Papers by Deborah Vickers
Journal De Physique Iv, 1994
ABSTRACT Emission spectra of the 3P0 → 3H4 transition in Pr: β" alumina single crystals ... more ABSTRACT Emission spectra of the 3P0 → 3H4 transition in Pr: β" alumina single crystals excited by both a broad-band blue source and by dye laser excitation at various wavelengths within the inhomogeneously-broadened 3H4 → 3P0 absorption line are considered. These spectra are strongly polarized, and are therefore due to Pr3+ ions in the Beevers-Ross (BR) sites. An approximately-axial model for the crystal field at a BR site predicts crystal field splitting of the 3H4 level and polarization selection rules which approximately match those we have observed.
Journal of The Acoustical Society of America, 1997
This experiment was intended to clarify the relative role of spread of excitation and suppression... more This experiment was intended to clarify the relative role of spread of excitation and suppression in simultaneous masking, for masker frequencies just below and well below the signal frequency. The experiment had two stages. In stage 1, growth-of-masking functions were measured in simultaneous masking for a 2200-Hz sinusoidal signal and a sinusoidal masker with frequency of either 1800 Hz or 500 Hz. Straight lines fitted to these data were used to determine masker levels that would give 10, 20, and 30 dB of masking. In stage 2, thresholds for detecting a brief 2200-Hz signal were measured using forward masking. It was reasoned that the threshold of the signal would give an indication of the amount of excitation evoked by the masker in the frequency region of the signal. Three forward maskers were used: (1) a 2200-Hz sinusoid at 10, 20, or 30 dB sensation level (SL); (2) a 2200-Hz sinusoid at the same levels as in (1) together with a sinusoid with frequency 500 or 1800 Hz at a level just sufficient to mask the 2200-Hz sinusoid. We refer to this as the "combined masker," (3) a 500-Hz or 1800-Hz sinusoid at the same levels as in (2) above. The 1800-Hz combined masker produced slightly less forward masking than the 2200-Hz masker (1), which might be explained in terms of suppression or as perceptual cueing. Both the 1800-Hz combined masker and the 1800-Hz component alone (3) gave significant amounts of forward masking (up to 18 dB), indicating that these maskers produced substantial excitation at 2200 Hz. This is consistent with the idea that the simultaneous masking of the 2200-Hz component in stage 1 was produced by spread of excitation rather than by suppression. The 500-Hz combined masker produced much less forward masking than the 2200-Hz component alone, indicating strong suppression of the 2200-Hz component of the combined masker by the 500-Hz component. However, both the 500-Hz combined masker and the 500-Hz component alone produced some forward masking. This is not consistent with the idea that masking of the 2200-Hz component in stage 1 (simultaneous masking) was produced solely by suppression.
Gait & Posture, 2000
Gait summary measures have been developed as a convenient method to communicate overall gait path... more Gait summary measures have been developed as a convenient method to communicate overall gait pathology. These measures are primarily used in the context of paediatric cerebral palsy and their use remains largely untested in other disability groups. This study assessed the suitability of gait summary measures for use with lower limb amputees. Modified (m) versions of three published gait summary
Gait & Posture, 2009
The Movement Analysis Profile (MAP) and the Gait Profile Score (GPS) have been used to summarise ... more The Movement Analysis Profile (MAP) and the Gait Profile Score (GPS) have been used to summarise overall gait pathology in children with cerebral palsy. This study investigated the use of the MAP/GPS with unilateral lower limb amputees. Fifteen unilateral lower limb amputees underwent three-dimensional gait analysis (3DGA). The MAP demonstrated increased deviations from normal values for all subjects. Pelvic obliquity, hip adduction/abduction and knee flexion/extension differentiated levels of amputation. Asymmetries were detected in all variables, except pelvic tilt and pelvic rotation.
