Abstract
Processing magnitudes constitutes a common experience across multiple dimensions, for example when one has to compare sizes, duration, numbers, sound height or loudness. From a cognitive point of view, however, it is still unclear whether all these experiences rely on a common system, or on distinct systems, with more or less strong associations. One particularly striking way of observing such interference between the spatial and numerical dimensions consists in eliciting a bias in size judgment through the mere perception of irrelevant numerical stimuli. In such experimental context though, two questions remain open. First, it is still unknown whether the direction of the bias is related to the magnitude of the number presented, or to their position in an ordinal sequence, and thus could be elicited by other non-numerical ordinal sequences such as letters of the alphabet. Second, it is still unclear whether the observed interactions generalize to other continuous dimension of magnitude such as brightness. In the study reported here, both letters and numbers were used in a size- and a brightness-reproduction task. We observed a dissociation between the two types of stimuli when reproducing size, the illusion being elicited solely by numbers. When reproducing brightness, however, neither the letters nor the numbers elicited a bias. These findings suggest that, while only numerical magnitude, and not letters, elicits a bias in size perception, the concurrent processing of magnitude and brightness does not bring about the same illusion, supporting the idea of a relative independence in the processing of these two dimensions.
Highlights
A number of studies in the field of numerical cognition converge toward the idea that numerical representations are rooted in intuitions about fundamental dimensions of our perceptual world, such as space and time
In order to compare the data from the size-reproduction task and the brightness-reproduction task, and avoid observing a task effect that would be an artifact of the scale, we standardized the data within each task by dividing the computed average estimation error for each subject and each condition by the standard deviation across the corresponding task
This interaction consisted in a larger overestimation in the brightness-reproduction task for the brighter starting value (0.64, i.e., an overestimation of 13.94 in rgb value), and underestimation for the darker starting value (−0.86, corresponding to −18.73 in rgb value), whereas a global overestimation was found in the size-reproduction task (0.43 for small starting size corresponding to 158.79 mm2 vs. 0.48 for large starting size corresponding to 176.22 mm2)
Summary
A number of studies in the field of numerical cognition converge toward the idea that numerical representations are rooted in intuitions about fundamental dimensions of our perceptual world, such as space and time. The neuroimaging studies notably point toward shared neural resources for numerical and spatial cognition, by showing an overlap between the activated areas involved in each process, in particular in the intra-parietal region (Fias et al, 2001; Dehaene et al, 2003; Pinel et al, 2004). On these grounds, some researchers have postulated the existence of a single system for the representation of magnitude that is shared across all continuous dimensions (Walsh, 2003; Bueti and Walsh, 2009). General processing of ordinality has shown to recruit neural resources in the intra-parietal region that are shared by numbers and other nonnumerical sequences, such as letters of the alphabet (Fias et al, 2007)
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