40 巻 (1969-1970) 5 号 p. 267-272
Recently, it is reported that (Sato, 1968a, b) at low range of flicker, apparent brightness enhances and observer's response variability increases as brightness enhances. These phenomena greatly depend on the relationship between stimulus frequency and temporal characteristics of neural activity, (e.g. refractory period, temporal summation) in visual system. According to observer's introspection, response variability is difficult to control voluntarily. This investigation was carried out in order to confirm the following hypothesis.
Hypothesis: At low range of flicker, apparent brightness and observer's response variability increase as brighthess enhances. Underlying mechanism of these phenomena is the principle of optimum efficiency of neural activity in relation to stimulus and neural response intensity, and this principle works only through the mediation of the factor of temporal configuration of stimuli. Therefore, as far as the stimulus is flicker, similar results will obtained if observers were given some other task than brightnessmatching.
Exp. 1: Increment thresholds of flicker target (4, 6, 8, 12.5, 19, 26, 35, 46 cps, diameter 1°) on background field (6°, 38.88mL, steady light) were measured. Observers were 15 undergraduate students in psychology (male and female). At 6 to 12.5cps, thresholds of all observers were lower than they were at 19 to 46cps. As thresholds decreased, response variability increased for all observers but three. These three observers showed large variability at 26 to 46cps (Table 1). It is clear that the decrease of thresholds, at lower range of flicker, was evoked by brightness enhancement. At above 19cps, obtained threshold was higher than that below 12.5cps. It suggests that apparent brightness of high frequency flicker obeys Talbot's law. An additional finding was that observers were divided into two types in terms of their response variability, and to confirm this finding Exp. 2 was conducted.
Exp. 2: Brightness of flicker targets (4, 6, 8, 12.5, 26, 35, 46cps., 11.23mL, diameter 1°) was matched by 16 observers to that of the steady target (diameter 1°, intensity variable). At 4 to 8cps, apparent brightness enhanced and response variability increased. But there were five observers out of sixteen, who showed higher variability at 26 to 46cps (Table 4). This confirmed the above finding that there were two types of observers (majority group and minority group) as to the response variability. There was not sex difference.