Reduced γ-aminobutyric acid in the superior temporal gyrus is associated with absolute pitch.

Absolute pitch (AP) is the ability to label the pitch of tones without any reference tones. Previous studies have shown that the anatomical and functional basis of AP exists in the superior temporal gyrus (STG), although the associated neurotransmitters remain unknown. We used proton magnetic resonance spectroscopy to quantify the concentration of γ-aminobutyric acid (GABA), an inhibitory neurotransmitter, in the bilateral STG of adult AP possessor and non-AP possessors. We found a significant negative correlation between AP scores and GABA concentration in the left STG. Furthermore, mean GABA concentration was significantly reduced in the AP possessors group compared to the non-AP possessors group. Our results suggest that less inhibition in the bilateral STG may enable AP possessors to associate categorical labels with tones.

Modulation of Emotional Category Induced by Temporal Factors in Emotion Recognition.

Categorical perception (CP), the perceptual experience whereby continuous sensory phenomena are perceived as distinct and separate percepts, is one of the most characteristic features of information processing in human cognition. CP is considered as the result of the integration of the top-down processing including background knowledge and verbal labeling and the bottom-up processing such as physical characteristics of the sensory signal. However, the underlying mechanisms governing the integration remain unclear. To address this issue, we focused on the temporal characteristics of CP of facial expression. In the current study, we investigated the contributions of temporal factors in CP processes, using facial expression recognition tasks as an example of CP. Participants completed an identification task and a discrimination task, well-established tasks for evaluating CP of facial expressions, with variable temporal parameters, that is, duration of stimulus presentation and delay time (interval between stimulus and response). The results demonstrated that the emotionally ambiguous stimuli are categorized more distinctively with the extension of delay length, not of stimulus duration. In contrast, the category boundary for facial expressions shifted toward "happy" with extention in stimulus duration, not in delay length. This dissociation between the impact of stimulus duration and delay suggests that there are two processes contributing to CP of facial emotion; one process may reflect the internal processing associated with the length of the delay period including verbal labeling of the stimuli, and the other process may reflect the temporal summation of stimulus inputs, associated with stimulus duration. These findings suggest that paying more attention to temporal factors in CP could be useful for further study of the mechanisms underlying CP.