Abstract
Points of Subjective Equality (PSEs) are usually measured with constant stimuli (CS) methods. However, it’s found time-consuming and inefficient in clinic settings such as in our recent studies investigating the Pulfrich phenomenon (Reynaud, A. & Hess, R. F. (2019), An unexpected spontaneous motion-in-depth Pulfrich phenomenon in amblyopia, Vision 3(4). 54). Thus, we wanted to develop a more efficient method to estimate the PSE and its variability. We have developed an adaptive (AD) method in which levels are chosen on a pre-defined scale such as for CS. However, instead of testing each level with the same number of repetitions, each stimulus will be chosen depending on the previous response of the participant. If the participant responded “up”, one random level in the lower range would be picked for the next trial. And if the participant responded “down”, one random level in the upper range would be picked for the next trial. This procedure would result in a bell-shaped distribution of the tested levels around the estimated PSE. We compared this method with traditional CS procedure on a task based on the Pulfrich phenomenon with a fixed number of total trials (75，150 and 300), while the PSEs of participants could be varied using different ND filters (0ND,±1ND). We observed a significant correlation among the PSEs obtained with the two methods. And in most cases, our adaptative method yielded a smaller variability of the estimates of both the PSE and the slope of the psychometric function. Therefore, we can conclude that the adaptive method is an efficient way of measuring PSEs with our Pulfrich paradigm. It could potentially be used for other psychophysical PSE estimation.