Abstract
The human brain creates an external world representation based on magnitude judgments by estimating distance, numerosity, or size. The magnitude and spatial representation are hypothesized to rely on common mechanisms shared by different sensory modalities. We explored the relationship between magnitude and spatial representation using two different sensory systems. We hypothesize that the interaction between space and magnitude is combined differently depending on sensory modalities. Furthermore, we aimed to understand the role of the spatial reference frame in magnitude representation. We used stimulus–response compatibility (SRC) to investigate these processes assuming that performance is improved if stimulus and response share common features. We designed an auditory and tactile SRC task with conflicting spatial and magnitude mapping. Our results showed that sensory modality modulates the relationship between space and magnitude. A larger effect of magnitude over spatial congruency occurred in a tactile task. However, magnitude and space showed similar weight in the auditory task, with neither spatial congruency nor magnitude congruency having a significant effect. Moreover, we observed that the spatial frame activated during tasks was elicited by the sensory inputs. The participants' performance was reversed in the tactile task between uncrossed and crossed hands posture, suggesting an internal coordinate system. In contrast, crossing the hands did not alter performance (i.e., using an allocentric frame of reference). Overall, these results suggest that space and magnitude interaction differ in auditory and tactile modalities, supporting the idea that these sensory modalities use different magnitude and spatial representation mechanisms.
Highlights
Magnitude estimation is the capacity to extract numerosity, luminance, or intensity of environmental features
We demonstrated with an Stimulus–response compatibility (SRC) task in the tactile modality that the effect of magnitude congruency was more substantial than that of spatial congruency
Group MM results were opposite those for group MA: a reverse SRC effect was present with uncrossed hands (t(177) = − 3.55, pbonf = 0.004, Cohen's d = − 0.85), so lower linear integrated speed-accuracy score (LISAS) values for spatial-incongruent trials and higher values for spatial-congruent trials
Summary
Magnitude estimation is the capacity to extract numerosity, luminance, or intensity of environmental features. Smaller numbers are associated with the left-hand space, and larger numbers are associated with the right-hand space This effect has been taken as evidence for the existence of a mental number line (MNL) (Restle 1970); in Western culture, this reflects a spatial continuum from left (small numbers) to the right (bigger number) (Dehaene 1992). In this context, the SNARC effect results from correspondence between MNL representation and action execution (Prpic et al 2016)
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