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R A Lutfi

Publications and source records attributed to R A Lutfi.

At least 19 recordsLinked to original sources
PubMed2001

Children's detection of pure-tone signals with random multitone maskers.

Preschoolers and adults were asked to detect a 1000-Hz signal, which was masked by a multitone complex. The frequencies and amplitudes of the components in the complex varied randomly and independently on each presentation. A staircase, cued two-interval, forced-choice procedure disguised as a "listening game" was used to obtain signal thresholds in quiet and in the presence of the multitone maskers. The number of components in the masker was fixed within an experimental condition and varied from 2 to 906 across experimental conditions. Thresholds were also measured with a broadband noise masker. Eight preschool children and eight adults were tested. Although individual differences were large, among both adults and children, there was little difference between the groups in the mean amount of masking produced by the maskers with large numbers of components (400 and 906). There was also a small but significant difference between adults and children in the mean amount of masking produced by the broadband noise. The difference between the groups was much larger with smaller numbers of components. Data obtained from the adults were basically similar to that previously reported [cf. Neff and Green, Percept. Psychophys. 41, 409-415 (1987); Oh and Lutfi, J. Acoust. Soc. Am. 104, 3489-3499 (1998)]: maskers comprised of 10-40 components produced as much as 30 to 60 dB of masking in some, but not all listeners. Those same maskers produced larger amounts of masking (70-83 dB) in many of the preschool children, although, as in the adult group, individual differences were large. The component-relative-entropy (CoRE) model [Lutfi, J. Acoust. Soc. Am. 94, 748-758 (1993)] was used to describe the differences in performance between the children and adults. According to this model the average child appears to integrate information over a larger number of auditory filters than the average adult.

Adult↗
PubMed2001

Auditory detection of hollowness.

The airborne sounds produced by freely vibrating hollow and solid bars were synthesized according to the equations of bar motion from theoretical acoustics, and were presented to listeners over headphones. In a two-interval, forced-choice task, listeners were asked to distinguish between the hollow and solid bar sounds as bar length was varied at random from one presentation to the next. All other physical properties of the bar were held constant across trials. Listener decision strategies for detecting hollowness in iron, aluminum, and wood bars were determined from regression weights describing the relation between the listener's response and the frequency, intensity, and decay modulus of the individual partials comprising these sounds. The obtained weights were compared to those of a hypothetical listener that bases judgments on the acoustic relations intrinsic to hollowness, as determined from the equations for motion. Results indicate that listeners adopt roughly one of two decision strategies, either basing judgments on the appropriate acoustic relations, or basing judgments predominantly on frequency alone. The decision strategy of some listeners also changed from one type to the other with a change in bar material or upon replication of the same condition. The results are interpreted in terms of the vulnerability of the intrinsic acoustic relations to small perturbations in acoustic parameters, as would be associated with listener internal noise. They demonstrate that basic limits of human sensitivity can have a profound effect on the identification of rudimentary source attributes from sound, even in conditions where acoustic variation is largely dictated by physical variation in the source.

Auditory Perception↗
PubMed2000

Effect of masker harmonicity on informational masking.

Detection thresholds for a tone in an unfamiliar tonal pattern can be greatly elevated under conditions of masker uncertainty [Neff and Green, Percept. Psychophys. 41, 409-415 (1987); Oh and Lutfi, J. Acoust. Soc. Am. 101, 3148 (1997)]. The present experiment was undertaken to determine whether harmonicity of masker tones can reduce the detrimental effect of masker uncertainty. Inharmonic maskers were comprised of m=2-49 frequency components selected at random on each presentation within 100-10000 Hz, excluding frequencies between 920-1080. Harmonic maskers were comprised of frequency components selected at random within this same range, but constrained to have a fundamental frequency of 200 Hz. For inharmonic maskers the signal was a 1000-Hz tone. For harmonic-maskers the signal was a tone whose frequency was either harmonically (1000 Hz) or inharmonically (1047 Hz) related to the masker. In all conditions the amount of masking was greatest for m = 20-40 components. At this point, harmonic maskers with harmonic signal produced an average of 9-12 dB less masking than inharmonic maskers. Harmonic maskers with inharmonic signal produced an average of 16-20 dB less masking.

Adult↗
PubMed1999

Level discrimination of single tones in a multitone complex by normal-hearing and hearing-impaired listeners.

