A neuropsychological theory is proposed that assumes category learning is a competition between separate verbal and implicit (i.e., procedural-learning-based) categorization systems. The theory assumes that the caudate nucleus is an important component of the implicit system and that the anterior cingulate and prefrontal cortices are critical to the verbal system. In addition to making predictions for normal human adults, the theory makes specific predictions for children, elderly people, and patients suffering from Parkinson's disease, Huntington's disease, major depression, amnesia, or lesions of the prefrontal cortex. Two separate formal descriptions of the theory are also provided. One describes trial-by-trial learning, and the other describes global dynamics. The theory is tested on published neuropsychological data and on category learning data with normal adults.

Neuroimaging and neuropsychological studies have implicated left inferior prefrontal cortex (LIPC) in both semantic and phonological processing. In this study, functional magnetic resonance imaging was used to examine whether separate LIPC regions participate in each of these types of processing. Performance of a semantic decision task resulted in extensive LIPC activation compared to a perceptual control task. Phonological processing of words and pseudowords in a syllable-counting task resulted in activation of the dorsal aspect of the left inferior frontal gyrus near the inferior frontal sulcus (BA44/45) compared to a perceptual control task, with greater activation for nonwords compared to words. In a direct comparison of semantic and phonological tasks, semantic processing preferentially

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 for 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 semanti...

For cognitive neuroscience to go forward a more explicit effort is needed to use neurophysiology to constrain how the brain produces human mental functions. This review begins with the suggestion that two fundamental features may be critical for this effort. The first is the connectivity of the brain, which occupies an intermediate position between complete redundant interconnections and independence. The term semiconnected is presented as a designation, which is an obvious derivation of the term semiconductors as used in engineering. The second is transient response plasticity where a given neuron or collection of neurons may show rapid changes in response characteristics depending on experience. Response plasticity is a ubiquitous property of the brain rather than a unique characteristic of "neurocognitive" regions. These two properties may be brought together when brain areas interact such that their aggregate function embodies cognition. Three examples are used to illustrate these ...

Over the last years evidence has accumulated that shows the possibility to analyze human brain activity on-line and translate brain states into actions such as selecting a letter from a virtual keyboard or moving a robotics device. These initial results have been obtained with either invasive approaches (requiring surgical implantation of electrodes) or synchronous protocols (where brain signals are time-locked to external cues). In this paper we describe a portable noninvasive brain-computer interface that allows the continuous control of a mobile robot in a house-like environment and also the operation of a virtual keyboard. The interface works asynchronously (the person makes selfpaced decisions on when to switch from one mental task to the next) and uses 8 surface electrodes to measure electroencephalogram signals from which a statistical classifier recognizes 3 different mental states. Here we report results with five volunteers during their brain-actuated interaction experiments with the mobile robot and the virtual keyboard. Two of the participants successfully moved the robot between several rooms, while the other three participants managed to write messages with the virtual keyboard. One of the latter volunteers is a physically impaired person suffering from spinal muscular atrophy.

& Phonological processes map sound information onto higher levels of language processing and provide the mechanisms by which verbal information can be temporarily stored in working memory. Despite a strong convergence of data suggesting both left lateralization and distributed encoding in the anterior and posterior perisylvian language areas, the nature and brain encoding of phonological subprocesses remain ambiguous. The present study used functional magnetic resonance imaging (fMRI) to investigate the conditions under which anterior (lateral frontal) areas are activated during speech-discrimination tasks that differ in segmental processing demands. In two experiments, subjects performed ‘‘same/ different’ ’ judgments on the first sound of pairs of words. In the first experiment, the speech stimuli did not require overt segmentation of the initial consonant from the rest of the word, since the ‘‘different’ ’ pairs only varied in the phonetic voicing of the initial consonant (e.g., dip–tip). In the second experiment, the speech stimuli required segmentation since ‘‘different’ ’ pairs both varied in initial consonant voicing and contained different vowels and final consonants (e.g., dip–ten). These speech conditions were compared to a tone-discrimination control condition. Behavioral data showed that subjects were highly accurate in both experiments, but revealed different patterns of reaction-time latencies between the two experiments. The imaging data indicated that whereas both speech conditions showed superior temporal activation when compared to tone discrimination, only the second experiment showed consistent evidence of frontal activity. Taken together, the results of Experiments 1 and 2 suggest that phonological processing per se does not necessarily recruit frontal areas. We postulate that frontal activation is a product of segmentation processes in speech perception, or alternatively, working memory demands required for such processing. &

