Perceptual Sensitivity to Tonal Alignment in Nuer.

This paper examines the perceptual threshold in patterns of tonal timing (alignment) of Falling versus Low tones. The results indicate a remarkable sensitivity among the listeners. In a perception experiment with 30 participants, we tested how native speakers of the West Nilotic language Nuer responded to stimuli in which the timing of the F0 fall that distinguishes Low versus Fall following a High target is manipulated. We measured the threshold for the responses to shift tone perception from 25% to 75%. The results show that listeners only needed an average of 19 ms to differentiate between the melodic shapes and as little as 13 ms for one item. Perceptual sensitivity this fine-grained is not expected based on what is known about the Just Noticeable Difference (JND) from previous studies. Results from non-tonal languages report a sensitivity threshold for tonal timing of at least 50 ms at category boundaries. This difference suggests that whether or not subjects speak a tone language may be a determining factor in their JND.