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Volker H. Franz, Constanze Hesse, Susanne Kollath; Grasping after a delay: More ventral than dorsal?. Journal of Vision 2007;7(9):157. doi: https://doi.org/10.1167/7.9.157.
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© ARVO (1962-2015); The Authors (2016-present)
It is often assumed that grasping is only controlled by the dorsal cortical stream if visual information about the target object is easily available. After a short delay between stimulus presentation and grasping the dorsal information should be decayed and the action should be guided by the ventral stream. Accordingly, grasping should not be affected by certain visual illusions under full-vision conditions, but it should be affected after a delay (because only the ventral stream is assumed to be deceived by these illusions). We tested this for the Müller-Lyer illusion. In experiment 1 (N=16), we investigated grasp illusion and perceptual illusion for full-vision and 5sec delay conditions. The perceptual illusion was independent of delay (p=.23), while grasping showed a strong increase of the illusion effects (p[[lt]].001). This replicates the increase of the motor illusion found in the literature. In experiment 2 (N=8), we tested whether the delay causes this increase by comparing open loop grasping (shutter goggles close when movement starts) with the 5sec delay condition. Illusion effects on grasping were constant (p=.90), suggesting that delay is not the critical factor. In experiment 3 (N=20), we systematically decreased the amount of visual feedback available during the grasping movement using the conditions: full vision, vision suppressed when fingers had traveled 2/3 or 1/3 of the way to the target object, open loop (goggles close when movement starts), and open loop after go-signal (goggles close with auditory go-signal). Illusion effects decreased the more visual feedback was provided (p=.001). This suggests that the critical factor is visual feedback and not different memory systems in dorsal and ventral streams.
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