Biomedical subjects

Robert A Lutfi

Publications and source records attributed to Robert A Lutfi.

7 recordsLinked to original sources

PubMed2006

Molecular analysis of the effect of relative tone level on multitone pattern discrimination.

Molecular psychophysics attempts to model the observer's response to stimuli as they vary from trial to trial. The approach has gained popularity in multitone pattern discrimination studies as a means of estimating the relative reliance or decision weight listeners give to different tones in the pattern. Various factors affecting decision weights have been examined, but one largely ignored is the relative level of tones in the pattern. In the present study listeners detected a level-increment in a sequence of 5, 100-ms, 2.0-kHz tone bursts alternating in level between 40 and 80 dB SPL. The level increment was made largest on the 40-dB tones, yet despite this all four highly-practiced listeners gave near exclusive weight to the 80-dB tones. The effect was the same when the tones were replaced by bursts of broadband Gaussian noise alternating in level. It was reduced only when the level differences were made <10 dB, and it was entirely reversed only when the low-level tones alternated with louder bursts of Gaussian noise. The results are discussed in terms of the effects of both sensory and perceptual factors on estimates of decision weights.

Auditory Perception↗

PubMed2005

Effects of informational maskers within and across trials.

The across-trial effect of maskers in conditions of informational masking was evaluated from performance on occasional trials in which the signal was presented alone. For 6 of 12 listeners participating in the study, a significant number of errors were obtained on signal-alone trials; in some cases equivalent to that signal+ masker trials. On immediately preceding trial blocks for which there were no intervening maskers, performance for these signals was perfect. The results indicate that informational maskers can have a significant effect on signal threshold, both within and across trials.

Acoustic Stimulation↗

PubMed2005

Classification and identification of recorded and synthesized impact sounds by practiced listeners, musicians, and nonmusicians.

Three experiments were conducted to test the viability of a low-parameter modal model for synthesizing impact sounds to be used in commercial and psychoacoustic research. The model was constrained to have four physically based parameters dictating the amplitude, frequency, and decay of modes. The values of these parameters were selected by ear to roughly match the recordings of ten different resonant objects suspended by hand and struck with different mallets. In experiment 1, neither 35 professional musicians nor 187 college undergraduates could identify which of the two matched sounds was the real recording with better than chance accuracy, though significantly better than chance performance was obtained when modal parameters were selected without the previously imposed physical constraints. In experiment 2, the undergraduates identified the source corresponding to the recorded and synthesized sounds with the same level of accuracy and largely the same pattern of errors. Finally, experiment 3 showed highly practiced listeners to be largely insensitive to changes in the acoustic waveform resulting from an increase in the number of free parameters used in the modal model beyond 3. The results suggest that low-parameter, modal models might be exploited meaningfully in many commercial and research applications involving human perception of impact sounds.

Adult↗

PubMed2004

Informational masking in hearing-impaired and normal-hearing listeners: sensation level and decision weights.

Informational masking (IM) refers to elevations in signal threshold caused by masker uncertainty. The purpose of this study was to investigate two factors expected to influence IM in hearing-impaired listeners. Masked thresholds for a 2000-Hz signal in the presence of simultaneous multitone maskers were measured in 16 normal-hearing (NH) and 9 hearing-impaired (HI) listeners. The maskers were 70 dB SPL average total power and were comprised of fixed-frequency components between 522 and 8346 Hz that were separated from each other by at least 1/3 oct and from the signal by at least 2/3 octs. Masker uncertainty was manipulated by randomly presenting each masker component with probability p = 0.1,0.2,...,0.9, or 1.0 across different trial blocks. Energetic masking was estimated as the amount of masking for p = 1.0, where masker uncertainty was minimum. IM was estimated as the amount of masking in excess of energetic masking. Decision weights were estimated by a regression of the listener's yes/no responses against the presence or absence of the signal and masker components. The decision weights and sensation levels (SLs) of the stimulus components were incorporated as factors in a model that predicts individual differences in IM based on the level variance (in dB) at the output of independent auditory filters [Lutfi, J. Acoust. Soc. Am. 94, 748-758 (1993)]. The results showed much individual variability in IM for the NH listeners (over 40 dB), but little IM for most HI listeners. When masker components were presented to a group of NH listeners at SLs similar to the HI listeners, IM was also similar to the HI listeners. IM was also similar for both groups when the level per masker component was 10 dB SL. These results suggest that reduced masker SLs for HI listeners decrease IM by effectively reducing masker variance. Weighting efficiencies, computed by comparing each listener's pattern of weights to that of an ideal analytic listener, were a good predictor of individual differences in IM among the NH listeners. For the HI listeners weighting efficiency and IM were unrelated because of the large variation in masker SLs among individual listeners, the small variance in IM, and perhaps because broadened auditory filters in some listeners increased the covariance in auditory filter outputs.

