Effect Of Click Rate Research Articles

Effects of click rate on bottlenose dolphin auditory brainstem response signal-to-noise ratio

Maximum Length Sequence (MLS) and Iterative Randomized Stimulation and Averaging (I-RSA) methods allow auditory brainstem response (ABR) measurements at high stimulus rates; however, it is not clear if high rates allow ABRs of a given signal-to-noise ratio (SNR) to be measured in less time than conventional averaging at lower rates. In the present study, ABR SNR was examined in six bottlenose dolphins using conventional averaging at rates of 25 and 100 Hz and the MLS/I-RSA approaches from 100 to 1250 Hz. Residual noise in the averaged ABR was estimated using root-mean-square values of the: waveform amplitude following the ABR, waveform amplitude after subtracting two subaverage ABRs, and amplitude variance at a single time point. For all approaches, residual noise decreased with the increasing measurement time. For a fixed recording time, SNR was highest at rates near 500 Hz, but optimal SNRs were only a few dB higher than that for conventional averaging at 100 Hz. Nonetheless, small improvements in SNR could result in significant time savings in reaching criterion SNR. The time savings allowed by the MLS and I-RSA methods will be discussed for both mean and individual data. [Work supported by U.S. Navy Living Marine Resources Program.]

The effect of click rate on ABR stability measured with the REPs/ABR protocol.

Previous studies reported to this Society regarding our repeated evoked potentials (REPs) protocol for auditory brainstem responses (ABRs) have used a click rate of approximately 11 per s. Revisions in the REPs/ABR protocol requiring collection of as many as 16 waveforms in a single session encourage test streamlining, such as increasing click rate. The ABR literature suggests that while click rates of 30/s and above may affect 11/s-based absolute ABR parameters such as peak latency and peak amplitude, fewer changes will be seen with rates lower than 30/s. There are no data on the effect of click rate on ABR peak stability, the dependent variable targeted by the REPs procedure. Eight young adults with normal hearing (four women and four men) were tested in a within-subjects five-session design. Each session involved collection of 4 left ear, 4 right ear, and 8 binaural ABR waveforms; in sessions 1 and 5 a click rate of 11.1 per s was used; for sessions 2, 3, and 4, responses were evoked at click rates of 22.2, 33.3, and 44.4 per s, respectively. Results indicate that click rates faster than 30/s do create the most changes in 11/s-based peak latency and amplitude, though the effects for all increases are differentially distributed by peak, ear condition, and individual subject. Changes in click rate also have marked effects on ABR stability, both latency and amplitude, with details highly specific to individuals. In general, however, changes in stability as a function of click rate occur in the context of replication of the overall shape of the ‘‘stability profile’’ for each subject, providing further evidence of the ‘‘fingerprint’’ nature of this means of characterizing individual auditory brainstems.

The effect of click rate on latency and interpeak interval of the brain-stem auditory evoked potentials in children from birth to 6 years

Latency and interpeak interval of the brain-stem auditory evoked potentials at different click rates were measured in 80 healthy children from birth to 6 years, and 21 adults. Clicks were presented at 10, 30, 50, 70 and 90/sec, and 70, 40 and 20 db HL. At high stimulus intensity (70 dB SL), all latencies of waves I, III and V and the I–V, I–III and III–V intervals showed a progressive prolongation with increasing repetition rate. The latency- and the interval-rate functions were similar for all age groups but their slopes were slightly steeper in younger than in older. As click rate increased from 10/sec to 90/sec, the latencies of waves I, III and V at different age groups were prolonged by 4–10%, 9–13% and 12–15% respectively, and the intervals of I–V, I–III and III–V were prolonged by 15–16%, 8–16% and 14–24% respectively. The mean increments of wave V latency and I–V interval in different age groups were 0.404–0.575 and 0.332–0.526 msec respectively with increasing click rate from 10 to 50/sec, and 0.697–1.009 and 0.629–0.776 msec respectively with increasing click rate from 10 to 90/sec. The younger the age the larger the absolute increments for all these BAEP parameters, but the increasing rates for a BAEP measure were similar among different age groups, exhibiting no age-dependent differences. The III–V/I–III interval ration in most age groups was increased by 3–10% with increasing click rate from 10 to 90/sec, suggesting that the III–V interval was affected by stimulus rate slightly more than I–III interval. At moderate (40 dB HL) and low (20 dB SL) intensity, all waves and intervals showed similar latency- and interval-rate functions to those at high intensity. This demonstrates that the shifting latencies and interpeak intervals with increasing click rate appeared to be independent of the stimulus intensities.

