Click Signals Research Articles

Effect of click rate on the latency of auditory brain stem responses in humans.

Auditory brain stem responses are the far-field reflections of electrical activity originating in the auditory pathway in its course from the cochlea to cortex that can be recorded from scalp electrodes using computer averaging techniques. There are seven components in the initial 10 msec following a click signal which have been shown to have an orderly change in latency as a function of signal intensity. The results of this study show that click repetition rate can also significantly affect the response latency measure. Responses were measured in six normal hearing subjects at click rates of 10, 30, 50 and 100/sec and af four intensity levels (30, 40, 50, and 60 dB sensation level). The mean latency shift of component V was approximately 0.5 msec when the responses at 10 and 100/sec were compared. This is equivalent to a 15-20 dB decrease in signal intensity at the 10/sec click rate. An analysis of the time of occurrence of this shift using brief click trains at 100/sec showed the shift in latency to be complete by the fifth click. The latency shift was similar at the four signal levels tested. The latency shift was similar at the four signal levels tested. The latency shift of component V appeared to be a monaural and therefore a potentially peripheral process. The results are interpreted as an objective measure of adaptation in the human auditory system with implications for the measurement in disorders of hearing.

Correlation between confirmed sites of neurological lesions and abnormalities of far-field auditory brainstem responses

Far-field auditory brainstem responses were recorded in ten patients in whom the distribution of pathology was defined at autopsy or at operation. The response normally consists of seven components in the initial 10 msec following click signals. Interruption of auditory pathway at the junction of VIII nerve with brainstem results in loss of response components after Wave I. Interruption of auditory pathway at the midbrain results in loss of response components after Wave III. We conclude that Wave I reflects activity of VIII nerve, Waves II and III reflect activity of cochlear nucleus, trapezoid body, and superior olive and Waves IV and V reflect activity of lateral lemniscus and inferior colliculus. The generators of Waves VI and VII were not defined.

CORRELATION BETWEEN PATHOLOGICALLY CONFIRMED SITES OF NEUROLOGICAL LESIONS AND ABNORMALITIES OF FAR-FIELD AUDITORY BRAINSTEM RESPONSES.

AMERICAN ASSOCIATION OF NEUROPATHOLOGISTS 159 CORRELAnON BEIWEEN PAntOLOCICALLY CONFIRMED SITES OF NEUROLOGICAL LESIONS AND ABNORMALITIES OF FAR-FIELD AUDITORY BRAINSTEM RESPONSES. A. Starr and A.E. Hamilton*. University of C4lifornia, Irvine, C4lifornia College of Medicine, Irvine, California. Far-field auditory brainstelll responses were recorded in nine patients in whom the distribution of the pathology was defined at autopsy in order to correlate the loss of the electrical components of the auditory res- ponse to the anatomic components of the auditory tract. lbe normal res- ponse consists of seven wave components in the initial ten miliseconds following click signals. A schwanoma of the eighth nerve resulted in the loss of the components after Wave I. Two patients with midbrain tumors had intact Waves I, II, and III, abnormal Waves IV and V, and absent Waves V and VI. A patient with a brainstem glioma which completely obliterated the midbrain and pons, a patient vbose pons and medulla vere completely infarcted. and a drug overdose patient with patchy brainstem encepbalomalacia and three patients with diffuse severe anoxic brainstem changes had clearly detectable Wave I's. The subsequent components were either absent or significantly altered in latency or amplibide. We con- clude that Wave I reflects the activity, Waves II and III reflect activity of the cochlear nucleus, trapezoid body and superior olive and Waves IV and V reflect the activity of the lateral lemniscus and inferior colliculus. The anatomic sources of Waves VI and VII vere not elucidated. (Supported in part by Grant PBS NS 11876 from the USPHS.)

