Abstract
Perception of objects often feels instantaneous. Object representation, however, is known to be an ongoing and possibly iterative process, one in which accumulated information is compared with current input until ambiguity about location or identity is resolved. According to this object-substitution account, not only discrimination, but awareness of an object should depend on how efficiently this disambiguation occurs. Objects that are less ambiguous should be more difficult to mask. We tested this hypothesis using a shape discrimination task. We asked observers to discriminate the aspect ratio of an ellipse shown for 20-msec within an array of circles. The target varied from extremely flat to extremely tall. Because aspect ratio is opponent-coded, the more elongated shapes should have been less ambiguous, not just in relevance to shape judgments, but also in their underlying representation. The target was surrounded by four dots that either offset simultaneously or lingered for 240-msec to induce masking, in both cases cuing the shape to be rated. On each trial, observers indicated the target shape's aspect-ratio and if it was visible. As expected, observers discriminated tall-vs-flat increasingly well when the targets had more extreme aspect ratios. More importantly, observers reported seeing elongated shapes more often than less extreme shapes. Crucially, this differential access to awareness only occurred on trials with masking. This is surprising since the shapes were otherwise identical in terms of attributes that should influence visibility (e.g., luminance, contrast, and area). These effects replicated across two additional experiments, which also ruled out alternative explanations such as proximity of the shapes to the masks. Our findings demonstrate that shapes with extreme aspect ratios are more readily available to awareness than shapes with ambiguous dimensionality. More generally, this work supports theories of object processing which suggest that ambiguity of visual representation gates access to awareness.
Meeting abstract presented at VSS 2018