Hierarchical Representation for Chromatic Processing across Macaque V1, V2, and V4.

The perception of color is an internal label for the inferred spectral reflectance of visible surfaces. To study how spectral representation is transformed through modular subsystems of successive cortical areas, we undertook simultaneous optical imaging of intrinsic signals in macaque V1, V2, and V4, supplemented by higher-resolution electrophysiology and two-photon imaging in awake macaques. We find a progressive evolution in the scale and precision of chromotopic maps, expressed by a uniform blob-like architecture of hue responses within each area. Two-photon imaging reveals enhanced hue-specific cell clustering in V2 compared with V1. A phenomenon of endspectral (red and blue) responses that is clear in V1, recedes in V2, and is virtually absent in V4. The increase in mid- and extra-spectral hue representations through V2 and V4 reflects the nature of hierarchical processing as higher areas read out locations in chromatic space from progressive integration of signals relayed by V1. • Color-response blobs comprise a uniform architecture across V1, V2, and V4 • Blobs evolve progressively in spatial scale and separation of hue representation • Two-photon imaging shows greater hue-specific cell clustering in V2 than in V1 • Chromotopic organization achieves greater spectral uniformity from V1 to V2 to V4 How does our visual brain generate perceptual color space? Liu et al. find that within a uniform blob-like architecture of hue responses, chromotopic maps develop progressively in scale and precision along the visual hierarchy of macaque V1, V2, and V4. Such hierarchical refinement improves spectral uniformity, better reflecting color perception. [ABSTRACT FROM AUTHOR]