Threshold temporal integration of chromatic stimuli.

We measured colorimetric purity thresholds as a function of stimulus duration for seven wavelengths between 430 and 650 nm. Purity thresholds were measured in a hue substitution mode. The purity-duration function showed decreasing purity as duration was increased to about 640 msec. Functions for different wavelengths could be fit by a fixed chromatic template displaced on the purity axis. Increment thresholds as a function of duration were measured for white and chromatic lights added to a homogeneous white stimulus field. The "white" function showed no integration beyond 160 msec and was fit by an achromatic template. The wavelength functions were not parallel; wavelengths at the spectral extremes showed longer integration times, similar to the purity-duration functions. Increment data could be fit by a vector sum of chromatic and achromatic templates.