.e., the deleterious effect of the first trials of a session on the performance on the last trials of a session). Results of the first experiment showed that the MB-lesioned subjects were impaired on their performance on the SA (they were more sensitive to interference than were controls) but not RA task. This finding is consistent with our hypothesis. In the second experiment, the ITI in the RA task was increased from 50 sec to 3 min. At the longer ITI (3 min), we found that the MB-lesioned subjects had the same deficit in performance that the MB-lesioned subjects had on the SA task at an ITI of 30 sec. Control mice also had a similar deficit in performance at the ITI of 5 min. We suggest that even in the RA task, the performance of MB-damaged subjects remains more sensitive to time-dependent interference than does the performance of controls. The significance of our study to the understanding of amnesia (especially Korsakoff's syndrome and frontal lobe pathology) is discussed.
Language and Reading in the Right Hemisphere: Highways or Byways of the Brain?
Authors: Baynes Kathleen
Published: February 2008

The literature pertaining to the representation of language in the right hemisphere of hemispherectomy and callosotomy patients is reviewed to ascertain whether it provides an empirical basis for the assertions that (1) the right hemisphere participates in the recovery of language in aphasia, (2) the right hemisphere mediates the reading errors of deep dyslexic and pure alexic patients, and (3) the right hemisphere plays a fixed role in normal reading processes. At present, there appears to be some support for the first assertion, limited support for the second (if individual variation in representation can be accepted), and disconfirming evidence for the third in the data from these populations.
Music Perception and Cognition Following Bilateral Lesions of Auditory Cortex
Authors: Tramo Mark Jude , Bharucha Jamshed J. , Musiek Frank E.
Published: February 2008

We present experimental and anatomical data from a case study of impaired auditory perception following bilateral hemispheric strokes. To consider the cortical representation of sensory, perceptual, and cognitive functions mediating tonal information processing in music, pure tone sensation thresholds, spectral intonation judgments, and the associative priming of spectral intonation judgments by harmonic context were examined, and lesion localization was analyzed quantitatively using straight-line two-dimensional maps of the cortical surface reconstructed from magnetic resonance images.

Despite normal pure tone sensation thresholds at 250–8000 Hz, the perception of tonal spectra was severely impaired, such that harmonic structures (major triads) were almost uniformly judged to sound dissonant; yet, the associative priming of spectral intonation judgments by harmonic context was preserved, indicating that cognitive representations of tonal hierarchies in music remained intact and accessible. Brainprints demonstrated complete bilateral lesions of the transverse gyri of Heschl and partial lesions of the right and left superior temporal gyri involving 98 and 20% of their surface areas, respectively. In the right hemisphere, there was partial sparing of the planum temporale, temporoparietal junction, and inferior parietal cortex. In the left hemisphere, all of the superior temporal region anterior to the transverse gyrus and parts of the planum temporale, temporoparietal junction, inferior parietal cortex, and insula were spared.

These observations suggest that (1) sensory, perceptual, and cognitive functions mediating tonal information processing in music are neurologically dissociable; (2) complete bilateral lesions of primary auditory cortex combined with partial bilateral lesions of auditory association cortex chronically impair tonal consonance perception; (3) cognitive functions that hierarchically structure pitch information and generate harmonic expectancies during music perception do not rely on the integrity of primary auditory cortex; and (4) musical priming may be mediated by broadly tuned subcomponents of the thala-mocortical auditory system.
The Perception of Structure from Visual Motion in Monkey and Man
Authors: Siegel R. M. , Andersen R. A.
Published: February 2008

The ability to perceive structure using motion information was examined using a reaction time task with two primate species. Homo sapien and Macaca mulatta subjects were quantitatively tested under identical conditions to detect the change from a control unstructured to a test structured motion stimulus. The structures underlying the test were rotations of a plane, expansion of a plane, and a rotation of a three-dimensional cylinder. On many of the stimulus conditions, the two species performed similarly, although there were some species differences. These differences may be due to the extensive training of the monkeys or the use of different cognitive strategies by the human subjects. These data provide support for the existence of a neural mechanism that uses flow fields to construct two- or three-dimensional surface representations.
Preserved Priming of Novel Objects in Patients with Memory Disorders
Authors: Schacter Daniel L. , Cooper Lynn A. , Tharan Mindy , Rubens Alan B.
Published: February 2008

