A Time-Course-Based Estimation of the Human Medial Olivocochlear Reflex Function Using Clicks

The auditory efferent system, especially the medial olivocochlear reflex (MOCR), is implicated in both typical auditory processing and in auditory disorders in animal models. Despite the significant strides in both basic and translational research on the MOCR, its clinical applicability remains under-utilized in humans due to the lack of a recommended clinical method. Conventional tests employ broadband noise in one ear while monitoring change in otoacoustic emissions (OAEs) in the other ear to index efferent activity. These methods, (1) can only assay the contralateral MOCR pathway and (2) are unable to extract the kinetics of the reflexes. We have developed a method that re-purposes the same OAE-evoking click-train to also concurrently elicit bilateral MOCR activity. Data from click-train presentations at 80 dB peSPL at 62.5 Hz in 13 young normal-hearing adults demonstrate the feasibility of our method. Mean MOCR magnitude (1.7 dB) and activation time-constant (0.2 s) are consistent with prior MOCR reports. The data also suggest several advantages of this method including, (1) the ability to monitor MEMR, (2) obtain both magnitude and kinetics (time constants) of the MOCR, (3) visual and statistical confirmation of MOCR activation.

Effects of Magnitude of Leading Stimulus on Prepulse Inhibition of Auditory Evoked Cerebral Responses: An Exploratory Study

An abrupt change in a sound feature (test stimulus) elicits a specific cerebral response, which is attenuated by a weaker sound feature change (prepulse) preceding the test stimulus. As an exploratory study, we investigated whether and how the magnitude of the change of the prepulse affects the degree of prepulse inhibition (PPI). Sound stimuli were 650 ms trains of clicks at 100 Hz. The test stimulus was an abrupt sound pressure increase (by 10 dB) in the click train. Three consecutive clicks, weaker (−5 dB, −10 dB, −30 dB, or gap) than the baseline, at 30, 40, and 50 ms before the test stimulus, were used as prepulses. Magnetic responses to the ten types of stimuli (test stimulus alone, control, four types of tests with prepulses, and four types of prepulses alone) were recorded in 10 healthy subjects. The change-related N1m component, peaking at approximately 130 ms, and its PPI were investigated. The degree of PPI caused by the −5 dB prepulse was significantly weaker than that caused by other prepulses. The degree of PPI caused by further decreases in prepulse magnitude showed a plateau level between the −10 dB and gap prepulses. The results suggest that there is a physiologically significant range of sensory changes for PPI, which plays a role in the change detection for survival.

Click Trains do not Alter Auditory Temporal Order Judgements

Brief periods of repetitive stimulation (click trains) presented either contiguous or simultaneous to an interval have been previously shown to impact on its perceived duration. In the current investigation we asked whether the perception of temporal order can be altered in a similar way. Participants completed a dichotic spectral temporal order judgement task with the stimuli titrated to their individual thresholds. Immediately prior to the judgement, participants were presented with five seconds of click trains, white noise or silence. We extended previous work on this topic by using each participant’s accuracy and response time data to estimate diffusion model parameters so that the cognitive mechanisms underlying any effect of click trains on the response could be disentangled. There was no effect of stimulation condition on participant’s accuracy, or diffusion model parameters (drift rate, boundary separation or non-decision time). The present findings therefore suggest that click trains do not influence temporal order perception. Additionally, the previous suggestion that click trains induce an increase in the rate of information processing was not supported for this temporal order task. Further work probing the limits and conditions of the click train effect will help to constrain and extend theoretical accounts of subjective timing.

Presentation of Binning-Based Inter-Click Interval Data from Passive Acoustic Monitoring of Free-Ranging Harbour Porpoises (Phocoena Phocoena)

C-PODs are used for Passive Acoustic Monitoring (PAM) of harbour porpoises (Phocoena phocoena) at an offshore open sea location in the German North Sea. Diel patterns of echolocation click trains are extracted from minimum inter-click interval (minICI) data by binning. The aim of this study is to reassess and refine minICI ranges of click train data with particular consideration to the binning widths. Emphasis is also placed on choosing an appropriate visualisation of these binned data. Key ecological results include presence of higher train rates during the day with intermediate minICI values defined by the range 6-28 ms and a higher train rate with short minICI values 1.25-2.00 ms at night. This indicates an increase in porpoise feeding behaviour, or change of style, at night. Click trains with long minICI values > 35 ms occur at an equal rate throughout both diel phases, suggesting a more routine behaviour, such as navigation. Results could be revealed only by judicious choice of binning widths, e.g. previously overlooked patterns within historical echolocation data. The classification methodology can be used to analyse echolocation trains from a variety of species and can be applied to any PAM data with the relevant click parameters.

