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Oliver Braddick, Hanna Gillespie-Gallery, Erin Babinsky; Do the characteristics of reaching from visual memory reflect ‘cautious reaching’?. Journal of Vision 2009;9(8):1156. doi: 10.1167/9.8.1156.
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Reaching actions show characteristic kinematics (long duration, extended period of deceleration) when the target is made invisible before the onset of the reach. These have been interpreted as reflecting dependence on a ventral-stream visual representation compared to the specialized, but fast-decaying, dorsal-stream representation which controls reaching when on-line visual information is available (Westwood & Goodale 2003; Goodale & Westwood, 2004) .However, an alternative interpretation is that the kinematic changes reflect increasingly cautious behaviour when visual information from the target is reduced.
We have examined this possibility by comparing reaching kinematics for a cylindrical ‘shot glass’ when empty, in the light or the dark, and when filled with water and so demanding a cautious approach. Both the full and empty glass could be presented with internal illumination alone (‘glowing’), giving visual information for the target but not for its spatial context or for hand position.
Reaches directed in the light toward a full glass showed increased duration, and period of deceleration compared to the empty glass. Kinematics of reaches to the glowing full glass showed no differences from those to an empty glass in the dark, suggesting that the ‘cautious’ reach to the visible full glass is a possible model for reaching behaviour in the absence of on-line visual information. Possible relationships between cautious reaching and the use of ventral vs dorsal representations will be discussed.
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