For vision and audition to accurately inform judgments about an object's location, the brain must reconcile the variable anatomical correspondence of the eyes and ears, and the different frames of reference in which stimuli are initially encoded. To do so, it has been suggested that multisensory cues are eventually represented within a common frame of reference. If this is the case, then they should be similarly susceptible to distortion of this reference frame. Following this reasoning, we asked participants to locate visual and auditory probes in a crossmodal variant of the induced Roelofs effect, a visual illusion in which a large, off-center visual frame biases the observer's perceived straight-ahead. Auditory probes were mislocalized in the same direction and with a similar magnitude as visual probes due to the off-center visual frame. However, an off-center auditory frame did not elicit a significant mislocalization of visual probes, indicating that auditory context does not elicit an induced Roelofs effect. These results suggest that the locations of auditory and visual stimuli are represented within a common frame of reference, but that the brain does not rely on stationary auditory context, as it does visual, to maintain this reference frame.
Public Significance StatementHuman observers maintain a map of their own location within the world around them, and this egocentric reference frame is used to encode the locations of nearby objects. This study demonstrates that observers use visual, but not auditory, cues to maintain this egocentric reference frame, as they attempt to determine the locations of nearby sights and sounds.
The ability to judge an object's orientation with respect to gravitational vertical relies on an egocentric reference frame that is maintained using not only vestibular cues but also contextual cues provided in the visual scene. Although much is known about how static contextual cues are incorporated into the egocentric reference frame, it is also important to understand how changes in these cues affect perception, since we move about in a world that is itself dynamic. To explore these temporal factors, we used a variant of the rod-and-frame illusion, in which participants indicated the perceived orientation of a briefly flashed rod (5-msec duration) presented before or after the onset of a tilted frame. The frame was found to bias the perceived orientation of rods presented as much as 185 msec before frame onset. To explain this postdictive effect, we propose a differential latency model, where the latency of the orientation judgment is greater than the latency of the contextual cues' initial impact on the egocentric reference frame. In a subsequent test of this model, we decreased the luminance of the rod, which is known to increase visual afferent delays and slow decision processes. This further slowing of the orientation judgment caused the frame-induced bias to affect the perceived orientation of rods presented even further in advance of the frame. These findings indicate that the brain fails to compensate for a mismatch between the timing of orientation judgments and the incorporation of visual cues into the egocentric reference frame.
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