Do Click Trains Dilate Time Perception due to Physiological Arousal?

Presentation of an auditory click-train before a stimulus leads to the relative overestimation of stimulus duration. This is thought to be due to an increase in the rate of the pacemaker (inferred from the slope when estimates are regressed against stimulus duration) of an internal clock, said to be triggered by physiological arousal. Work with emotional stimuli suggests similar temporal dilations, and there is (mixed) evidence suggesting this effect may be due to physiological arousal. We therefore aimed to test the assertion that click trains increase duration estimates due to increased physiological arousal. We compared estimates of tone durations following negative sounds, neutral sounds, click trains, and silence, while recording pupil size and heart rate as measures of arousal. Contrary to click train literature, estimates did not significantly differ following any of the stimulation types, possibly due to large trial baseline periods. However, pupil size change was significantly higher during negative and neutral sounds than both click trains and silence, and higher during click trains than silence. Heart rate change was higher during negative sounds than click trains. Finally, while pupil size change did not correlate with estimation slopes, heart rate change correlated with estimation slopes for neutral sounds and click trains (significantly) and negative sounds and silence (moderate and anecdotal Bayes factors respectively). In conclusion, there was evidence to suggest that click trains increased physiological arousal (pupil size) compared to silence, and that higher arousal (heart rate) during click trains correlates with estimation slopes (pacemaker rate) following click trains.

A Model and Vibrational Analysis of a Dolphin’s Acoustic System

In this paper, a vibrational model of a dolphin’s acoustic system is presented. The working mechanism encompasses the dolphin’s lungs and nasal passage which hosts air pockets, the phonic lips, anterior and posterior bursae, the melon, lower jaw, and the brain. However, this study’s components of interest were the phonic lips, anterior bursa, and the surrounding muscle tissues. The phonic lips were modeled as rigid plates, surrounding muscles were modeled as springs, and the bursa was modeled as a damper. The chosen mechanical elements produced an underdamped system. There were two cases considered: a system in which the dolphin produces one click and a system in which the dolphin produces a series of clicks, called a click train. The former case is produced when the posterior phonic lip quickly and suddenly impacts the anterior phonic lip. Therefore, this was modeled as an impulse input. The latter case is produced when the posterior and anterior lip periodically engage one another. This was modeled as a sawtooth input. Using commercial computer software, a total of four different scenarios were considered, a healthy dolphin scenario and sick dolphin scenario for each input type.

Underwater click train production by the hippopotamus (Hippopotamus amphibius) suggests an echo-ranging function

Common hippos (Hippopotamus amphibius) live in murky waters and produce a variety of acoustic signals including underwater click trains considered to be social in function. We tested the hypothesis that click trains may function for underwater detection. We used observational and experimental methods involving 16 captive hippos to document the occurrence of click trains in different contexts and describe the acoustic parameters of the clicks. Male and female hippos produced click trains correlated with searching underwater for food items placed in their pools. Males produced click trains when alone supporting the hypothesis that these signals function for detection and are not only social in function. The frequency bandwidth of individual clicks varied and most were below 10 000 Hz. Click train production by hippos during underwater searches suggests a rudimentary form of echo-ranging that may function when other sensory systems are limited in their aquatic environment.

The Development of Echolocation in Bottlenose Dolphins (Tursiops truncatus)

This study aimed to expand on previous efforts to evaluate the ontogeny of echolocation in Atlantic bottlenose dolphins (Tursiops truncatus). Data consisted of echolocation recordings and concurrent behavioral observations taken from one calf in 2000 and from five additional dolphin calves and their mothers in 2002 housed at the U.S. Naval facility in San Diego, CA. A total of 361 echolocation click train samples from calves were recorded weekly over the first 6 months of the calves’ lives. The earliest calf echolocation train was recorded at 22 days postpartum and the number of echolocation attempts from calves increased steadily with age. Calf echolocation trains increased in duration and the number of clicks per train with age while train density (clicks/sec) and interclick interval values remained more consistent. Calves swimming independent of their mothers produced more click trains, especially when multiple calves were present in the social grouping. When considering these results in the context of possible maturation of a calf’s melon physiology, it seems very likely that the first two months of life are critical for the development of echolocation and related behaviors. While the first click train recorded in this sample was approximately 3 weeks of age by two different calves, it is possible that dolphin calves may innately produce functional sonar clicks immediately after birth, which were not captured in the current study. Future research will need to investigate this possibility using more controlled conditions and a better understanding of the anatomy and physiology of the sonar system of neonates as well as the possible role of the mother in echolocation development.