Ernest A. Peterson

Electrical Output of Lizard Ear: Relation to Hair-Cell Population

Cochlear potentials measured in several species of lizard show a close correlation between maximum electrical output and number of hair cells, whereas there is no uniform relation to sensitivity. These results are interpreted as indicating structural differentiation and frequency discrimination in spatial terms in the more advanced lizard ears.

Cochlear Potentials in the Kangaroo Rat, Dipodomys merriami

Our present interest in the kangaroo rat stems from its unusual ear anatomy. The bullae are unusually large, occupying over half the cranial volume. Each bulla is divided into three separate compartments, two large mastoid spaces which communicate independently with a ventrally placed endotympanic space which contains the tympano-ossicular system (see fig. 1). It has been estimated (Webster 1962) that the total volume of these three chambers in a single bulla of a 40-g animal is about 0.5 ml. Of the volume, 49% is devoted to the anterior mastoid, 33% to the posterior mastoid, and 18% to the endotympanic space. The second point of interest in the kangaroo rat ear is the relationship between the size of the tympanic membrane and the size of the oval window. This relationship, termed the transformer ratio (Wever and Lawrence 1954) is derived from the following considerations: (1) the area of the tympanic membrane compared with the area of the stapes footplate in the oval window, and (2) the lever action

Anxiety, Meprobamate, D-Amphetamine and the Intra-Subject Variability of Word Associates

Two experiments on the intra-subject variability of word associates are reported. Exp. 1 indicates that Ss high in anxiety have more variable word associates than Ss low in anxiety. Exp. 2 investigated the joint effects of anxiety and the drugs, meprobamate and d-Amphetamine. Meprobamate reduced variability, d-Amphetamine increased variability. There was a significant drug × anxiety interaction. High-anxiety Ss were more variable than low-anxiety Ss under meprobamate and placebo conditions but less variable under d-Amphetamine conditions. The results are discussed in conjunction with the Hullian proposal of additivity of different sources of drive. It is concluded that other sources of drive detract from the drive-arousing properties of anxiety.

Modes of Auditory Response in the Fissiped Carnivores

As part of a program to furnish preliminary but scientifically acceptable estimates of hearing for a broad sample of representative mammals, ac cochlear potentials (CM) were measured in at least one representative from each of the seven fissiped carnivore families. A total of 66 individuals from 12 species were studied. Several response parameters including CM sensitivity level, response bandwidth, and maximum output were used to evaluate peripheral auditory efficiency. It was found that although interspecies differences in performance were great, it was possible to establish common patterns of response. The relation of these groupings to conventional taxonomic classification and to possible artifacts associated with the method of recording will be discussed. [This research was supported by the U. S. Public Health Service under a grant from the National Institute of Neuroogical Diseases and Blindness.]

Some Electrophysiological Aspects of Hearing in the Bat Eptesicus fuscus

For one bat, it was possible to ascertain the magnitude of cochlear‐microphonic potentials elicited by pure‐tone stimuli of threshold SPL. These potentials at the threshold of hearing varied from 0.008 μV at 70 kHz to 30 μV at 2.5 kHz. The function relating these “threshold potentials” to frequency was strikingly similar in shape to the curve depicting the way hearing thresholds varied with frequency; the covariation was great even in a region around 40 kHz, where the hearing threshold function displayed a large insensitivity peak. There appeared to be no single magnitude of hair‐cell potential that inevitably gave rise to a just‐perceptible hearing sensation. Thus, it is unlikely that density of cochlear stimulation (e.g., microvolts/millimeters of basilar membrane or microvolts/neural unit) bears any simple relation to the initiation of “threshold level” impulses in the auditory nerve. Data from other animals agree with the above.