1957 年 28 巻 4 号 p. 210-222
Obonai (this journal, 1949, 19, 177-183) reported that the rate of figure-ground reversal decreased as the size of stimulus pattern increased and that the rate increased as the brightness gradient between figure-sectors and their surroundings, the illuminance of stimulus field and the number of sectors increased. We re-examined these relationships.
The stimulus pattern used in this study was a circle devided into six sectors. Three alternate sectors were white or light gray, and the other sectors were black or dark gray. The surrounding field was middle gray or white. (See Fig. 1 of the text).
Regular figure-ground reversal cycles were frequently interrupted by what we call the undefined phase in which neither of the two areas appeared as figure. This fact made it difficult to determine unequivocally the number of reversal or the time of reversal. So we adopted, as a measure of the rate of reversal, the average number of appearances of two areas per minute i. e. N = (nw + nb) / 2.
We analyzed the influence of the size of stimulus pattern through fifteen series of experiments which varied in stimulus pattern, illumination, set, subjects and experimental design. In only two of the series, we obtained statistically significant results. We concluded that Obonai's result was a special case with some particular types of subjects under some particular stimulus conditions.
We did not find the influence of brightness gradient upon the rate of reversal when the brightnesses of the two areas were varied symmetrically. But we found that, when the brightness of one area was kept constant, the rate of reversal increased as the brightness gradient between the other area and the surroundings became more similarto that of the former.
We found also that the rate increased as the illuminance of stimulus field increased. On the other hand, the influence of the number of sectors was not clear in our experiment.
Above mentioned changes in the rate of reversal were partly due to the changes in the time of undefined phase. The level of the rate of reversal varied considerably from subject to subject and individual levels were relatively constant through many experiments.
The influence of those stimulus factors upon the rate of reversal was rather slight and not general, contrary to Obonai's results. It was suggested that the rate of figureground reversal was determined by the conditions of the organism rather than by stimulus set-up.