抄録
Distance from a stimulus, stimulus size and orientation with respect to the observer are relevant metric properties of visual space. However, whether and how these metrics are related to each other is not well known. Some studies have shown that estimates of egocentric distances are usually more accurate than judgments of exocentric distances, suggesting that there is dissociation between ‘localization’ judgments and ‘size’ judgments. Other investigations have revealed that the orientation of the stimulus influences the accuracy of size estimations.
To better understand the relationships between these metric properties of visual space, we conducted an experiment to compare size perception as a function of orientation from viewer egocentric and exocentric frames of reference (FoR). Observers were instructed to draw two circles on a screen by clicking with a mouse when the screen was positioned on either the frontoparallel plane or the ground plane.
From an egocentric FoR, egocentric distance and direction were processed asymmetrically, as knowledge of the particular combination of both size and orientation was always needed to compute visual direction. However, in terms of the accuracy of size estimates (S’/S) from an exocentric FoR, size and orientation were independent for all conditions. Therefore, the orientation did not need to be computed in order to compute the size. Regarding exocentric direction or orientation (α’/α), size and orientation were only dependent when the two points were presented successively. In conclusion, these findings suggest that orientation and distance always interact and that distance, visual direction or orientation require an egocentric cue.