Adult↗

PubMed2003

Children's detection of pure-tone signals: informational masking with contralateral maskers.

When normal-hearing adults and children are required to detect a 1000-Hz tone in a random-frequency multitone masker, masking is often observed in excess of that predicted by traditional auditory filter models. The excess masking is called informational masking. Though individual differences in the effect are large, the amount of informational masking is typically much greater in young children than in adults [Oh et al., J. Acoust. Soc. Am. 109, 2888-2895 (2001)]. One factor that reduces informational masking in adults is spatial separation of the target tone and masker. The present study was undertaken to determine whether or not a similar effect of spatial separation is observed in children. An extreme case of spatial separation was used in which the target tone was presented to one ear and the random multitone masker to the other ear. This condition resulted in nearly complete elimination of masking in adults. In young children, however, presenting the masker to the nontarget ear typically produced only a slight decrease in overall masking and no change in informational masking. The results for children are interpreted in terms of a model that gives equal weight to the auditory filter outputs from each ear.

Adolescent↗

PubMed2003

Psychometric functions for informational masking.

The term informational masking has traditionally been used to refer to elevations in signal threshold resulting from masker uncertainty. In the present study, the method of constant stimuli was used to obtain complete psychometric functions (PFs) from 44 normal-hearing listeners in conditions known to produce varying amounts of informational masking. The listener's task was to detect a pure-tone signal in the presence of a broadband noise masker (low masker uncertainty) and in the presence of multitone maskers with frequencies and amplitudes that varied at random from one presentation to the next (high masker uncertainty). Relative to the broadband noise condition, significant reductions were observed in both the slope and the upper asymptote of the PF for multitone maskers producing large amounts of informational masking. Slope was affected more for some listeners and conditions while asymptote was affected more for others; consequently, neither parameter alone was highly predictive of individual thresholds or the amount of informational masking. Mean slopes and asymptotes varied nonmonotonically with the number of masker components in a manner similar to mean thresholds, particularly when the estimated effect of energetic masking on thresholds was subtracted out. As in past studies, the threshold data were well described by a model in which trial-by-trial judgments are based on a weighted sum of levels in dB at the output of independent auditory filters. The psychometric data, however, complicated the model's interpretation in two ways: First, they suggested that, depending on the listener and condition, the weights can either reflect a fixed influence of masker components on each trial or the effect of occasionally mistaking a masker component for the signal from trial to trial. Second, they indicated that in either case the variance of the underlying decision variable as estimated from PF slope is not by itself great enough to account for the observed changes in informational masking.

Acoustic Stimulation↗

PubMed2003

One factor underlies individual differences in auditory informational masking within and across age groups.

Masked threshold for a pure-tone signal can be substantially elevated whenever the listener is uncertain about the spectral or temporal properties of the masker, an effect referred to as auditory informational masking. Individual differences in the effect are large, with young children being most susceptible. When masker uncertainty is introduced by randomizing the frequencies of a multitone masker on each presentation, the function relating a child's pure-tone signal threshold to the number of masker components is found to be substantially elevated above that of most adults. The age effect and the individual differences among adults are not well understood, though a difference in the shapes of the masking functions suggests that different detection strategies may be involved. The present study reports results from a principal components analysis of informational masking functions obtained from 38 normal-hearing children ranging in age from 4 to 16 years and 46 normal-hearing adults ranging in age from 19 to 38 years. The premise underlying the analysis is that if different detection strategies are involved, they should add independent sources of variance to the masking functions. Hence, more than one principal component (PC) should be required to account for a substantial proportion of the variance in these functions. The results, instead, supported the operation of a single underlying strategy with all but 17% of the variance accounted for by the first PC within and across age groups. An analysis of variance on the first two PCs showed that only the first changed with age, and a cluster analysis of the masking functions showed complete separation of clusters along this PC for all but 1 listener. The results are taken to suggest that large individual differences informational masking at all ages reflect differences in the extent to which masker uncertainty adds variance to the decision variable of an otherwise optimal decision strategy.

Adolescent↗