Abstract
The effects of visual contextual illusions on motor behaviour vary largely between experimental conditions. Whereas it has often been reported that the effects of illusions on pointing and grasping are largest when the movement is performed some time after the stimulus has disappeared, the effect of a delay has hardly been studied for saccadic eye movements. In this experiment, participants viewed a briefly presented Müller-Lyer illusion with a target at its endpoint and made a saccade to the remembered position of this target after a delay of 0, 0.6, 1.2 or 1.8 s. We found that horizontal saccade amplitudes were shorter for the perceptually shorter than for the perceptually longer configuration of the illusion. Most importantly, although the delay clearly affected saccade amplitude, resulting in shorter saccades for longer delays, the illusion effect did not depend on the duration of the delay. We argue that visually guided and memory-guided saccades are likely based on a common visual representation.
Highlights
Visual contextual illusions can affect our perception as well as our motor behaviour
The Müller-Lyer illusion, for example, changes the perceived length of a line segment through its inward or outward flanking arrowheads. This illusion can affect the amplitude of pointing movements (e.g. Post and Welch 1996; de Grave et al 2004) and saccadic eye movements (e.g. Binsted and Elliott 1999; de Grave et al 2006), as well as the maximum grip aperture of grasping movements (Daprati and Gentilucci 1997; Franz et al 2001), it has been argued that the latter is not caused by the illusory size (Biegstraaten et al 2007)
We investigated whether the variability in horizontal saccade amplitude is influenced by the duration of the delay
Summary
Visual contextual illusions can affect our perception as well as our motor behaviour. The Müller-Lyer illusion, for example, changes the perceived length of a line segment through its inward or outward flanking arrowheads. This illusion can affect the amplitude of pointing movements Binsted and Elliott 1999; de Grave et al 2006), as well as the maximum grip aperture of grasping movements (Daprati and Gentilucci 1997; Franz et al 2001), it has been argued that the latter is not caused by the illusory size (Biegstraaten et al 2007). It has been suggested that a longer preview of the Müller-Lyer illusion induces smaller effects on maximum grip aperture (Bruno and Franz 2009). We will focus on a second temporal factor: the delay between the stimulus disappearance and the execution of the response
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