A conditional-on-a-single-stimulus (COSS) analysis procedure [B. G. Berg, J. Acoust. Soc. Am. 86, 1743-1746 (1989)] was used to estimate how well normal-hearing and hearing-impaired listeners selectively attend to individual spectral components of a broadband signal in a level discrimination task. On each trial, two multitone complexes consisting of six octave frequencies from 250 to 8000 Hz were presented to listeners. The levels of the individual tones were chosen independently and at random on each presentation. The target tone was selected, within a block of trials, as the 250-, 1000-, or 4000-Hz component. On each trial, listeners were asked to indicate which of the two complex sounds contained the higher level target. As a group, normal-hearing listeners exhibited greater selectivity than hearing-impaired listeners to the 250-Hz target, while hearing-impaired listeners showed greater selectivity than normal-hearing listeners to the 4000-Hz target, which is in the region of their hearing loss. Both groups of listeners displayed large variability in their ability to selectively weight the 1000-Hz target. Trial-by-trial analysis showed a decrease in weighting efficiency with increasing frequency for normal-hearing listeners, but a relatively constant weighting efficiency across frequency for hearing-impaired listeners. Interestingly, hearing-impaired listeners selectively weighted the 4000-Hz target, which was in the region of their hearing loss, more efficiently than did the normal-hearing listeners.

Adult↗
PubMed1999

Correlational analysis of acoustic cues for the discrimination of auditory motion.

The sound of a source moving in a straight path and passing directly in front of the listener on the azimuthal plane was synthesized over headphones to include three dynamic cues for motion: Doppler effect, overall intensity, and interaural time difference. Discriminability of a change in displacement, velocity, and acceleration of this source was measured using a standard two-interval, forced-choice procedure. In each case, the relative reliance or weight given to the three acoustic cues was estimated from correlations of the listener's response with small independent pertubations imposed on cues from trial to trial. Group estimates of threshold agreed well with results from past studies, while the obtained pattern of weights depended on the individual, starting velocity, and discrimination task. For the discrimination of displacement at moderate velocity (10 m/s), responses were most highly correlated with intensity or interaural time difference. For the discrimination of velocity and, to a lesser extent, acceleration, responses were most highly correlated with Doppler effect. At higher velocity (50 m/s) responses in all discrimination tasks were most strongly correlated with Doppler effect with few exceptions. Randomizing source spectrum or roving distance of the source from trial to trial did not significantly affect the pattern of results. The results suggest that motion perception is mutable, and not in all cases based on a single invariant acoustic cue.

Auditory Perception↗
PubMed1999

Informational masking by everyday sounds.

Tone-in-noise detection is severely degraded when only a few spectral components of the noise are presented at random on each trial [Neff and Green, Percept. Psychophys. 41, 409-415 (1987)]. The elevations in threshold are attributed to uncertainty regarding the noise caused by sparse sampling of noise components-informational masking is the term used to describe the result. The present experiment was undertaken to determine how informational masking is affected when sparse sampling is from a set of common everyday sounds instead of noise. On each presentation a different masker waveform of constant total power was synthesized from the magnitude and phase of a fixed number, m, of spectral components (m = 2-921 across blocks of trials). The components were selected at random from 1 of 50 common environmental sounds (e.g., baby crying, door slamming, phone ringing), or 1 of 50 samples of Gaussian noise. Masked thresholds for a 1.0-kHz signal in the presence of both types of maskers were obtained using an adaptive, two-interval, forced-choice procedure. Results with noise replicated earlier, results showing largest elevations in threshold for 10-20 sampled components. Results with everyday sounds showed a similar pattern with thresholds elevated above those for noise by as much as 10 dB at the larger values of m. The differences in masked thresholds were systematically related to differences in the ensemble variance of masker spectra, as predicted by a model previously applied to noise [Lutfi, J. Acoust. Soc. Am. 94, 748-758 (1993)]. Not predicted was the result of a subsequent trial-by-trial analysis in which 9-11 dB less masking was observed for samples from everyday sounds rated as easily recognized by listeners. The results suggest that listeners fail to exploit lawful dependencies among spectral components of everyday sounds to aid detection, unless enough information is available for the sound to be easily recognized.

Adult↗
PubMed1998

Nonmonotonicity of informational masking.

Neff and Green [Percept. Psychophys. 41, 409-415 (1987)] report that the masking of single tones by random-frequency multitone maskers varies nonmonotonically with number of masker components (peaking at 10-50 components). In this paper it is shown that such results are well predicted by a model (the component-relative-entropy model, CoRE) wherein thresholds increase linearly with the ensemble variance of masker spectra smoothed by peripheral auditory filters [R. A. Lutfi, J. Acoust. Soc. Am. 94, 748-758 (1993)]. Three experiments were conducted. In the first, the nonmonotonic relation was replicated for 9 of 11 listeners in conditions similar to those of Neff and Green. In the second, the frequencies of masker components were fixed and the levels of components were varied randomly across presentations to simulate Gaussian noise. In this case, the nonmonotonicity and the total amount of masking for these listeners were shown to be significantly reduced. In the third experiment, masked thresholds for the signal were found to vary monotonically with the frequency spacing of masker components for a fixed number of masker components. Large individual differences among listeners were obtained in some experimental conditions. Individual as well as mean thresholds were well predicted by the CoRE model with an appropriate selection of the values of the two free parameters of the model for each listener.

Adult↗
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↗