抄録
Although auditory neurons are selective for absolute pitch, we easily perceive relative pitch. How can this be achieved? Previously, we investigated the cue used by rats to discriminate between amplitude-modulated (AM) sounds, and found that the relationship regarding the AM depth of sound stimuli was important for the discrimination. In the present study, we investigated the cue used by rats for sound pitch discrimination at different bandwidths. Water-deprived rats were exposed to 5 kHz (S-) and 10 kHz (S+) pure sounds, and licking a spout during the presentation of 10 kHz sound (S+) was rewarded with water, while licking during 5 kHz (S-) was not. After the rats were trained with this manner in two consecutive days, the performances in discriminating between 10 kHz (S+) and 20 kHz (S-), or 10 kHz (S-) and 20 kHz (S+) were evaluated, and the former performance was better than the latter, indicating that the rats used absolute pitch for discriminating S+ and S-. However, if similar experiment was performed using 7 kHz, 10 kHz and 14 kHz sounds, the learning was dependent on relative pitch. These results suggest that absolute pitch was used as the cue to discriminate sound pitch at broad bandwidth while relative pitch was used at narrow bandwidth. Preliminary experiments with bilateral auditory cortex ablation suggest that sound pitch discrimination using relative pitch might be dependent on the auditory cortex while sound pitch discrimination using absolute pitch might not. [Jpn J Physiol 54 Suppl:S168 (2004)]
