Biomedical subjects

Virginia M Richards

Publications and source records attributed to Virginia M Richards.

11 recordsLinked to original sources

PubMed2006

Potential benefits of across-aid communication for bilaterally aided people: listening in a car.

We explored whether transferring signals between two hearing aids could improve speech intelligibility in noise. This was evaluated using a simulated conversation in a car; speech was presented to the right ear and car noise was presented either to the right or both ears. In three cross-aid communication conditions, the noise in the right ear was scaled and subtracted from the noise in the left ear. Speech intelligibility was determined for a group of normally hearing listeners and a group with bilateral hearing loss. The hearing-impaired group had relatively higher intelligibility scores when the car noise was diotic, whereas the normal-hearing group had relatively higher intelligibility scores in the binaural (dichotic) conditions. The cross-aid conditions led to improved intelligibility compared to the reference conditions. The results indicate that the transfer of signals between hearing aids may be of benefit when listening to speech in a car.

Adolescent↗

PubMed2006

Estimates of effective frequency selectivity based on the detection of a tone added to complex maskers.

In Experiment 1, the validity of parameters associated with the roex(p, r) auditory filter shape was examined for three different types of maskers: (a) A noise masker, (b) a random 12-tone masker whose frequencies varied on a burst-by-burst basis [multiple-burst different (MBD)], and (c) a random 12-tone masker whose frequencies were the same across bursts [multiple-burst same (MBS)]. First, the power spectrum model of masking was used to estimate auditory filter shapes for four observers. Second, the resulting auditory filter shapes were used in a computer simulation that provided an estimate of internal noise for each observer. Third, relative weights across frequency were estimated for each observer and each masker type. For the noise masker, these analyses provided predictions and relative weights that were consistent across the three analyses. For the MBD and MBS maskers, there was little consistency; neither the estimated internal noise nor the estimated relative weights reliably supported a single-filter model of detection. In Experiment 2, the time course for the detection of a tone added to an MBD masker was evaluated by estimating relative weights jointly in time and frequency. The relative weights at the signal frequency formed a rough inverse "U" across time.

Acoustic Stimulation↗

PubMed2006

Coherence detection: effects of frequency, frequency uncertainty, and onset/offset delays.

The detectability of a sequence of equal-frequency (coherent) tonal components embedded in random, multiburst maskers was evaluated. The masker was comprised of tonal components located in a time-by-frequency spectrogram with eight 30 ms time columns and 29 frequency rows ranging logarithmically from 200 to 5000 Hz. The probability that a tone occurred in any one cell of the spectrogram, p, was the independent variable. The signal and masker components were of equal duration and equal level. Using a yes/no procedure, threshold values of p were estimated for five signal frequencies (220, 445, 1000, 2245, 4490 Hz) and when the signal frequency was random. Thresholds were worst for the random-frequency signal and best for the fixed 1000 Hz signal. In additional conditions, the value of p was fixed and the signal components were delayed relative to the masker components. A 1 ms delay provided better sensitivity (d' grew from 0.5 to 1) for all but the lowest signal frequency tested. An analysis of no-signal trials revealed that false alarm rates were higher when components falling at the signal frequency were consecutive than when they were distributed across bursts. Thus, coherence rather than total energy at the signal frequency is important for signal detection.

Acoustic Stimulation↗

PubMed2005

The effect of diotic and dichotic level-randomization on the binaural masking-level difference.

Detection thresholds for tones in narrow-band noise were measured for two binaural configurations: N(o)S(o) and N(o)S(pi). The 30-Hz noise band had a mean overall level of 65 dB SPL and was centered on 250, 500, or 5000 Hz. Signals and noise were simultaneously gated for 500, 110, or 20 ms. Three conditions of level randomization were tested: (1) no randomization; (2) diotic randomization--the stimulus level (common to both ears) was randomly chosen from an uniformly distributed 40-dB range every presentation interval; and (3) dichotic randomization--the stimulus levels for each ear were each independently and randomly chosen from the 40-dB range. Regardless of binaural configuration, level randomization had small effects on thresholds at 500 and 110 ms, implying that binaural masking-level differences (BMLDs) do not depend on interaural level differences for individual stimuli. For 20-ms stimuli, both diotic and dichotic randomization led to markedly poorer performance than at 500- and 110-ms durations; BMLDs diminished with no randomization and dichotic randomization but not with diotic randomization. The loss of BMLDs at 20 ms, with degrees-of-freedom (2WT) approximately 1, implies that changes in intracranial parameters occurring during the course of the observation interval are necessary for BMLDs when mean-level and mean-intracranial-position cues have been made unhelpful.

