Eye Position Reflects the Spatial Coding of Numbers and Arithmetic Operations
(2017) 9th IoNS Young Researcher Day — Location: Brussels, Belgium
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- Authors
Salvaggio, Samuel 
- Abstract
- Introduction The unique ability of humans to comprehend numbers has been related to a mechanism by which numbers are imagined on a sort of mental blackboard where they are represented in ascending order along a left-to-right orientend continuum. In this study, we recorded eye movements to obtain direct evidence of the visuospatial processes taking place during number manipulation and study their time course in number comparison and mental arithmetic tasks. Hypotheses In the first experiment, we tested the hypothesis that participants look more rightwards when comparing numbers bigger than reference than when comparing numbers lower than reference because of their right-sided position on the hypothesized mental continuum. In the second experiment, we tested the hypothesis that participants look more rightwards when solving addition than when solving subtractions because addition implies searching the answer on the right side of the continuum and subtraction on the left side. Methodology We used an eye-tracker with high spatio-temporal resolution to study horizontal gaze patterns in two experiments that combined the free exploration of visual scenes with a concurrent verbal numerical task. The first experiment required participants to compare numbers (from 20 to 70) to a reference (45). The second experiment investigated the mental solving of addition (43+4) and subtraction problems (53-6). The numbers were presented auditorily through headphones Results In the first experiment, we observed that the eye position deviated relatively to the magnitude of numbers. Participants’ eyes shifted more rightwards when the number was greater than reference than when it was smaller. This shift appeared earlier for numbers far from the reference (e.g. 23 relative to 45), presumably because hearing the decade of these numbers suffices to take the decision. In the second experiment, the solving of addition problems shifted the eye more rightwards than the solving subtraction problems at two different time windows. The first period was right after hearing the sign of the arithmetic operation, and the second period happenned right before the participants’ response. Take home message These results show that the mechanisms underlying number comprehension and mental calculation are intrinsically related to the mechanisms that allow us to move attention to the left and right side of space. Furthermore, they show that the timing of attention shifts is determined by linguistic aspects of number processing, including the serial order of number words, their organization in units and decades, and the sign of arithmetic operations.
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Citations
Salvaggio, S., Masson, N., & Andres, M. (2017). Eye Position Reflects the Spatial Coding of Numbers and Arithmetic Operations. 9th IoNS Young Researcher Day, Brussels, Belgium. https://hdl.handle.net/2078.5/175641