Eye understand: physiological measures as novel predictors of adaptive learning

Abstract

Reversal learning is facilitated by tonic firing of midbrain striatal dopamine and through phasic striatal dopamine release, thought to be reflected by Spontaneous Eye Blink Rate (SEBR). Arousal during learning has also been associated with performance. This study aimed to investigate whether SEBR and arousal predict learning performance during reversal learning. Twenty horses completed a reversal learning task. Performance was measured using a Reversal Learning Performance Index. SEBR was measured at rest and during learning as a proxy of tonic and phasic striatal dopamine respectively. Heart rate variability (RMSSD) and Infrared Thermography of eye temperature (IRT) were measured as indicators of arousal. SEBR did not change in response to reversal learning but RMSSD was higher (p = 0.008) and IRT decreased during trials (left eye: p = 0.002; right eye: p = 0.05). A negative binomial GLM was able to predict performance (p < 0.0005). Baseline RMSSD was associated with higher performance following an inverted U-shaped association (p = 0.04) consistent with a Yerkes-Dodson relationship. SEBR did not predict learning performance. Increased left eye temperature predicted higher performance (p = 0.0003). This is consistent with lateralised blood flow to the left brain hemisphere (responsible for learning targeted responses) and thought to be the first observation of this phenomenon during learning.