Biomedical subjects

S Sheft

Publications and source records attributed to S Sheft.

17 recordsLinked to original sources

PubMed1998

The role of the envelope in processing iterated rippled noise.

Iterated rippled noise (IRN) is generated by a cascade of delay and add (the gain after the delay is 1.0) or delay and subtract (the gain is -1.0) operations. The delay and add/subtract operations impart a spectral ripple and a temporal regularity to the noise. The waveform fine structure is different in these two conditions, but the envelope can be extremely similar. Four experiments were used to determine conditions in which the processing of IRN stimuli might be mediated by the waveform fine structure or by the envelope. In experiments 1 and 3 listeners discriminated among three stimuli in a single-interval task: IRN stimuli generated with the delay and add operations (g = 1.0), IRN stimuli generated using the delay and subtract operations (g = -1.0), and a flat-spectrum noise stimulus. In experiment 2 the listeners were presented two IRN stimuli that differed in delay (4 vs 6 ms) and a flat-spectrum noise stimulus that was not an IRN stimulus. In experiments 1 and 2 both the envelope and waveform fine structure contained the spectral ripple and temporal regularity. In experiment 3 only the envelope had this spectral and temporal structure. In all experiments discrimination was determined as a function of high-pass filtering the stimuli, and listeners could discriminate between the two IRN stimuli up to frequency regions as high as 4000-6000 Hz. Listeners could discriminate the IRN stimuli from the flat-spectrum noise stimulus at even higher frequencies (as high as 8000 Hz), but these discriminations did not appear to depend on the pitch of the IRN stimuli. A control experiment (fourth experiment) suggests that IRN discriminations in high-frequency regions are probably not due entirely to low-frequency nonlinear distortion products. The results of the paper imply that pitch processing of IRN stimuli is based on the waveform fine structure.

Attention↗

PubMed1997

Modulation detection interference with two-component masker modulators.

Thresholds were measured for detecting amplitude modulation of a single tonal carrier in the presence of modulated maskers. The masker modulator contained either one or two sinusoidal components. As found in previous studies, there was a detrimental effect of masker modulation on the detection of probe modulation. Interference was obtained with a 4-Hz separation between the two components of the masker modulator with the probe modulated at the 4-Hz beat rate. The amount of interference obtained with the two-component masker modulator was greater than that produced by the individual components of the masker modulator. The amount of interference increased with the depth of the masker-modulator beating and the number of masker carriers. The interference due to beating of the masker-modulator components was reduced when the beat rate was increased from 4 to 10 Hz. Results obtained with two-component masker modulators indicate a masking effect not predicted by a spectral representation of the probe and masker envelopes.

Auditory Perception↗

PubMed1997

Binaural modulation detection interference.

The ability to detect amplitude modulation (AM) of a tonal probe can be disrupted by the presence of modulated masking tones. Two experiments examined whether a disparity in the interaural parameters of the probe and masker can reduce the amount of interference. In the first experiment, the effects of interaural time and intensity differences were studied in separate sets of conditions. With low-frequency carriers, the detection of 10-Hz probe modulation in the presence of 10-Hz masker modulation was not significantly affected by interaural time differences. With higher-frequency carriers, dichotic stimuli were generated through combinations of diotic, dichotic, or monotic probe and masker presentations in which the probe and masker did not share a common interaural intensity difference. In these conditions, the amount of interference was affected by the interaural configuration. However, monotic level differences between the probe and masker may have contributed to the effect of interaural configuration. In the second experiment, the probe and masker were presented through separate speakers in an enclosed listening environment. Spatial separation between the sources for the probe and masker led to a small reduction in the amount of interference. When the masker modulation rate was varied with the probe AM rate fixed at 10 Hz, the extent of tuning in the modulation domain in the sound-field conditions was similar to that obtained with diotic stimulus presentation over headphones.

Analysis of Variance↗

PubMed1996

A time domain description for the pitch strength of iterated rippled noise.

Two versions of a cascaded add, attenuate, and delay circuit were used to generate iterated rippled noise (IRN) stimuli. IRN stimuli produce a repetition pitch whose strength relative to the noise can be varied by changing the type of circuit, the attenuation, or the number of iterations in the circuit. Listeners were asked to discriminate between various pairs of IRN stimuli which differed in the type of network used to generate the sounds or the number of iterations (n = 1, 2, 3, 4, 7, and 9). Performance was determined for IRN stimuli generated with delays of 2, 4, and 8 ms and for four bandpass filter conditions (0-2000, 250-2000, 500-2000, and 750-2000 Hz). Some IRN stimuli were extremely difficult to discriminate despite relatively large spectral differences, while other IRN stimuli produced readily discriminable changes in perception, despite small spectral differences. these contrasting results are inconsistent with simple spectral explanations for the perception of IRN stimuli. An explanation based on the first peak of the autocorrelation function of IRN stimuli is consistent with the results. Simulations of the processing performed by the peripheral auditory system (i.e., interval histograms and correlograms) produce results which are consistent with the involvement of these temporal processes in the perception of IRN stimuli.

