Number magnitude affects spatial decisions: Evidence of spatial-numerical associations with complex movements

The Spatial-Numerical Association effects describe the spatial relationship between number magnitude and response side, with small numbers usually associated with left sided responses and large numbers with right sided responses. Typically, these effects are demonstrated using response time differences in simple key press tasks, where participants are required to process the magnitude (magnitude classification task) or parity (parity judgement task) of a number. The present study investigated whether similar spatial biases (left/right) also occur for decisions that involve more complex movements, namely walking. Using a free response task, presented in a virtual reality environment, participants were shown a number from 1 to 9, that was presented directly in front of them. At the beginning of each trial participants were required to process either the number's magnitude (Experiment 1) or parity (Experiment 2). They were then asked to walk freely in any direction towards a semi-circular target area, while continuing to process information in working memory. The results showed a higher frequency of leftward walking decisions for smaller numbers and rightward walking decisions for larger numbers in both experiments, as well as compatible deviations of walking trajectory. These findings are consistent with previous literature on SNAs. This study highlights that in a free response task both spatial decisions and spontaneous movements are influenced by number magnitude, both when magnitude is task-relevant and when it is task-irrelevant.