Spatial updating of the Müller-Lyer illusion A de Brouwer1, P Medendorp2, E Brenner3, J B Smeets4 |
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1MOVE Research Institute, VU University Amsterdam, Netherlands |
| Spatial updating refers to the process of maintaining stable spatial representations, even as we move. By using a double-step saccade task, we tested the role of contextual information in the updating process. Subjects briefly viewed the Müller-Lyer illusion with a target at its endpoint (T-ML), while fixating at the other endpoint of the illusion. Next, the fixation point jumped to a position above or below T-ML, orthogonal to the orientation of the illusion. After a delay, subjects had to make a saccade to the remembered position of T-ML. We tested whether the update contains information that is influenced by the illusion. While the amplitude of saccades parallel to the Müller-Lyer illusion is usually affected by the illusion, saccades orthogonal to the illusion are not [De Grave et al., 2006, Exp Brain Res, 175(1), 179-82]. Our results show systematic errors in the endpoint of the second saccade, in the direction of the illusion. Thus, the updated representation of T-ML was affected by the illusion, suggesting that positions are not coded in a purely retinotopic frame of reference, but are also based on contextual information. This demonstrates that spatial updating mechanisms for motor control do not resist visual illusions. |
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