Latino Studies at New York University

Chengcheng Huang

Doctoral Candidate
Computational Biology Program
Courant Institute of Mathematical Sciences
New York University

December 11, 2012

Frequency Shift Detector Model for Shepard Tone Comparison

Shepard tones are complex acoustical stimuli, comprised of octave-spaced pure tones. The special spectrally periodic structure of Shepard tones can help elucidate the internal representation and comparison mechanisms of pitches. A sequentially played pair of Shepard tones can be perceived as ascending or descending depending on the relative positions of their base pitches. It becomes ambiguous when two Shepard tones are separated by a half octave (tritone). Recent studies have shown that using a sequence of Shepard tones with base pitches between the tritone pair can greatly bias the shift perception in the same direction of the bias tones, while neurological recordings suggested repulsive shift of the neural tone representations. In this study, we developed two circuits of frequency shift detectors for upward and downward shift respectively, with asymmetric inhibition. Those circuits receive input from a tonotopic array of bistable units as neural representations of tones and make a decision as ascending or descending by comparing the responses of upward and downward circuits. Our model can compare Shepard tone pairs and biased tritone pairs. Results of the comparisons are consistent with psychophysical studies. Moreover, our model can work with long silence gaps between biasing sequences and test pairs as used in experiments.