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Biomedical subjects

B A Wright

Publications and source records attributed to B A Wright.

At least 37 records · Page 2Linked to original sources
PubMed1995

Detectability of simultaneously masked signals as a function of signal bandwidth for different signal delays.

The improvement in signal detectability as signal onset is delayed from masker onset was measured as a function of signal bandwidth for wideband and notched-noise maskers. The signal was centered at 2500 Hz. In two conditions, the 20-ms signal was gated 1 or 250 ms after the onset of a 420-ms masker. Although there were marked individual differences, the signal was consistently more difficult to detect in the short-delay than in the long-delay condition. The difference in detectability decreased as signal bandwidth increased and was similar in magnitude across the masker types. This result indicates that an across-channel process contributes to the improvement in detectability as the signal delay is increased, because the masking components at the signal frequency in the wideband masker exerted very little influence on the size of the effect. In a third condition, the signal was gated 1 ms after the onset of a 23-ms masker. The signal was hardest to detect in this burst condition, and performance varied differently as a function of signal bandwidth in this than in the other two conditions, particularly for the notched-noise maskers. This outcome suggests the presence of a second across-channel process that is sensitive to masker offsets, especially when there are no masking components at the signal frequency. Finally, the pattern of results obtained across the three conditions using the wideband masker was consistent with the idea that the critical bandwidth narrows as the signal is delayed from masker onset.

Auditory Perception↗
PubMed1995

Detecting signals of unexpected or uncertain durations.

Expectation of signal duration influences the signal detectability. This is demonstrated in two experiments in which percent correct was measured for both tonal and noise signals whose durations were either unexpected or uncertain. In both experiments, the signal at each duration was set to have a d' of about 1.5 when that duration was presented alone and expected. When the six subjects were led to expect a short- or a long-duration signal using the probe-signal method, the detectability of signals decreased to near chance as the signal duration deviated from the expected value (experiment 1). When the subjects were led to expect a range of durations, the detectability was only slightly worse than when each signal was presented alone (experiment 2). Those results suggest that listeners adjust their temporal-integration intervals according to the demand of the specific task. Finally, the results obtained with the noise signal were analyzed using the multiple-look model and a modified energy-detector model. Assuming that the integration interval is matched to the expected signal duration, both models predict the detection of signals having unexpected durations reasonably well. Both models, however, fail to predict the small effect of duration uncertainty.

Audiometry, Pure-Tone↗
PubMed1994

Improving the detectability of a brief tone in noise using forward and backward masker fringes: monotic and dichotic presentations.

A brief tonal signal simultaneously masked by a brief noise burst became easier to hear when the masker duration was increased. The signal was a 1000-Hz tone, 4 ms in duration; the masker was a wideband noise having a spectral notch 1400 Hz wide centered at 1000 Hz. Compared to performance with a 22-ms burst masker, average detection threshold across five subjects improved by 15 dB when a 150-ms masker "fringe" preceded the signal (forward fringe), and by 9 dB when the masker fringe followed the signal (backward fringe). Little improvement was observed in either condition when the fringe was presented to the ear contralateral to the signal/burst complex. However, when the fringe was presented to both ears and the signal/burst complex to just one ear, the forward fringe was about as helpful as when the stimuli were presented monotically, but the benefit of the backward fringe was substantially reduced. The backward-fringe advantage was restored by reducing the level, or delaying the onset, of the contralateral component of the fringe. The results suggest that the forward-fringe advantage is a robust phenomenon that is largely insensitive to input to the contralateral ear. In contrast, the backward-fringe advantage appears to be a fragile effect that can be affected by inputs from both ears.

Acoustic Stimulation↗
PubMed1994

Detection of unexpected tones with short and long durations.

The detectability of short and long unexpected tones masked by a continuous wideband noise was assessed using a probe-signal method. This method leads the listener to expect a target frequency by presenting the signal most often at that frequency, and only occasionally at other unexpected probe frequencies. The probe-signal contour (percent correct as a function of probe frequency) was considerably broader with 5-ms than with 295-ms signals. However, auditory filter shapes measured using the notched-noise technique were very similar for those two signal durations, indicating that the results obtained in the probe-signal conditions do not simply reflect peripheral frequency selectivity. Further supporting this interpretation, probe tones having the same frequency but a different duration from the target were poorly detected. It is proposed that the subject listens through a time-frequency window whose location and shape in the time-frequency plane is determined by the duration and frequency of the target.

