Dissociating the Time Courses of Two Neural Mechanisms Underlying the Rod-and-Frame Illusion

(In-Person) Oral Panel—Neuron & Cognition

Witkin and Asch (1948) developed the rod-and-frame illusion (RFI) to investigate how the visual system uses context to determine an object’s orientation by providing a distorted visual field and examining its effects on orientation judgments. The RFI is thought to be driven by a combination of local and global mechanisms. The local mechanism is brought about by low-level visual properties causing an orientation contrast effect between the rod and edges of the frame. The global mechanism is the product of a compromise between the visual and vestibular systems. In this study, we examine the time courses associated with the local and global mechanisms thought to underlie the RFI. We also examined the effect on illusion magnitude when we isolated the global mechanism.Participants performed a two-alternative forced choice task where they made orientation judgments (clockwise or counterclockwise of vertical) of the RFI stimulus and a new type of stimulus, the knob-and-frame illusion (KFI), designed to isolate the global effect. We varied stimulus onset asynchronies to determine when the frame begins to bias perception of vertical and when the illusion reaches its full magnitude for each stimulus type. As predicted, we found the RFI had a greater illusion magnitude than the KFI. We found that the KFI and RFI unfolded under similar time courses. The influence of the frame began with negative SOAs and built until reaching a plateau early in the positive SOAs.