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R A Lutfi

Publications and source records attributed to R A Lutfi.

At least 19 recordsLinked to original sources
PubMed1997

Spectral weights in level discrimination by preschool children: synthetic listening conditions.

On most auditory discrimination and detection tasks young children perform more poorly than adults. The current experiment applies a technique which potentially can reveal the extent to which the adult-child performance difference results from suboptimal attentional strategies or simply greater internal noise in the children. In this experiment preschool children and adults were asked to discriminate between complex tones comprised of three random-amplitude sinusoidal components. A trial-by-trial correlational analysis [R. A. Lutfi, J. Acoust. Soc. Am. 97, 1333-1334 (1995)] provided an estimate of the weight listeners placed on the level information from individual spectral components in making the discrimination. The patterns of weights were interpreted as measures of "attentional strategy." Both children and adults produced reliable patterns of weights. This is an especially important result since measuring a single weighting pattern requires large numbers of trials and hence multiple sessions with the children. While individual weighting patterns were reliable, weighting patterns differed both within and across groups. Moreover, neither the children nor the adults produced weighting patterns that would maximize percent correct in the task. A substantial proportion of the responses from both children and adults could be predicted from their weighting patterns even when performance was near chance. However, differences in overall performance between children and adults could not be accounted for by differences in their weighting functions.

Acoustic Impedance Tests↗
PubMed1997

Spectral weights in level discrimination by preschool children: analytic listening conditions.

In this series of experiments, adult and child listeners were required to attend to a target tone in the presence of two distracters and to indicate in which of two intervals the target tone had the higher level. The attentional weight listeners placed on each component was estimated by computing the correlation between the level change of each component across intervals and the listener's response. In the first experiment, weights were obtained as a function of the mean level of the distracters (250 and 4000 Hz) for a 1000-Hz target. No consistent differences between the weighting functions of children and adults were observed. In a second experiment, weights were obtained as a function of the harmonic relationship between the distracters (250 and 4000 Hz, or 270 and 4320 Hz) and the 1000-Hz target. No difference was observed between the weighting functions computed with harmonic and inharmonic complexes. In the final experiment, each component of the complex (250, 1000, and 4000 Hz) was identified as the target in separate blocks of trials. In general, adults were able to weight the target component appropriately regardless of its frequency, while children tended to weight all components equally. The results suggest that preschool listeners may exhibit poorer attentional selectivity than adults.

Adult↗
PubMed1997

Auditory discrimination of material changes in a struck-clamped bar.

The principles of theoretical acoustics were applied to approximately reconstruct the sound pressure waveform at the ear as would be generated by an idealized struck-clamped bar. The result is an inharmonic sum of damped sinusoids whose individual acoustic parameters (frequency, intensity, and decay modulus) are, for a fixed geometry and fixed driving force, uniquely determined by the material composition of the bar. In the standard 2IFC procedure, listeners were asked to discriminate changes in material composition based on their perception of the acoustic waveform. Listener strategies for discriminating such changes were estimated by perturbing slightly the individual acoustic parameters from trial to trial and computing correlations with the listener's response [cf. R. A. Lutfi and E. Oh, J. Acoust. Soc. Am. 95, 2963(A) (1994)]. In general, the correlations reveal that listeners fail to make optimal use of the information in the acoustic waveform by tending to give undue weight, for a given material change, to changes in component frequency. In some case, the accompanying reduction in performance efficiency amounted to 80%.

Acoustics↗
PubMed1996

Spectral weights for overall level discrimination in listeners with sensorineural hearing loss.

A conditional-on-a-single-stimulus (COSS) analysis procedure [B. G. Berg, J. Acoust. Soc. Am. 86, 1743-1746 (1989)] was used to measure the weight or relative reliance that normal-hearing and hearing-impaired listeners give to different frequencies in the discrimination of the overall level of a multitone complex. On each trial, two multitone-tone complexes comprised of six octave frequencies from 250 to 8000 Hz were presented to subjects. The levels of the frequencies for each complex were randomly varied. The listeners task was to identify the complex with the higher overall intensity level. Normal-hearing listeners used a variety of listening strategies to perform the task, showing no general preference to weight one component over another. Hearing-impaired listeners, however, showed a general tendency to give greatest weight to the spectral information in the region of their hearing loss. Thirteen of the 14 hearing-impaired listeners, all of whom had a high-frequency sensorineural hearing loss, weighted one or more of the high-frequence components in the complex the greatest.