Acoustic Stimulation↗
PubMed1994

Detection of unexpected tones in gated and continuous maskers.

The effect of gating a wideband masker on the detectability of tones having unexpected frequencies was assessed using a probe-signal method. This method leads the listener to expect a target frequency by presenting the signal most often at that frequency, and measures sensitivity to other unexpected frequencies via occasionally presented probe tones. For 295-ms signals, the probe-signal contours (percent correct as a function of probe frequency) of two of four subjects were considerably broader for a 295-ms masker than for a continuous masker. For 5-ms signals, the probe-signal contours of four of five subjects were quite broad and similar for both gated and continuous maskers. When the probe-signal contours were expressed as the attenuation in decibels of the probes, the resulting "probe-signal filters" were frequently broader than auditory filters measured using notched noise in the same subjects. This suggests that subjects may monitor multiple auditory filters under some conditions in the probe-signal task. Signal threshold tended to be higher for conditions showing wider probe-signal filters, indicating a potential link between changes in signal threshold due to masker gating and the number of frequency channels that are monitored.

Acoustic Stimulation↗
PubMed1994

Comodulation masking release for single and multiple rates of envelope fluctuation.

Two experiments are presented that investigate the influence of envelope fluctuation rate upon the magnitude of comodulation masking release (CMR). In Experiment 1, thresholds were measured for a tonal signal centered in either one or five masker bands. The maskers were either narrow-band noises or 100% sinusoidally amplitude-modulated (SAM) tones. The five masker bands had either the same (coherent) or different (incoherent) envelopes. Envelope rate was varied by manipulating either the noise bandwidth (10-200 Hz) or the SAM rate (10-128 Hz). The CMR values were largest for slow envelope rates. In Experiment 2, envelope coherence was simultaneously manipulated at two rates by amplitude modulating (10 Hz) narrow-band noises (100 Hz). The modulation depth was 100%, 83%, or 50%. The CMR based on the coherence of the noise carriers was about 5 dB, regardless of the SAM coherence or the modulation depth. The CMR based on the SAM coherence decreased from about 19 to 2 dB as modulation depth decreased, regardless of the noise-carrier coherence. Thresholds were highest when the envelope fluctuations were incoherent at both rates and were lowest when the envelope fluctuations were coherent at both rates. These data suggest that the auditory system is able to make across-frequency envelope comparisons at both envelope rates simultaneously.

Adult↗
PubMed1994

Stereotaxic needle core biopsy of breast lesions using a regular mammographic table with an adaptable stereotaxic device.

OBJECTIVE: Fine-needle aspiration and stereotaxic needle core biopsy (SNCB) are techniques used in the workup of breast lesions suggestive of cancer. Many surgeons are reluctant to rely on fine needle results, and until now, SNCB could be done only with a dedicated biopsy table. Our study was done to determine whether SNCB could be performed safely and effectively with a regular mammography unit and an added stereotaxic device. SUBJECTS AND METHODS: SNCB was performed on 254 patients by using a Siemens Mammomat 2 regular mammography table with an added stereotaxic device. Patients were referred from a breast screening center, a local tertiary care center, and from our own center. Patients who had unequivocal histopathologic evidence of a benign process (133 of 254 patients) did not undergo surgical biopsy and are being followed up mammographically. The remainder (121 patients) all had surgical biopsies. RESULTS: Sufficient material for histologic analysis was obtained in 249 (98%) of 254 cases. In 31 of 254 cases, sampling was problematic. This group comprised cases in which the patient moved within the compression device, the mammographic and histologic diagnoses were discordant, or calcifications were not present in the core sample when the indication for SNCB was the presence of microcalcifications. This group all had open biopsies. In 25 of 254 cases, the pathologic findings were suggestive of cancer. Cancer was detected in 11 of these cases on open biopsy. Of the 14 benign cases, 11 showed atypical features or ductal hyperplasia on open biopsy. Malignant tumor was diagnosed in 60 of 254 cases by SNCB. Corresponding malignant tumor was seen in 59 of 60 of the open biopsy specimens. CONCLUSION: The SNCB technique is not limited to use on a dedicated biopsy table but can be readily adapted to a regular mammography unit. It is a safe, reliable and cost-effective procedure that often spares the patient a surgical procedure.