Amnesic patients perform poorly on explicit memory tests that require conscious recollection of recent experiences, but frequently show preserved facilitations of performance or priming effects on implicit memory tasks that do not require conscious recollection. We examined implicit memory for novel visual objects on an object decision test in which subjects decide whether structurally possible and impossible objects could exist in three-dimensional form. Patients with organic memory disorders showed robust priming effects on this task---object decision accuracy was higher for previously studied objects than for nonstudied objects---and the magnitude of priming did not differ from matched control subjects or college students. However, patients showed impaired explicit memory for novel visual objects on a recognition test. We argue that priming is mediated by the structural description system, a subsystem of the perceptual representation system, that operates at a presemantic level and is preserved in amnesic patients.
Syntactically Based Sentence Processing Classes: Evidence from Event-Related Brain Potentials
Authors: Neville Helen , Nicol Janet L. , Barss Andrew , Forster Kenneth I. , Garrett Merrill F.
Published: February 2008

Theoretical considerations and diverse empirical data from clinical, psycholinguistic, and developmental studies suggest that language comprehension processes are decomposable into separate subsystems, including distinct systems for semantic and grammatical processing. Here we report that event-related potentials (ERPs) to syntactically well-formed but semantically anomalous sentences produced a pattern of brain activity that is distinct in timing and distribution from the patterns elicited by syntactically deviant sentences, and further, that different types of syntactic deviance produced distinct ERP patterns.

Forty right-handed young adults read sentences presented at 2 words/sec while ERPs were recorded from over several positions between and within the hemispheres. Half of the sentences were semantically and grammatically acceptable and were controls for the remainder, which contained sentence medial words that violated (1) semantic expectations, (2) phrase structure rules, or (3) WH-movement constraints on Specificity and (4) Subjacency. As in prior research, the semantic anomalies produced a negative potential, N400, that was bilaterally distributed and was largest over posterior regions. The phrase structure violations enhanced the N125 response over anterior regions of the left hemisphere, and elicited a negative response (300-500 msec) over temporal and parietal regions of the left hemisphere. Violations of Specificity constraints produced a slow negative potential, evident by 125 msec, that was also largest over anterior regions of the left hemisphere. Violations of Subjacency constraints elicited a broadly and symmetrically distributed positivity that onset around 200 msec. The distinct timing and distribution of these effects provide biological support for theories that distinguish between these types of grammatical rules and constraints and more generally for the proposal that semantic and grammatical processes are distinct subsystems within the language faculty.
Deficits in Selective Attention Following Bilateral Anterior Cingulotomy
Authors: Janer Kevin W. , Pardo José V.
Published: February 2008

Positron emission tomographic (PET) studies of normal humans undergoing specific cognitive activation paradigms have identified a region of the anterior cingulate cortex as a component of an anterior, midline attentional system involved in high-level processing selection. However, deficits in attention have not been demonstrated in patients following bilateral anterior cingulotomy, a procedure that results in lesions of adjacent anterior cingulate cortex. Task paradigms used in PET studies that recruit the anterior cingulate cortex were applied to normal, control subjects and to a patient before and after cingulotomy to provide highly sensitive and functionally targeted reaction time measures of attentional performance. In contrast to unchanged performance in several neuropsychological measures, this patient demonstrated specific deficits in attention during the subacute postoperative period, which resolved spontaneously several months after surgery. Such impairment is consistent with the evolving view of the anterior cingulate's involvement in high-level processing selection. These data show the feasibility of using information from PET activation studies of normals in the design of novel chronometric tasks useful for probing abnormalities in specific cognitive operations associated with discrete cortical regions.
Role of Anterior and Posterior Attention Networks in Hemispheric Asymmetries during Lexical Decisions
Authors: Nakagawa Atsuko
Published: February 2008

