Detection of light and flicker at low luminance levels in the human peripheral visual system. II. A mechanistic model

A model describing the processing of quantal effects at low luminance levels is evaluated with respect to generally known experimental results for the temporal domain. The model consists of two sequential stages: a square-root scaler and a simple integrate-to-threshold detector. It is shown that with this model the experimental behavior of the absolute light threshold in relation to the flash duration and to the interval for periodic stimuli can be correctly described. When the detection mechanism is changed to a mechanism that detects a fixed minimum number of changes per time unit, the model can describe experimental data obtained at low luminance levels on the increment and decrement thresholds, the modulation transfer function, and the flicker experiments with varying light-dark ratio. From the data fitting it is concluded that in the near-peripheral visual field, adaptation processes have typical time constants of the order of 100 msec, whereas in the far periphery these processes have typical time constants ranging from 50 to 5000 msec, depending on stimulus size. The sampling time of the visual system for the above mentioned stimuli lies between 350 and 1500 msec.