Acoustic Stimulation↗

PubMed2004

Cuing effects for informational masking.

The detection of a tone added to a random-frequency, multitone masker can be very poor even when the maskers have little energy in the frequency region of the signal. This paper examines the effects of adding a pretrial cue to reduce uncertainty for the masker or the signal. The first two experiments examined the effect of cuing a fixed-frequency signal as the number of masker components and presentation methods were manipulated. Cue effectiveness varied across observers, but could reduce thresholds by as much as 20 dB. Procedural comparisons indicated observers benefited more from having two masker samples to compare, with or without a signal cue, than having a single interval with one masker sample and a signal cue. The third experiment used random-frequency signals and compared no-cue, signal-cue, and masker-cue conditions, and also systematically varied the time interval between cue offset and trial onset. Thresholds with a cued random-frequency signal remained higher than for a cued fixed-frequency signal. For time intervals between the cue and trial of 50 ms or longer, thresholds were approximately the same with a signal or a masker cue and lower than when there was no cue. Without a cue or with a masker cue, analyses of possible decision strategies suggested observers attended to the potential signal frequencies, particularly the highest signal frequency. With a signal cue, observers appeared to attend to the frequency of the subsequent signal.

Adult↗

PubMed2004

Masker-first advantage for cues in informational masking.

The detectability of a pure-tone signal may be reduced by adding a small number of randomly drawn masker tones remote from the signal frequency, an effect attributed to informational masking. A pretrial cue consisting of either the upcoming signal or masker releases informational masking, but a pretrial cue of the signal-plus-masker stimulus does not. In these experiments the relative potency of pre- and posttrial cues in releasing informational masking was examined. In separate conditions the masker-alone and signal-plus-masker stimuli were cues. The results indicated a masker-first advantage, i.e., sensitivity was superior when a masker cue preceded a yes/no trial interval compared to (a) when a signal-plus-masker preceded the trial, and (b) when either cue type followed the yes/no trial interval. A masker-first advantage was also obtained when the results from a two-interval forced-choice same/different task were examined. In contrast, a masker-first advantage was not obtained when the frequency of the signal to be detected was random. For detection tasks using random multi-tone maskers there may be differences in processing efficiency depending on the order in which stimuli are presented. The "masker-first advantage" may depend, in part, on observers maintaining their attention at the signal frequency.

Acoustic Stimulation↗

PubMed2003

Examination of a linear model in an informational masking study.

When multitone maskers are used in a two-interval, forced choice experiment, the amount of masking is larger when the masker is randomly chosen on each presentation interval compared to on each trial (the same masker in the two listening intervals). These conditions are referred to as having within- versus between-trial randomization. If it is assumed that an observer's ultimate detection decision depends on a single decision variable (DV), it is probable that the DV's variance will be substantially larger in the within-trial randomization condition compared to the between-trial randomization condition. The goal of the current experiment is to evaluate the degree to which this stimulus-based change in DV variance can account for the difference in thresholds in the within-versus between-trial randomization conditions. Thresholds are measured for the detection of a tone added to a six-component masker in between- and within-trial randomization conditions. The slopes of the psychometric functions provide an estimate of the variance in the DV for the between- and within-trial randomization conditions. Additionally, a channel model is fitted to the psychophysical results in the within-trial randomization condition. The resulting model is then used to predict the value of the DV for each trial, and ultimately to estimate the proportion of the total variance in the within-trial randomization condition that is attributable to changes in maskers across intervals. The variance of the DV in the between-trial randomization condition accounted for approximately 65% of the total variance in the DV in the within-trial randomization condition. Stimulus-based interval-by-interval masker randomization accounted for approximately 20% of the total variance of the within-trial randomization DV. The remaining 15% of the DV variance in the within-trial randomization condition remained unaccounted for. This result is fairly stable whether the maskers are drawn from a small versus large pool of potential maskers.

Attention↗

PubMed2003

Multiple bursts, multiple looks, and stream coherence in the release from informational masking.

