Difference thresholds for intensity perception of whole-body vertical vibration: effect of frequency and magnitude

Difference thresholds for seated subjects exposed to whole-body vertical sinusoidal vibration have been determined at two vibration magnitudes [0.1 and 0.5 ms(-2) root mean square (r.m.s.)] and at two frequencies (5 and 20 Hz). For 12 subjects, difference thresholds were determined using the up-and-down transformed response method based on two-interval forced-choice tracking. At both frequencies, the difference thresholds increased by a factor of five when the magnitude of the vibration increased from 0.1 to 0.5 ms(-2) r.m.s. The median relative difference thresholds, Weber fractions (deltaI/I), expressed as percentages, were about 10% and did not differ significantly between the two vibration magnitudes or the two frequencies. It is concluded that for the conditions investigated the difference thresholds for whole-body vibration are approximately consistent with Weber's Law. A vibration magnitude will need to be reduced by more than about 10% for the change to be detectable by human subjects; vibration measurements will be required to detect reductions of less than 10%.     

Mathematical models for the apparent masses of standing subjects exposed to vertical whole-body vibration

Linear lumped parameter models of the apparent masses of human subjects in standing positions when exposed to vertical whole-body vibration have been developed. Simple models with a single degree-of-freedom (d.o.f.) and with two (d.o.f.) were considered for practical use. Model parameters were optimised using both the mean apparent mass of 12 male subjects and the apparent masses of individual subjects measured in a previous study. The calculated responses of two (d.o.f.) models with a massless support structure showed best agreement with the measured apparent mass and phase, with errors less than 0.1 in the normalised apparent mass (i.e., corresponding to errors less than 10% of the static mass) and errors less than 5° in the phase for a normal standing posture. The model parameters obtained with the mean measured apparent masses of the 12 subjects were similar to the means of the 12 sets of parameters obtained when fitting to the individual apparent masses. It was found that the effects of vibration magnitude and postural changes on the measured apparent mass could be represented by changes to the stiffness and damping in the two (d.o.f.) models.     

Power absorbed during whole-body vertical vibration: Effects of sitting posture, backrest, and footrest

Previous studies have quantified the power absorbed in the seated human body during exposure to vibration but have not investigated the effects of body posture or the power absorbed at the back and the feet. This study investigated the effects of support for the feet and back and the magnitude of vibration on the power absorbed during whole-body vertical vibration. Twelve subjects were exposed to four magnitudes (0.125, 0.25, 0.625, and 1.25 m s⁻² rms) of random vertical vibration (0.25-20 Hz) while sitting on a rigid seat in four postures (feet hanging, maximum thigh contact, average thigh contact, and minimum thigh contact) both with and without a rigid vertical backrest. Force and acceleration were measured at the seat, the feet, and the backrest to calculate the power absorbed at these three locations. At all three interfaces (seat, feet, and back) the absorbed power increased in proportion to the square of the magnitude of vibration, with most power absorbed from vibration at the seat. Supporting the back with the backrest decreased the power absorbed at the seat at low frequencies but increased the power absorbed at high frequencies. Supporting the feet with the footrest reduced the total absorbed power at the seat, with greater reductions with higher footrests. It is concluded that contact between the thighs and the seat increases the power absorbed at the seat whereas a backrest can either increase or decrease the power absorbed at the seat.     

Magnitude-dependence of equivalent comfort contours for fore-and-aft, lateral and vertical whole-body vibration

It is currently assumed that the same frequency weightings, derived from studies of vibration discomfort, can be used to evaluate the severity of vibration at all vibration magnitudes from the threshold of vibration perception to the vibration magnitudes associated with risks to health. This experimental study determined equivalent comfort contours for the whole-body vibration of seated subjects over the frequency range 2-315 Hz in each of the three orthogonal axes (fore-and-aft, lateral and vertical). The contours were determined at vibration magnitudes from the threshold of perception to levels associated with severe discomfort and risks to health.At frequencies greater than 10 Hz, thresholds for the perception of vertical vibration were lower than thresholds for fore-and-aft and lateral vibration. At frequencies less than 4 Hz, thresholds for vertical vibration were higher than thresholds for fore-and-aft and lateral vibration. The rate of growth of sensation with increasing vibration magnitude was highly dependent on the frequency and axis of vibration. Consequently, the shapes of the equivalent comfort contours depended on vibration magnitude. At medium and high vibration magnitudes, the equivalent comfort contours were reasonably consistent with the frequency weightings for vibration discomfort in current standards (i.e. W_b and W_d). At low vibration magnitudes, the contours indicate that relative to lower frequencies the standards underestimate sensitivity at frequencies greater than about 30 Hz. The results imply that no single linear frequency weighting can provide accurate predictions of discomfort caused by a wide range of magnitudes of whole-body vibration.     