Abstract — Why is it that people cannot keep their hands still when they talk? One reason may be that gesturing actually lightens cognitive load while a person is thinking of what to say. We asked adults and children to remember a list of letters or words while explaining how they solved a math problem. Both groups remembered significantly more items when they gestured during their math explanations than when they did not gesture. Gesturing appeared to save the speakers’ cognitive resources on the explanation task, permitting the speakers to allocate more resources to the memory task. It is widely accepted that gesturing reflects a speaker’s cognitive state, but our observations suggest that, by reducing cognitive load, gesturing may also play a role in shaping that state. Gesturing occurs across ages, tasks, and cultures (Feyereisen & de Lannoy, 1991). Although in theory gesture could be nothing more than meaningless hand waving, recent research has found that gesturing conveys meaningful information (Clark, 1996; Goldin-Meadow, Mc-Neill, & Singleton, 1996; Kendon, 1980; McNeill, 1992), information that is not always found in the speech it accompanies (Goldin-Meadow, Alibali, & Church, 1993). For example, a speaker might say, “I ran all the way upstairs ” while moving her index finger upward in a spiral. It is through the speaker’s gestures, and only her gestures, that the listener knows the staircase is a spiral. Moreover, gesture is noticed. The information that gesture conveys frequently has an impact on the message listeners take from the communication (Alibali, Flevares,

Abstract not found

studies, which offer higher spatial resolution, will shed new light on when and why encoding yields subsequent remembering. Keywords: subsequent memory effect; episodic encoding; episodic memory; event-related potentials; fMRI; PET 1. INTRODUCTION In the course of a typical day, humans experience many complex events: perceiving faces and other objects, reading words and text passages, interpreting the meaning of spoken phrases, and the like. Yet, at the end of the day, only a subset of these experiences are memorable, with many of the day's events having been forgotten. To understand human memory, it is critically important to determine why some experiences can be later remembered, whereas others are subsequently forgotten. Considerable behavioural and neuropsychological evidence indicates that the ability to remember a given experience is affected by many factors, including the kinds of processing operations that are engaged at the time of encoding and retrieval, and interactions

Written Chinese as logographic script differs notably from alphabets such as English in visual form, orthography, phonology, and semantics. Thus, research on the Chinese language is important to advance our understanding of the universality and particularity of the organization of language systems in the brain. In this study, we examine the neural systems associated with logographic reading using functional magnetic resonance imaging. Two experimental tasks were devised, one based on semantic decision and the other on homophone decision. Compared to the fixation baseline, peak activations resulting from semantic as well as homophony decisions were localized in the left middle frontal gyrus (BA 9). Left inferior frontal cortex also mediated Chinese processing. In addition, more right hemisphere cortical regions (i.e., BAs 47/45, 7, 40/39, and the right visual system) were involved in reading Chinese relative to reading English. This is attributed to the square shape of the logograph which requires an elaborated analysis of the spatial information and locations of various strokes comprising the logographic character. We suggest that the left middle frontal area (BA 9) coordinates and integrates the intensive visuospatial analysis demanded by logographs ’ square configuration and the semantic (or phonological) analysis required by the present experimental tasks. Our study has implicated brain regions common to both logographic and alphabetic languages as well as brain regions specialized in processing logographs. © 2001 Academic Press