The effect of transcutaneous auricular vagus nerve stimulation (taVNS) on visual perceptual learning of faces through noise

Abstract

This study sought to examine the effect of transcutaneous auricular Vagus Nerve Stimulation (taVNS) on visual perceptual learning of faces (face learning). Research about taVNS is limited and there has been no attempt to combine this area with face learning prior to this study. Experiment 1 (n = 12) measured both sensory (i.e. when a sensation of stimulation becomes present) and sub-sensory thresholds (i.e. when a sensation stops being present) in order for the researchers to familiarise themselves with and select the stimulation devices (Chattanooga’s Cefar® TENS, the NeuroTrac® TENS, and the Parasym™ devices) for the main experiment. Stimulation was delivered at sub-sensory thresholds in the main experiment. Experiment 2 used a single-subject/psychophysics design (n = 4), in which each participant took part in multiple sessions over the course of 6 days. All participants experienced both Active Stimulation (taVNS directed at the left tragus and previously correlated with neuroplasticity) and Sham Stimulation (directed at the left earlobe and expected to have no effect) in a counterbalanced order. Stimulation was delivered during a face learning task where participants were required to match a gradually less obscured face with its unobscured double as quickly as possible. There was a significant effect of Repetition (i.e. how many times a face was encountered) which indicates that face learning took place during this experiment. There was no significant effect of Stimulation Type (i.e. whether the vague nerve was stimulated via the tragus). Due to this, there is no sufficient evidence supporting the hypothesis that taVNS enhances or inhibits face learning. Although the difference was not significant, Active Stimulation appeared to be linked to a slight initial advantage, but less prominent learning than Sham Stimulation.