Humans↗

PubMed1996

Responses of ventral cochlear nucleus units in the chinchilla to amplitude modulation by low-frequency, two-tone complexes.

For a tone that is amplitude modulated by two tones (fmod1 and fmod2), neither the stimulus waveform nor the half-wave rectified waveform has spectral energy at the envelope beat frequency (fmod2-fmod1). The response of ventral cochlear nucleus units in the chinchilla were recorded for best frequency tones that were amplitude modulated by low-frequency, two-tone complexes. Fourier analysis of poststimulus time histograms shows spectral peaks at fmod2-fmod1 in addition to the peaks at fmod1 and fmod2. The peaks in the neural spectra arise from compressive nonlinearities in the auditory system. The magnitudes of these spectral peaks are measures of synchrony at each frequency component. For all units, synchrony at fmod1 and fmod2 is greater than the synchrony at fmod2-fmod1. For a given unit, synchrony at fmod1 and fmod2 remains relatively constant as a function of overall level, whereas synchrony at fmod2-fmod1 decreases as the level increases. Synchrony was quantified in terms of the Rayleigh statistic (z), which is a measure of the statistical significance of the phase locking. In terms of z, phase locking at fmod1 and fmod2 is largest in chopper units, whereas onset-chopper units and primarylike units having sloping saturation in their rate-level functions show the smallest amount of phase locking. Phase locking at fmod2-fmod1 is also largest in chopper units, and smallest in onset-chopper units and primarylike units with sloping saturation.

Acoustic Stimulation↗

PubMed1996

A simulated "cocktail party" with up to three sound sources.

Listeners identified spoken words, letters, and numbers and the spatial location of these utterances in three listening conditions as a function of the number of simultaneously presented utterances. The three listening conditions were a normal listening condition, in which the sounds were presented over seven possible loudspeakers to a listener seated in a sound-deadened listening room; a one-headphone listening condition, in which a single microphone that was placed in the listening room delivered the sounds to a single headphone worn by the listener in a remote room; and a stationary KEMAR listening condition, in which binaural recordings from an acoustic manikin placed in the listening room were delivered to a listener in the remote room. The listeners were presented one, two, or three simultaneous utterances. The results show that utterance identification was better in the normal listening condition than in the one-headphone condition, with the KEMAR listening condition yielding intermediate levels of performance. However, the differences between listening in the normal and in the one-headphone conditions were much smaller when two, rather than three, utterances were presented at a time. Localization performance was good for both the normal and the KEMAR listening conditions and at chance for the one-headphone condition. The results suggest that binaural processing is probably more important for solving the "cocktail party" problem when there are more than two concurrent sound sources.

Adolescent↗

PubMed1995

Sound production in Pituophis melanoleucus (Serpentes: Colubridae) with the first description of a vocal cord in snakes.

The pine, gopher, or bull snake (Pituophis melanoleucus) makes two different defensive sounds. Hisses are characterized by lack of frequency and amplitude modulation; bellows have a brief initial period of high-amplitude, broad-frequency sound followed by a longer period of lower-amplitude, constant-frequency sound. Both defensive sounds contain distinct harmonic elements. The modulation and harmonic nature of these sounds seems to be unique among snakes. The larynx of Pituophis is unusual in having an epiglottal keel, a dorsal expansion of the cricoid cartilage, previously proposed to contribute to sound production; however, this study shows that it plays only a small role in increasing the amplitude of bellows. Within the larynx of Pituophis is a "vocal cord," the laryngeal septum, which is a flexible, horizontal shelf of tissue that divides the anterior portion of the larynx. Removal of the laryngeal septum alters the defensive sounds and eliminates their harmonic elements. The laryngeal septum is unique among previously described vertebrate vocal cords or folds because it is supported by the cricoid (as opposed to arytenoid) cartilage and is a single (as opposed to bilaterally paired) structure.

Animals↗

PubMed1995

The synthetic-analytic listening task for modulated signals.

