Squeaky wheels: Friction-generated sound supports auditory differentiation and scaling of rotating ellipse shapes.

Acoustical analysis indicates that sounds generated as the rims of ellipses rotate against a fixed contactor vary regularly with ellipse shapes (defined by minor-to-major axis length ratios), potentially supporting human ability to differentiate and scale the shapes. In four experiments, we documented human ability to do so. Experiment 1 demonstrated reliable and ordinally correct shape judgments. Experiment 2 showed equivalent judgments over rotation speeds (10, 15, 20 rpm), suggesting reliance on relational information in the acoustic signal. Experiment 3 (using scalar judgments) and Experiment 4 (using multiple-choice judgments) tested perceptual learning effects. Some improvement occurred in both experiments, with a moderate advantage for multiple-choice judgments. Individual variability was notable across all experiments: Individual correlation magnitudes (actual vs. judged shape) ranged from .00 to > .9. Past research revealed associations of shape with impact noise; the current experiments are the first apparent demonstrations of human ability to associate planar object shape from friction-generated sound. Results are interpreted as consistent with Gibson's theory of information-based perception. (PsycINFO Database Record