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Romi Nijhawan, Beena Khurana; Homologous mechanisms for spatial localization in vision and action: Evidence from motor flash-lag anisotropy. Journal of Vision 2004;4(8):844. doi: 10.1167/4.8.844.
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Background: A flash presented in alignment with an invisible limb that the subject voluntarily moves is perceived as trailing behind the instantaneous sensed position of the limb. Are mechanisms that produce this motor flash-lag (FLE-m) and the standard visual flash-lag (FLE-v) the same? Methods: Ss performed two tasks in a darkened lab. 1) In the FLE-m task they rotated their supported right forearm constrained to move in the horizontal plane. The invisible tip of their extended index finger moved along a 1/4 circle either clockwise or counter-clockwise. A fixation point (FP) was located in the middle of the movement trajectory. A flash was presented at a fixed distance from the FP while the finger-tip approached or receded away from the FP. 2) In the FLE-v task Ss performed no action. They simply viewed a moving object following the same 1/4 circle trajectory as their finger-tip in the FLE-m task. Again a flash was presented at a fixed distance from the FP while the moving object approached or receded away from the FP. The S judged the sensed position of their finger-tip or the visual position of the moving object in relation to the flash. Results: The magnitude of the FLE in both the FLE-m and FLE-v tasks was 2–3 times greater when the moving item (finger-tip or visual object) approached the FP than when it receded away from the FP. Conclusion: The similarity of this “flash-lag anisotropy” across the motor and visual domains reflects a common mechanism for spatial localization in the two domains. A plausible neural correlate of this anisotropy is the behavior of premotor neurons that have a common code for ‘visual space’ and ‘motor space’ (Rizzolatti et al., 1997; Graziano et al., 1997).
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