Amplitude Change with Click Rate in Human Brainstem Auditory-Evoked Responses

The effect of click rate on wave amplitude of human brainstem auditory-evoked response (BAER) was examined at repetition rates of 10, 30, 50, 70 and 90 Hz in 80 healthy children aged 1 month to 6 years and in 21 adults. As repetition rate was increased from 10 to 90 Hz at 70 dB HL, the amplitudes in different age groups decreased by 33-45% (0.109-179 microV) for wave I and 25-41% (0.055-0.145 microV) for wave V. The older the children, the larger the absolute decrements of wave amplitudes with increasing repetition rate, but the relative decrements or reduction rates of wave amplitudes exhibited no systematically age-related differences. The V/I amplitude ratio tended to increase with increasing repetition rate in most age groups, suggesting that the amplitude of wave I is affected by the repetition rate slightly more than that of wave V. The patterns of the changes in wave amplitudes with repetition rate at lower intensity levels were essentially similar.

Effect of click rate and delay on breakdown of the precedence effect.

The precedence effect was tested as a function of echo-click delay and click rate after an abrupt switch in location between leading and lagging clicks. Click trains at three rates, 1/sec, 2/sec, and 4/sec, with delays ranging between 2 and 20 msec, were presented to subjects in an anechoic chamber. Duration of the click train after the switch in location was 12 sec, and echo click perceptibility was assessed throughout this period. The number of echo clicks heard was an increasing monotonic function of delay. The subjects reported a "fade-out" of echo clicks after a set number of clicks at each delay, regardless of rate. This result was interpreted as a buildup in inhibition of echoes produced by the ongoing click train. Suppression of echoes was stronger when the leading click originated from the right side than from the left side.

Effect of click rate and delay on breakdown of the precedence effect

The precedence effect was tested as a function of echo-click delay and click rate after an abrupt switch in location between leading and lagging clicks. Click trains at three rates, lIsec, 2/sec, and 4/sec, with delays ranging between 2 and 20 msec, were presented to subjects in an anechoic chamber. Duration of the click train after the switch in location was 12 sec, and echo click per­ ceptibility was assessed throughout this period. The number of echo clicks heard was an increas­ ing monotonic function of delay. The subjects reported a fade-out of echo clicks after a set num­ ber of clicks at each delay, regardless of rate. This result was interpreted as a buildup in inhibition of echoes produced by the ongoing click train. Suppression of echoes was stronger when the lead­ ing click originated from the right side than from the left side. Under normal room conditions, we localize a sound at its source, while failing to localize or even recognize the presence of numerous reflected sounds from surround­ ing surfaces. This perceptual phenomenon is known as the precedenceeffect or law ofthe first wavefront be­ cause we weight the original, or first-arriving, sound more heavily than any later-arriving sounds. In a classic study, Wallach, Newman, and Rosenzweig (1949) simulated nat­ ural room reverberations by playing the same sound through two loudspeakers, with one output leading the other by a few milliseconds. As the delay between the original sound and the lagging sound was increased, the listener eventually perceived the lagging sound at its lo­ cus. Blauert (1983, pp. 224-225) defined the echo threshold as the shortest delay at which a single auditory event breaks apart and the lagging sound is localized in a different direction from the original sound. Echo sup­ pression at short delays is produced by inhibitory processes, probably in the central auditory system (Zurek, 1987). Recently, Clifton (1987) reported that a breakdown of this echo suppression can be produced if the location of leading and lagging sounds is suddenly switched. The experimental situation was a train of clicks from two loudspeakers placed at ±90° off the listener's midline, with one output leading the other by about 5 msec (see Figure lA for diagram). The listener initially localized the clicks solely at the leading side. When the leading and lagging sides were switched within an interclick interval, the listener heard clicks from both loudspeakers for sev­ eral seconds before echo suppression was reestablished.