Adult↗
PubMed1996

Observer weighting of concurrent binaural information.

Two experiments examined how listeners weight binaural information of individual components in a multicomponent complex when they are instructed to use this information in various ways. On each experimental trial of the first experiment, a two-component complex consisting of a 553- and 753-Hz pure tone was presented to listeners over headphones. Each component had an interaural difference of time (IDT) that was randomly chosen from a single distribution. Listeners were to indicate the apparent position of the intracranial image relative to the midline on the basis of either the IDT of the 753-Hz component, the sum of the IDTs of the two components, or the difference between the two IDTs. Observer weights for the component IDTs were derived by computing the point-biserial correlations between the IDTs of the components and the listeners' left-right judgments. Three of the four listeners were found to adjust their weighting of the binaural information appropriately for each listening task, while the fourth listener consistently gave almost no weight to the 553-Hz component regardless of the listening condition. In a second experiment, listeners were instructed to attend to the randomly selected IDT of one of three components (553, 753, or 953 Hz) and to indicate whether the intracranial image produced by that component was to the left or right of midline. Only one of six listeners gave greatest weight to the target component regardless of its frequency. The other five listeners gave significant weight to all three components in all listening conditions. In all cases, individual differences in percent correct performance could be attributed largely to individual differences in weights with little variation in internal noise.

Auditory Perception↗
PubMed1996

Psychometric functions for the discrimination of spectral variance.

An experiment was conducted to measure the shape of the psychometric function for the discrimination of spectral variance. The stimuli were simultaneous tone complexes comprised of the six octave frequencies from 250 to 8000 Hz. On each presentation the levels of components in dB were drawn independently and at random from one of two normal distributions having identical means but different variances (sigma N = 1 dB, sigma S = 2-10 dB). In the standard two-interval, forced-choice procedure, the listeners' task was to indicate which complex had the greater variance in component level. The shape of the psychometric function for all five listeners was markedly different from that of an observer limited only by additive internal noise. It was consistent with an observer that gives weight to only one or two components in the complex. However, this result was inconsistent with the weighting functions computed from the trial-by-trial data from these listeners. Both measures can be reconciled if it is assumed that listener weights vary from trial to trial, or that decisions are based on the one tone in the complex having the maximum level.

Adult↗
PubMed1994

Discrimination of random, time-varying spectra with statistical constraints.

In the present study, a sample-discrimination procedure is used to examine how various statistical constraints on random, time-varying spectra might aid listeners in discriminating among these signals. Time-varying spectra were constructed by adding five sequences of tones, five tones in each sequence, centered at the octave frequencies from 250 to 4000 Hz. The levels, frequencies, and durations of the tones varied randomly from one presentation to the next. The signal to be detected was an increment in the level of tones comprising the sequence centered at 1000 Hz (the target sequence). Three main conditions were examined in which the parameter values of tones varied independently of one another (equal-variance condition), covaried across tone sequences (cross-channel covariance condition), or covaried among themselves for each tone (cross-parameter covariance condition). For the latter two conditions, two special cases were examined in which the target sequence varied independently of nontarget sequences or varied according to the same statistical rules. For five of six listeners, comparisons of performance to that of an ideal, within-channel observer gave clear evidence of an ability to take advantage of cross-channel statistical constraints, but only when the target sequence varied independently of its context. Results offer no evidence for listeners' ability to take advantage of cross-parameter constraints. Trial-by-trial analyses in the equal-variance condition identify factors other than the appropriate weighting of information as primarily responsible for suboptimal performance, though individual differences complicate this interpretation. A failure of simple detection-theoretic models to account for these results is discussed in terms of possible perceptual rules governing sound source identification of real-world objects.

Adult↗
PubMed1994

Effect of component-relative-entropy on the discrimination of simultaneous tone complexes.

Results are reported from a number of experiments investigating the effects of stimulus uncertainty on the discrimination of simultaneous multitone complexes. With few exceptions the data were well described by a model in which average threshold for the detection of a change in one or more components varies with the components' relative entropy (CoRE) in the complex [R.A. Lutfi, J. Acoust. Soc. Am. 94, 748-758 (1993)]. In different experiments, thresholds for the detection of a change in target level were found to be linearly related to CoRE for manipulations in the number of targets, the number of context tones, and the relative degree of level perturbation on tones from trial to trial. The slopes of the functions did not change with measures taken at different points on the psychometric function, and in most cases were close to the theoretical value of b = -1.0, as predicted by strict application of the model. Also as predicted (but for the exception of one listener) increasing the level of the target beyond that of the context had little or no effect on threshold. A correlational analysis of the trial-by-trial data revealed a tendency of listeners to give negative weight to frequencies immediately above the target, and to adjust weights in response to changes in the relative degree of level perturbation. Though inconsistent with the basic premise of the model, the variation in weights was not so great as to materially affect the predictions for mean thresholds.