Biopsy, Needle↗
PubMed1993

Detection of viruses in environmental samples: suitability of commercial rotavirus and adenovirus test kits.

Commercially marketed kits are now available for rapid viral assay of clinical specimens. This study was conducted to determine the suitability of these kits for use in environmental testing. Eight rotavirus kits and one enteric adenovirus kit were screened for sensitivity using simian rotavirus SA11, human rotavirus Wa, and adenovirus 41. The most sensitive rotavirus kit and the adenovirus kit were selected for further evaluation using virus-seeded and unseeded sewage samples. The selected rotavirus kit proved capable of detecting virus at the 10(1) PFU/ml level. The enteric adenovirus kit was similarly sensitive, detecting virus at the 10(1) TCID50/ml level. Neither kit was adversely affected by the presence of sewage. Kit assay revealed 3 of 30 unseeded sewage samples to be positive for rotavirus. Adenovirus positive samples were not detected among the 30 samples. These results were confirmed using electron microscopy. It was concluded that sensitive commercial kits could provide a reasonable alternative to cell culture for the presumptive testing of environmental samples.

Adenoviridae↗
PubMed1993

Manipulations of the duration and relative onsets of two-tone forward maskers.

The effects of absolute and relative masker duration were investigated using one- and two-tone forward maskers. In the absolute-duration conditions, the duration (D) of a one-component on-frequency (M1; Dm1-alone) or off-frequency (M2; Dm2-alone) masker or the common duration of a two-component masker (Dm1 = Dm2) was varied. Masked threshold increased as duration increased in all three conditions. In the relative-duration conditions, the duration of one masker component was fixed at a relatively long value and the duration of the other component was varied (Dm1 > Dm2 or Dm2 > Dm1). In the Dm1 > Dm2 condition, masked threshold decreased as the duration of Dm2 was increased. In the Dm2 > Dm1 conditions, masked threshold increased and then decreased slightly as the duration of Dm1 was increased. Masked threshold was frequently lower in the M1+M2 than in the M1-alone conditions, indicating psychophysical suppression. Further, masked threshold in the Dm2 > Dm1 condition was always higher than in the corresponding absolute-duration condition (Dm1 = Dm2) having the same M1 duration, indicating masker enhancement. A two-stage neural model was proposed to account for these forward-masking data.

Acoustic Stimulation↗
PubMed1993

Adaptation of suppression as an explanation of enhancement effects.

Delaying the onset of a signal relative to the onset of a simultaneous notched masker often improves the ability of subjects to "hear out" the signal at both threshold and suprathreshold levels. Viemeister and Bacon [J. Acoust. Soc. Am. 71, 1502-1507 (1982)] suggested that such signal-enhancement effects might be attributable to adaptation of the suppression directed from the masker to the signal, thereby releasing the signal from suppression. In support of their hypothesis, Viemeister and Bacon reported that a masker, preceded by an enhancer having no component at the signal frequency, produced more forward masking than did the masker by itself. Here the masker enhancement described by Viemeister and Bacon, signal enhancement, and two-tone suppression were measured in the same six subjects. Parametric manipulations of the masker-enhancement stimulus produced results similar to those previously reported for parallel investigations of signal enhancement, indicating that the two types of enhancement are closely related effects. Although the present data reveal an inverse relationship between the amounts of suppression and enhancement, suggesting that the two processes may be interrelated, no support was obtained for the hypothesis that adaptation of suppression can account for enhancement.

Adaptation, Physiological↗
PubMed1992

Evidence that adaptation of suppression cannot account for auditory enhancement or enhanced forward masking.

Delaying the onset of a signal relative to the onset of a simultaneous notched masker often improves the ability of listeners to 'hear out' the signal at both threshold and suprathreshold levels. Viemeister & Bacon (J. acoust. Soc. Am., 71, 1502-1507 (1982)) suggested that such auditory enhancement effects could be accounted for if the suppression produced by the masker on the signal frequency adapted, thereby releasing the signal from suppression. In support of their hypothesis, Viemeister & Bacon reported that a masker preceded by an enhancer having no component at the signal frequency produced more forward masking than did the masker by itself. Here evidence is provided from five new experiments showing that adaptation of psychophysical two-tone suppression is inadequate to account either for auditory enhancement effects or for the enhanced forward masking demonstrated by Viemeister & Bacon.

Acoustic Stimulation↗
PubMed1992

The role of envelope fluctuations in an apparent demonstration of suppression in simultaneous masking.