Cross-modality determination of the subjective growth function for whole-body vertical,sinusoidal, vibration

A cross-modality matching technique with both noise and vibration stimuli has been used to establish the subjective growth of whole body vertical sinusoidal vibration intensity. The results show that in the frequency range 5–80 Hz the growth functions are of the Stevens' power law form, ψ = kφ^m where ψ represents the subjective magnitude of the stimulus and φ the objective magnitude. The value of the important growth parameter m is found to be greatly influenced by the choice of which stimulus (noise or vibration) serves as the dependent variable. The results of the study suggest that the concept of a vibration growth function should be regarded with a certain amount of caution.     

Effect of phase on discomfort caused by vertical whole-body vibration and shock--experimental investigation

An experimental study has investigated the effect of "phase" on the subjective responses of human subjects exposed to vertical whole-body vibration and shock. The stimuli were formed from two frequency components: 3 and 9 Hz for continuous vibrations and 3 and 12 Hz for shocks. The two frequency components, each having 1.0 ms(-2) peak acceleration, were combined to form various waveforms. The effects of the vibration magnitude on the discomfort caused by the input stimuli were also investigated with both the continuous vibrations and the shocks. Various objective measurements of acceleration and force at the seat surface, the effects of different frequency weightings and second and fourth power evaluations were compared with judgments of the discomfort of the stimuli. It was found that a 6% to 12% increase in magnitude produced a statistically significant increase in discomfort with both the continuous vibrations and the shocks. Judgments of discomfort caused by changes in vibration magnitude were highly correlated with all of the objective measurements used in the study. The effects on discomfort of the phase between components in the continuous vibrations were not statistically significant, as predicted using evaluation methods with a power of 2. However, small changes in discomfort were correlated with the vibration dose value (VDV) of the Wb frequency-weighted acceleration. The effect of phase between frequency components within the shocks was statistically significant, although no objective measurement method used in the study was correlated with the subjective judgments.     

Modelling resonances of the standing body exposed to vertical whole-body vibration: Effects of posture

Lumped parameter mathematical models representing anatomical parts of the human body have been developed to represent body motions associated with resonances of the vertical apparent mass and the fore-and-aft cross-axis apparent mass of the human body standing in five different postures: ‘upright’, ‘lordotic’, ‘anterior lean’, ‘knees bent’, and ‘knees more bent’. The inertial and geometric parameters of the models were determined from published anthropometric data. Stiffness and damping parameters were obtained by comparing model responses with experimental data obtained previously.The principal resonance of the vertical apparent mass, and the first peak in the fore-and-aft cross-axis apparent mass, of the standing body in an upright posture (at 5–6 Hz) corresponded to vertical motion of the viscera in phase with the vertical motion of the entire body due to deformation of the tissues at the soles of the feet, with pitch motion of the pelvis out of phase with pitch motion of the upper body above the pelvis. Upward motion of the body was in phase with the forward pitch motion of the pelvis. Changing the posture of the upper body had minor effects on the mode associated with the principal resonances of the apparent mass and cross-axis apparent mass, but the mode changed significantly with bending of the legs. In legs-bent postures, the principal resonance (at about 3 Hz) was attributed to bending of the legs coupled with pitch motion of the pelvis in phase with pitch motion of the upper body. In this mode, extension of the legs was in phase with the forward pitch motion of the upper body and the upward vertical motion of the viscera.     

