Stimulus Sound Pressure Level Research Articles

Acoustical role of ear canal in exposure to the typical occupational noise levels.

Background: Exposure to noise associated with injuries has become a public health issue in recent years. This study aimed to show the role of the acoustical structure of the ear canal on the typical occupational sound pressure levels at different frequencies. Methods: This cross-sectional study was done on 20-30-year-old participants. White noise was used at 3 levels, including 75, 85, and 95 dB as the stimulus sound pressure levels (SSPLs). The speakers had a 1.5-meter distance from the participants and at the height of 87 centimeters from the lab ground and were located in front of the participants. The SSPLs were measured outside (cavum part of the external ear) and inside the right ear of each participant. Measurements were done at the total sound pressure level and in the 1/1 octave frequencies. The duration for each measurement was 10 seconds. The independent sample t test was used for the statistical analysis, and the equality of means were rejected at p<0.05. Results: There were 30 (50%) males out of the 60 participants. The mean ± SD for the age of all the participants was 23.29±2.93 years. The total sound pressure level difference between the inside and outside of the ears of male and female participants was statistically significant (p<0.001) at the stimulus sound pressure levels. The peak resonance was observed in the frequencies 2000 Hz and 8000 Hz for males and 8000 Hz for females. Conclusion: The ear canal can amplify the sounds and increase the sound pressure levels. This amplification was found to be greater for males than for females.

Individual variation influences avoidance behaviour of invasive common carp (

Uncontrolled biological invasions are reducing freshwater ecosystem diversity and resilience. Research is needed to evaluate whether non-structural deterrents are feasible within lock or canal environments. This study examined common carp (Cyprinus carpio) and buffalo hybrid (Ictiobus) movement patterns in response to acoustic and stroboscopic deterrents. Twelve strobe lights and one underwater speaker were deployed across the centre of a ship slip, with an environment analogous to a navigation canal. Common carp (n = 6) and Ictiobus (n = 4) were implanted with acoustic telemetry tags, and their behaviours were examined under control, stroboscopic, and acoustic stimuli for 60-min trial periods. Trials were run during the day and night for six straight days. Linear models determined that the stroboscopic and acoustic stimuli altered fish positioning within the ship slip, but produced weaker avoidance responses than those observed elsewhere. Weak responses were likely due to a strong preference for the open end of the ship slip and a lack of acoustic refuge during the acoustic treatment. Avoidance responses also differed widely among individuals of the same species, with fish expressing repeatability of avoidance radius size across trials. Ambient and stimulus sound-pressure levels should be carefully considered when deploying acoustic deterrents.

In-air and underwater auditory evoked cortical responses in the dolphin

Auditory signal processing in dolphins is of special interest because these animals echolocate and possess high upper-cutoffs of hearing (∼140 kHz). The few previous measurements of auditory cortical responses (ACRs) in dolphins have been performed in air or with a restrained dolphin half submerged in water. Our goal was to record ACRs from an unrestrained dolphin fully submerged in water utilizing far-field sound stimulation. We performed a series of experiments in air and under water manipulating stimulus presentation rate and level. An increasing stimulus rate from 2 to 4 Hz showed only a nominal decrease in ACR potential; a greater decrease in ACR amplitude occurred with an 8-Hz rate. Decreasing stimulus sound pressure level (SPL) decreased the ACR in a manner consistent with auditory brainstem responses to similar SPLs. Taken together, these findings support the idea that valid cortical potentials can be obtained in air and underwater, though differences in ACR amplitude and polarity require further investigation. Brainstem responses are consistent between both environments; however, the cortical response is attenuated underwater, and a polarity reversal along the anterior-posterior axis observed in air is not present underwater.

