Triphasic temporal impulse responses and Mach bands in time.

The effect of inducing stimuli on the luminance of a brief test stimulus (2.5'-wide line) required to match the brightness of a comparison stimulus was measured at various stimulus onset asynchronies (SOAs). Assuming that the test brightness is determined by the peak response to the test stimulus, the difference in the test brightness in the absence and in the presence of an inducing stimulus as a function of the SOA was employed as a measure of the temporal response to the inducing stimulus. The temporal responses to brief decremental inducing stimuli (a 2.5'-wide line and a 30'-wide bar) consisted of three oscillations, the middle one being the largest. The triphasic form of the temporal impulse responses was confirmed by measuring the temporal step responses to these stimuli. The step responses consisted of alternating positive and negative phases which might be regarded as a temporal analogue of the Mach bands in space. The data obtained were described by a model of the weighting function which was assumed to be a spatiotemporal Gabor-like function.