Is step initiation in response to facial expressions modulated by lateralized auditory cues?

Objective: The left and right hemispheres of the brain play differential roles in emotion processing, grounded in hemispheric asymmetry. Literature suggests an involvement of the left hemisphere (cortex) for approach motivation and an involvement of the right hemisphere for avoidance motivation. We tested whether we could directly prime approach–avoidance tendencies by selectively activating the left or right hemisphere. We did this by presenting a monoaural cue, consisting of a brief tone presented to the left or right ear, preceding a visual cue to approach or avoid a facial stimulus. Method: Participants (N = 52) stood on a force plate and performed a single step forward or backward in response to the valence of a facial stimulus, displaying an emotion. Each stimulus was preceded by a brief acoustic cue randomly presented to either ear, assumed to selectively activate the contralateral hemisphere. We recorded the center of pressure, from which we derived reaction times, defined as the transition from quiet standing to step initiation. Results: The tone had no effect on the speed of gait initiation. However, the tone induced a brief postural shift in the same direction as ear stimulated. We also observed an interaction between gender of the visual stimulus and the emotion displayed. Conclusions: We failed to observe an effect of ear (hemisphere) stimulated on the time to initiate a step toward or away from a facial expression. This finding is at odds with a comparable study that did find priming effects in a comparable language categorization task. The results are discussed in terms of the hemispheric specialization of approach–avoidance tendencies and methods to selectively prime either hemisphere.