Selective Adaptation to Color Contrast in Human Primary Visual Cortex

Abstract

How neural activity produces our experience of color is controversial, because key behavioral results remain at odds with existing physiological data. One important, unexplained property of perception is selective adaptation to color contrast. Prolonged viewing of colored patterns reduces the perceived intensity of similarly colored patterns but leaves other patterns relatively unaffected. We measured the neural basis of this effect using functional magnetic resonance imaging. Subjects viewed low-contrast test gratings that were either red-green (equal and opposite long-and middle-wavelength cone contrast, L-M) or light-dark (equal, same-sign, long-and middlewavelength cone contrast, LϩM). The two types of test gratings generated approximately equal amounts of neural activity in primary visual cortex (V1) before adaptation. After exposure to high-contrast L-M stimuli, the L-M test grating generated less activity in V1 than the LϩM grating. Similarly, after adaptation to a high-contrast LϩM grating, the LϩM test grating generated less activity than the L-M test grating. Behavioral measures of adaptation using the same stimuli showed a similar pattern of results. Our data suggest that primary visual cortex contains large populations of color-selective neurons that can independently adjust their responsiveness after adaptation. The activity of these neural populations showed effects of adaptation that closely matched perceptual experience.

Object-Selective Cortex Exhibits Performance-Independent Repetition Suppression

“…The mean suppression ratio across voxels in V1 was 0.90 Ϯ 0.016, which was significantly greater than that for LO (P Ͻ 10 Ϫ10 ) or pFus (P Ͻ 10 Ϫ10 ; 1-tailed t-test). These results are consistent with previous studies (Grill-Spector and Malach 2001;Grill-Spector et al 1999) and validate the notion that RS in object-selective cortex is distinct from adaptation phenomena observed in early visual cortex (Boynton and Finney 2003;Engel and Furmanski 2001).…”

Contrast adaptation and representation in human early visual cortex

“…While individual neurons in single-unit studies may show a range of susceptibility to adaptation (Sclar et al, 1989), our measurements are sensitive to the activity of large populations of neurons and therefore indicate that on the whole, contrast gain changes shift contrast response to the range that is functionally beneficial. Previous block design imaging experiments (Kastner et al, 2004), which have compared contrast response functions measured with ascending versus descending contrasts, may not have been as sensitive to adaptation changes as event-related studies (this study and Engel and Furmanski, 2001). Changes in contrast response functions measured with BOLD imaging have been noted in surround suppression experiments (Zenger-Landolt and Heeger, 2003), sharing some similarities with the effect we find with adaptation.…”

“…Imaging studies have conflicting reports on whether (Engel and Furmanski, 2001) or not (Kastner et al, 2004) contrast adaptation can be detected in human visual cortex at all, and…”

Neuromagnetic Correlates of Streaming in Human Auditory Cortex

“…Selective adaptation by feature-specific neurons might be a general neural mechanism subserving perceptual organization, because it has also been observed in the auditory cortex for interaural phase disparity (Malone et al, 2002) and in the visual cortex for various features, such as orientation (Boynton and Finney, 2003) or color contrast (Engel and Furmanski, 2001). Selective adaptation of feature-specific neurons may help account for the streaming of complex tones (with peripherally unresolved harmonics), which cannot be explained by spectral channeling along the tonotopic axis (Vliegen and Oxenham, 1999;Cusack and Roberts, 2000;Grimault et al, 2002;Roberts et al, 2002).…”