Gait & Posture, 2009
Abstracts / Gait & Posture 30S (2009) S1-S153 S41 . Roll-over shape and forward travel. dard gait... more Abstracts / Gait & Posture 30S (2009) S1-S153 S41 . Roll-over shape and forward travel. dard gait lab, comprising a force plate and a motion capture system. During the stance phase, a biological ankle-foot system acts like a smoothly curved solid object. The CoP progresses forward from heel to toe, similar to that of a rolling wheel with a particular radius. Hansen et al.
Journal of The Acoustical Society of America, 1999
... Brian CJ Moore, Deborah A. Vickers, Christopher J. Plack, Andrew J. Oxenham. Abstract. ... Th... more ... Brian CJ Moore, Deborah A. Vickers, Christopher J. Plack, Andrew J. Oxenham. Abstract. ... The measures of loudness recruitment were used to derive a parameter HL, the amount of the hearing loss attributable to OHC damage [BCJ Moore and BR Glasberg, Auditory Neurosci. ...
Hughes Electronics has developed a novel surface micromachining process for fabricating extremely... more Hughes Electronics has developed a novel surface micromachining process for fabricating extremely low cost integrated tunneling sensors for a wide variety of military and commercial applications. Previously fabricated bulk micromachined tunneling devices have demonstrated the high displacement sensitivity (approximately 4.0 X 10-5 nm/(root)Hz at 500 Hz) obtainable with tunneling transduction. However, these early devices were fabricated with processes that yielded
Journal of The Acoustical Society of America, 1999
This paper describes further tests of a model for loudness perception in people with cochlear hea... more This paper describes further tests of a model for loudness perception in people with cochlear hearing loss. It is assumed that the hearing loss ͑the elevation in absolute threshold͒ at each audiometric frequency can be partitioned into a loss due to damage to outer hair cells ͑OHCs͒ and a loss due to damage to inner hair cells ͑IHCs͒ and/or neurons. The former affects primarily the active mechanism that amplifies the basilar membrane ͑BM͒ response to weak sounds. It is modeled by increasing the excitation level required for threshold, which results in a steeper growth of specific loudness with increasing excitation level. Loss of frequency selectivity, which results in broader excitation patterns, is also assumed to be directly related to the OHC loss. IHC damage is modeled by an attenuation of the calculated excitation level at each frequency. The model also allows for the possibility of complete loss of IHCs or functional neurons at certain places within the cochlea ͑''dead'' regions͒. The parameters of the model ͑OHC loss at each audiometric frequency, plus frequency limits of the dead regions͒ were determined for three subjects with unilateral cochlear hearing loss, using data on loudness matches between sinusoids presented alternately to their two ears. Further experiments used bands of noise that were either 1-equivalent rectangular bandwidth ͑ERB͒ wide or 6-ERBs wide, centered at 1 kHz. Subjects made loudness matches for these bands of noise both within ears and across ears. The model was reasonably accurate in predicting the results of these matches without any further adjustment of the parameters.
