Perception of two-tone mixtures by the goldfish

Abstract

A stimulus generalization paradigm combined with classical respiratory conditioning was used to investigate the perceptual similarities and dissimilarities between single tones and two-tone complexes. Groups of 8 animals were given 40 classical conditioning trials to 6-s pure tones (200, 500, or 700 Hz) and then tested for generalization to two-tone complexes made up of the conditioning tone and a second tone spaced plus or minus 2, 4, 8, 16, 32, 64, 128, 256, 512 Hz from the conditioning tone frequency. Generalization (assumed to be monotonic with judged similarity) reached a minimum for complexes having frequency differences of 36 to 64 Hz, and increased to near 100% for the largest frequency differences (256 or 512 Hz). The dip in generalization at 36–64 Hz suggests that beats at these rates result in a salient perceptual quality that could be similar to roughness or intermittency. The rise in generalization for the larger frequency differences suggests either that roughness gives way to smoothness (a presumed quality of the single conditioning tone), or that the goldfish hears out the conditioning tone in the two-tone complex (analytic listening). These hypotheses will be evaluated in future experiments. [Work supported by the NIH, NIDCD.]