The synthetic-analytic listening task (SALT) developed by Dye and colleagues [Dye et al., J. Acoust. Soc. Am. 96, 2720-2731 (1994)] was applied to a task in which an amplitude-modulated tonal carrier was presented as a target during the standard stimulus. The standard stimulus was followed by a test stimulus in which the target along with another amplitude-modulated carrier (the distractor) was presented. The listener determined if in the test stimulus, the target (which was presented along with the distractor) was higher or lower in modulation depth than when the target was presented alone as the standard stimulus. The target and distractor were either 1- or 4-kHz carriers modulated at one of ten depths of modulation during the test stimulus at modulation rates ranging from 4 to 64 Hz. SALT was used to estimate the relative weight listeners assigned to the target and distractor as a function of the difference between their modulation rates, both for target carrier frequencies above and for target carrier frequencies below the distractor carrier frequency. When the target and distractor were modulated at the same rate, the target and distractor weights were equal, indicating synthetic listening. When the target and distractor differed in modulation rate, the listener gave more weight to the target suggesting a form of analytic listening. The result demonstrate the applicability of SALT to studies of modulation and reinforce the claim that different spectral components modulated with the same modulation pattern are processed synthetically.

Auditory Perception↗

PubMed1994

Detection of bandlimited noise masked by wideband noise in the chinchilla.

Six chinchillas were trained to detect a 1 s bandlimited noise signal in the presence of a continuous, wideband noise masker. As the bandwidth of the noise signal increased, there was a decrease in detection threshold. Threshold signal-to-noise ratios for the bandlimited noise signal were independent of the level of the noise masker. The slope of the bandwidth function obtained for the chinchilla is similar to the slopes reported for human subjects, approximating the predicted slope of the ideal energy detector.

Acoustic Stimulation↗

PubMed1994

Modulation detection interference: across-frequency processing and auditory grouping.

Modulation Detection Interference (MDI) is the loss of sensitivity in processing amplitude modulation of a probe tone when a masker is similarly modulated. MDI was measured in four experiments to investigate two past claims concerning MDI: 1) That MDI represents across-spectral processing, and 2) that MDI is the consequence of the auditory system using common patterns of amplitude modulation to group spectral components into a single auditory source. Experiment I studied MDI when the envelope phase of the masker and probe modulators were different and was used to address the issue of the extent to which MDI is a consequence of spectral grouping based on common amplitude modulation. Measures of MDI for conditions in which the frequency separation between the probe and masker carriers was varied (Experiment II), estimates of modulation depth discrimination (Experiment III), and signal detection thresholds for brief sinusoidal signals masked by amplitude modulated tones (Experiment IV) were all used to address issues related to across-spectral processing of amplitude modulation. The conclusions of these studies is that MDI is largely an across-frequency phenomenon and that the role of auditory grouping based on a common pattern of modulation can not be ruled out as having a relationship to MDI.

Acoustic Stimulation↗

PubMed1994

Stimulus classification procedure for assessing the extent to which binaural processing is spectrally analytic or synthetic.

A two-dimensional stimulus classification paradigm was used to assess the extent to which listeners' processing of interaural delays at low frequencies is spectrally analytic or synthetic. Listeners were presented with a 753-Hz target with an interaural delay that varied from trial to trial, taking on one of ten values, five leading to the left ear and five leading to the right. A 553-Hz distractor component was simultaneously presented, with its interaural delay also presented at one of ten different values. During a block of 100 trials, each of the possible combinations of target and distractor delay was presented once, and only once, in a random order. Listeners were instructed to make left-right judgments based on the target delay. Each condition was repeated ten times, and the slopes of the best linear boundaries between left and right responses were used to derive the relative weights given to the target and distractor in judgments of laterality. Six of the nine listeners gave increasing weight to the target as the duration of the signals was increased from 25 or 50 to 400 ms. Three listeners showed little change with duration; one consistently gave equal weight to the target and distractor, two consistently gave greater weight to the target than to the distractor. The utility of classification paradigms in the study of multidimensional acoustic signals is discussed.

Adult↗

PubMed1993

Increment detection of bandlimited noises in the chinchilla.

A positive reinforcement, adaptive tracking procedure was used to study the intensity discrimination abilities of six chinchillas to noise signals. Increment detection thresholds were obtained using a two-down, one-up tracking rule. The effect of overall noise masker level and the effect of noise bandwidth on increment detection thresholds were studied. The continuous noise masker and the signal increment had equal bandwidths. Increment detection thresholds are independent of overall level for wideband noise; the asymptotic DL for wideband noise is 1.334 dB. In addition, increment detection thresholds decrease as the bandwidth of the noise increases. The observed slope of the bandwidth function for the chinchilla is independent of overall level and is around -2.8 dB/decade. The slope of the bandwidth function obtained for the chinchilla is similar to values reported for human subjects under similar conditions, but is less than the slope predicted by the ideal energy detector model.