Adult↗
PubMed1993

A model of auditory pattern analysis based on component-relative-entropy.

Recently results from detection and information theory have been used to predict performance of human observers in experiments involving the discriminability of changes in individual components of unfamiliar or uncertain tone patterns [R. A. Lutfi, J. Acoust. Soc. Am. 91, 3391-3401 (1992)]. In this paper, the theoretical analysis is expanded to yield a general rule of pattern analysis that accounts for nearly all of the major results of such experiments conducted over the last 18 years. The rule can be stated as follows: Component discriminability in an unfamiliar tone pattern (profile or sequence) is a linearly increasing function of the component's relative entropy (CoRE) in the pattern. Ancillary: The threshold for detection of a change decreases by one order of magnitude (factor of 10) for each one bit increase in CoRE. This precise relation of threshold to CoRE is demonstrated repeatedly in a review of past studies, and is shown to account for the relative effects of a variety of important variables and their interactions. Such variables include the total duration of the pattern; the number of tones in the pattern; the number of tones subject to change; the relative level and duration of individual tones in the pattern; the relative variability and the physical dimension of the tones' parameters that are subject to change; the number and position of targets in the pattern; the psychophysical procedure used (method of adjustment versus same-different), the type of discrimination task (frequency versus intensity discrimination), and the manner of presentation of the tones (simultaneous or sequential). The CoRE rule seems to reflect a general property of auditory analysis wherein the perception of patterns in an ensemble is dominated by those features that dominate the variance of the ensemble.

Auditory Perception↗
PubMed1992

Informational processing of complex sound. III: interference.

In this study, theoretical results from information theory and detection theory are applied to provide a formal analysis of the interaction of target and context uncertainty on the discrimination of brief multitone sequences. The experiments employ a sample-discrimination task in which the performance of an ideal observer is held constant while the relative variability of the target sigmaT and context sigmaC is varied. Listener performance in these experiments was less than ideal but increased monotonically with sigmaT/sigmaC whether the task was to discriminate the frequency or the intensity of the target. Performance was also constant for a constant sigmaT/sigmaC regardless of the target's position in the sequence. The results are consistent with a class of models in which the decision variable is a weighted sum of the tone values comprising the sequence. Weighting functions computed from the trial-by-trial date suggest that limits in performance result from trial-by-trial variability in the weights. The decision variable also serves as the basis for an analysis in which performance is linearly related to the information rate of the context independent of target position or task. In this analysis, target and context uncertainty contribute additively to the overall uncertainty associated with the decision variable.

Adult↗
PubMed1990

Informational processing of complex sound. II. Cross-dimensional analysis.

A series of experiments investigated listeners' ability simultaneously to process information across different acoustic dimensions. On each trial, the listener heard a pair of brief n-tone sequences (n = 1 to 12). The frequency, intensity, and duration of each tone in the sequence varied randomly from trial to trial. On average, the values of these three parameters were greater for one sequence, the target, than the other, the nontarget. The listener's task was to identify the target on each trial. For an ideal observer in this task, d' performance grows as the square root n. Obtained d' grew at a rate slightly less than the square root of n. Close to cube root of n growth was observed when the average difference occurred in only one of the three tone parameter values within a block of trials. Although performance fell short of ideal, optimum weights were consistently given to each tone and each parameter. The results are consistent with a model in which performance depends predominantly on the information content of the sounds regardless of how the information is "packaged" in the stimulus. Transmitted information is estimated to be 0.9-2.0 bits within a single acoustic dimension, 2.1-3.0 bits when distributed across dimensions.

Adult↗
PubMed1989

Informational processing of complex sound. I: Intensity discrimination.

