A metanalysis of the effect of the Müller-Lyer illusion on saccadic eye movements: No general support for a dissociation of perception and oculomotor action

Abstract

Milner and Goodale's (1995) proposal of a functional division of labor between vision-for-perception and vision-for-action is supported by neuropsychological, brain-imaging, and psychophysical evidence. However, there remains considerable debate as to whether, as their proposal would predict, the effect of contextual illusions on vision-for-action can be dissociated from that on vision-for-perception. Meta-analytical efforts examining the effect of the Müller-Lyer (ML) illusion on pointing (Bruno, Bernardis, & Gentilucci, 2008) or grasping (Bruno & Franz, 2009) have been conducted to resolve the controversy. To complement this work, here we re-analyzed 17 papers detailing 21 independent studies investigating primary saccades to target locations that were perceptually biased by the ML illusion. Using a corrected percent illusion effect measure to compare across different studies and across experimental conditions within studies, we find that saccadic eye movements are always strongly biased by the illusion although the size of this effect can be reduced by factors such as display duration and between-trials variability in display length and orientation, possibly due to a process of saccadic adaptation. In contrast to some reports, we find no general support for differences between voluntary and reflexive saccades or between saccades performed in conjunction with a pointing movement and saccades performed without pointing. We conclude that studies on the effect of the Müller-Lyer illusion do not provide evidence for a functional dissociation between primary saccades and perception.

Dynamic modulation of illusory and physical target size on separate and coordinated eye and hand movements

“…However, there was some influence of the illusion on pointing constant error at the end of movement execution, consistent with past research (for review, see Bruno et al, 2010). Given the similarity in IL and MT responses to physical and illusory size manipulation observed in pointing and saccades, we were able to compare the findings from these two effectors directly, and examine the potential for shared underlying mechanisms.…”

“…Furthermore, others have shown that measures other than grasp aperture are susceptible to visual illusions, such as movement amplitude (de Grave, Brenner, & Smeets, 2004), or how the object is lifted or gripped (Brenner & Smeets, 1996; Jackson & Shaw, 2000). Several studies have shown that both saccadic and pointing movements are susceptible to the Müller-Lyer illusion, such that when lines are perceived as longer, movements to their perceived endpoints have longer amplitudes (for review, see Bruno et al, 2010). Thus, it is argued that illusory perception does have an effect on aspects of action.…”

“…The effect of illusory rather than physical size on saccade execution in the form of movement time has yet to be examined, though previous studies have shown that some aspects of saccadic eye movement execution are influenced by illusions (for review, see Bruno, Knox, & de Grave, 2010). For example, McCarley, Kramer, and DiGirolamo (2003), and DiGirolamo, McCarley, Kramer, and Griffin (2008) showed that the amplitudes of both voluntary and reflexive saccades were scaled with the illusory lengths of lines that were physically the same size.…”

Frontal eye field, where art thou? Anatomy, function, and non-invasive manipulation of frontal regions involved in eye movements and associated cognitive operations

“…However, such dissociation is controversial and might be an experimental artifact. Indeed, without any visual feedback, hand and eye movements (and consequently the “vision for action”) can also be affected by the illusion (Bruno and Franz, 2009; Bruno et al, 2010). Similarly, in illusions where the perceived depth is different from the actual depth, the vergence movements are sometimes subject to the depth cues of the physical world (Wismeijer et al, 2008), and sometimes to the illusory percept (Sheliga and Miles, 2003).…”

Dissociations between vision for perception and vision for action depend on the relative availability of egocentric and allocentric information

“…Visual illusions have been extensively used to examine dissociations between vision for perception and vision for action (for meta-analyses and reviews, see Bruno, Bernardis, & Gentilucci, 2008;Bruno & Franz, 2009;Bruno, Knox, de Grave, 2010;Milner & Goodale, 2008). Aglioti, DeSouza, and Goodale (1995) were the first to report that when participants were asked to grasp the inner circle of an Ebbinghaus illusion configuration, their actions (more specifically, their maximum grip apertures) were not affected by the illusion, whereas verbal judgments of the size of the inner circle showed the typical illusion effects (for similar results, see Haffenden & Goodale, 1998).…”