Journal of The Acoustical Society of America, 1997
Thresholds for a 6.5-kHz sinusoidal signal, temporally centered in a 400-ms broadband-noise maske... more Thresholds for a 6.5-kHz sinusoidal signal, temporally centered in a 400-ms broadband-noise masker, were measured as a function of signal duration for normally hearing listeners and listeners with cochlear hearing loss over a range of masker levels. For the normally hearing listeners, the slope of the function relating signal threshold to signal duration ~integration function! was steeper at medium masker
Hearing Research, 2002
Masking patterns were measured for hearing-impaired subjects with varying degrees of hearing loss... more Masking patterns were measured for hearing-impaired subjects with varying degrees of hearing loss. In one set of conditions, three subjects were tested using narrowband noise ('noise') and sinusoidal ('tone') maskers and narrowband noise signals. The maskers had centre frequencies of 0.25, 0.5, 1.0 and 4.0 kHz and levels of 60, 80 and 100 dB SPL. Masking patterns for both the noise and tone maskers showed irregularities ('dips'), especially for signal frequencies up to 500 Hz above the masker frequency. The irregularities occurred for all masker levels and for all subjects for at least one masker frequency and they occurred for a relatively constant range of masker-signal frequency separations, suggesting that they were the result of beat detection. In another set of conditions, masking patterns were measured using two subjects, for a 2.0-kHz tone masker with a level of 100 dB SPL and tone and noise signals. For the tone masker alone (baseline condition), the masking patterns again exhibited prominent dips above, and sometimes below, the masker frequency. The addition of a lowpass noise to the masker, intended to mask combination tones, had little effect for one subject. For the other subject, who had near-normal absolute thresholds at low frequencies, the noise elevated thresholds for masker-signal frequency separations between 500 and 1500 Hz. For this subject, an extra tone with a frequency equal to the masker-signal frequency separation, added in place of the lowpass noise, had a very similar effect to that produced by the lowpass noise, suggesting that he was detecting a simple difference tone in the baseline condition. The addition of a pair of high-frequency tones (MDI tones^intended to reduce the detectability of beats) to the masker elevated thresholds for signal frequencies from 1500 to 2500 Hz for one subject and from 1500 to 3500 Hz for another subject. The addition of lowpass noise and MDI tones to the masker produced masking patterns very similar to those observed when the MDI tones alone were added to the masker. Overall, the results suggest that the irregularities in the masking patterns were caused mainly by the detection of beats and not by the detection of combination tones. ß
British Journal of Audiology, 2000
International journal of audiology, 2009
Listeners with high-frequency dead regions (DRs) benefit from amplification of frequencies up to ... more Listeners with high-frequency dead regions (DRs) benefit from amplification of frequencies up to 1.7 times the edge frequency, f(e), of the DR. Better consonant identification might be achieved by replacing the band from f(e) to 1.7f(e) with a higher spectral band. We aimed to identify the optimal band, using simulations with normal-hearing listeners. In experiment 1, nonsense syllables were lowpass filtered to simulate DRs with f(e) of 0.5, 0.75, and 1.0 kHz. Identification was measured for each of these base bands alone and with a bandpass-filtered band added (but not transposed). The added band either extended from f(e) to 1.7f(e) or its center frequency was increased, keeping bandwidth fixed in ERB(N)-number. Performance improved with increasing center frequency and then reached an asymptote or declined. Experiment 2 used a mid-frequency base band, and a lower-frequency added band. The results also showed a beneficial effect of frequency separation of the added and base bands. E...
Journal of The Acoustical Society of America, 1996
Journal of the Optical Society of America B, 1992
The threshold for self-pumped optical phase conjugation by means of backward stimulated photorefr... more The threshold for self-pumped optical phase conjugation by means of backward stimulated photorefractive scattering has been dramatically lowered by inserting a retroreflecting screen into the path of the beam after the beam leaves a BaTiO 3 crystal. Stable ref lectivities of as much as -60% and good phase-conjugate fidelity have been demonstrated in a crystal that has too low a gain-length product to exhibit unseeded backward stimulated scattering. Precise control of the threshold for stimulated scattering is demonstrated by adjusting the seed intensity. Reflectivity and fidelity are experimentally characterized at 515 nm as a function of the following parameters: pump and seed intensities, crystal angle with respect to the incident beam direction, crystal interaction length, crystal-lens separation, and aberration strength. Operation at 633, 730-800, and 839 nm is demonstrated also. 0740-3224/92/091726-09$05.00
