Temporal integration in the visual system: influence of temporal dispersion on figure-ground discrimination

Psychophysical measurements were carried out with a microcomputer-controlled matrix of 32 X 32 light emitting diodes to determine temporal parameters of figure-ground separation processes. The task was to detect a figure that was dispersed in time. Between each two figure elements n noise elements were interspersed. The results of these experiments indicate that the discrimination of figures hidden in dynamic noise is possible even if figure elements are dispersed in time over several hundred milliseconds. The maximal dispersion time still compatible with figure discrimination (Tmax) depends critically on the number n of interspersed noise elements, on the subject's expectancy and on the number of elements used for the generation of the figure. For simple figures such as triangles Tmax could be as long as 1.5 sec when n was 4. Our experimental results suggest that the neuronal representation of the briefly displayed (less than 6 msec) pattern elements outlasts their physical presence by at least 400 msec. This persistence of neuronal representations must occur at a level of processing where retinotopy is still preserved, since the only cue for figure-ground discrimination is the difference in the local density of figure and noise elements.