Purchase this article with an account.
J. G. Chambeaud, J. F. Barraza; Spatiotemporal Boundary Formation: Similar Performance for Modal and Amodal Completion. Journal of Vision 2010;10(7):1220. doi: 10.1167/10.7.1220.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
There is a controversy about whether modal and amodal completion are driven by the same or by different mechanisms. In this sense, there are experimental and theoretical evidence in the literature supporting both hypotheses. In this study, we present the results of three experiments showing that performance for modal and amodal completion in the case of Spatiotemporal Boundary Formation (SBF) are similar. We use the type of stimuli used Shipley and Kellman (1993) to explore SBF and introduced disparity to produce modal and amodal percepts. In the first experiment we performed a Vernier acuity task between two motion-defined bars and tested the threshold for a range of disparities (+3, +1, 0, -1, -3), speeds (1, 2, 4 deg/s), and dot densities (4 and 8 dots/deg2). Results show that Vernier threshold does not depend on the amount of disparity for all experimental conditions. Moreover, there are no significant differences between thresholds obtained with positive and negative disparities, which would suggest a similarity between modality and amodallity. We wondered whether this result would keep the same for other tasks used in previous experiments such as form discrimination. In the second experiment, we used the same type of stimulus but asked the observers to discriminate between thinned and fattened bars. Results show no differences between modal and amodal perception, consistently with the first experiment. In the third experiment we measured Vernier thresholds for three temporal windows (50, 100, 350 ms), since it was found, in previous studies, some differences between modal and amodal perception for short stimulus presentation. Results show that for 100 ms four of six subjects present slight differences between thresholds obtained with positive and negative disparities. These results show that mechanisms underlying modal and amodal completion have the same efficiency, which could suggests that they are actually the same.
This PDF is available to Subscribers Only