Auditory categorization in pigeons

Satoru Ishikawa

Kyoto University, Japan

There are many studies on the ability for categorizing or conceptualizing objects in nonhuman animals (Thompson, 1995, Watanabe, Lea, & Dittrich, 1993). However, as our knowledge on these cognitive processes is mostly limited to the visual modality, we are unable to discuss about similarities and differences of categorization processes among various sensory modalities such as vision and audition. In the present research, I studied category discrimination in the auditory modality. I prepared two categories, the 'Strings' and the 'Flute', differing in timbre. Each category had 20 stimuli made by combinations of five fundamental frequencies and four elements changed in frequency modulation (FM) and temporal envelope. Four pigeons (Columba livia) were trained to discriminate these categories with auditory-visual cross-modal symbolic matching-to-sample (MTS) tasks (Ishikawa & Iwamoto, 1995). Auditory stimuli were presented as a sample of MTS tasks, and two colored squares (red/green) were presented as comparison stimuli. Two pigeons learned this discrimination, but the remaining two pigeons did not learn within one hundred training sessions. After training, the two pigeons who had learned this discrimination received two generalization tests. One of the tests was to investigate generalization to novel elements differing in temporal envelope and frequency modulation (novel timbre test), the other was to investigate generalization to novel fundamental frequencies (novel pitch test). Twenty novel stimuli were presented in each test. In the novel timbre test, two pigeons showed good generalization to the test stimuli. In the novel pitch test, one pigeon generalized discrimination to the test stimuli. The other bird generalized discrimination to the test stimuli with 'Flute', but did not do so to the test stimuli with 'Strings'. These results demonstrated that pigeons were able to discriminate two categories depending on the difference of timbre. However, it is also suggested that generalization to novel stimuli could be affected by other factors such as fundamental frequency.

Ishikawa, S., & Iwamoto, T. (1995). Timbre discrimination in pigeons using conditional matching-to-sample task. Japanese Journal of Animal Psychology, 45, 43-50 (in Japanese).

Thompson, R. K. R. (1995). Natural and relational concepts in animals. In H. L. Roitblat and J.-A. Meyer (Eds.), Comparative approaches to cognitive science (pp. 175-224). Cambridge, MA: MIT Press.

Watanabe, S., Lea, S. E. G., & Dittrich, W. H. (1993). What can we learn from experiments on pigeon concept discrimination? In H. J. Bishof and H. P. Zeigler (Eds.), Avian vision and cognition (pp. 351-376). Cambridge, MA: MIT Press.

Ishikawa, Satoru

Department of Psychology, Kyoto University

Yoshida Honmachi, Sakyo-ku, Kyoto 606-8501, Japan

ishikawa@kupsy.kyoto-u.ac.jp