A DISSOCIATION BETWEEN BRAIN ACTIVITY AND PERCEPTION - CHROMATICALLY OPPONENT CORTICAL-NEURONS SIGNAL CHROMATIC FLICKER THAT IS NOT PERCEIVED

When two isoluminant colors alternate at frequencies >10 Hz, we percei ve only one fused color with a minimal sensation of brightness flicker . In spite of the perception of color fusion, color opponent (CO) cell s at early stages of the visual pathway are known to respond to chroma tic flicker at frequencies far exceeding the perceptual fusion frequen cy. To explain color fusion, several groups have predicted that CO cel ls in V1-unlike the retina and lateral geniculate nucleus-should not f ollow high-frequency flicker, To test this prediction we recorded from 12 CO cells in various V1 layers, We found, contrary to expectations, that these neurons follow high frequency flicker well above heterochr omatic fusion frequencies. All followed 15 Hz flicker and 10/12 follow ed 30 Hz flicker, For three cells, we tested 60 Hz luminance flicker a nd found clear responses. We thus present evidence of cortical activit y in alert, trained monkeys that is clearly representing visual stimul ation, yet is not perceived. Our data call into question explanations of perceptual phenomena that invoke a low temporal frequency cut-off o f CO cells in V1 to account for the failure to perceive fast temporal changes in the chromatic domain. Copyright (C) 1997 Elsevier Science L td.