Event perception and sensory storage

Abstract

The experiments studied the ability to perceive visual, events of a very simple kind: the appearance and disappearance of isolated dots in random dot patterns. The aim of the investigation was to explore the limits of this ability and clarify the relationship, between event perception and sensory storage. The first series of experiments studied the ability to detect the appearance and disappearance of single dots. Under appropriate conditions such changes can be detected in a pattern containing 1024 dots with 98% accuracy. This level of accuracy was largely maintained over manipulation of the number of dots in the pattern, pattern size and separation between dots. Performance was unaffected by whether pattern luminance was uniform or not. It is argued that to explain this performance the notion of sensory integration must be augmented by the concept of sensory differentiation. The ability to detect events was further investigated as a function of pattern complexity and ISI. The storage underlying event detection has a very high capacity and a short duration. The second series of experiments investigated the ability to perceive patterns of events. Letters defined by either appearances or disappearances were accurately identified; thus a pattern which was not visible was made visible by its disappearance. A measure of localization was obtained by requiring subjects to judge whether three events were aligned. It is concluded that both onset and offset of a pattern convey information about form but that acuity for events is poorer than for sustained stimuli. The possibility that event perception is achieved by integration at short stimulus durations was investigated by varying the durations of the patterns before and after the events. Little evidence for event perception by integration was found; increasing the durations of the patterns either improved performance or had little or no effect on it. The final experiment examined a conflict between the present results and studies of visual integration. The ability to perceive mixtures of appearances and disappearances was investigated and found to be poorer than the ability to process either type of event alone. The ability to detect and locate events is highly developed. This ability seems well adapted to the detection and perception of significant change in the natural environment. In contrast to the increasing scepticism concerning the function of sensory storage it is concluded that event perception is an important visual function in which sensory storage is clearly implicated.