Figure 2. Probability Distribution of response.

a, Mean probability distribution of responses for each coherence ratio (n = 13, only between −50° to +50°). The bin size of 5 degree was determined based on mean motor error measured in a separate experiment (See Supplementary Information). ‘0’ in the scale of relative direction indicates the global motion direction. The blue and red bars correspond to the relative direction of the 1^st (−20°) and 2^nd (+20°) motion directions, respectively. Vertical error bars, ±1 SEM. b, Mean probability of response at the central direction as a function of the coherence ratio (n = 13). Vertical error bars, ±1 SEM. A vertical purple bar represents the mean psychophysical threshold of local-motion with a horizontal purple bar, ±1 SEM (from the results of the motion threshold test: See Methods and Supplementary Information). The probability of response at 34% coherence ratio was significantly higher than that at 10, 22, and 70% coherence ratios (n = 13, p < 0.01 for each t test with Bonferroni correction).