Abstract
Two dots bound together by placement on an object's surface appear further apart than the same two dots not surrounded by an object, suggesting that space within objects is perceptually expanded ("object-based warping," Vickery & Chun, 2010, Psychological Science). One possible cause for this illusion is attention, which may concentrate within the boundaries of an object and distort spatial perception. We explored potential links between attention and object-based warping by manipulating the attentional requirements of a spatial adjustment task. Subjects (N=20) viewed displays consisting of "reference" dots on one side of the screen, and "adjustment" dots on the other. They manipulated adjustment dot spacing to match the spacing of the reference dots. The reference dots were either surrounded by a closed rectangular contour ("object") or not. In addition, we manipulated the contrast of the dots: reference and adjustment dots were presented in high- or low-contrast (black or gray, on a light-gray background), creating four contrast conditions (high-reference/high-adjust, low-reference/high-adjust, etc.). We reasoned that low-contrast dots would require a higher concentration of attention during this task. Replicating prior work, assessments of dot spacing was influenced by the presence of the object; within all four contrast conditions, subjects reported that object-surrounded dots were spaced further apart than equivalent non-object displays (all p< .001). Overall, non-object dots were reported as 2.9% further apart than reality , compared with 6.1% for object-surrounded dots. Critically, contrast also affected distortions. In non-object conditions, when reference dots were low-contrast and adjustment dots were high-contrast, distortions were greater (5.3%) compared to when both sets of dots were high-contrast (3.3%) or both were low-contrast (2.1%; both p< .001). These results demonstrate that attention can drive similar space-distorting effects as the presence of an object, and support the possibility that object-based warping may be due to effects of object presence on attention.
Meeting abstract presented at VSS 2018