Detecting the recruitment phenomenon in adults using 80-Hz auditory steady-state response

ObjectivesThe ASSR is used widely as an objective measurement of hearing in clinical settings because of its high frequency specificity. The recruitment phenomenon is generally detected using subjective evaluations which require direct communication with the patient. If the recruitment phenomenon can be detected with ASSR, it would facilitate diagnosis in patients with developmental disorders and infants. Subjects and methodsWe examined 2 groups of subjects: 10 subjects with unilateral hearing impairment in whom the recruitment phenomenon was detected by the alternate binaural loudness balance test and 12 normal subjects. We compared the relationships between the ASSR response and the stimulus sound pressure level in the 2 groups using the 80-Hz ASSR. ResultsThe amplitude of ASSR was significantly higher in the impaired ear in hearing-impaired subjects compared to a normal ear in normal subjects. The latency of ASSR was significantly shorter in the impaired ear in hearing-impaired subjects than in the normal ear in the normal subjects. ConclusionThis study showed that the recruitment phenomenon caused the higher amplitude and the shorter latency observed in hearing-impaired subjects in the 80-Hz auditory steady-state response (ASSR) in comparison with normal subjects.

A differentially amplified motion in the ear for near-threshold sound detection

The ear is a remarkably sensitive pressure fluctuation detector. In guinea pigs, behavioral measurements indicate a minimum detectable sound pressure of ~20 μPa at 16 kHz. Such faint sounds produce 0.1 nm basilar membrane displacements, a distance smaller than conformational transitions in ion channels. It seems that noise within the auditory system would swamp such tiny motions, making weak sounds imperceptible. Here, a new mechanism contributing to a resolution of this problem is proposed and validated through direct measurement. We hypothesize that vibration at the apical end of hair cells is enhanced compared to the commonly measured basilar membrane side. Using in vivo optical coherence tomography, we demonstrated that apical-side vibrations peak at a higher frequency, had different timing, and were enhanced compared to the basilar membrane. These effects depend nonlinearly on the stimulus level. The timing difference and enhancement are important for explaining how the noise problem is circumvented.

Underwater hearing in California sea lions (Zalophus californianus): Expansion and interpretation of existing data

Measurements of underwater hearing sensitivity of pinnipeds have been made for 9 of 33 species, with most studies involving just one or two trained individuals. There is a need to refine and expand this limited knowledge base to improve understanding of hearing and possible anthropogenic noise effects, especially in cases where data may be extrapolated to other species (see National Research Council 2000, Southall et al. 2007). Schusterman et al. (1972) published what is still the only complete underwater audiogram for a California sea lion (Zalophus californianus). The purpose of this brief communication is to present hearing data from another trained California sea lion for comparison with the classic audiogram. Schusterman et al. (1972) originally tested the underwater hearing ability of an adult male sea lion—identified as “Sam”—using an operant conditioning method of vocal response. Sam was trained to either vocalize upon detecting a 500 ms pure tone signal or to remain silent when no signal was detected. The signals were varied in level in an adaptive, up-down fashion to obtain hearing thresholds at frequencies from 0.25 to 64 kHz. Thresholds were defined as the stimulus sound pressure level (SPL) in dB re: 1 bar corresponding to the 75% correct detection probability at each test frequency. The underwater hearing sensitivity of another captive California sea lion—an adult female identified as “Rio”—was later evaluated at relatively low frequencies (0.1–6.4 kHz) during similar auditory detection tasks conducted by Kastak and Schusterman (1998) and then again by Southall et al. (2005). The absolute threshold measurements obtained in these studies were subsequently extended to cover the full functional hearing range. The higher frequency data for Rio

Auditory brainstem response in the lesser scaup (Aythya affinis), a species of diving duck.

The auditory brainstem response (ABR) is an effective approach to describing auditory sensitivity in a variety of animals. In this investigation, we used the ABR to estimate the auditory sensitivity of a species of diving duck, the lesser scaup (Aythya affinis). The typical lesser scaup ABR waveform showed two to three prominent peaks that occurred within the first 5 ms after onset of the stimulus. Peak amplitude increased and peak latency decreased with increasing stimulus sound pressure level (SPL). Threshold was defined as 2.5 dB below the lowest SPL that evoked a visual response (visual detection method). The best range of hearing for this species was from 500 to 5000 Hz, with sensitivity peaking between 1500 and 3000 Hz. Both the waveform morphology and response characteristics of the peaks to changing stimulus intensity are similar to those found in other avian species, such as screech owls (Megascops asio) and budgerigars (Melopsittacus undulatus).