Dynamic and subjective responses of seated subjects exposed to simultaneous vertical and fore-and-aft whole-body vibration: The effect of the phase between the two single-axis components

Subjective and dynamic responses of seated subjects exposed to simultaneous vertical and fore-and-aft sinusoidal whole-body vibration were investigated. The effect of the phase difference between the vertical and the fore-and-aft vibration on the responses was of a particular interest in this study. Fifteen subjects were exposed to dual-axis vibrations at six frequencies (2.5-8 Hz) and at eight phases between the two single-axis components (0-315°). The magnitude of vibration in each axis was constant at 0.7 m s⁻² rms. Discomfort caused by vibration was measured by the method of magnitude estimation. The motion of the body were measured at the head and three locations along the spine with accelerometers attached to the body surface. The most significant effect of the phase between the two single-axis components on the discomfort was observed at 5 Hz: about 40% difference in the median discomfort estimate caused by changing the phase. The transmissibilities from vertical seat vibration to vertical motions of the spine varied from 0.5 to 2.0 by changing the phase between the two single-axis components at frequencies from 2.5 to 5 Hz. The effect of the phase observed in the dynamic response was not predicted by the superposition of the responses to each single-axis vibration. The discomfort caused by the dual-axis vibration tended to be correlated better with the combinations of the dynamic responses measured in the two axes than with the dynamic responses in a single axis.     

Analyses of biodynamic responses of seated occupants to uncorrelated fore-aft and vertical whole-body vibration

The apparent mass and seat-to-head-transmissibility response functions of the seated human body were investigated under exposures to fore-aft (x), vertical (z), and combined fore-aft and vertical (x and z) axis whole-body vibration. The coupling effects of dual-axis vibration were investigated using two different frequency response function estimators based upon the cross- and auto-spectral densities of the response and excitation signals, denoted as H₁ and H_v estimators, respectively. The experiments were performed to measure the biodynamic responses to single and uncorrelated dual-axis vibration, and to study the effects of hands support, back support and vibration magnitude on the body interactions with the seatpan and the backrest, characterized in terms of apparent masses and the vibration transmitted to the head. The data were acquired with 9 subjects exposed to two different magnitudes of vibration applied along the individual x- and z-axis (0.25 and 0.4 m/s² rms), and along both the axis (0.28 and 0.4 m/s² rms along each axis) in the 0.5-20 Hz frequency range. The two methods resulted in identical single-axis responses but considerably different dual-axis responses. The dual-axis responses derived from the H_v estimator revealed notable effects of dual-axis vibration, as they comprised both the direct and cross-axis responses observed under single axis vibration. Such effect, termed as the coupling effect, was not evident in the dual-axis responses derived using the commonly used H₁ estimator. The results also revealed significant effects of hands and back support conditions on the coupling effects and the measured responses. The back support constrained the upper body movements and thus showed relatively weaker coupling compared to that observed in the responses without the back support. The effect of hand support was also pronounced under the fore-aft vibration. The results suggest that a better understanding of the seated human body responses to uncorrelated multi-axis whole-body vibration could be developed using the power-spectral-density based H_v estimator.     

A model of the vertical apparent mass and the fore-and-aft cross-axis apparent mass of the human body during vertical whole-body vibration

The apparent mass of the human body reflects gross movements caused by whole-body vibration and can be used to predict the influence of body dynamics on seat transmissibility. With vertical excitation, various models fit the measured vertical apparent mass of the human body, but experiments also show high fore-and-aft forces on the seat (the fore-and-aft cross-axis apparent mass) that have not influenced current models. This paper defines a model that predicts the vertical apparent mass and the fore-and-aft cross-axis apparent mass of the seated human body during vertical excitation. A three degree-of-freedom model with vertical, fore-and-aft and rotational (i.e. pitch) degrees of freedom has been developed with twelve model parameters (representing inertia, stiffness, damping, and geometry) optimised to the measured vertical apparent mass and the measured fore-and-aft cross-axis apparent mass of the body. The model provides close fits to the moduli and phases for both median data and the responses of 12 individual subjects. The optimum model parameters found by fitting to the median apparent mass of 12 subjects were similar to the medians of the same parameters found by fitting to the individual apparent masses of the same 12 subjects. The model suggests the seated human body undergoes fore-and-aft motion on a seat when exposed to vertical excitation, with the primary resonance frequency of the apparent mass arising from vertical motion of the body. According to the model, changes in the vertical, fore-and-aft, or rotational degree of freedom have an effect on the resonance in the fore-and-aft cross-axis apparent mass.     

