de Grave D D J, Franz V H, Gegenfurtner K R, 2005, "The influence of the Brentano illusion on saccades and pointing movements" Perception 34 ECVP Abstract Supplement
The influence of the Brentano illusion on saccades and pointing movements
D D J de Grave, V H Franz, K R Gegenfurtner
When making an eye and hand movement towards the same target, the eye and hand can either use the same source of visual information to perform the task or a different one. Using the same information is efficient; however, if this information contains an error, this causes the eye as well as the hand to be incorrect. In this study, we tried to find out whether saccades and pointing movements use the same source of information when eye and hand movements are performed either in the same or in separate trials. Three experiments were performed with the Brentano illusion, which primarily influences judgments of length, but not those of position. A task will only be influenced by this illusion if the task requires a visual estimate of length. In an earlier study (de Grave et al, 2004 Experimental Brain Research 155 56 - 62), it was found that the hand uses illusory length information when pointing to a visual target. If the eye uses the same information to perform a saccade, we expect a similar effect of the illusion on saccades as on pointing. In the first experiment ('combined'), subjects were required to make saccades as well as pointing movements in the same trial from one end vertex of the Brentano illusion towards the middle vertex. In the other two experiments ('separate'), the same stimuli were used but now subjects had to make either only pointing movements while keeping fixation or only saccadic eye movements. The Brentano illusion influenced eye and hand movements in all three experiments (saccades combined: 26%±3%; pointing combined: 27%±2%; saccades separate: 27%±2%; pointing separate: 31%±2%). No difference in illusion effect was found between the different experiments, which favours the interpretation that similar sources of information are used in eye and hand movements.
[Supported by a grant from the Deutsche Forschungsgemeinschaft (DFG: FR 2100/1-1) and by the European Research Training Network: Perception for Recognition and Action (PRA).]
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