Polarity-sensitive perceptual adaptation to temporal sawtooth modulation of luminance

Exposure to a large uniform field modulated in luminance by a sawtooth function, repeating between 1 and 5 times per second, raised the threshold for detection of a test stimulus of similar waveform by a factor of 2 to 4.5. In comparison, the threshold elevation for a test stimulus of the inverse waveform was only half as great. This polarity-sensitive adaptation fits with Jung's hypothesis that separate channels signal 'brightening' and 'darkening' in the human visual system. Introduction of spatial contrast such as random noise does not affect adaptation to temporal luminance gradients, but does lead to some interocular transfer. The transferred component, however, shows no sensitivity to the polarity of the test stimulus.