Spatial biases during mental arithmetic: evidence from eye movements on a blank screen.

Matthias Hartmann,Fred W Mast,Martin H Fischer

doi:10.3389/fpsyg.2015.00012

Matthias Hartmann, Fred W Mast + Show 1 more

Open Access

https://doi.org/10.3389/fpsyg.2015.00012

Copy DOI

Abstract

While the influence of spatial-numerical associations in number categorization tasks has been well established, their role in mental arithmetic is less clear. It has been hypothesized that mental addition leads to rightward and upward shifts of spatial attention (along the “mental number line”), whereas subtraction leads to leftward and downward shifts. We addressed this hypothesis by analyzing spontaneous eye movements during mental arithmetic. Participants solved verbally presented arithmetic problems (e.g., 2 + 7, 8–3) aloud while looking at a blank screen. We found that eye movements reflected spatial biases in the ongoing mental operation: Gaze position shifted more upward when participants solved addition compared to subtraction problems, and the horizontal gaze position was partly determined by the magnitude of the operands. Interestingly, the difference between addition and subtraction trials was driven by the operator (plus vs. minus) but was not influenced by the computational process. Thus, our results do not support the idea of a mental movement toward the solution during arithmetic but indicate a semantic association between operation and space.

Highlights

In Western cultures small numbers are typically represented to the left of larger numbers, both in external space and in cognitive space, following the concept of the “mental number line” (e.g., Dehaene et al, 1993; Hubbard et al, 2005; Fischer and Shaki, 2014a)
Most evidence for a spatial bias in mental arithmetic comes from tasks that imposed a specific spatial setting, for example by requiring participants to respond with a left or a right key (i.e., Masson and Pesenti, 2014), or involving movements along a specific spatial axis (Pinhas and Fischer, 2008; Lugli et al, 2013; Marghetis et al, 2014; Wiemers et al, 2014)
Most importantly in the context of the present study, spontaneous eye movements follow spatial-numerical associations: Loetscher et al (2010) were able to predict the magnitude of numbers in their participants’ mind during random number generation, based on the direction and magnitude of spontaneous saccades occurring before the number was spoken out

Summary

Introduction

In Western cultures small numbers are typically represented to the left of larger numbers, both in external space (e.g., on rulers and timetables) and in cognitive space, following the concept of the “mental number line” (e.g., Dehaene et al, 1993; Hubbard et al, 2005; Fischer and Shaki, 2014a). Patients suffering from hemispatial neglect after right-hemispheric brain lesion show selective deficits for subtraction but not for addition problems, in line with their selective deficit in orienting attention toward the left side of space (Dormal et al, 2014) Despite this empirical evidence, the exact mechanism leading to the spatial bias during mental arithmetic is far from clear (Fischer and Shaki, 2014b). Most evidence for a spatial bias in mental arithmetic comes from tasks that imposed a specific spatial setting, for example by requiring participants to respond with a left or a right key (i.e., Masson and Pesenti, 2014), or involving movements along a specific spatial axis (Pinhas and Fischer, 2008; Lugli et al, 2013; Marghetis et al, 2014; Wiemers et al, 2014). Rightward and upward saccades were more frequent when the number was larger than the previous one (see Loetscher et al, 2008)

Objectives

Methods

Discussion

Conclusion