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Linda L. Chao
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1999) 11 (1): 25–35.
Published: 01 January 1999
Abstract
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Positron emission tomography (PET) was used to investigate whether retrieving information about a specific object attribute requires reactivation of brain areas that mediate perception of that attribute. During separate PET scans, subjects passively viewed colored and equiluminant gray-scale Mondrians, named colored and achromatic objects, named the color of colored objects, and generated color names associated with achromatic objects. Color perception was associated with activations in the lingual and fusiform gyri of the occipital lobes, consistent with previous neuroimaging and human lesion studies. Retrieving information about object color (generating color names for achromatic objects relative to naming achromatic objects) activated the left inferior temporal, left frontal, and left posterior parietal cortices, replicating previous findings from this laboratory. When subjects generated color names for achromatic objects relative to the low-level baseline of viewing gray-scale Mondrians, additional activations in the left fusi-form/lateral occipital region were detected. However, these activations were lateral to the occipital regions associated with color perception and identical to occipital regions activated when subjects simply named achromatic objects relative to the same low-level baseline. This suggests that the occipital activa-tions associated with retrieving color information were due to the perception of object form rather than to the top-down influence of brain areas that mediate color perception. Taken together, these results indicate that retrieving previously acquired information about an object's typical color does not require reactivation of brain regions that subserve color perception.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1998) 10 (2): 167–177.
Published: 01 March 1998
Abstract
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Neurological patients with focal lesions in the dorsolateral prefrontal cortex and age-matched control subjects were tested on an auditory version of the delayed-match-to-sample task employing environmental sounds. Subjects had to indicate whether a cue (S1) and a subsequent target sound (S2) were identical. On some trials, S1 and S2 were separated by a silent period of 5 sec. On other trials, the 5-sec delay between S1 and S2 was filled with irrelevant tone pips that served as distractors. Behaviorally, frontal patients were impaired by the presence of distractors. Electrophysiologically, patients generated enhanced primary auditory cortex-evoked responses to the tone pips, supporting a failure in inhibitory control of sensory processing after prefrontal damage. Intrahemispheric reductions of neural activity generated in the auditory association cortex and additional intrahemispheric reductions of attention-related frontal activity were also observed in the prefrontal patients. Together, these findings suggest that the dorsolateral prefrontal cortex is crucial for gating distracting information as well as maintaining distributed intrahemispheric neural activity during auditory working memory.