Biomedical subjects
Publications and source records attributed to R S Heffner.
The behavioral audiograms of two cats were determined in order to establish the upper and lower hearing limits for the cat. The hearing range of the cat for sounds of 70 dB SPL extends from 48 Hz to 85 kHz, giving it one of the broadest hearing ranges among mammals. Analysis suggests that cats evolved extended high-frequency hearing without sacrifice of low-frequency hearing.
The ability of three wild Norway rats to localize sound was determined for single clicks and 100-ms white noise bursts. Chance level localization thresholds were 12 degrees for clicks and 9.7 degrees for white noise. A comparison of these results with published localization thresholds for the domestic albino rat yielded no significant differences. It appears that the combined effects of domestication and albinism have not affected the ability of the laboratory rat to localize sound. Instead, the relatively poor localization acuity of these rats appears to be part of the normal variation in sound localization acuity found among different species of mammals.
The audiograms of two wood rats and three grasshopper mice were determined with a conditioned avoidance procedure. The wood rats were able to hear tones from 940 Hz to 56 kHz at a level of 60 dB (SPL), with their best sensitivity of -3 dB occurring at 8 kHz. The hearing of the grasshopper mice ranged from 1.85 kHz to 69 kHz at 60 dB (SPL), with their best sensitivity of 9 dB also occurring at 8 kHz. These results support the relation between interaural distance and high-frequency hearing and between high- and low-frequency hearing. The inability of the grasshopper mouse to hear low frequencies as well as other desert rodents such as kangaroo rats and gerbils demonstrates that not all rodents found in deserts have developed good low-frequency hearing. The degree to which general and specific selective pressures have played a role in the evolution of rodent hearing is discussed.
Seven dogs were tested for their sensitivity to pure tones following lesions of the brachium of the inferior colliculus and medial geniculate body. Bilateral section of the brachium of the inferior colliculus consistently resulted in an average hearing loss of as much as 37 dB in the midrange of the animals' audiograms. Lesions of the medial geniculate appear to produce a similar hearing loss if the ventral division of the medial geniculate is completely destroyed.
Japanese macaques were trained to discriminate two forms of their coo vocalization before and after unilateral and bilateral ablation of the temporal cortex. Unilateral ablation of the left superior temporal gyrus, including auditory cortex, resulted in an initial impairment in the discrimination, but similar unilateral ablation of the right superior temporal gyrus had no effect. Bilateral temporal lesions including auditory cortex completely abolished the ability of the animals to discriminate their coos. Neither unilateral nor bilateral ablation of cortex dorsal to and sparing the auditory cortex had any effect on the discrimination. The perception of species-specific vocalizations by Japanese macaques seems to be mediated by the temporal cortex, with the left hemisphere playing a predominant role.
The idea that large mammals localize sounds more accurately than small mammals has been noted frequently and is usually explained by reference to their large interaural distance and the correspondingly broad binaural time (delta t) and spectral (delta fi) differences between their two ears. Sound-localization thresholds for single clicks and 100-ms noise bursts were determined for horses, and the magnitude of the binaural time (delta t) and spectral (delta fi) cues for sound direction were measured on a horse. Although horses have relatively large interaural distances and physically broad binaural-localization cues available to them, their sound direction thresholds were markedly poorer than those of other large mammals--averaging 22 degrees for noise and 30 degrees for clicks. It appears that sound-localization acuity is not determined simply by the physical availability of binaural cues.
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A morphometric analysis of the corticospinal tract's relation to digital dexterity was performed on 21 species theoretically related to man's ancestral lineage. The results indicate that the Primate line is not unique among mammals with respect to the cortical control of digital dexterity. A comparative analysis suggests that two changes took place early in Primate evolution: a reduction in functional distance (i.e. number of synapses) between neocortex and spinal motor neurons innervating the digits, and an extension of direct neocortical influence beyond the cervical segments of the spinal cord. A further change progressed throughout Primate evolution, from the mid-Eocene to the present, in which the overall size of the corticospinal tract increased steadily as though consolidating the cortical influence over body musculature, especially that of the digits.
Forty-seven cattle from 8 separate herds in southeastern Kansas were examined for ear mites (Raillietia auris). Ear mites were directly observed in 12 of the animals while 19 others showed signs of infestation consisting of ulceration and blockage of the auditory canal by a thick plug of pus. The observed occurrence of infestation in 66 percent of the animals examined is higher than expected based on previous reports.
A young Indian elephant was tested to determine its absolute sensitivity, frequency-discrimination thresholds, and sound-localization thresholds. The elephant was found to have an audibility curve similar to that of other mammals but one that is more sensitive to low frequencies and less sensitive to high frequencies than any other mammalian audiogram including human's. The elephant's sensitivity to frequency differences at low frequencies was found to equal that of humans. Finally, the elephant was found to be very accurate at localizing sounds in the azimuthal plane, with thresholds around 1 degree for broad-band noise. The elephant's ability to localize pure tones suggested that it could use both binaural time- and intensity-difference cues to localize sound.
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