Effect of silence duration in intervocalic velar plosive on voicing perception for normal and hearing-impaired subjects

For normally hearing subjects shortening the silence duration of an intervocalic voiceless plosive induces a misperception of voicing. The time boundary for this effect is about 60 ms, which corresponds to a possible forward masking effect at the frequency of voicing. If recovery from masking is indeed involved, hearing-impaired subjects, who may have prolonged forward masking, can be expected to show abnormally long time boundary for voicing misperception. This study investigated the perception of voicing of an intervocalic plosive for a natural speech sample "aka" as a function of occlusive silence duration for normally hearing and hearing-impaired subjects. To investigate a correlation with forward masking, a second test was performed on the subjects. The same first a of the "aka" was selected and at its end was concatenated a voiced murmur taken from an "aga" elocution from the same speaker, and the minimum duration of the voiced murmur necessary for it to be perceived was measured. About half of the hearing-impaired subjects needed an abnormally long silence duration to avoid voicing misperception. The data indicate a significant correlation between the results of the two tests with a slope of regression line close to unity, and thus support the hypothesis of a voicing perception ruled by recovery from forward masking. Increase in silence duration of voiceless plosives might then be a beneficial acoustical processing for some hearing-impaired subjects.     

Power absorbed during whole-body fore-and-aft vibration: Effects of sitting posture,backrest, and footrest

Although the discomfort or injury associated with whole-body vibration cannot be predicted directly from the power absorbed during exposure to vibration, the absorbed power may contribute to understanding of the biodynamics involved in such responses. From measurements of force and acceleration at the seat, the feet, and the backrest, the power absorbed at these three locations was calculated for subjects sitting in four postures (feet hanging, maximum thigh contact, average thigh contact, and minimum thigh contact) both with and without a rigid vertical backrest while exposed to four magnitudes (0.125, 0.25, 0.625, and 1.25 m s^?2 rms) of random fore-and-aft vibration. The power absorbed by the body at the supporting seat surface when there was no backrest showed a peak around 1 Hz and another peak between 3 and 4 Hz. Supporting the back with the backrest decreased the power absorbed at the seat at low frequencies but increased the power absorbed at high frequencies. Foot support influenced both the magnitude and the frequency of the peaks in the absorbed power spectra as well as the total absorbed power. The measurements of absorbed power are consistent with backrests being beneficial during exposure to low frequency fore-and-aft vibration but detrimental with high frequency fore-and-aft vibration.     

Difference thresholds for vibration of the foot: Dependence on frequency and magnitude of vibration

The smallest change in vibration intensity for the change to be perceptible (i.e. intensity difference threshold) has not previously been reported for vibration of the foot. This study investigated the influence of vibration magnitude and vibration frequency on intensity difference thresholds for the perception of vertical sinusoidal vibration of the foot. It was hypothesised that relative intensity difference thresholds (i.e. Weber fractions) for 16-Hz vibration mediated by the non-Pacinian I (NPI) channel would differ from relative intensity difference thresholds for 125-Hz vibration mediated by the Pacinian (P) channel. Absolute thresholds, difference thresholds, and the locations of vibration sensation caused by vertical vibration of the right foot were determined for 12 subjects using the up-down-transformed-response method together with the three-down-one-up rule. The difference thresholds and locations of sensation were obtained at six reference magnitudes (at 6, 9, 12, 18, 24, 30 dB above absolute threshold—i.e. sensation levels, SL). For 16-Hz vibration, the median relative difference thresholds were not significantly dependent on vibration magnitude and were in the range 0.19 (at 30 dB SL) to 0.27 (at 9 dB SL). For 125-Hz vibration, the median relative difference thresholds varied between 0.17 (at 9 dB SL) and 0.34 (at 30 dB SL), with difference thresholds from 6 to 12 dB SL significantly less than those from 18 to 30 dB SL. At vibration magnitudes slightly in excess of absolute thresholds (i.e. 6-12 dB SL) there were no significant differences between Weber fractions obtained from the P channel (at 125 Hz) and the NPI channel (at 16 Hz). At 24 and 30 dB SL, the 125-Hz Weber fractions were significantly greater than the 16-Hz Weber fractions. Differences in the 125-Hz Weber fractions may have been caused by a reduction in the discriminability of the P channel at high levels of excitation, resulting in one or more NP channel mediating the difference thresholds at magnitudes greater than 18 dB SL. At high magnitudes, a change of channel mediating the Weber fractions may have been responsible for different Weber fractions with 16- and 125-Hz vibration.     

