Auditory temporal processing: two-tone flutter fusion and a model of temporal integration

Auditory temporal processing was examined using a flutter-fusion paradigm in which two tones were separated by a silent interval. The listener's task was to judge when the two tones, presented in a background noise, fused perceptually. The fusion point was studied in a series of six experiments. In the first five experiments, the duration of the first stimulus (T1) was the dependent variable. In the last experiment, the duration of the second stimulus (T2) was the dependent variable. An inverse relationship was found between T1 duration and the interstimulus interval (ISI) such that, when ISI was decreased, T1 duration had to be increased to maintain fusion. When ISI was plotted as a function of T1 duration, the data were represented by a negative exponential equation. Increasing the level of the tones, increasing the bandwidth of the background noise, or presenting the stimuli dichotically lowered the duration of T1 necessary for fusion. Changing the frequency of the tones had no effect on fusion. Decreasing the duration of T2 and holding T1 constant also resulted in fusion. A neurophysiological model implicating ON and OFF neural response interactions is postulated to account for the data.     

Asymmetric lateral inhibitory neural activity in the auditory system: a magnetoencephalographic study

Background  

Decrements of auditory evoked responses elicited by repeatedly presented sounds with similar frequencies have been well investigated by means of electroencephalography and magnetoencephalography (MEG). However the possible inhibitory interactions between different neuronal populations remains poorly understood. In the present study, we investigated the effect of proceeding notch-filtered noises (NFNs) with different frequency spectra on a following test tone using MEG.     

Auditory temporal resolution in birds: discrimination of harmonic complexes

The ability of three species of birds to discriminate among selected harmonic complexes with fundamental frequencies varying from 50 to 1000 Hz was examined in behavioral experiments. The stimuli were synthetic harmonic complexes with waveform shapes altered by component phase selection, holding spectral and intensive information constant. Birds were able to discriminate between waveforms with randomly selected component phases and those with all components in cosine phase, as well as between positive and negative Schroeder-phase waveforms with harmonic periods as short as 1-2 ms. By contrast, human listeners are unable to make these discriminations at periods less than about 3-4 ms. Electrophysiological measures, including cochlear microphonic and compound action potential measurements to the same stimuli used in behavioral tests, showed differences between birds and gerbils paralleling, but not completely accounting for, the psychophysical differences observed between birds and humans. It appears from these data that birds can hear the fine temporal structure in complex waveforms over very short periods. These data show birds are capable of more precise temporal resolution for complex sounds than is observed in humans and perhaps other mammals. Physiological data further show that at least part of the mechanisms underlying this high temporal resolving power resides at the peripheral level of the avian auditory system.     

Auditory temporal integration in the rhesus macaque (Macaca mulatta).

Temporal integration for pure tones was examined in two rhesus macaques. The subjects were required to respond to a brief sound (a tone burst) that deviated from a previous series of sounds (noise bursts) on a trial (a deviant-stimulus detection paradigm). Psychometric functions and thresholds were determined from correct detections (hit proportions) alone, and from d' scores. Two models describing the decline in threshold as a function of stimulus duration, one a power function the other an exponential, were tested against the data. When the decline (slope) in threshold per log stimulus duration is used as a rate measure, our results yield a lower estimate of temporal integration rate in rhesus than did a previous study [Clack, J. Acoust. Soc. Am. 40, 1140-1146 (1966)]. Both studies, however, gave slope estimates of integration rate that were higher than in most other species. Comparison of the models using data from several species, revealed that the exponential, but not the power model, could account for two sources of variation in threshold measurement. One source is due to the range across threshold as a function of duration (the linear rate component), and is described by the constant of proportionality Ik in the model. The other source of variation arises from the rate of decline within this range (the nonlinear rate component), and is described by the time constant tau. In terms of this model, differences in rate estimates between Clack's study and ours (and between rhesus and other species) are primarily due to the linear component. The nonlinear rate component was about equal for our study and Clack's (tau = approximately 150 ms): a time constant that is just slightly larger (indicating a rate of temporal integration slightly slower) than for most other species examined.     

Carrier-dependent temporal processing in an auditory interneuron

Signal processing in the auditory interneuron Omega Neuron 1 (ON1) of the cricket Teleogryllus oceanicus was compared at high- and low-carrier frequencies in three different experimental paradigms. First, integration time, which corresponds to the time it takes for a neuron to reach threshold when stimulated at the minimum effective intensity, was found to be significantly shorter at high-carrier frequency than at low-carrier frequency. Second, phase locking to sinusoidally amplitude modulated signals was more efficient at high frequency, especially at high modulation rates and low modulation depths. Finally, we examined the efficiency with which ON1 detects gaps in a constant tone. As reflected by the decrease in firing rate in the vicinity of the gap, ON1 is better at detecting gaps at low-carrier frequency. Following a gap, firing rate increases beyond the pre-gap level. This "rebound" phenomenon is similar for low- and high-carrier frequencies.     

Auditory processing efficiency deficits in children with developmental language impairments

The "temporal processing hypothesis" suggests that individuals with specific language impairments (SLIs) and dyslexia have severe deficits in processing rapidly presented or brief sensory information, both within the auditory and visual domains. This hypothesis has been supported through evidence that language-impaired individuals have excess auditory backward masking. This paper presents an analysis of masking results from several studies in terms of a model of temporal resolution. Results from this modeling suggest that the masking results can be better explained by an "auditory efficiency" hypothesis. If impaired or immature listeners have a normal temporal window, but require a higher signal-to-noise level (poor processing efficiency), this hypothesis predicts the observed small deficits in the simultaneous masking task, and the much larger deficits in backward and forward masking tasks amongst those listeners. The difference in performance on these masking tasks is predictable from the compressive nonlinearity of the basilar membrane. The model also correctly predicts that backward masking (i) is more prone to training effects, (ii) has greater inter- and intrasubject variability, and (iii) increases less with masker level than do other masking tasks. These findings provide a new perspective on the mechanisms underlying communication disorders and auditory masking.     

