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Gord Binsted, Crystal Ehresman, Matthew Heath, Deb Saucier; Execution generated illusory motor bias: two systems, one representation. Journal of Vision 2007;7(9):156. doi: https://doi.org/10.1167/7.9.156.
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Previous research has suggested that the neural substrates of visual perception (i.e. ventral stream; inferior temporal projections) are separate from those for the visually control of actions (i.e. dorsal stream; parietal projections). Further, (Glover 2004) has posited a supplementary separation of the dorsal pathway between the planning and control of action: planning (inferior parietal) being under the influence of perception while online control (superior parietal) works on metrically precise visual information. This study analyzed eye and hand movements directed toward both configurations of the Müller-Lyer in an entirely closed-loop procedure. Participants were asked to point to the right vertex of a visual stimulus in two conditions: the control condition where the figure (in-ML, neutral, out-ML) remains unchanged throughout the movement and the experimental condition where the figure (neutral) changes to an illusory configuration (in-ML, out-ML) after movement onset. Based on the planning and control hypothesis two effects were predicted: (1) action-bias should reduce throughout execution due to online control in control trials (2) action-bias should be absent in experimental trials, and (3) saccadic-bias should only be present during control trials. Counter to the planning and control position, but consistent with previous work from our group (see Heath et al 2004, 2006), action-bias was not only present (and not mediated by online control) in both experimental and control conditions but become more pronounced throughout execution (experimental). Further, while primary saccades were influence by illusory configurations (control conditions; see Binsted & Elliott 1999), illusory bias developed within the secondary “corrective” saccades during experimental trials. These results support the position that a unitary spatial representation underlies both action (planning or control) and perception and, further, that this representation is common to both the manual and oculomotor systems.
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