Pure-Tone Auditory Behavioral Thresholds in Three Species of Lemurs

Abstract

Absolute thresholds were determined for pure tones of frequencies 100 Hz-40 kHz by the method of constant stimuli using a two-bar operant technique. Lemurs of three subspecies were trained to press a white bar to turn on a tone lasting 5 sec. During the tone, a single press on a second (black) bar resulted in food reward. Failure to respond simply terminated the trial. Response in the absence of tone was scored as a false positive response and resulted in a «-sec shock of from 0.6 to 1.3 mA. Thresholds, based on a response probability of 0.5, indicate a lesser sensitivity in the low and middle frequencies than found in the anthropoid primates, but an apparent extension of sensitivity into the higher frequencies beyond the upper-frequency cutoff points found for the anthropoids. I. PROCEDURE A. SubjectsSix lemurs, males and females of each of three species (lemur catta, lemur macaco fulvus, and lemur macaco macaco), served as subjects. Their weights, breeding behavior, and dentition indicate that three were adult and three adolescent (see Table I). All were healthy; one (No. 2023) was extremely fat and had also been previously treated with antibiotics for a jaw infection. The animals were deprived of food and received ad lib water during training and testing. The extent of deprivation may be estimated from the weight data included in Table I. B. ApparatusThe animals were trained and tested in a small cage inside a double-walled IAC chamber. Standard audiometric and programming equipment was used to generate and control the sound stimulus, food, and, later, shock. A Western Electric 555 speaker produced

Vocal Tract Morphology Determines Species-Specific Features in Vocal Signals of Lemurs (Eulemur)

“…It is interesting to evaluate our results in relation to the perceptual abilities of lemurs. Studies of the hearing abilities of Eulemur fulvus and E. macaco suggest that the perceptual sensibility of these two species is optimal at frequencies between 2000 and 15 000-20 000 Hz (Mitchell et al 1970), thus in the range of formants F2-F4 that we investigated in this study.…”

What Do Primates Hear? A Meta-analysis of All Known Nonhuman Primate Behavioral Audiograms

“…Considering only the free-field studies (speakerderived), researchers have employed numerous approaches such as averaging the intensity from numerous positions, using only the value from the most intense position (hot-spots), measuring from the approximate position of the center of the head, measuring from the approximate position of the pinna, and using models of the subjects with microphones placed at the ear position. Though the last approach might seem intuitively to be the most precise because it incorporates sound field disturbances caused by the subject itself, only 2 laboratories have used it (Bennett et al 1983;Mitchell 1970;Mitchell et al 1970Mitchell et al , 1971. A potential problem with the hot-spot approach is that it assumes that the subject will sample a sound from the most intense area; hence sampling away from the area will produce threshold estimates that are too high.…”

“…Taken at face value, there appear to be few reasons to reject the audiogram for Eulemur macaca produced in the study by Mitchell et al (1970). They employed a fairly standard conditioning procedure and psychophysical techniques and used an extended range speaker to deliver the test tones.…”

“…? Bragg and Dreher 1969 Double-walled soundproof room Noncalibrated Sound-treated room Head position Heffner and Masterson 1970 Double-walled chamber Head position Gourevich 1970 Double-walled chamber Probe tube Mitchell et al 1970 Double-walled chamber Pinna position with dummy animal Mitchell 1970 Double-walled chamber Pinna position with dummy animal Mitchell et al 1971 Double-walled chamber Pinna position with dummy animal Green 1971Green , 1975 Double-walled chamber (40-60 dB) Probe tube Gillette et al 1973 Double-walled chamber Hot-spots Pugh et al 1973 Double-walled chamber Probe tube Stebbins 1973 Double-walled chamber Probe tube Beecher 1974a Double-walled chamber with cotton Head position Beecher 1974a…”

AUDITORY SENSITIVITY AND EQUAL LOUDNESS IN THE SQUIRREL MONKEY (SAIMIRI SCIUREUS)1

“…One view receiving considerable support (Bragg and Dreher, 1969;Clack and Herman, 1963;Mitchell, Gillette, Vernon, and Herman, 1970;Mitchell, Vernon, and Herman, 1971) was advanced by Harris (1943). Harris pared the effectiveness of his aversive control technique with an appetitive procedure used by Wendt (1934) and concluded that aversive stimuli provide a more efficient means of conditioning behavior and collecting reliable data.…”