Effect of click repetition rate on the latency of human auditory brainstem responses

Auditory brainstem responses are the far‐field reflection of electrical activity originating in the auditory pathway in its course from the cochlea to cortex that can be recorded from scalp electrodes using computer averaging techniques. There are seven components in the initial 10 msec following a click signal which have been shown to have an orderly change in latency as a function of signal intensity. The results of this study show that click repetition rate can also significantly affect the response latency measure. Responses were measured in ten normal hearing subjects at click rates of 10 to 100/sec and at four intensity levels (30, 40, 50, 60 dB SL). The mean latency shift of component V was 0.5 msec when responses at 10 and 100/sec were compared. This is equivalent to a 20‐dB decrease of signal intensity at the 10/sec click rate. An analysis of the time of occurrence of this shift using brief click trains at 100/sec showed the shift to be complete by the fifth click. The latency shift was similar at the four signal levels tested. The results are interpreted as an objective measure of adaptation in the human auditory system with implication for the measurement in disorders of hearing.

Auditory brain stem responses in neurological disease.

A sequence of seven low-amplitude (nanovolt) potentials that occur in the initial 10 msec following click signals can be recorded from scalp electrodes in human subjects using computer averaging techniques. The potentials, termed auditory brain stem responses, are thought to be the far-field reflection of electrical events originating in the auditory pathway during its course through the brain stem. We have studied auditory brain stem responses in a variety of neurological disorders and found them to be of assistance in evaluating the mechanisms of coma, the localization of midbrain and brain stem tumors, the localization of demyelination of the brain stem, and tumors, the localization of demyelination of the brain stem, and the presence of diminished brain stem circulation.

Underwater localization of click and pulsed pure-tone signals by the California sea lion (Zalophus californianus).

The objective of this study was to measure the ability of the sea lion (Zalophus californianus) to localize click and pulsed pure−tone signals presented in the horizontal plane. In the first experiment the Minimum Audible Angle (MAA) was determined for a click signal consisting of one cycle of a 1.0−kHz signal presented with a repetition rate of 30 Hz. Thresholds at 63% and 75% correct responses were 6° and 9°, respectively. A second experiment examined the sea lion’s ability to localize pulsed pure tones ranging in frequency from 0.25 to 4.0 kHz at only one angular displacement. The pure tones were presented in the form of a pulse train, each pulse having a duration of 20 msec, rise−fall time of 5 msec, and a repetition rate of 30 Hz. The pulsed pure−tone localization function showed that as signal frequency was increased from 250 Hz to 1.0 kHz, the sea lion’s ability to localize the signal remained relatively constant, while above 1.0 kHz there was a sharp decrement in localization ability. Subject Classification: 65.62; 80.60.

Lateralization performance of squirrel monkey (Samiri sciureus) to binaural click signals.

AN IMPORTANT FUNCTION of the auditory system is to determine the locus of a sound source. Two of the prim;iry <tcoustic cues for localization are the interaural time difference (/11) and the interaural intensity difference (/11). In man, the presentation through paired earphones of dichotic stimuli having interaural time separations of less than l or 2 msec gives rise to a unitary aroustic image localized someplace within the head. Under the.,c experimental conditions, the a~!ics~ment o( the i ntracranial position of the acoustic image is a process ohen referred to as lateralization (3). In lateralization experiments, in contrast to localization, it is possible to vary the two interaural cues independently. However, the neural processes invoked both in the localization of an external sound source and in the lateralization of an internal image are thought to be similar. Lateralization has been well studied psychophysically in humans (4, 5, 7-10, 13, I 8, 19, 21, 23, 27, 30) ancl neurophysiologically in cats (1 1, 20, 22, 24), and attempts to correlate the two types of data have been made (11, 22). To avoid such generic differences there is a need for the collection of psychophysical data from animals amenable to neuropliysiological study. In the present paper we describe results of psychophysical lateralization experiments in squirrel monkeys using dichotic clicks that can he compared with a companion paper (25) in which si11glc-u11it response to the same click signals was obtained in another group of monkeys.