The role of the left and right hemisphere was examined during semantic priming by antonyms, remote associates, and unrelated words. Targets presented directly to the left hemisphere showed an early facilitation and a late developing inhibition, while targets presented directly to the right hemisphere showed a late developing facilitation of strong and weak associations and little evidence of inhibition. When a visual cue was given prior to each target word, reaction times were facilitated equally in both visual fields and for all prime target relationships. When the priming task was combined with shadowing, reaction times generally increased and all evidence of inhibition in left hemisphere processing disappeared. This supported the idea that the inhibition found in the left hemisphere was due to its interaction with the anterior attention network.
Right Hemisphere Processing Superiority During Sustained Visual Attention
Authors: Whitehead Roger
Published: February 2008

Normal subjects showed a right hemisphere processing superiority in reaction times to visual stimuli under conditions of sustained visual attention. This asymmetry was predicted based on findings in studies of blood flow, clinical populations, and physiology on lateralization of the noradrenergic system. The asymmetry was eliminated when an auditory event was delivered simultaneously with the visual target suggesting a common pathway between voluntary sustained alerting and more automatic alerting effects of external stimuli. The act of sustaining alertness also interacted with covert orienting of attention as would be expected if alerting influenced the efficiency of covert shifts of attention.
The Development of Inhibition of Return in Early Infancy
Authors: Clohessy Anne Boylan , Posner Michael I. , Rothbart Mary K. , Vecera Shaun P.
Published: February 2008

The posterior visual spatial attention system involves a number of separable computations that allow orienting to visual locations. We have studied one of these computations, inhibition of return, in 3-, 4-, 6-, 12-, and 18--month-old infants and adults. Our results indicate that this computation develops rapidly between 3 and 6 months, in conjunction with the ability to program eye movements to specific locations. These findings demonstrate that an attention computation involving the mid-brain eye movement system develops after the third month of life. We suggest how this development might influence the infant's ability to represent and expect visual objects.
Impaired Velocity Perception in Patients with Lesions of the Cerebellum
Authors: Ivry* Richard B. , Diener H. C.
Published: February 2008

In three psychophysical experiments, cerebellar patients were impaired in making perceptual judgments of the velocity of moving stimuli. Performance was normal when the judgment concerned the position of the stimuli (Experiment 1). The dissociation between the velocity and position tasks suggests the cerebellar group was selectively impaired in velocity perception. EOG data were obtained in Experiments 2 and 3 to assess whether the deficit was oculomotor in origin. Perceptual errors were not correlated with the occurrence of intrusive eye movements. These results provide a novel demonstration of the role of the cerebellum in perceptual functions that require precise timing.
Lateralized Control of Eye Movements in Attention Deficit Hyperactivity Disorder
Authors: Rothlind Johannes C. , Posner Michael I. , Schaughency Elizabeth A.
Published: February 2008

How does a complex syndrome that involves abnormalities in impulse control and sustained attention influence simple oculomotor responses to visual stimuli? We found that normal children, like adults, were faster in moving their eyes in directions controlled by the right cerebral hemisphere under conditions where there was no warning of the impending target. ADHD children did not show this asymmetry. We speculate that this result reflects a deficit in the vigilance network that serves to maintain the alert state.
Facilitation of Working Memory in Humans by a D2 Dopamine Receptor Agonist
Authors: Luciana Monica , Depue Richard A. , Arbisi Paul , Leon Arthur
Published: February 2008

