New look at Bloch’s law for contrast

Abstract

It has been commonly reported that the temporal integration of grating contrast proceeds more slowly as spatial frequency is increased. Such results have been based on the critical duration for sensitivity to contrast pulses varying in duration, but the analyses have not assumed full integration at short durations and have neglected the effects of probability summation over time. To take such effects into account, we discuss a class of analytical models based on nonlinear temporal integration. On the assumption that the temporal impulse response of the visual system determines contrast integration over time, we develop both a high-threshold model and a signal-detection approach involving multiple and independent nonlinear signal detectors with a time-limited integration span. The redefined critical durations predicted by the models and verified by the data are about 35 msec and vary by no more than 10 msec across spatial frequency. This variation is entirely attributable to a change in the strength of inhibition with spatial frequency, and the analysis implies that the excitatory component is constant at all spatial frequencies, contrary to previous accounts.

Analysis of simple reaction time to sinusoidal grating by means of a linear filter model of the detection process

“…It has been shown that temporal properties of the visual system at threshold level can be described well with a linear filter model in which it is assumed that the visual system consists of a set of spatiotemporal linear ftlters (Bergen & Wilson, 1985;Gorea & Tyler, 1986;Watson, 1979Watson, , 1986Watson & Nachrnias, 1977). If one assumes that RT is determined by the sensory signal near threshold level," the linear filter model may be applied to obtain the time course of the sensory signal in the vicinity of the critical level, and the sensory processing delay (the visual latency) involved in RT may thereby be estimated.…”

“…The second of these steps was carried out according to a linear filter model of the detection process that has been notably successful for predicting the temporal properties of the visual system at threshold levels (Bergen & Wilson, 1985;Gorea & Tyler, 1986;Watson, 1979Watson, , 1986Watson & Nachmias, 1977). The linear filter model also aided in the fourth step, Relati ve contrast…”

Optimizing the temporal dynamics of light to human perception

“…Broca and Sulzer, instead, found a peak in perceived contrast with increased duration. Bloch's result prevailed as the accepted model of basic temporal vision (10,11), so much so that it was elevated to the status of a perceptual law. Yet the discrepancy between Bloch's law and the Broca-Sulzer effect remains unexplained.…”

Revealing information by averaging

“…Temporal integration is related to the ability of the HVS to sum the quantity of light exposed over time [11]. According to Bloch's law, the perceived luminous energy is a constant formed by the product of luminance and exposing time.…”