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An auditory detection experiment was performed with rats as subjects, and the data were analyzed with a signal detection model. Rats were run at fixed sound pressure levels, and their responses were partitioned so that operating characteristics could be constructed. Measures of detectability, (d(e))((1/2)), were calculated from the operating characteristics, and show that (d(e))((1/2)) is a function of sound pressure levels, rising as these levels rise.

Auditory intensity discrimination in the rat has been examined in a frequency range of 2-30 kHz., at sensation levels of 20 and 40 db. Minimum mean difference limens at these two sensation levels were found to be 2.3 and 1.3 db., respectively, at 8 kHz. These values were compared with those of man, cat, and goldfish. They were found to be of the same magnitude, except for relative shifts along the frequency axis.While the current auditory literature contains many studies concerned with the absolute thresholds of a variety of infrahuman organisms, few investigations have been made of other aspects of hearing, such as the measurement of differential sensitivity for intensity. Of the studies which do exist, the cat appears to be the only mammal investigated in depth. Rosenzweig (1946) found that the cat was able to discriminate a change in intensity of 2.0 db. at 125 Hz., 2.4 db. at 1 kHz., and 5.0 db. at 8 kHz., at sensation levels of 40, 60, and 60 db., respectively. Raab and Ades (1946) found at the same frequencies and sensation levels values of 2.90 db., 1.82 db., and 3.89 db. Both investigations utilized avoidance conditioning. Elliot and McGee (1965) tested cats at 60 db. above threshold at frequencies between 125 Hz. and 8 kHz. and found difference limens of approximately 1.5 db. up to 1 kHz., with a rise to 2.5 db. at 8 kHz., again utilizing avoidance conditioning. More recently, Jacobs and Tavolga (1967) found goldfish capable of discriminating tones differing by 3-6 db. and found no change in the difference limen over a range of 30 db., from a level about 20 db. above threshold. The smallest limen was found in the 300-400 Hz. region, and increased sharply above 1 kHz. The smallest limen was found in the region of greatest sensitivity.Henry (1938) tested rats in a discrimina-

An adaptation of the Ratliff and Blough technique has been developed for auditory measurement in rats. Thresholds for a 2000-cy/sec tone were determined over a period of weeks. Kanamycin, an ototoxic agent, was then administered, and the gradual rise in threshold was followed.