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Joong Nam Yang, Daniel Ts'o, Nikolaus Szeverenyi; Neuronal resources for perceptual judgment localized in the human brain. Journal of Vision 2006;6(6):534. doi: 10.1167/6.6.534.
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PURPOSE: Is there a common area in the human brain that is involved in perceptual decision-making regardless of visual attributes or perceptual modalities? To answer this question, we combined a psychophysical paradigm of difference scaling with fMRI.
METHODS: We used the method of difference judgment for perceptual decision. Two small colored rectangles with different widths (less than 1 degree/visual angle) were presented on each side of a fixation point in one interval, and second set in the next interval. Subjects responded with a button press to indicate which set had the greater difference in color, area, speed or orientation. We extended this paradigm to auditory stimuli; subjects performed difference judgment on two intervals of tone durations.
RESULTS: Passive viewing of stimuli led to retinotopically-appropriate BOLD responses in the para-foveal regions for color, form, and in MT and STS for motion. With active perceptual judgment, areas in V4/V8 complex were additionally activated for color and form. Surprisingly, however, for each of the four visual attributes, the lateral/ posterior region of the parietal lobe that includes IPS was consistently activated. For auditory stimuli, passive listening led to activation in the auditory cortex, while difference judgment also produced additional activation in IPS. Absence of the button press did not change the results.
CONCLUSIONS: (1) Perceptual judgment is distributed in neuronal representation, and (2) The lateral/posterior areas of the parietal lobe in the distributed representation are consistently activated during both visual and auditory judgments.
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