Auditory discrimination of material changes in a struck-clamped bar

The principles of theoretical acoustics were applied to approximately reconstruct the sound pressure waveform at the ear as would be generated by an idealized struck-clamped bar. The result is an inharmonic sum of damped sinusoids whose individual acoustic parameters (frequency, intensity, and decay modulus) are, for a fixed geometry and fixed driving force, uniquely determined by the material composition of the bar. In the standard 2IFC procedure, listeners were asked to discriminate changes in material composition based on their perception of the acoustic waveform. Listener strategies for discriminating such changes were estimated by perturbing slightly the individual acoustic parameters from trial to trial and computing correlations with the listener's response cf. R. A. Lutfi and E. Oh, J. Acoust. Soc. Am. 95, 2963(A) (1994). In general, the correlations reveal that listeners fail to make optimal use of the information in the acoustic waveform by tending to give undue weight, for a given material change, to changes in component frequency. In some case, the accompanying reduction in performance efficiency amounted to 80%.