An evaluation of sensory noise in the human visual system

It is assumed that the activity of a visual channel may be represented as V(t) = g(t) + xi(t), where g(t) is the deterministic response of the channel due to the presentation of a stimulus and xi(t) is the trajectory of a wide-sense stationary Gauss process. The stimulus is detected if the event (V(t) greater than S for at least one t epsilon[0, T]) occurs. Two approximations for the probability of this event are proposed, and it is demonstrated how they may be employed to estimate (i) the value of the second spectral moment lambda 2 of the noise process xi t, where lambda 2 reflects the speed of the fluctuations of the trajectories xi(t), and (ii) the value of the internal threshold S. The commonly made assumption of peak--detection is shown to serve as a very good first approximation in particular if the channel is of transient type or--in case of detection by a channel of sustained type--if the stimulus durations are not too long.