The Journal of the Acoustical Society of America, 1999
The active mechanism in the cochlea is thought to depend on the integrity of the outer hair cells... more The active mechanism in the cochlea is thought to depend on the integrity of the outer hair cells (OHCs). Cochlear hearing loss is usually associated with damage to both inner hair cells (IHCs) and OHCs, with the latter resulting in a reduction in or complete loss of the function of the active mechanism. It is believed that the active mechanism contributes to the sharpness of tuning on the basilar membrane (BM) and is also responsible for compressive input-output functions on the BM. Hence, one would expect a close relationship between measures of sharpness of tuning and measures of compression. This idea was tested by comparing three different measures of the status of the active mechanism, at center frequencies of 2, 4, and 6 kHz, using subjects with normal hearing, with unilateral or highly asymmetric cochlear hearing loss, and with bilateral loss. The first measure, HLOHC, was an indirect measure of the amount of the hearing loss attributable to OHC damage; this was based on loudness matches between the two ears of subjects with unilateral hearing loss and was derived using a loudness model. The second measure was the equivalent rectangular bandwidth (ERB) of the auditory filter, which was estimated using the notched-noise method. The third measure was based on the slopes of growth-of-masking functions obtained in forward masking. The ratio of slopes for a masker centered well below the signal frequency and a masker centered at the signal frequency gives a measure of BM compression at the place corresponding to the signal frequency; a ratio close to 1 indicates little or no compression, while ratios less than 1 indicate that compression is occurring at the signal place. Generally, the results showed the expected pattern. The ERB tended to increase with increasing HLOHC. The ratio of the forward-masking slopes increased from about 0.3 to about 1 as HLOHC increased from 0 to 55 dB. The ratio of the slopes was highly correlated with the ERB (r = 0.92), indicating that the sharpness of the auditory filter decreases as the compression on the BM decreases.
The Journal of the Acoustical Society of America, 2001
People with high-frequency sensorineural hearing loss differ in the benefit they gain from amplif... more People with high-frequency sensorineural hearing loss differ in the benefit they gain from amplification of high frequencies when listening to speech. Using vowel-consonant-vowel ͑VCV͒ stimuli in quiet that were amplified and then low pass filtered with various cutoff frequencies, Vickers et al. ͓J. Acoust. Soc. Am. 110, 1164 -1175 ͑2001͔͒ found that the benefit from amplification of high-frequency components was related to the presence or absence of a cochlear dead region at high frequencies. For hearing-impaired subjects without dead regions, performance improved with increasing cutoff frequency up to 7.5 kHz ͑the highest value tested͒. Subjects with high-frequency dead regions showed no improvement when the cutoff frequency was increased above about 1.7 times the edge frequency of the dead region. The present study was similar to that of Vickers et al. but used VCV stimuli presented in background noise. Ten subjects with high-frequency hearing loss, including eight from the study of Vickers et al., were tested. Five had dead regions starting below 2 kHz, and five had no dead regions. Speech stimuli at a nominal level of 65 dB were mixed with spectrally matched noise, amplified according to the ''Cambridge'' prescriptive formula for each subject and then low pass filtered. The noise level was chosen separately for each subject to give a moderate reduction in intelligibility relative to listening in quiet. For subjects without dead regions, performance generally improved with increasing cutoff frequency up to 7.5 kHz, on average more so in noise than in quiet. For most subjects with dead regions, performance improved with cutoff frequency up to 1.5-2 times the edge frequency of the dead region, but hardly changed with further increases. Calculations of speech audibility using a modified version of the articulation index showed that application of the Cambridge formula was at least partially successful in making high-frequency components of the speech audible for subjects with dead regions, and that such subjects often failed to benefit from increased audibility of the speech at high frequencies.
