Auditory intensity discrimination in the blackbird and pigeon

Redwing blackbirds, brown-headed cowbirds, and pigeons were trained using operant conditioning techniques to respond to small increases in the intensity of pulsed tone trains at three frequencies: 0.5, 1.0, and 2.0 kHz. All three species produced similar intensity difference limens (DLs) at the frequencies tested. Intensity DLs decreased as sensation level increased at all three frequencies, with the slopes of these sensation level functions being greatest at 2 kHz. The minimal intensity DLs at 50 dB sensation level were 3.3, 2.7, and 2.8 dB at 0.5, 1.0. and 2.0 kHz, respectively, averaged over the three species. Some subjects who were required to detect decreases in intensity produced intensity DLs two to three times larger than the DLs obtained when these subjects were required to detect increases in intensity. Comparative aspects of intensity discrimination will be discussed, and the relations between intensity discrimination and other aspects of hearing will also be considered.