title: Context is quick, knowledge is slow: rapid time-course of contextual modulations in the horizontal-vertical illusion.
abstract: One of the oldest visual illusions consists of observers' tendency to estimate vertical lines as longer than equal horizontal lines. This Horizontal-Vertical Illusion has been studied widely; however, most studies may not generalize to natural contexts because they have not addressed the low-level processes that occur rapidly and in response to context-free lines vs the possibility for high-level processes that arise over time in response to context. These issues were investigated via a novel design: rapid time-sequencing embedded within the context of natural images. Participants saw different levels of context and the Horizontal-Vertical Illusion was measured. In traditional Horizontal-Vertical Illusion displays without natural context, there was a robust invariance of the illusion to stimulus duration. Within context, however, there was strong modulation: the magnitude of the illusion decreased by over 50% or increased over 30%, depending upon placement within context. Knowledge of object properties such as size or line length did not account for this effect. It appears that previous domain-general investigations of the Horizontal-Vertical Illusion did not address the specific higher-order processes that produce the illusion in natural contexts.
authors.affiliation: Department of Psychology and Communication Studies, University of Idaho, USA.
authors.forename: Russell E
authors.initials: RE
authors.lastname: Jackson
authors.forename: T C
authors.initials: TC
authors.lastname: Cook
authors.forename: Aaron R
authors.initials: AR
authors.lastname: Seitz
mesh_terms: D000328:Adult; D006801:Humans; D019359:Knowledge; D009483:Neuropsychological Tests; D009903:Optical Illusions / Q000502:physiology*; D011897:Random Allocation; D013028:Space Perception / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult