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Jeffrey Weiler, Ali Mulla, Taryn Bingley, Matthew Heath; Extrinsic manipulations of the mental number line do not impact SNARC-related influences on the planning and control of action. Journal of Vision 2010;10(7):1062. doi: 10.1167/10.7.1062.
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The spatial numerical association of response codes (so-called SNARC effect) manifests as faster reaction times (RT) to judgments of numerical magnitude in left and right space when cued by low and high numbers, respectively. In addition, Fischer (2003:Vis Cogn) reported that movement times (MT) associated with goal-directed reaching movements are influenced in a direction consistent with the SNARC effect. These findings have been explained by the presence of a mental number line with smaller and larger digit magnitudes preferentially represented in left and right space, respectively. In the present study, we sought to determine whether the magnitude of the SNARC effect for goal-directed reaching is influenced by the premovement manipulation of a real number line. Prior to response cuing participants were briefly (50 ms) presented with an ascending (i.e., digit magnitude increasing from left to right), or descending (i.e., digit magnitude decreasing from left to right) number line. In addition, we included a control condition wherein a number line was not presented in advance of response cuing. Following premovement cuing, low (1,2) or high (8,9) digits were presented and used to visually cue the onset of a left or right space reaching response. Results for RT and MT did not elicit a SNARC effect: a finding consistent across the different premovement visual cuing conditions (i.e., ascending, descending, no number line). Interestingly, however, when total response time was analyzed (RT+MT) a SNARC effect was observed. Based on these findings, we propose that the SNARC effect for reaching responses is represented as an aggregation of the temporal properties of both movement planning and control. Further results suggest that the SNARC effect is refractory to extrinsic manipulations of the mental number line.
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