August 2016
Volume 16, Issue 12
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2016
Size averaging is based on distal, not proximal object sizes
Author Affiliations
  • Natalia Tiurina
    National Research University Higher School of Economics, Moscow, Russia
  • Igor Utochkin
    National Research University Higher School of Economics, Moscow, Russia
Journal of Vision September 2016, Vol.16, 56. doi:10.1167/16.12.56
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      Natalia Tiurina, Igor Utochkin; Size averaging is based on distal, not proximal object sizes. Journal of Vision 2016;16(12):56. doi: 10.1167/16.12.56.

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      © 2017 Association for Research in Vision and Ophthalmology.

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Abstract

Observers are good at rapid estimation of the average size of multiple objects (Ariely, 2001; Chong & Treisman, 2003). We tested whether the average is calculated along a "raw" (proximal) stimulus size (where only visual angle is important) or relies on the distal size of an object (which requires taking distance information into account). Our participants performed the size averaging task adjusting the size of a probe circle. Using a stereoscope, we changed the apparent distance of ensemble members from the observer. In Experiment 1, all ensemble members shifted by the same disparity angle in both eyes, so that they seemed at different distances but always in one plane. The probe was always in a same plane (zero disparity). We found that presenting ensembles in apparently remote planes made observers to overestimate their mean size in comparison to what is expected from simple visual angle averaging. In Experiment 2, ensemble members were presented at different planes so that (1) visual angle reduced with the apparent distance, making apparent sizes of individual members more similar, (2) visual angle increased with the apparent distance, increasing this apparent dissimilarity, and (3) all members were presented at the zero disparity plane. We found that the mean error in probe averaging in condition (1) was significantly smaller than in other conditions. This finding is in line with previous studies also showing that similarity between ensemble members in one plane reduce the error. As the items in condition (1) could look more similar than in the others only due to the distance cues, we conclude that observers took into these cues into account. Our main theoretical conclusion is that the visual system appears to work with bound objects rather than their separate features when representing their global properties such as the average size.

Meeting abstract presented at VSS 2016

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