Journal of Biomechanics, 2006
This paper documents research that quantifies and describes the biomechanics of normal gait on in... more This paper documents research that quantifies and describes the biomechanics of normal gait on inclined surfaces. Experimental, investigative. It is necessary to walk on inclined surfaces to negotiate the natural and built environments. Little research has been conducted on the biomechanics of normal gait on inclined surfaces. The gait of 11 healthy male volunteers was measured using a Vicon system 370 on an inclinable walkway. Gait was measured at 0 degrees , 5 degrees , 8 degrees and 10 degrees of incline. Passive optical markers were placed on each subject and they walked at a self-selected speed up and down the walkway. Ground reaction forces and EMG were measured. Gait data were analysed in Vicon Clinical Manager. Changes in the dynamics of the lower limbs with respect to incline angles are described. Between subject and between condition differences in biomechanical parameters were significant. Hip flexion increased at heel strike with inclines from -10 degrees to +10 degrees . Knee flexion and ankle dorsiflexion at heel strike increased with increasing angle walking up, but not down. Changes in joint moments and powers due to change in the angle of incline or direction of walking were observed. The mechanisms by which the body enables walking up and downhill, specifically raising and lowering the centre of mass, and preventing slipping, can be seen in the alteration in the dynamics of the lower limbs. Increases in range of motion and muscle strength requirements need to be considered in the design of lower limb prostheses and in orthopaedic and neurological rehabilitation. Gait, prosthetics, rehabilitation, balance and falls.
International Journal of Audiology, 2013
The Toy Discrimination Test measures children's ability to discriminate spoken wo... more The Toy Discrimination Test measures children's ability to discriminate spoken words. Previous assessments of reliability tested children with normal hearing or mild hearing impairment, and most studies used a version of the test without a masking sound. We assessed test-retest reliability for children with hearing impairment using maskers of broadband noise and two-talker babble. Stimuli were presented from a loudspeaker. The signal-to-noise ratio (SNR) was varied adaptively to estimate the speech-reception threshold (SRT) corresponding to 70.7% correct performance. Participants completed each masked condition twice. Fifty-five children with permanent hearing impairment participated, aged 3.0 to 6.3 years. Thirty-four children used acoustic hearing aids; 21 children used cochlear implants. For the noise masker, the within-subject standard deviation of SRTs was 2.4 dB, and the correlation between first and second SRT was + 0.73. For the babble masker, corresponding values were 2.7 dB and + 0.60. Reliability was similar for children with hearing aids and children with cochlear implants. The results can inform the interpretation of scores from individual children. If a child completes a condition twice in different listening situations (e.g. aided and unaided), a difference between scores ≥ 7.5 dB would be statistically significant (p <.05).
British Journal of Audiology, 1995
This experiment simulated the threshold elevation and loudness recruitment associated with three ... more This experiment simulated the threshold elevation and loudness recruitment associated with three different types of hearing loss: moderate flat (condition R2), severe flat (condition R3), and moderate-to-severe sloping (condition RX). This was done to allow an examination of the effects of these factors on the intelligibility of speech, in isolation from other factors that are normally associated with cochlear hearing loss, such as reduced frequency selectivity. The speech was presented at a fixed input level of 65 dB SPL, against a background of a noise whose spectrum was shaped to match the long-term average spectrum of the speech. The level of the background noise varied from 65 to 74 dB SPL. The simulation was performed by splitting the input signal into 13 frequency bands, and processing the envelope in each band so as to create loudness sensations in a normal ear that would resemble those produced in an impaired ear with recruitment. The bands were then recombined. All tests were performed using subjects with normal hearing. The simulation of hearing loss produced decrements in performance. The speech in condition R3 was inaudible. For conditions R2 and RX, the speech-to-noise ratios had to be up to 6 dB higher than in the control condition (R1, unprocessed stimuli) to achieve similar levels of performance. When linear amplification according to the NAL prescription was applied before the simulation, performance improved markedly for conditions R2 and RX, and did not differ significantly from that for R1. For condition R3, performance with simulated NAL amplification remained below that for condition R1; the decrement in performance was equivalent to about a 1 dB change in speech-to-noise ratio. The results of the present experiment show much smaller decrements in performance than those of an earlier experiment using a single talker as the interfering sound (Moore and Glasberg, 1993). It appears that loudness recruitment and threshold elevation have larger effects for a fluctuating background sound than for a steady background sound, and linear amplification is more effective in the latter case.
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Papers by Deborah Vickers