Spectral Tuning of Opponent Pathways is Temporally Dependent

Psychophysical test and field sensitivity data suggest that the spectral sensitivities of red/green opponent channels (red/green cells) become progressively nonopponent with decreases in stimulus size or duration. Recent data show that the shape of the field sensitivity depends not on field size per se but on the relative size of test and field. The present study examined the effect on field sensitivity of variations in the temporal parameters of stimulation. The results suggest a more complicated interaction than is observed in the spatial domain. Spectral tuning depends not only on the relative durations of test and field but also on the offset asynchrony between the two lights. Only when the test is extinguished prior to the field do the data show evidence of red/green activity. When the two lights coterminate. the field sensitivity resembles a nonopponent function, regardless of stimulus duration