Recent studies on the neurobiology of cognition have focused on the ability of the prefrontal cortex (PFC) to support processes of working memory, i.e, mnemonic processes by which information relevant for a correct response is temporarily maintained to be reevaluated or updated on a trial-by-trial basis. Of most recent interest is the role played by dopamine (DA) in spatial working memory processes of the principal sulcal region of the PFC. Although D1 DA receptors appear to modulate these mnemonic processes in monkeys, several lines of research suggest that D2 DA receptors could also be relevant to cognitive functions. Therefore, we assessed the effects of a specific D2 receptor agonist (bromocriptine) and placebo on visuospatial delayed response performance in human subjects. During delay periods of 0 or 8 sec, subjects were required to remember the spatial location of rapidly presented visual cues displayed in peripheral vision within a 360° circumference. The extent to which D2 receptor activation by bromocriptine facilitated working memory in the 8–sec delay condition relative to placebo performance was assessed. As a means of providing validation of bromocriptine's D2 receptor effect, maximum inhibition of prolactin (PRL) secretion, which is inhibited specifically by activation of D2 receptor sites, was determined. Additionally, tasks having no working memory component were administered to rule out nonspecific effects of bromocriptine on sensory, arousal, attentional, and motor factors. Results demonstrated a significant facilitatory effect of bromocriptine on spatial delayed response performance (i.e., 8–sec delay performance). Results could not be explained by nonspecific effects of bromocriptine. Thus, findings of this study suggest that spatial working memory is facilitated by D2 receptor activation. The role that DA may play in human cognitive processes is discussed within the larger theoretical framework of DA's general role in the facilitation of goal-directed behavior. In the case of cognition, DA may facilitate processes that serve to guide motivated behavior through complex environments.
Is Cognitive Neuropsychology Plausible? The Perils of Sitting on a One-Legged Stool
Authors: Kosslyn Stephen M. , Intriligator James M.
Published: February 2008

We distinguish between strong and weak cognitive neuropsychology, with the former attempting to provide direct insights into the nature of information processing and the latter having the more modest goal of providing constraints on such theories. We argue that strong cognitive neuropsychology, although possible, is unlikely to succeed and that researchers will fare better by combining behavioral, computational, and neural investigations. Arguments offered by Caramazza (1992) in defense of strong neuropsychology are analyzed, and examples are offered to illustrate the power of alternative points of view.
Savings in Relearning Face—Name Associations as Evidence for “Covert Recognition” in Prosopagnosia
Authors: Wallace Marcie A. , Farah Martha J.
Published: February 2008

Prosopagnosic patients appear to be impaired at recognizing faces. However, recent evidence for “covert recognition” in prosopagnosia has been taken to suggest that the impairment is not in face recognition per se, but rather in conscious access to face recognition. The most widely used test for covert recognition of faces in prosopagnosia is the face-name relearning task, in which some prosopagnosics have been found to learn correct names for previously familiar faces more easily than incorrect names. Although this phenomenon is consistent with face recognition operating normally but out of reach of conscious awareness, it may also be consistent with an impairment in face recognition per se. Perhaps savings in relearning is sufficiently sensitive to the residual information contained in degraded face representations that are not detectable by overt measures of recognition. If so, then we should expect to observe this same savings in relearning when overt recognition is obliterated for reasons other than brain damage. In the present study, we used forgetting of face-name associations in normal subjects as a way of degrading recognition ability. We found the same dissociation between overt recognition performance and savings in relearning as observed in prosopagnosic patients. This implies that the performance of prosopagnosic patients in these tasks does not demand explanation in terms other than an impairment in face recognition per se.
Multiple Memory Systems: What and Why
Authors: Nadel Lynn
Published: February 2008

Evidence from a variety of domains converges on the view that there are multiple learning/memory systems, but there is no clear understanding of what these systems are, and why they should exist. I review an hypothesis about multiple memory systems postulated by O'Keefe and Nadel (The hippocampus ac a Cognitive map, Oxford: Clarendon Press, 1978), in particular our assertions about the nature of two kinds of systems (the locale and taxon systems), and what differentiates them from each other. I concentrate on our assumption that systems differ in terms of the type of information they process, rather than in terms of the temporal duration over which they function. Our “content-driven” dichotomy is contrasted with several other current views, none of which appears to explain extant data, or provides clear predictions about when one or the other kind of system would be engaged. Finally, 1 briefly consider why such distinct systems might have evolved.
Variations in Synaptic Plasticity and Types of Memory in Corticohippocampal Networks
Authors: Lynch Gary , Granger Richard
Published: February 2008

