Task demands modulate decision and eye movement responses in the chimeric face test: examining the right hemisphere processing account

Jason C Coronel,Kara D Federmeier

doi:10.3389/fpsyg.2014.00229

Jason C Coronel, Kara D Federmeier

Open Access

https://doi.org/10.3389/fpsyg.2014.00229

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Abstract

A large and growing body of work, conducted in both brain-intact and brain-damaged populations, has used the free viewing chimeric face test as a measure of hemispheric dominance for the extraction of emotional information from faces. These studies generally show that normal right-handed individuals tend to perceive chimeric faces as more emotional if the emotional expression is presented on the half of the face to the viewer's left (“left hemiface”). However, the mechanisms underlying this lateralized bias remain unclear. Here, we examine the extent to which this bias is driven by right hemisphere processing advantages vs. default scanning biases in a unique way—by changing task demands. In particular, we compare the original task with one in which right-hemisphere-biased processing cannot provide a decision advantage. Our behavioral and eye movement data are inconsistent with the predictions of a default scanning bias account and support the idea that the left hemiface bias found in the chimeric face test is largely due to strategic use of right hemisphere processing mechanisms.

Highlights

Hemispheric specialization is a fundamental feature of how the human brain is organized for cognition
We further examine the mechanisms at work in the elicitation of this bias by examining the effect that task demands have for eye gaze patterns and choice behavior in the chimeric faces test
To calculate the lateralization quotient (LQ) score, we obtained the number of times an individual selected the face in which the emotional expression was located in the right hemiface and subtracted from this value the number of times the participant selected the face in which the emotional expression was in the left hemiface

Summary

Introduction

Hemispheric specialization is a fundamental feature of how the human brain is organized for cognition. Even though the two chimeric faces contain the same information, as one is just a mirror image of the other, neurologically intact right-handed individuals have a tendency to pick the face in which the emotional expression is conveyed on the viewer’s left side (the “left hemiface”; for a review and metaanalysis, see Voyer et al, 2012) This left hemiface bias is robust and has been replicated using samples from different cultures (Vaid and Singh, 1989) and age groups (bias emerges as early as 5 years old: Failla et al, 2003) and in versions of the test that make significant modifications to the stimuli. These biases are reflected in reaction times as well as decision proportions: participants are generally faster to respond on trials in which they pick the left hemiface than those in which they pick the right hemiface (Bourne, 2008)

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