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. 2003 Apr;6(4):414-20.
doi: 10.1038/nn1024.

Neuronal correlates of perception in early visual cortex

David Ress  1 , David J Heeger
Affiliations

Neuronal correlates of perception in early visual cortex

David Ress et al. Nat Neurosci. 2003 Apr.

Abstract

We used functional magnetic resonance imaging (fMRI) to measure activity in human early visual cortex (areas V1, V2 and V3) during a challenging contrast-detection task. Subjects attempted to detect the presence of slight contrast increments added to two kinds of background patterns. Behavioral responses were recorded so that the corresponding cortical activity could be grouped into the usual signal detection categories: hits, false alarms, misses and correct rejects. For both kinds of background patterns, the measured cortical activity was retinotopically specific. Hits and false alarms were associated with significantly more cortical activity than were correct rejects and misses. That false alarms evoked more activity than misses indicates that activity in early visual cortex corresponded to the subjects' percepts, rather than to the physically presented stimulus.

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Figures

Fig. 1
Fig. 1
An ideal-observer model of contrast detection. The observer makes his/her decision on each trial by comparing a noisy internal response (e.g., average firing rate of an appropriate subpopulation of neurons) with a fixed criterion. According to this model, the mean responses (across trials) for the 4 trial categories should rank: hits > false alarms > misses > correct rejects.
Fig. 2
Fig. 2
Experimental stimuli: (a) plaid background; (b) plaid + vertical-grating target; (c) noise background; (d) noise + vertical-grating target. (Noise-background targets had randomized orientation and spatial phase.)
Fig. 3
Fig. 3
Typical fMRI responses for individual subjects: (a, b) time series from V1; (c, d) response amplitudes; (a, c) plaid background; (b, d) noise background. Error bars are standard error of the mean (s.e.m).
Fig. 4
Fig. 4
fMRI response amplitudes averaged across subjects. (a, b) Response amplitudes from gray matter regions corresponding to the cortical representations of the stimulus annulus. (c, d) Response amplitudes from cortical representations of a peripheral region of the visual field. (a, c) Plaid background. (b, d) Noise background. Error bars are s.e.m.
See this image and copyright information in PMC

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