Discrimination of short duration tones by elderly subjects.

The ability to discriminate the frequency of short duration tone pulses was investigated with 28 elderly subjects. In a previous study, Cranford, Stream, Rye, and Slade (1982) found that subjects with unilateral temporal lobe lesions were impaired in their ability to discriminate small changes in the frequency of such signals at ears located opposite the lesions. In the present study, although considerable intersubject variability was observed, several subjects exhibited deficits on the brief tone frequency difference limen test similar to that observed with temporal lobe lesion patients, but present at both ears.

Detection v discrimination of brief-duration tones. Findings in patients with temporal lobe damage.

Based on earlier experiments with cats, we have developed two new hearing tests to evaluate the ability of patients with temporal lobe damage to discriminate tones of short temporal duration. Earlier published studies suggested that patients exhibit notably increased thresholds for detecting tone pulses shorter than 200 ms in length when the signals are presented to the ear located contralateral to the damaged hemisphere. Our experiments with cats indicated that auditory cortex lesions had no effect on the cats' ability to detect brief tones but did impair their ability to discriminate small changes in the frequency of such signals.

Visual tracking of auditory stimuli.

A white noise sound stimulus was emitted successively in an anechoic chamber across 24 loudspeakers equally spaced in the horizontal plane in a semicircle with diameter of 11 ft. Eye movements produced by each of 20 normal-hearing young adults in the center of this arc who tracked the sound at 10 different velocities (15--180 degrees/sec) were recorded with standard ENG methods. During each rotating cycle of the stimulus the eyes were able to follow the sound with discrete saccades, but did not produce nystagmic-like movements.

Emerging characteristics of the acoustic reflex in infants.

One hundred ninety-nine infants (birth to 15 weeks) were administered an impedance battery to describe emerging characteristics of the acoustic reflex in this age range. Tympanometry results suggest that the middle ear system changes from a highly flaccid state at birth to a relatively normal compliance by 15 weeks. Acoustic reflexes were observed infrequently in the newborn population and gradually increased as a function of age, but never exceeding 43% of the ears tested.

The biphasic acoustic reflex: a new perspective.

The anatomic, neurologic, and physiologic characteristics of the middle ear structures have created confusion concerning the nature of the intraaural muscle reflex. After reviewing the relevant literature, we correlated this information with our studies of human temporal bones and computer analyses of the acoustic reflex responses of individuals with normal hearing. Our hypothesis is that although the stapedius is the initiator of the reflex and the primary contributor to ossicular chain fixation, the tensor tympani is responsible for the major observed response.