A Limiting Channel Capacity of Visual Perception: Spreading Attention Divides the Rates of Perceptual Processes

This study investigated effects of divided attention on the temporal processes of perception. During continuous watch periods, observers responded to sudden changes in the color or direction of any one of a set of moving objects. The set size of moving objects was a primary variable. A simple detection task required responses to any display change, and a selective task required responses to a subset of the changes. Detection rates at successive points in time were measured by response time (RT) hazard functions.The principal finding was that increasing the set size divided the detection rates-and these divisive effects were essentially constant over time and over the time-varying influence of the target signals and response tasks. The set size, visual target signal, and response task exerted mutually invariant influence on detection rates at given times, indicating independent joint contributions of parallel component processes. The lawful structure of these effects was measured by RT hazard functions but not by RTs as such. The results generalized the time-invariant divisive effects of set size on visual process rates found by Lappin, Morse, & Seiffert (Attention, Perception, & Psychophysics, 78, 2469-2493, 2016). These findings suggest that the rate of visual perception has a limiting channel capacity.