Temporal frequency modulates the strength of the inhibitory interaction between motion sensors tuned to coarse and fine scales.

Abstract

The perceived direction of motion of a brief moving fine scale pattern reverses when a static coarse scale pattern is added to it (Henning & Derrington, 1988). This impairment in motion direction discrimination has been explained by the inhibitory interaction between motion sensors tuned to fine and coarse scales. This interaction depends on the particular spatial frequencies mixed, the size of the stimulus, and the relative contrast of the components (Serrano-Pedraza, Goddard, & Derrington, 2007; Serrano-Pedraza & Derrington, 2010). In this research we wanted to study the effect of speed or temporal frequency on the interaction between motion sensors. We performed three experiments where we measured duration thresholds in a motion direction discrimination task, and we also measured the proportion of correct responses. The stimuli used in the experiments were horizontally drifting vertical Gabor patches of 4° diameter (2σxy). In the first two experiments, five stimulus configurations of moving (m) and static (s) components were used: two simple stimuli, 1m c/° and 3m c/°; and three complex stimuli, 1m + 3m, 1m + 3s, and 1s + 3m. Results show that for all conditions but 1s + 3m, duration thresholds decrease (proportion of correct responses increase) with increasing speed. However, in condition 1s + 3m, duration thresholds increase from 0.5°/s to 2°/s and then decrease with increasing speed. In the third experiment we tested whether the interaction between scales is tuned to speed or temporal frequency using different conditions: 1s + 4m, 1s + 6m, 0.5s + 1.5m, and 2s + 6m. Results from duration thresholds suggest that the strength of the inhibitory interaction between motion sensors tuned to coarse and fine scales is temporal frequency tuned with a maximum around 6 Hz and a minimum between 6 and 12 Hz in the case of the proportion of correct responses.