Spatial task context makes short-latency reaches prone to induced Roelofs illusion

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.

Contextual factors determine the use of allocentric information for reaching in a naturalistic scene

“…Furthermore, a temporal delay between stimulus presentation and action performance can influence the weighting of egocentric and allocentric information with stronger weighting of allocentric information for delayed than immediate movements (Bridgeman, Peery, & Anand, 1997;Chen, Byrne, & Crawford, 2011;Hay & Redon, 2006;Obhi & Goodale, 2005). Importantly, allocentric information is also incorporated in immediate reaches as recently demonstrated by a study on the Roelofs effect (Taghizadeh & Gail, 2014) and as we demonstrated in our experiments. Since allocentric coding is supposed to be stronger for delayed than immediate reaches (Bridgeman et al, 1997;Chen et al, 2011;Hay & Redon, 2006;Obhi & Goodale, 2005), the allocentric weights we observed here could have even been higher with a temporal delay before the reach.…”

The Müller-Lyer illusion affects visuomotor updating in the dorsal visual stream

“…While several studies support the hypothesis that illusions do not affect the visual control of action, but only affect perception and memory-guided actions (e.g., Aglioti et al, 1995;Bridgeman et al, 1997;Westwood et al, 2000), other studies have found evidence against this hypothesis (e.g., Brenner and Smeets, 1996;Franz et al, 2009;Taghizadeh and Gail, 2014). For example, the Müller-Lyer illusion not only changes the perceived length of a line by its inward or outward pointing arrowheads, but can also change the amplitude of pointing movements and saccadic eye movements along its shaft (e.g., Binsted and Elliott, 1999;Post and Welch, 1996) 1 .…”

Spatial coding for memory-guided reaching in visual and pictorial spaces

“…However, allocentric information also crucially contributes to spatial coding for action. For example, although the presence of landmarks results in more accurate and less variable reaches in both online and delayed movement tasks (Krigolson & Heath, 2004;Obhi & Goodale, 2005), cue-irrelevant background information can lead to spatial distortions of pointing or reaching movements (Diedrichsen, Werner, Schmidt, & Trommershäuser, 2004;Taghizadeh & Gail, 2014). Further studies could show that the main factors driving the influence of allocentric information are landmark stability, as well as its reliability as a cue (Byrne & Crawford, 2010;Camors, Jouffrais, Cottereau, & Durand, 2015).…”