Acoustic Stimulation↗

PubMed1990

A comparison among three measures of cross-spectral processing of amplitude modulation with tonal signals.

Results were obtained from three paradigms used to study cross-spectral processing of envelope modulation [comodulation masking release (CMR), comodulation detection difference (CDD), and modulation detection interference (MDI)]. When tonal carriers separated by two octaves (flanking tone at 1000 Hz and target tone at 4000 Hz) were amplitude modulated at 20 Hz, there was no evidence of a cMR or CDD effect, but there was substantial MDI.

Acoustic Stimulation↗

PubMed1990

Temporal integration in amplitude modulation detection.

Thresholds for detecting sinusoidal amplitude modulation (AM) of a wideband noise carrier were measured as a function of the duration of the modulating signal. The carrier was either; (a) gated with a duration that exceeded the duration of modulation by the combined stimulus rise and fall times; (b) presented with a fixed duration that included a 500-ms carrier fringe preceding the onset of modulation; or (c) on continuously. In condition (a), the gated-carrier temporal modulation transfer functions (TMTFs) exhibited a bandpass characteristic. For AM frequencies above the individual subject's TMTF high-pass segment, the mean slope of the integration functions was - 7.46 dB per log unit duration. For the fringe and continuous-carrier conditions [(b) and (c)], the mean slopes of the integration functions were, respectively, - 9.30 and - 9.36 dB per log unit duration. Simulations based on integration of the output of an envelope detector approximate the results from the gated-carrier conditions. The more rapid rates of integration obtained in the fringe and continuous-carrier conditions may be due to "overintegration" where, at brief modulation durations, portions of the unmodulated carrier envelope are included in the integration of modulating signal energy.

Adult↗

PubMed1989

Across-critical-band processing of amplitude-modulated tones.

Two experiments using two-tone sinusoidally amplitude-modulated stimuli were conducted to assess cross-channel effects in processing low-frequency amplitude modulation. In experiment I, listeners were asked to discriminate between two sets of two-tone amplitude-modulated complexes. In one set, the modulation phase of the lower frequency carrier tone was different from that of the upper frequency carrier tone. In the other stimulus set, both amplitude-modulated carriers had the same modulator phase. The amount of phase shift required to discriminate between the two stimulus sets was determined as a function of the separation between the two carriers, modulation depth, and modulation frequency. Listeners could discriminate a 50 degrees-60 degrees phase shift between the modulated envelopes for tones separated by more than a critical band. In experiment II, the modulation depth required to detect modulation of a probe carrier was measured in the presence of an amplitude-modulated masker. The threshold for detecting probe modulation was determined as a function of the separation between the masker and probe carriers, the phase difference between the masker and probe modulators, and masker modulation depth (in all conditions, the rate of probe and masker modulation was 10 Hz). The threshold for detecting probe modulation was raised substantially when the masker tone was also modulated. The results are consistent with theories suggesting that amplitude modulation helps form auditory objects from complex sound fields.

Auditory Perception↗

PubMed1989

Modulation interference in detection and discrimination of amplitude modulation.

Two experiments were conducted to assess the effect of the rate of sinusoidal amplitude modulation (SAM) of a masker tone on detection of SAM of a probe tone (experiment 1) or on SAM-rate discrimination for the probe tone (experiment 2). When modulated at the same rate as the probe, the masker interfered with both the detection of probe modulation and the discrimination of the rate of probe modulation. The interference was obtained when the masker was either higher or lower in frequency than the probe (the probe and masker were separated by 2 oct). The amount of interference in detecting probe modulation (experiment 1) decreased as the common base rate of modulation was increased from 5 to 200 Hz. For rate discrimination (experiment 2), the amount of interference remained approximately the same for base rates of 2-40 Hz, the range over which rate discrimination was measured. In both experiments, the amount of interference was reduced when the masker was modulated at a different rate than the probe.

Acoustic Stimulation↗

PubMed1989

Congenital midline cervical cleft.

We present a case of congenital midline cervical cleft (CMCC), a sporadic lesion with a predilection for white females. It characteristically occurs in the midline ventral neck and consists of a cephalad skin tag, a mucosal surface, and a caudal sinus. There is an associated submucosal fibrous cord and interwoven bundles of skeletal muscle. This is occasionally tethered to the mandible and/or sternum causing neck contractures. CMCC is usually isolated, but rare cases have been associated with midline clefts of the tongue, lower lip, mandible, and sternum. The embryogenesis is unclear but arguments are given here that CMCC represents ectopic first branchial arch derivatives, including the lower lip and/or tongue.

Branchial Region↗