Abstract
While intuition suggests that visual information sampling through time is continuous, some have argued instead that sampling occurs in temporally discrete moments (VanRullen, & Koch, 2003). Of related interest is the question of how visual information is integrated through time. For example, is the information simply summed? We attempted to clarify the nature of visual information sampling and integration through time using a temporal response classification approach. Five subjects were asked to decide which of two movies, presented successively at the center of the screen, was the brightest. Each movie consisted in a sequence of 30 Gaussian blobs (200 ms) of different contrasts and subtending one degree of visual angle. A patch of spatial bit noise displayed through a Gaussian aperture was presented for 200 ms at the movies' location immediately before and after each movie. The contrast of the Gaussian blobs varied randomly through time. Specifically, on each trial, both movies had the same average and maximum contrast values across their temporal extent, but they differed in the temporal distribution of the contrasts. Thus, the brightness decision could only be influenced by the interaction between the participant's sampling/integration profile and the temporal sequence of contrasts in the stimuli. The sequence of contrasts that “optimally” led to a bright percept was computed for each participant by performing multiple regressions on the contrast temporal sequences and the participant's decisions. Three participants out of five showed a clear oscillation in their information sampling function (ranging between 5 and 15 Hz), and a linear decrease of information intake through time; the other participants reported being incapable of performing the task. Our results support the hypothesis that the visual system samples information in a discrete manner. They also indicate that the weight given to the information sampled decreases as information accumulates.