The vibration discomfort of standing persons: 0.5-16-Hz fore-and-aft, lateral, and vertical vibration

To minimise the discomfort of standing people caused by vibration of a floor, it is necessary to know how their sensitivity to vibration depends on the frequency of the vibration. This study was designed to determine how the discomfort of standing people exposed to horizontal and vertical vibration depends on vibration frequency over the range 0.5-16 Hz. Using the method of magnitude estimation, sixteen subjects judged the discomfort caused by fore-and-aft, lateral, and vertical sinusoidal vibration at each of the sixteen preferred one-third octave centre frequencies from 0.5 to 16 Hz at each of nine magnitudes. Subjects also reported the main cause of their discomfort. Equivalent comfort contours were constructed, reflecting the effect of frequency on subject sensitivity to vibration acceleration. With horizontal vibration, at frequencies between 0.5 and 3.15 Hz the discomfort was similar when the vibration velocity was similar, whereas at frequencies between 3.15 and 16 Hz the discomfort was similar when the vibration acceleration was similar. At frequencies less than 3.15 Hz, the subjects experienced problems with their stability, whereas at higher frequencies vibration discomfort was mostly experienced from sensations in the legs and feet. With vertical vibration, discomfort was felt in the lower-body and upper-body at all frequencies. The frequency weightings in current standards for predicting the vibration discomfort of standing persons have been greatly influenced by the findings of studies with seated subjects: the weightings are consistent with the experimentally determined frequency-dependence of discomfort caused by vertical vibration but inconsistent with the experimentally determined frequency-dependence of discomfort caused by horizontal vibration. The results suggest that the responses of seated and standing people are similar for vertical vibration, but differ for horizontal vibration, partly due to greater instability in standing persons.     

Effective seat-to-head transmissibility in whole-body vibration: Effects of posture and arm position

Seat-to-head transmissibility is a biomechanical measure that has been widely used for many decades to evaluate seat dynamics and human response to vibration. Traditionally, transmissibility has been used to correlate single-input or multiple-input with single-output motion; it has not been effectively used for multiple-input and multiple-output scenarios due to the complexity of dealing with the coupled motions caused by the cross-axis effect. This work presents a novel approach to use transmissibility effectively for single- and multiple-input and multiple-output whole-body vibrations. In this regard, the full transmissibility matrix is transformed into a single graph, such as those for single-input and single-output motions. Singular value decomposition and maximum distortion energy theory were used to achieve the latter goal. Seat-to-head transmissibility matrices for single-input/multiple-output in the fore-aft direction, single-input/multiple-output in the vertical direction, and multiple-input/multiple-output directions are investigated in this work. A total of ten subjects participated in this study. Discrete frequencies of 0.5-16 Hz were used for the fore-aft direction using supported and unsupported back postures. Random ride files from a dozer machine were used for the vertical and multiple-axis scenarios considering two arm postures: using the armrests or grasping the steering wheel. For single-input/multiple-output, the results showed that the proposed method was very effective in showing the frequencies where the transmissibility is mostly sensitive for the two sitting postures and two arm positions. For multiple-input/multiple-output, the results showed that the proposed effective transmissibility indicated higher values for the armrest-supported posture than for the steering-wheel-supported posture.     

Low back pain in drivers: The relative role of whole-body vibration, posture and manual materials handling

A cross-sectional study was conducted to investigate the relative role of whole-body vibration (WBV), posture and manual materials handling (MMH) as risk factors for low back pain (LBP). Using a validated questionnaire, information about health history, posture and MMH performed was obtained from 394 workers who drove vehicles as part of their job (according to seven predefined occupational groups) and 59 who did not. The intention was to reflect a wide range of exposures with the lower end of the exposure spectrum defined as that of non-manual workers who do not drive as part of their job. Based on the questionnaire responses and direct measurements of vibration exposure, personal aggregate measures of exposure were computed for each of the respondents, i.e., total vibration dose (TVD), posture score (PS) and manual handling score (MHS). Odds ratios (and 95% confidence intervals) for back pain were obtained from logistics regression models and log-linear backward elimination analysis was performed. The findings showed that ‘combined exposure’ due to posture and one or both of vibration and MMH, rather than the individual exposure to one of the three factors (WBV, posture, MMH) is the main contributor of the increased prevalence of LBP.     

