Visual Illusion

Effects of visual illusions on action: Testing the perception-action, planning-control and common-representation model hypothesis.

The results of the present study suggest that the illusion has an effect on action.

Participants, having closed their eyes, pointed at the end of the shorter and longer version of the Muller-Lyer figure with an average error of Ð'-3.50cm and Ð'-0.05cm, respectively. The results of the mean difference subjected to a t-test were consistent with planning-control and common-representation hypothesis models, which state that the illusion will have an effect on pointing accuracy. However the experiment results were not consistent with the perception-action model, which declares that an illusion effects action planning, but not online control. Consequently, the present study is consistent with previous research, which suggests a relationship between illusion and the accuracy of movement.

The connection between visual illusion and pointing accuracy may suggest that visual illusion and movement planning have more in common. Several studies examined the link between visual illusion and grasping (Carey, 2001, Franz et al., 2001). Franz, et al. (2001) found that the Muller-Lyer illusion had a significant effect on grasping. They argue that standard perceptual measures are used to examine visual illusions: the size of comparison stimulus is adjusted to match the size of a target stimulus. Furthermore, the illusion effect is larger when the stimuli are displayed shorter and smaller when they appear for a longer period of time (Franz, 2001). The single representation model proposed by Franz (2001) states that Ð''a single visual representation is used for perception and for guidance of action'. Franz (2001, as cited in Glover, 2002) argues that Ð''perception and action access a common visual representation that is susceptible to illusion'.

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