Bottlenose dolphin (Tursiops truncatus) steady-state evoked responses to multiple simultaneous sinusoidal amplitude modulated tones

Auditory steady-state evoked potentials were measured in a bottlenose dolphin (Tursiops truncatus) in response to single and multiple sinusoidal amplitude modulated (SAM) tones. Tests were conducted in air using a "jawphone" sound projector. Evoked potentials were recorded noninvasively using surface electrodes embedded in suction cups. Sound stimuli consisted of SAM tones with 1, 2, 3, or 4 carrier frequencies (10, 20, 30, 40 kHz), each with a unique modulation frequency. Stimulus sound pressure levels were varied in 5-dB steps from approximately 120 to 60-75 dB re 1 microPa, depending on frequency. Evoked potentials followed the temporal envelope of each stimulus, resulting in spectral components at each unique modulation frequency. Spectral analysis was used to evaluate the response amplitude for each carrier as a function of stimulus level. There were no significant differences between thresholds obtained with single and multiple stimuli at 10, 30, and 40 kHz. At 20 kHz, thresholds obtained with three components were higher than those obtained with four components, possibly revealing interactions between stimuli with less than one octave frequency separation. The use of multiple SAM stimuli may offer substantial advantages for studies of marine mammal hearing, where testing time and access to subjects are typically limited.

Event‐related potential measures of the disruptive effects of trains of auditory stimuli during waking and sleeping states

Acoustic backup alarms have been reported to particularly disrupt sleep. The present study simulated backup alarms by presenting trains of five consecutive 500 ms duration audible tones, with the time between the onset of each tone being 1 s and the time between trains (offset to onset) between 15 and 20 s. In different conditions, the tones were set at either 80 or 60 dB sound pressure level (SPL). Twelve young adults spent two consecutive nights in the laboratory. Stimuli were presented only on the second night. Measures of traditional sleep architecture (sleep stages) were not affected by the acoustic trains. Event-related potentials were also measured following presentation of the stimuli. In the waking state, the initial 80 dB stimulus elicited a large amplitude N1, peaking at about 100 ms, followed by a positive peak, P3, peaking at about 325 ms. N1 was attenuated following presentation of the 60 dB stimulus. The amplitude of N1 was much reduced following presentation of the subsequent second to fifth stimuli in the train. During non-rapid eye movement (NREM) sleep, the initial 80 dB stimulus elicited a large and later negativity (N350) that was reduced in amplitude for the 60 dB stimulus. A K-Complex (a composite N350 and a much larger N550) was elicited following 35% of the initial 80 dB tones and 12% of the initial 60 dB tones. The amplitude of N550 did not, however, significantly vary as a function of stimulus SPL. During REM sleep, N1 continued to be elicited by the initial louder stimulus, but the later positive wave was not apparent. A late negativity peaking at about 350 ms was, however, apparent. When queried the next morning, subjects rarely indicated that the stimulus presentations disturbed their sleep. This might be because of the absence of the late positivity. The presence of the long latency negativities (N350 and N550) might serve to protect sleep from obtrusive sound during sleep.

Codes for sound-source location in nontonotopic auditory cortex.