In the simultaneous multitone masking paradigm introduced by Neff and Green [Percept. Psychophys. 41, 409-415 (1987)] the masker typically is a small number of tones having frequencies and levels that are randomly drawn on every presentation. Large amounts of masking for a pure-tone signal often occur that are thought to reflect central, rather than peripheral, limitations on processing. Previous work from this laboratory has indicated that playing a rapid succession of randomly drawn multitone maskers in each observation interval dramatically reduces the amount of masking that is observed relative to a single burst (SB). In this multiple-bursts-different (MBD) procedure, the signal tone is the only constant frequency component during the sequence of bursts and tends to perceptually segregate from the masker. In this study, the number of masker bursts and the interburst interval (IBI) were varied. The goals were to determine how the release from masking relative to the SB condition depends on the number of bursts and to examine whether increasing the IBI would cause each burst to be processed independently. If the latter were true, it might disrupt the perception of signal stream coherence, thereby diminishing the MBD advantage. However, multiple independent looks could also lead to an improvement in performance. For those subjects showing large amounts of informational masking in the SB condition, substantial reduction in masked thresholds occurred as the number of masker bursts increased, while masking increased as IBI lengthened. The results were not consistent with a simple version of a multiple-look model in which the information from each burst was combined optimally, but instead appear to be attributable to mechanisms involved in the perceptual organization of sounds.

Adolescent↗

PubMed2002

Varying feedback to evaluate detection strategies: the detection of a tone added to noise.

The effectiveness of rewarding strategies associated with different models of detection was evaluated for a tone-in-noise detection task. In three experiments, a tone was added to a narrowband noise masker in a two-interval, forced-choice procedure with feedback. In the first experiment the observer's task was to detect which interval had the added tone. In the second experiment the task was to indicate which interval was more intense. In the third experiment the task was to indicate which interval had the sound with the less modulated envelope. In terms of correct signal detection, thresholds were nearly the same for all three experiments. However, for three of the observers the psychometric functions indicate that observers altered their responses in accordance with the changes in feedback contingencies. This indicates that neither changes in level nor changes in envelope pattern alone can account for the detection of a tone added to noise for these observers. The fourth observer was sufficiently insensitive that the pattern of feedback associated with the level and envelope models did not differ substantially, and for her feedback had little impact on behavior. The results indicate that changes in feedback provide a means of testing alterative psychophysical models. Moreover, the results suggest that it is difficult to model the detection of a tone added to noise in terms of a single cue or a simple combination of cues. Observers are free to choose from at least two cues, and can do so.

Acoustic Stimulation↗

PubMed2002

Effects of a limited class of nonlinearities on estimates of relative weights.

Perturbation analyses have been applied in recent years to determine the relative contribution of individual stimulus components in detection and discrimination tasks. Responses to stimulus samples are compared to stimulus parameters to determine the details of the decision rule. Often, a linear model is assumed and it is of interest to determine the relative contribution of different stimulus elements to the decision. Here, biases in estimated relative weights are considered for the case where the decision variable is given by D = (sigma(alphaiXn(i))k)m and the stimulus components, the Xi, are normally distributed, of equal variance, and mutually independent. The alphai are the "true" combination weights, and n, k, and m are positive reals. The method used to estimate relative weights is the correlation coefficient between the Xi and the observer's responses. Estimates of relative alphai do not depend on m but may depend on the mean values of the Xi and the values of n and k (a dependence on the variance, sigmai2, holds even for linear transformations).

Computer Simulation↗

PubMed2002

Informational masking with small set sizes.

Informational masking refers to interference in the detectability of a sound, or discrimination of some property of a sound, beyond that which can be attributed to interactions at the auditory periphery. In the current experiments the signal to be detected was a tone added to a 6-tone masker, and informational masking was introduced by randomly choosing the frequencies of the tones that comprise the masker. The primary question was whether small numbers of maskers could replace randomly drawn maskers without sacrificing the underlying detection schemes adopted by observers. Similar to the method used by Wright and Saberi [J. Acoust. Soc. Am. 105, 1765-1775 (1999)], detection thresholds were measured for different masker set sizes, where set size refers to the number of 6-tone maskers from which any one masker was drawn. Set sizes of 3, 6, 12, and 24 were tested as well as conditions in which the maskers were chosen at random. In addition, observers' memory for maskers was coarsely evaluated. Large differences in thresholds were found across observers and across different masker sets. Even for set sizes of 24, the memory test suggests some recognition of maskers for some observers. Post hoc analysis of the data included an evaluation of the relative contribution of different frequencies using a single linear model. As a base for comparison, a linear model fitted to each condition was also evaluated. Although the data were fitted better using many rather than one linear model, the reduction in quality of fit was modest. This result suggests substantial consistency in decision strategies regardless of masker set size.

Adult↗