This paper reports on some initial experiments using the sample discrimination paradigm to investigate normal-hearing listeners' ability to process information in complex, nonspeech sounds. An important feature of the sample discrimination experiment is that the value of the difference to be discriminated randomly varies from trial to trial. It is this variation that yields potential information. In the present study, listeners heard a pair of multitone complexes (or sequences) on each trial. The individual levels of the tones were drawn from two normal distributions differing only in mean. The listener's task was to identify the sound having the higher mean tone level. For an ideal observer in these experiments, performance in d' grows as the square root n, where n is the number of tones. Obtained d' grew more nearly as the cube root of n regardless of whether the tones were played sequentially or simultaneously or whether they were increased in number from high frequencies to low or from low frequencies to high. A preliminary model is proposed in which discrimination performance depends predominantly on the information content of the sounds and is largely independent of the physical dimensions along which the sounds vary. Information content is defined in terms of the variance of the underlying stimulus distributions and a stimulus equivocation factor that is derived from the data. Based on this model, transmitted information is estimated to be between 1.0 and 2.6 bits.

Acoustic Stimulation↗
PubMed1988

Complex interactions between pairs of forward maskers.

The present study was conducted to determine to what extent the combined effects of two forward maskers can be predicted from addition of their individual effects. The maskers were 50-Hz wide noise bands with center frequencies ranging from 1.8 to 2.2 kHz. The signal was a brief, 2.0-kHz tone burst. When the maskers were gated on and off together, the combination produced sometimes more and sometimes less masking than predicted depending on the particular pair and the relative amounts of masking produced by the individual members of the pair. The greatest discrepancy occurred, however, when the masker pair was presented simultaneously with the signal or when the forward maskers were presented in sequence. In the latter case, the obtained threshold exceeded the predicted threshold by as much as 34 dB.

Adolescent↗
PubMed1988

Interpreting measures of frequency selectivity: is forward masking special?

In a previous article [Lutfi, J. Acoust. Soc. Am. 76, 1045-1050 (1984)], the following relation was used to predict measures of frequency selectivity obtained in forward masking from measures obtained in simultaneous masking: F(g) = G + H(g) - H(0), where, for a given masker level, F is the amount of forward masking (in dB) as a function of signal-masker frequency separation (g), H is the amount of simultaneous masking, and G is the amount of forward masking for g = 0. In the present study, the relation was tested for a wider range of signal and masker frequencies, masker levels, and signal delays. The relation described thresholds from all conditions well with the inclusion of one free parameter lambda corresponding to a constant frequency increment, F(g) = G + H(g + lambda) - H(lambda). The parameter lambda was required to account for observed shifts in the frequency of maximum forward masking. It is argued that a single tuning mechanism can account for commonly observed differences between simultaneous- and forward-masked measures of frequency selectivity.

Adult↗
PubMed1987

Masking additivity in the hearing-impaired.

The purpose of the present study was to investigate how the effects of maskers combine in hearing-impaired listeners. The levels of two narrow bands of noise separated in frequency were selected so that each band individually produced the same amount of masking of a sinusoidal signal. Thresholds for the signal were then measured in the presence of both bands combined. For normal-hearing listeners, the effect of combining maskers was nonlinear, but, additive. A cube-root transformation of the masking produced by the individual and combined maskers preserved an additive relation among the effects of these maskers. This type of nonlinear additivity also characterized the results from the hearing-impaired listeners when the maskers were restricted to a region of normal sensitivity. In contrast, the effect of combining maskers was linear, additive without transformation, when the maskers were restricted to a region of significant loss. In many instances, the auditory filter model of masking may describe the detection performance of hearing-impaired listeners better than that of normal-hearing listeners.

Adult↗
PubMed1986

Two- versus four-tone masking, revisited.

Canahl [J. Acoust. Soc. Am. 50, 471-474 (1971)] measured thresholds for a 1.0-kHz sinusoid masked either by two or by four surrounding tones. He reported four-tone masked thresholds that exceeded, by 5-7.5 dB, the energy sum of the masking produced by the individual tone pairs. The present paper reports on a series of experiments investigating the effects of several factors on this 5-7.5 dB "excess" masking. In each experiment, thresholds for a 1.0-kHz 250-ms sinusoid were measured as a function of the overall level of two or four equal amplitude sinusoids with frequencies arithmetically centered around 1.0 kHz. For conditions similar to those of the Canahl experiment, 5-6 dB of excess masking was obtained independent of the level of the masking tones. Randomly varying overall level across presentations had no effect on the excess masking. The excess masking was reduced or eliminated when the masking tones were generated using an amplitude modulation technique, when they were gated on and off with the signal, or when their waveshapes were fixed across trials. Canahl's result may reflect listeners' ability to detect the signal as a change in the waveshape of the multitone masker.

Attention↗