Abstract
The perceptual localization of an object is often more prone to illusions than an immediate visuomotor action towards that object. The induced Roelofs effect (IRE) probes the illusory influence of task-irrelevant visual contextual stimuli on the processing of task-relevant visuospatial instructions during movement preparation. In the IRE, the position of a task-irrelevant visual object induces a shift in the localization of a visual target when subjects indicate the position of the target by verbal response, key-presses or delayed pointing to the target (“perception” tasks), but not when immediately pointing or reaching towards it without instructed delay (“action” tasks). This discrepancy was taken as evidence for the dual-visual-stream or perception-action hypothesis, but was later explained by a phasic distortion of the egocentric spatial reference frame which is centered on subjective straight-ahead (SSA) and used for reach planning. Both explanations critically depend on delayed movements to explain the IRE for action tasks. Here we ask: first, if the IRE can be observed for short-latency reaches; second, if the IRE in fact depends on a distorted egocentric frame of reference. Human subjects were tested in new versions of the IRE task in which the reach goal had to be localized with respect to another object, i.e., in an allocentric reference frame. First, we found an IRE even for immediate reaches in our allocentric task, but not for an otherwise similar egocentric control task. Second, the IRE depended on the position of the task-irrelevant frame relative to the reference object, not relative to SSA. We conclude that the IRE for reaching does not mandatorily depend on prolonged response delays, nor does it depend on motor planning in an egocentric reference frame. Instead, allocentric encoding of a movement goal is sufficient to make immediate reaches susceptible to IRE, underlining the context dependence of visuomotor illusions.
Highlights
Goal-directed, object-oriented reach movements require accurate localization of the target object, yet object localization can be prone to visual illusions
The average localization error for individual subjects shows that the induced Roelofs effect (IRE) was characterized by varying effect strength with most but not all subjects showing an IRE at the single subject level
Our two experiments were designed such that subjects were required to encode first the cue and the reach target relative to the position of a reference object, i.e., in an allocentric reference frame
Summary
Goal-directed, object-oriented reach movements require accurate localization of the target object, yet object localization can be prone to visual illusions. The fact that in many cases visual perceptual localization is more prone to illusions than immediate visuomotor responses (Smeets and Brenner, 2001) is typically taken as strong evidence for two functionally independent visual processing streams, a ventral “vision-for-perception” pathway, and a dorsal “vision-for-action” pathway (Goodale and Milner, 1992; see Schenk et al, 2011 and Westwood and Goodale, 2011 for recent reviews). The IRE depends on the mode of the subjects’ behavioral response to indicate this position, e.g., key-presses vs immediate reaches towards the target (see details below). This observation was originally taken as evidence for the dual-visual-stream or perceptionaction hypothesis (Bridgeman et al, 1997), attributing the IRE to ventral stream perceptual processing. We thereby test if the Frontiers in Human Neuroscience www.frontiersin.org
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