We evaluated two hypothetical codes for sound-source location in the auditory cortex. The topographical code assumed that single neurons are selective for particular locations and that sound-source locations are coded by the cortical location of small populations of maximally activated neurons. The distributed code assumed that the responses of individual neurons can carry information about locations throughout 360 degrees of azimuth and that accurate sound localization derives from information that is distributed across large populations of such panoramic neurons. We recorded from single units in the anterior ectosylvian sulcus area (area AES) and in area A2 of alpha-chloralose-anesthetized cats. Results obtained in the two areas were essentially equivalent. Noise bursts were presented from loudspeakers spaced in 20 degrees intervals of azimuth throughout 360 degrees of the horizontal plane. Spike counts of the majority of units were modulated >50% by changes in sound-source azimuth. Nevertheless, sound-source locations that produced greater than half-maximal spike counts often spanned >180 degrees of azimuth. The spatial selectivity of units tended to broaden and, often, to shift in azimuth as sound pressure levels (SPLs) were increased to a moderate level. We sometimes saw systematic changes in spatial tuning along segments of electrode tracks as long as 1.5 mm but such progressions were not evident at higher sound levels. Moderate-level sounds presented anywhere in the contralateral hemifield produced greater than half-maximal activation of nearly all units. These results are not consistent with the hypothesis of a topographic code. We used an artificial-neural-network algorithm to recognize spike patterns and, thereby, infer the locations of sound sources. Network input consisted of spike density functions formed by averages of responses to eight stimulus repetitions. Information carried in the responses of single units permitted reasonable estimates of sound-source locations throughout 360 degrees of azimuth. The most accurate units exhibited median errors in localization of <25 degrees, meaning that the network output fell within 25 degrees of the correct location on half of the trials. Spike patterns tended to vary with stimulus SPL, but level-invariant features of patterns permitted estimates of locations of sound sources that varied through 20-dB ranges. Sound localization based on spike patterns that preserved details of spike timing consistently was more accurate than localization based on spike counts alone. These results support the hypothesis that sound-source locations are represented by a distributed code and that individual neurons are, in effect, panoramic localizers.

The effect of tympanic membrane perforation size on umbo velocity in the rat.

The tympanic membrane (TM) in adult rats was surgically exposed and laser interferometry was used to measure TM velocity at the umbo for frequencies between 1.0 and 40.0 kHz. Velocity measures were obtained for five conditions: TM intact, and four progressively larger holes cut into the posterior region of the membrane. Photomicrographs of each condition were used to calculate the percentage of pars tensa lost to the perforation. The relation between TM velocity and stimulus sound pressure level (SPL) was also examined for each of the conditions. The results revealed a systematic loss in low-frequency velocity as perforation size increased. These observations were consistent with clinical reports of low-frequency hearing loss in the perforated human TM. The rat appears to be a successful model for studying this form of conductive pathology.

Effects of ear-canal standing waves on measurements of distortion-product otoacoustic emissions

At frequencies above 3 kHz, standing waves in the ear canal complicate calibration of stimulus sound-pressure levels (SPLs) for measurements of distortion-product otoacoustic emissions (DPOAEs). In the literature, two stimulus-presentation strategies have been used for DPOAE measurements. In the "in-the-ear adjustment" strategy, the voltage command to the speakers is adjusted to maintain a constant stimulus SPL across frequency at the DPOAE-measurement microphone. In the "iso-voltage" strategy, the voltage presented to the speakers is held constant across frequency, on the basis of the assumption that the frequency response of the speakers is approximately flat at the eardrum in the average human ear canal. Because of standing-wave effects, there are large, systematic but idiosyncratic differences of stimulus SPL between the two strategies. DPOAE-versus-frequency functions ("DPOAE audiograms") obtained using both stimulus-presentation strategies in the same ears are presented. The differences of stimulus SPL between the two strategies, and the associated differences of DPOAE amplitude, are described and quantified. Around frequencies of standing-wave minima at the DPOAE probe, the in-the-ear adjustment strategy resulted in smaller DPOAEs at high L1 = L2, but much larger DPOAEs at low L1 = L2, than did the iso-voltage strategy. For any L1, the DPOAE-amplitude differences between the two strategies varied systematically with L1-L2. At the stimulus levels used to construct previously published population norms for clinical applications (i.e., L1 > or = 65 dB SPL), there are only small differences of mean DPOAE amplitudes, and of the standard deviations of these means, between the two strategies.

2-Deoxyglucose uptake patterns in response to pure tone stimuli in the aged rat inferior colliculus

