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Andreas Jarvstad, Ulrike Hahn, Paul Warren, Simon Rushton; Exploring the limits of optimal motor-planning. Journal of Vision 2009;9(8):1107. doi: 10.1167/9.8.1107.
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Performance in cognitive- and perceptuo-motor decision making tasks is known to dissociate (Trommershäuser, Maloney, & Landy, 2008). A potential explanation for this dissociation is the explicit nature of cognitive tasks and the implicit nature of motor tasks (Seydell, McCann, Trommershäuser, & Knill, 2008). However, there is evidence that performance remains optimal, or nearly optimal, for motor tasks requiring explicit choice (Trommershäuser, Landy, & Maloney, 2006; Seydell et al., 2008) — seemingly eliminating the implicit/explicit factor as an explanation. Here the explanatory value of the implicit/explicit dimension was re-evaluated. A speeded reaching task for targets in the fronto-parallel plane was undertaken. The task involved two components — target choice (explicit) and aim point choice (implicit). On each trial, two targets varied in size (small/large), and distance (far, medium, near) and elevation (up/down), relative to a central dock. Target hits were rewarded (with the value depending on target size) and misses were penalized. Some evidence was found that participants' target choice behaviour suffered while aim point choice remained close to optimal. Furthermore, there is some evidence that participants' under-utilise the available response time for some target configurations — a potential further source of sub-optimality. Interestingly, estimation of overall optimality of observers appeared to be dependent on the analysis method used (e.g., non-parametric vs. parametric bootstrapping). Taking these findings into account, there may thus be reason to re-evaluate the optimality of participants' behaviour in perceptuo-motor tasks involving both target- and aim point choice.
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