Auditory sensitivity in the rat.

Abstract

The problem to which this paper is addressed issues from recent studies of the behavior called the neurotic pattern (6) or audiogenic seizure (9). Soon after this behavior was first reported (6), its crucial environmental determinant was shown to be an acoustic stimulus (8, 9), and as a consequence experimental work has been directed toward the quantitative definition of the role of acoustic variables in the production of the behavior. In particular, we undertook to determine the relative effectiveness of different frequencies in instigating the seizures ( 7), and we found 20 kilocycles per second (kc) to be considerably more effective than frequencies very much below this value. We could not, in fact, obtain seizures with frequencies below 12 kc. These facts immediately suggested that the rat not only hears 20 kc but is quite sensitive to it and-that the entire audiogram of the rat is disposed, therefore, at much higher frequencies than is the audiogram of man.The literature lends some support to this suggestion, even though it contains no conclusive evidence for it. The rat, it is reported (5), is incapable of employing pure tones below 1 kc for discrimination, but it can respond quite readily to noises at that level. A finding of this kind can be plausibly explained by assuming that the animal hears high frequencies well and responds to these in the noise, but that it is. quite deaf to low frequencies. There is, in fact, evidence from another quarter (Henry, 4) to support this assumption. In order for a rat to be able to localize a tone of 1 kc, the intensity of the tone must be very great, but at 8 kc, on the other hand, the rat requires no greater intensity than man. Unfortunately frequencies above 8 kc were not employed in this work, but the trend of the results leads one to expect that, had the higher frequencies been used, the rat would have been proven to be better than man.Although there are many other studies of hearing in the rat, those mentioned seem most relevant to the question which has been raised by the study of audiogenic seizures. They do not, however, answer the question, even though they point to the hypothesis that the disposition of sensitivity at various frequencies is distinctly different in man and the rat. This hypothesis appeared well worth investigating by making careful measurements of the rat's hearing throughout an extensive range of frequencies.

Auditory sensitivity of the albino rat.

“…Five other published audiograms have been omitted. Of these, three are omitted because of inadequate calibration of stimulus intensities (Blackwell & Schlosberg, 1943;Gould & Morgan, 1942;Henry, 1938), a fourth is omitted because of the immeasurable effect of a progressive presbycusis during testing (Clack & Harris, 1963), and the fifth is omitted because noise bands instead of pure tones were used as stimuli (Harrison & Turnock, 1975). undoubtedly contribute to this variation.…”

Audibility in the rat.

“…In particular, the frequencies of maximum sensitivity have not been determined. Previous studies were either unable to measure the intensity of the signals used (Blackwell & Schlosberg, 1943;Gould & Morgan, 1942) or did not produce frequencies high enough to locate the region of maximum sensitivity (Clack & Harris, 1963;Cowles & Pennington, 1943;Gourevitch, 1965;Jamison, 1951). These studies suggested, however, that maximum auditory sensitivity was probably located above 10 kc.…”

The fractional reduction in noxious stimulation required to produce "just noticeable" learning.

“…There appear to be no discrimination studies with rats lo compare with the present results on this subject. What evidence is available (1,6,5,8,15) on absolute thresholds, however, suggests that the threshold for reinforcement (94 db.) found in the present study is much higher than absolute thresholds for sound with rats.…”