Fastl and Bechly [J. Acoust. Soc. Am. 74, 754-757 (1983)] reported that the threshold of a brief 900-Hz signal simultaneously masked by a band of noise. 100 Hz wide, centered at 1000 Hz, was reduced by approximately 8 dB by the addition of an 1150-Hz tone having a level of 20 dB above that of the narrow-band masker. They concluded that this decrease in threshold was a demonstration of suppression in simultaneous masking. Here it is argued that Fastl and Bechly's results simply reflect the poorer detectability of signals masked by higher-frequency fluctuating maskers (their narrow-band masker) than by relatively flat-envelope maskers (their composite narrow-band plus tonal masker). The results of three experiments support the masker-envelope explanation. In the first experiment, as in the report of Fastl and Bechly, the masker centered at 1000 Hz (M1) was a narrow-band noise and the masker centered at 1150 Hz (M2) was a tone. Fastl and Bechly's result was replicated. However, thresholds obtained when M1 was presented alone (the M1-only condition) were more affected by the starting level of the signal within each adaptive track than were thresholds obtained when M1 and M2 were presented together (the M1+M2 condition). This result paralleled a previous report that starting level influenced performance more with fluctuating than with flat-envelope maskers. For the four of seven subjects wh showed learning, there was also more improvement in the M1-only than in the M1 + M2 condition. In the second experiment, M1 was a tone and M2 was a narrow-band noise.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1992

Temporal decline of masking and comodulation masking release.

Masking sounds can be continuously present, gated simultaneously with the signal, or gated somewhat prior to the signal. This continuum of relative onset times was explored using waveforms of the sort commonly employed in studies of comodulation masking release (CMR). There was a 50-Hz masker band centered on the 1250-Hz tonal signal, and four 50-Hz flanker bands centered at 850, 1050, 1450, and 1650 Hz. In some conditions, all four flanker bands had the same temporal envelope, and the masker band either had that same envelope (correlated presentations) or a different envelope (uncorrelated presentations). In other conditions, all five bands had different temporal envelopes (all-uncorrelated presentations). The masker band and/or the four flanker bands were either gated nearly simultaneously with the signal (burst conditions) or were gated prior to the signal by a duration that was systematically varied (fringed conditions). The eight listeners could be partitioned into three groups on the basis of their response to these fringing manipulations. Two listeners (the large fringers) showed a gradual improvement in detectability with increasing fringe duration (called a temporal decline of masking), while three others (the small fringers) showed little improvement in detectability. For the remaining three subjects, there was evidence of a "learning" effect that changed them from large fringers to small fringers over a 10-week period of listening. When present, the temporal decline of masking was greater for the correlated than for the uncorrelated comodulation condition; as a consequence, the difference in detectability between them (the comodulation masking release or CMR) increased with fringe duration. By fringing the masker and flanker bands separately and in combination, it was revealed that the temporal declines of masking were primarily attributable to the fringing of the flanker bands. In contrast, large CMRs required long fringes on both the masker and flanker bands. The above results were obtained with 50-ms signals, but generally similar data were obtained with a signal duration of 240 ms. The difficulties raised for experimentalists and theorists by such long-term practice effects are discussed.

Adult↗
PubMed1990

Comparison of fortified calf serum, serum substitutes and fetal calf serum with or without extenders for propagation of cell cultures for virus plaque assays.

Two studies comparing sewage-isolated and laboratory stock viruses were conducted to determine if alternative forms of serum or serum extenders could be used in place of fetal bovine serum without a significant loss of viral titer. In the first study, BGM cells were grown in standard MEM-L15 medium which was supplemented with Nuserum, Sigma serum replacement (CPSR-1), HyClone defined iron supplemented calf bovine serum, fetal bovine serum (FBS) or FBS supplemented with either SerXtend or Mito serum extenders. Comparison of virus titers showed that CPSR-1 gave the best overall results and was comparable to FBS. Of the serum extenders, only SerXtend improved virus recovery from sewage samples. In the second study, all sera were tested with and without SerXtend. In these experiments, SerXtend enhanced virus sensitivity of the BGM cell line grown in the HyClone serum but reduced the sensitivity of those cultured in Sigma serum. In both series, the growth of BGM cells was monitored for 12 weeks and all test products were shown to support long-term cell growth.

Analysis of Variance↗