Middle- and long-latency auditory evoked responses recorded from the vertex of normal and chronically lesioned cats

A prolonged sequence of auditory evoked potentials with latencies ranging from 1 to 250 msec was recorded from the vertex of the awake restrained cat. This sequence was reproduceable within and across subjects and was not altered by complete neuromuscular paralysis. The effects of click rate, pentobarbital, and chronic lesions of a number of different brain areas were evaluated for each of the potentials. Vertex waves 1–5, previously shown to originate from generators in the primary auditory pathway of the brain stem, were followed by smaller and less well defined waves 6 and 7, with peak latencies in the 6–8 msec and 10–12 msec range respectively. These potentials were not abolished by fast click rates (i.e. up to 50/sec) nor by moderate levels of pentobarbital. Correlative extra- and intracranial studies indicated that wave 6 occurred in the same latency range as the medial geniculate body, pars principalis potential, and that wave 7 occurred in the same latency range as the primary ectosylvian cortical potential. The intracranial potentials showed click recovery functions and barbiturate resistance which were similar to those of waves 6 and 7, and wave 7 disappeared following aspiration of ectosylvian cortex. These data suggest that waves 6 and 7 reflec generators in medial geniculate body and ectosylvian gyrus. In contrast to the stability of potentials 1 through 7, the longer latency waves were relatively unstable. Wave A occurred in a latency range of 17–25 msec, wave B, 35–45 msec, wave C, 50–75 msec, and wave D, 150–200 msec. All of these waves showed marked amplitude fluctuations, disappeared as click rates increased to 10/sec, and were abolished by moderate levels of pentobarbital. After bilateral aspiration of middle suprasylvian gyrus, ectosylvian gyrus, or frontal lobes, wave A continued to appear. After hemispherectomy, which removed all cortex, basal ganglia and limbic lobes, wave A was not abolished and appeared enhanced in one animal. Thus, the generator system of wave A appears to be largely independent of auditory cortex and adjacent association cortex, but may be modulated by other forebrain systems. Wave C continued to appear after aspiration of suprasylvian and ectosylvian gyri and after frontal lobectomy, but disappeared after hemispherectomy. Thus, wave C reflects a generator system which differs from that of wave A, but which also appears to be largely independent of the primary geniculo-cortical auditory pathway. These data suggest the following conclusions: waves 1 through 7, which show high fidelity, rate-resistant, barbiturate-insensitive acoustic transmission, appear to reflect activation of the primary auditory system from acoustic nerve to auditory cortex. Subsequent, longer-latency vertex potentials seem to be generated through other forebrain systems which receive auditory information in parallel from the brain stem, rather than serially from the primary geniculo-cortical pathway and association cortex relays. The relevance of data in the cat model to the human vertex potentials is discussed.

Intensity and rate functions of cochlear and brainstem evoked responses to click stimuli in man.

The complex of five waves, which are the responses to click stimuli of the auditory nerve and the brainstem auditory nuclei, were recorded in ten human subjects by means of earlobe and scalp electrodes. The rate of the stimuli was varied from 5/s to 80/s and their intensity was varied over a 70 dB intensity range in order to study the rate and intensity functions of each of the response components. With increasing click intensity, the amplitude of the first wave (generated by the auditory nerve) increased proportionally while the amplitudes of the later waves (generated by the brainstem auditory nuclei) reached their maximum amplitudes at intermediate click levels (saturation), and at high intensities occasionally even decreased in amplitude. The latency of each of the waves decreased by similar amounts as the intensity was increased. With increasing click rates, the amplitude of the first wave decreased the most, while there were smaller effects on the amplitude of the later waves. There was no effect of click rate on the latency of the first wave, but the latency of the later waves increased with click rate, the effect being greater on the later waves. In the rate functions, the latency change of a wave was greater than that of the waves preceding it (accumulative effect). These results are explained by overlapping convergence and divergence in the ascending auditory pathway. These results support the notion that the principal component of each wave is activated by the principal component of the previous wave. These results may explain the relative ease with which several workers record the fourth wave of the complex, and their preference for this response.