Response adaptation to red-green color and achromatic contrast in the human visual cortex: an fMRI study.

Eur J Neurosci. 2015 Sep 28;

Authors: Mullen KT, Chang DH, Hess RF

Abstract
How responses to color in the human brain are organized within the visual pathways is controversial. A key issue is whether there are modular pathways that respond selectively to color or whether there are common neural substrates for both color and achromatic contrast. We used fMRI adaptation to investigate the responses of early and extrastriate visual areas to color and achromatic contrast. High contrast red-green (RG) and achromatic (Ach) sinewave rings (0.5cpd, 2Hz) were used as both adapting stimuli and test stimuli in a block design. We found robust adaptation to RG or Ach contrast in all visual areas. Cross adaptation between RG and Ach contrast occurred in all areas indicating the presence of integrated, color and achromatic responses. Notably we reveal contrasting trends for the two test stimuli. For the RG test, while unselective processing (robust cross adaptation to both RG color and Ach contrast) was most evident in the early visual areas (V1, V2), selective responses, revealed as greater adaptation between the same stimuli than cross-adaptation between different stimuli, emerge in ventral cortex, in V4, and VO in particular. For the Ach test, unselective responses are again most evident in early visual areas but Ach selectivity emerges in dorsal cortex (V3a, hMT+). Our findings support a strong presence of integrated mechanisms for color and achromatic contrast across the visual hierarchy, with a progression towards selective processing in extrastriate visual areas. This article is protected by copyright. All rights reserved.

PMID: 26414774 [PubMed - as supplied by publisher]