If Synaptic long-term potentiation (LTP) represents a memory storage mechanism, its induction and expression characteristics may constitute rules governing encoding and read-out of memory in cortical circuitry, The presence of variants of the LTP effect in different anatomical networks provides grounds for predictions about the types of memory operations to which potentiation contributes. Computer modeling studies incorporating the complex rules for LTP induction and the characteristics of expressed potentiation can be used to make such predictions specific. We review ttie types of synaptic plasticity found in the successive stages of the corticohippocampal pathway, and present results indicating that LTP does participate in definably different forms of memory, suggesting a classification of memory types differing somewhat from categories deduced from behavioral studies. Specifically, the results suggest that subtypes of memory operate serially, in an “assembly line” of specialized functions, each of which adds a unique aspect to the processing of memories. The effects of lesions on the encoding versus expression of memory can be interpreted from the perspective of this hypothesis.
MEM: Mechanisms of Recollection
Authors: Johnson Marcia K.
Published: February 2008

The MEM framework (Johnson, 1991a, b; Johnson & Hirst, 1992; Johnson & Multhaup, 1992) consists of a relatively small set of component cognitive processes configured into memory subsystems. Here MEM is used to discuss “recollection,” particularly the mechanisms by which aspects of experience become bound together to yield the phenomenal experience of contextually specific, event-like memories. I consider how central aspects of complex events are bound to each other and propose that these same cognitive activities operate to bind central and contextual elements into “episodic” memories. Attention is particularly focused on the role of reactivation in establishing complex memories and in strengthening or consolidating them over time.
Toward a Noncomputational Cognitive Neuroscience
Authors: Globus Gordon G.
Published: February 2008

The near universally accepted theory that the brain processes information persists in current neural network theory where there is "subsymbolic" computation (Smolensky, 1988) on distributed representations. This theory of brain information processing may suffice for simplifying models simulated in silicon but not for living neural nets where there is ongoing chemical tuning of the input/output transfer function at the nodes, connection weights, network parameters, and connectivity. Here the brain continually changes itself as it intersects with information from the outside. An alternative theory to information processing is developed in which the brain permits and supports "participation" of self and other as constraints on the dynamically evolving, self-organizing whole. The noncomputational process of "differing and deferring" in nonlinear dynamic neural systems is contrasted with Black's (1991) account of molecular information processing. State hyperspace for the noncomputational process of nonlinear dynamical systems, unlike classical systems, has a fractal dimension. The noncomputational model is supported by suggestive evidence for fractal properties of the brain.
Visual Processing without Awareness: Evidence from Unilateral Neglect
Authors: Berti Anna , Rizzolatti Giacomo
Published: February 2008

Can visual processing be carried out without visual awareness of the presented objects? In the present study we addressed this problem in patients with severe unilateral neglect. The patients were required to respond as fast as possible to target stimuli (pictures of animals and fruits) presented to the normal field by pressing one of the two keys according to the category of the targets. We then studied the influence of priming stimuli, again pictures of animals or fruits, presented to the neglected field on the responses to targets. By combining different pairs of primes and targets, three different experimental conditions were obtained. In the first condition, "Highly congruent," the target and prime stimuli belonged to the same category and were physically identical; in the second condition, "Congruent," the stimuli represented two elements of the same category but were physically dissimilar; in the third condition, "Noncongruent," the stimuli represented one exemplar from each of the two categories of stimuli. The results showed that the responses were facilitated not only in the Highly congruent condition, but also in the Congruent one. This finding suggests that patients with neglect are able to process stimuli presented to the neglected field to a categorical level of representation even when they deny the stimulus presence in the affected field. The implications of this finding for psychological and physiological theory of neglect and visual cognition are discussed.