The tonotopic map of the inferior colliculus (IC) of aged rats (25 months old) was examined to determine whether age-related changes known to occur in the cochlea are reflected in the 2-deoxyglucose (2-DG) uptake pattern of the IC. Because aged animals have hearing losses, auditory brainstem response thresholds were measured. Animals with threshold shifts of no greater than 30 dB relative to young animals were used. Animals were injected with radiolabeled 2-DG and stimulated with continuous pure tones presented at 70 dB above the behavioral thresholds for young animals at either 1, 4 or 32 kHz for one hour in a sound attenuated booth. The stimulus sound pressure levels were chosen to achieve comparable sensation levels between the young and aged animals. The tonotopic map of the IC in aged rats was different from that reported previously for young animals (Ryan et al., 1988), in that, the regions stimulated by 1 and 4 kHz were shifted towards the higher frequencies and the uptake areas were twicc as broad for the aged animals as for the young animals. The observed 2-DG uptake patterns are consistent with an activation pattern of a high intensity stimulus and a loss of responsive elements in the cochlear apex. Similar broad and shifted bands of activated tissue may contribute to difficulties in auditory perception in aged humans with increased thresholds and sound amplification.

Threshold and suprathreshold temporal integration effects in the crossed and uncrossed human acoustic stapedius reflex

Threshold and suprathreshold temporal integration (TI) effects were studied in the crossed and uncrossed human acoustic stapedius reflex. Changes in reflex threshold were compared at four stimulus durations and for six threshold response criteria; suprathreshold effects were similarly compared at four stimulus durations and at five stimulus sound-pressure levels. Our results showed that reflex thresholds were significantly lower for the uncrossed condition and for longer duration stimuli. Both effects were dependent on threshold response criteria. Threshold TI measurements in both crossed and uncrossed conditions were equivalent at low criterion levels (0%-4%, p greater than 0.05) but were significantly larger in the crossed condition at higher criterion levels (5%-6%, p less than 0.05). Prominent suprathreshold effects also occurred. The main effect was characterized by significantly larger reflex magnitudes in the uncrossed condition. Duration dependent slope differences in magnitude intensity functions (MIFs) were also observed and were characterized by steeper slopes for longer duration stimuli. Saturation effects and/or intensity-dependent slope decelerations in MIFs were predominant in the uncrossed condition and for stimulus durations exceeding 20 ms. These data provide further quantitative evidence for asymmetric threshold and suprathreshold response properties of the crossed and uncrossed human acoustic stapedius reflex and demonstrate the dependence of these effects on stimuli of different durations.

Implantable hearing aids: Changes in the auditory-evoked potential of the monkey in response to increased loading of the stapes

This study examines the effects on the hearing response in the monkey resulting from an increasing load on the stapes exerted by an implantable middle ear transducer. The transducer was placed on the distal end portion of the long process of the incus in monkeys and progressively advanced in small increments in the direction of the long axis of the stapes. Auditory-evoked potentials were recorded to assess the hearing response induced by the vibration of the transducer at each point. A decrease in response equivalent to a change in stimulus sound pressure level of approximately 20 dB occurred as the load on the stapes increased. Frequency response may also change. Our results imply that, to achieve maximum efficiency, the load placed on the ossicles by a vibrating transducer must be minimized.

聴覚の反応時間測定法に関する研究

In order to determine auditory reaction time, different test methods for central conducting modes (simple reaction, choice reaction, simultaneous reaction and time lag reaction) were carried out on normal subjects. As test sounds, pure tone, white noise and Japanese vowels were employed. The following results were obtained. 1) The results were simple reaction time 186 ms, choice reaction time 283 ms, simultaneous reaction time 288 ms and time lag reaction time 370 ms (delay time 50 ms), 361 ms (delay time 100 ms), 298 ms (delay time 200 ms) and 273 ms (delay time 400 ms). 2) Simple reaction time by stimulus sound pressure level of over 40 dB sensation level was almost a certain value, the determination of reaction time of about 40 dB sensation level was considered to be suitable. 3) In each sound and each examination method, no significant differences between reaction times according to left and right ears were found. 4) According to examination method, the tendency of significant shortening was found only in white noise. This was considered to be due to broad frequency component of white noise or its tonality, accordingly if it was used as test sound, it needed to be loudness balanced with other test sound. 5) In simultaneous reaction and time lag reaction, such acoustic psychological problems as binaural fusion, interaural attentional switching mechanism and warning effect of preceding sound needed to be considered. 6) In the subjects having normal auditory function, it might be estimated that identification time may be about 100 ms and discrimination time may be about 70-80 ms. 7) Auditory reaction time includes the time required in central information conducting process as direct real time, and conveniency of its examination items were superior to the other methods. Also, the analyses of identification time and discrimination time were considered to be applicable for the diagnosis of quantitative auditory function of the central auditory handicapped persons in future.

