Attention modulated learning effect of facial emotion discrimination on the theta band neural oscillations

Visual perceptual learning refers to intensive training on a perceptual task that leads to substantial improvement in perceptual ability. However, its neural substrates, particularly how attention modulates learning-related neural oscillations, remain unclear. Here, we utilized a facial emotion discrimination task combined with an electroencephalogram (EEG) technique to investigate the neural oscillatory substrates underlying perceptual learning on social information and the modulation mechanisms by attention. Twenty-four participants were trained for eight days on the perceptual discrimination task. Before and after the training, we measured discrimination thresholds and electrophysiological responses to emotional faces under two attentional conditions: attending to emotion (trained attribute) or gender (untrained attribute). Psychophysical results revealed a strong emotion specificity of learning, which echoed previous findings. More importantly, we found that learning mainly enhanced brain oscillatory activities in the theta band. First, learning primarily enhanced theta amplitude in the left hemisphere, regardless of attentional conditions. Second, theta phase synchronization was enhanced in the left hemisphere only when participants attended to facial emotions; this enhancement disappeared when attention was directed to gender. These results suggest a left-lateralized learning effect on theta band oscillations. Attention modulated the learning effect on phase synchronization rather than on oscillation amplitude.