Effect of voluntary periodic muscular activity on nonlinearity in the apparent mass of the seated human body during vertical random whole-body vibration

The principal resonance frequency in the driving-point impedance of the human body decreases with increasing vibration magnitude—a nonlinear response. An understanding of the nonlinearities may advance understanding of the mechanisms controlling body movement and improve anthropodynamic modelling of responses to vibration at various magnitudes. This study investigated the effects of vibration magnitude and voluntary periodic muscle activity on the apparent mass resonance frequency using vertical random vibration in the frequency range 0.5-20 Hz. Each of 14 subjects was exposed to 14 combinations of two vibration magnitudes (0.25 and 2.0 m s⁻² root-mean square (rms)) in seven sitting conditions: two without voluntary periodic movement (A: upright; B: upper-body tensed), and five with voluntary periodic movement (C: back-abdomen bending; D: folding-stretching arms from back to front; E: stretching arms from rest to front; F: folding arms from elbow; G: deep breathing). Three conditions with voluntary periodic movement significantly reduced the difference in resonance frequency at the two vibration magnitudes compared with the difference in a static sitting condition. Without voluntary periodic movement (condition A: upright), the median apparent mass resonance frequency was 5.47 Hz at the low vibration magnitude and 4.39 Hz at the high vibration magnitude. With voluntary periodic movement (C: back-abdomen bending), the resonance frequency was 4.69 Hz at the low vibration magnitude and 4.59 Hz at the high vibration magnitude. It is concluded that back muscles, or other muscles or tissues in the upper body, influence biodynamic responses of the human body to vibration and that voluntary muscular activity or involuntary movement of these parts can alter their equivalent stiffness.     

Target spectral, dynamic spectral, and duration cues in infant perception of German vowels

Previous studies of vowel perception have shown that adult speakers of American English and of North German identify native vowels by exploiting at least three types of acoustic information contained in consonant-vowel-consonant (CVC) syllables: target spectral information reflecting the articulatory target of the vowel, dynamic spectral information reflecting CV- and -VC coarticulation, and duration information. The present study examined the contribution of each of these three types of information to vowel perception in prelingual infants and adults using a discrimination task. Experiment 1 examined German adults' discrimination of four German vowel contrasts (see text), originally produced in /dVt/ syllables, in eight experimental conditions in which the type of vowel information was manipulated. Experiment 2 examined German-learning infants' discrimination of the same vowel contrasts using a comparable procedure. The results show that German adults and German-learning infants appear able to use either dynamic spectral information or target spectral information to discriminate contrasting vowels. With respect to duration information, the removal of this cue selectively affected the discriminability of two of the vowel contrasts for adults. However, for infants, removal of contrastive duration information had a larger effect on the discrimination of all contrasts tested.     

Factors affecting the use of noise-band vocoders as acoustic models for pitch perception in cochlear implants

Although in a number of experiments noise-band vocoders have been shown to provide acoustic models for speech perception in cochlear implants (CI), the present study assesses in four experiments whether and under what limitations noise-band vocoders can be used as an acoustic model for pitch perception in CI. The first two experiments examine the effect of spectral smearing on simulated electrode discrimination and fundamental frequency (FO) discrimination. The third experiment assesses the effect of spectral mismatch in an FO-discrimination task with two different vocoders. The fourth experiment investigates the effect of amplitude compression on modulation rate discrimination. For each experiment, the results obtained from normal-hearing subjects presented with vocoded stimuli are compared to results obtained directly from CI recipients. The results show that place pitch sensitivity drops with increased spectral smearing and that place pitch cues for multi-channel stimuli can adequately be mimicked when the discriminability of adjacent channels is adjusted by varying the spectral slopes to match that of CI subjects. The results also indicate that temporal pitch sensitivity is limited for noise-band carriers with low center frequencies and that the absence of a compression function in the vocoder might alter the saliency of the temporal pitch cues.     

Frequency discrimination of complex signals, frequency selectivity, and speech perception in hearing-impaired subjects

Frequency discrimination of spectral envelopes of complex stimuli, frequency selectivity measured with psychophysical tuning curves, and speech perception were determined in hearing-impaired subjects each having a relatively flat, sensory-neural loss. Both the frequency discrimination and speech perception measures were obtained in quiet and noise. Most of these subjects showed abnormal susceptibility to ambient noise with regard to speech perception. Frequency discrimination in quiet and frequency selectivity did not correlate significantly. At low signal-to-noise ratios, frequency discrimination correlated significantly with frequency selectivity. Speech perception in noise correlated significantly with frequency selectivity and with frequency discrimination at low signal-to-noise ratios. The frequency discrimination data are discussed in terms of an excitation-pattern model. However, they neither support nor refute the model.