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David Aguilar-Lleyda, Elisabet Tubau, Joan López-Moliner; Biases in number representation as a by-product of optimising visuomotor responses: evidence from a number line reaching task. Journal of Vision 2014;14(10):424. doi: 10.1167/14.10.424.
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© ARVO (1962-2015); The Authors (2016-present)
Numeric value seems to be analogically represented in a mental number line, with value increasing from left to right. In traditional number line tasks, participants estimate the position a number would have on a line representing a numerical range. While some views claim a logarithmic or a linear representation, the fact that part/whole decisions are made led others to defend that these tasks are better interpreted as proportion estimation. Indeed, perceptual proportion estimation models predict a pattern of smaller number overestimation and bigger number underestimation. Plus, these models take into account reference points commonly adopted by participants such as the line edges and center. Reaching to a number line has been used to reveal underlying cognitive processes and the nature of numeric representation scales. Here we used this task to test numeric representation on a number line. After a number appeared, participants moved a stylo over a tablet from a starting point towards the point of the line matching the number. We tested different numeric scales and target-number dispositions. Movement trajectories were straight without differences among scales, but there was a consistent pattern of under-overestimation. This bias can be interpreted as both a prior spatial-numeric representation (increasing left-to-right value) and spatial reference points affecting the endpoint estimation in the visuomotor mapping. When target disposition matched prior representation, the line edges acted as anchors attracting the endpoint. In those with a numeric discontinuity in the center, these perceptual anchors were overridden resulting in attraction towards the center. Finally, with a reversed disposition the prior substantially diminished the perceptual effect of the edges. Thus, the direction and strength of the reported underestimation-overestimation patterns (or vice versa) can be explained by different elements contributing to the selection of the final position in a way that is consistent with an optimality framework.
Meeting abstract presented at VSS 2014
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