Abstract
Brief visual cues are often used to induce involuntary shifts of attention to locations away from the center of gaze. However, it is not fully understood how displacements of the focus of attention alter visual processing and, in particular, the perceived structure of objects in the visual field. The present study addressed this question by presenting cues that were either within or outside the contour of a subsequently presented oval and measuring how cue placement altered the perceived shape of the ovals. On every trial two white dots were briefly presented as cues (50ms) at equal eccentricities along the horizontal or vertical meridian (8° or 14°). Following a 100ms ISI one of fifteen blue ovals was presented for 100ms. The ovals were centered at fixation and had horizontal radii of 5°, 11°, or 14°. The height of the ovals was +0%, ±5%, ±10% the horizontal radius. Participants responded after every trial whether the oval was wider or taller than a perfect circle. The cues were paired with ovals such that cue positions (inside/outside contour; horizontally/vertically aligned) were uninformative of which dimension of the oval was larger. There were 40 cue-oval combinations and 25 repeats per configuration. There was a significant Cue Side x Cue Configuration x Oval Height interaction showing that when the cues were located within the oval contour the percentage of taller responses increased for vertically aligned cues and decreased for horizontally aligned cues relative to when the cues were placed outside the oval contour. However, this pattern of responses was only seen for the middle Oval Heights (0% = circle) and not the most extreme (e.g. ±10%). This double dissociation cannot be explained by a simple response bias and suggests that the relative position of cues can systematically alter subsequent processing of an object's spatial structure.