Gap detection in the starling (Sturnus vulgaris)

Psychoacoustic gap-detection thresholds in four European starlings (Sturnus vulgaris) were determined in a GO/NOGO procedure using the method of constant stimuli. The median minimum detectable gap in a broadband noise (590 Hz to 8 kHz) presented at 45 dB SPL was 1.8 ms. Gap-detection thresholds were independent of the sound pressure level of the stimulus at this level and above. Below 45 dB the minimum detectable gap length increased with decreasing sound pressure level and was 4.3 ms at a stimulus sound pressure level of 25 dB, which corresponds to a sensation level of below 10 dB. The results are discussed in relation to forward masking and intensity-difference limens in birds and with respect to the time constants of the peripheral auditory system of the starling. The psychoacoustical thresholds are compared with neurophysiological gap-detection thresholds in the auditory forebrain of the starling.

Factors affecting pitch judgments as a function of spectral composition.

Stimulated by a recent paper by Platt and Racine (1985), we discuss the factors that probably are involved in certain inconsistencies observed in pitch judgments of tones with different spectral composition. Typically, discrepancies reported in the literature are of the order of 10 cents in magnitude. We point out that measurement of such small pitch effects is heavily dependent on systematic individual differences, and that, when individual differences are averaged out (as is essentially the case in Platt and Racine’s experiments), verification of the actual auditory stimulus sound pressure level (SPL) within a few decibels is necessary. Utilizing the virtual-pitch theory, we evaluate the effects of frequency, SPL, and earphone-frequency response. Furthermore, we present experimental and theoretical data on pitch of piano tones relevant to the problem. The study elucidates that, taking into account the factors mentioned, agreement between the various data considered, as well as theoretical understanding, actually is much better than would be apparent at first sight.

Factors influencing the acoustic-immittance characteristics of the acoustic reflex.

Measurements of the aural acoustic-immittance (admittance and impedance) characteristics of the middle-ear transmission system in humans during the quiescent (static) and reflexive states were made (N = 36) utilizing a signal-averaging technique. Three pure tones (750, 1000, and 2000 Hz) and broadband noise stimuli elicited the acoustic reflex in 2-dB steps at sound-pressure levels from 84-116 dB (tones) and 66-116 dB (noise) during ascending- and descending-intensity level runs. The contralateral middle-ear activity was monitored with a 220-Hz probe by digitizing the conductance and susceptance outputs of an admittance meter. A computer corrected for the ear-canal volume utilizing measurements made at ear-canal pressures of 0 and --350 daPa and then converted the conductance and susceptance values into admittance and impedance units. The results were reported in absolute and relative immittance units, including components, as a function of both stimulus sound-pressure level and intensity level above the acoustic-reflex threshold. The static immittance of the middle ear changed nonlinearly over time to lower admittance or higher impedance values. The influence of this static-immittance shift on the reflex magnitude was discussed. The largest mean reflex magnitude and the slowest rate of growth were observed with broadband noise, although eight of the 36 subjects demonstrated the largest reflex magnitude in response to one or more of the tonal stimuli. Although static-immittance values and acoustic-reflex thresholds were poorly correlated, the reflex magnitudes were proportional to static immittance. The variability of the reflex measures was similar to the variability of the static-immittance values. Finally, bi-directional changes in resistance during the reflexive state were observed and discussed.

The influence of sound pressure level upon the potency of phenobarbitone sodium and meprobamate against audiogenic seizures in mice

Groups of mice responding to a 115 dB electric bell sound stimulus with pre-convulsive running were treated with 2.5 mg/kg phenobarbitone sodium and retested at 115, 120, 125 and 130 dB. A negative linear relationship exists between sound pressure level and the percentage of animals protected by phenobarbitone sodium. Protective dose 50% (PD50) values for phenobarbitone sodium and meprobamate were dependent upon stimulus sound pressure level, increasing with intensity.