Mouth versus eyes: Gaze fixation during perception of sung interval size.

We used eye tracking to examine the relative influence of the mouth and eyes on perception of sung interval size. Frequency and duration of gaze were tracked while participants rated the size of intervals produced by two singers in three signal-to-noise conditions, corresponding to high, medium and low audibility. All intervals ascended in pitch direction and ranged in size from 0 to 12 semitones. Both the frequency and duration of gaze fixations revealed that the mouth was the most salient aspect of the visual channel. However, gaze was diverted away from the mouth and toward the eyes with increasing audibility, interval size, and tonal consonance of intervals. A linear regression model incorporating all of these variables accounted for 50% of the variability in gaze duration for the mouth and 45% of the variability in gaze duration for the eyes. Results are discussed in the context of dynamic allocation of attentional resources on the basis of early registration of sensory input. This is the first study of singing to incorporate eye-tracking methodology.