Space-time relations: The effects of variations in stimulus and interstimulus interval duration on perceived visual extent

Abstract

Three experiments were performed to study several variables influencing spatio-temporal relationships in the perception of visual extent (tau phenomenon). Ss were required to equate two visual extents demarcated by three temporally successive and spatially discrete flashes of light. All three experiments demonstrated that a larger spatial extent demarcated in a shorter time interval appeared equal to a shorter spatial extent demarcated in a longer time interval. The first experiment represented an attempt to supplement the findings of an earlier experiment by exploring the upper and lower temporal limits of this phenomenon. Utilizing interstimulus intervals (ISIs) ranging from 0.1 to 10 sec continued tau effects were observed. The results of the second experiment showed that it was the absolute difference (S-V) rather than the ratio difference (S/V) in variable and standard ISIs that governs the resulting tau effect. The third experiment demonstrated the significant effects of delimiting stimulus duration on the tau phenomenon. A relatively brief, i.e., 0.1 sec, stimulus duration significantly heightens the phenomenon in comparison to a relatively long, i.e., 4 sec., stimulus duration. These studies yield additional findings regarding the roles of order of variable and standard presentation and initial variable extent size. New directions for research in this area are discussed.