Temporal processing in the aging auditory system.

Measures of monaural temporal processing and binaural sensitivity were obtained from 12 young (mean age = 26.1 years) and 12 elderly (mean age = 70.9 years) adults with clinically normal hearing (pure-tone thresholds < or = 20 dB HL from 250 to 6000 Hz). Monaural temporal processing was measured by gap detection thresholds. Binaural sensitivity was measured by interaural time difference (ITD) thresholds. Gap and ITD thresholds were obtained at three sound levels (4, 8, or 16 dB above individual threshold). Subjects were also tested on two measures of speech perception, a masking level difference (MLD) task, and a syllable identification/discrimination task that included phonemes varying in voice onset time (VOT). Elderly listeners displayed poorer monaural temporal analysis (higher gap detection thresholds) and poorer binaural processing (higher ITD thresholds) at all sound levels. There were significant interactions between age and sound level, indicating that the age difference was larger at lower stimulus levels. Gap detection performance was found to correlate significantly with performance on the ITD task for young, but not elderly adult listeners. Elderly listeners also performed more poorly than younger listeners on both speech measures; however, there was no significant correlation between psychoacoustic and speech measures of temporal processing. Findings suggest that age-related factors other than peripheral hearing loss contribute to temporal processing deficits of elderly listeners.     

Evoked magnetoencephalographic responses to omission of a tone in a musical scale

The musical scale is a basis for melodies and can be a simple melody by itself. The present study investigated magnetoencephalographic (MEG) responses to omissions of one tone out of the C major scale. The tone preceding the omitted "target" tone was either prolonged or repeated. In another series, the tone after the target tone was repeated. In "normal" oddball experiments, the complete C major scale was presented more frequently than an incomplete scale lacking one tone, and in "reverse" oddball experiments, the roles were exchanged. In the normal oddball experiments, omission of any tone produced a response significantly different in amplitude from the standard response in the group of non-musicians, although the responses differed depending on the types of omission. The leading tone (B in the C major scale) was shown to elicit a large response when omitted and also when its presence was emphasized. The Reverse oddball experiments showed that repeated presentation of an incomplete scale lacking one tone temporarily reduced the influence of the complete scale but could not even temporarily replace it working as "standard." In addition, an auxiliary study was done to see possible influence of rhythmic variations.     

Auditory temporal acuity in relation to category boundaries; speech and nonspeech stimuli

Experiments were conducted to determine the underlying resolving power of the auditory system for temporal changes at the onset of speech and nonspeech stimuli. Stimulus sets included a bilabial VOT continuum and an analogous nonspeech continuum similar to the "noise-buzz" stimuli used by Miller et al. [J. Acoust. Soc. Am. 60, 410-417 (1976)]. The main difference between these and earlier experiments was that efforts were made to minimize both the trial-to-trial stimulus uncertainty and the cognitive load inherent in some of the testing procedures. Under conditions of minimal psychophysical uncertainty, not only does discrimination performance improve overall, but the local maximum, usually interpreted as evidence of categorical perception, is eliminated. Instead, discrimination performance for voice onset time (VOT) or noise lead time (NLT) is very accurate for short onset times and generally decreases with increasing onset time. This result suggests that "categorization" of familiar sounds is not the result of a psychoacoustic threshold (as Miller et al. have suggested) but rather of processing at a more central level of the auditory system.     

Diffractive-optical processing of temporal signals, part Ⅰ: basic principles

The topic of this paper is the utilization of time for optical information processing. As clock rates in computing and communication systems increase and reach the THz border, optical techniques for signal filtering, shaping and clock distribution become attractive. We discuss the use of optics in temporal processing and consider in particular diffractive solutions. In part one of this paper, we discuss the basic concepts of temporal optics.     

Dynamic temporal pulse shaping in advanced ultrafast laser material processing

Phase-manipulated ultrafast laser pulses and temporally tailored pulse trains with THz repetition rates are promising new tools for quality micromachining of brittle dielectrics, allowing to adapt the laser energy delivery rate to the material properties for optimal processing. Different materials respond with specific reaction pathways to the sudden energy input depending on the efficiency of electron generation and on the ability to release the energy into the lattice. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show that this can result in lower stress, cleaner structures, and allow for a material-dependent optimization process. Received: 7 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +49-30/6392-1229, E-mail: stoian@mbi-berlin.de RID="**" ID="**"Now at Katana Technologies GmbH, Albert-Einstein-Ring 7, 14532 Kleinmachnow, Germany     

Diffractive-optical processing of temporal signals, part Ⅱ: optical tapped-delay line

The topic of this presentation is the utilization of time for optical information processing. As clock rates in computing and communication systems increase and reach the THz border, optical techniques for signal filtering, shaping and clock distribution become attractive. We discuss the use of optics in temporal processing and consider in particular diffractive solutions. In this paper, we describe the use of double diffraction for implementing an ultrafast tapped-delay line.     

Vocal aging and the impact on daily life: a longitudinal study

Longitudinal studies on vocal aging are scarce, and information on the impact of age-related voice changes on daily life is lacking. This longitudinal study reports on age-related voice changes and the impact on daily life over a time period of 5 years on 11 healthy male speakers, age ranging from 50 to 81 years. All males completed a questionnaire on vocal performance in daily life, and perceptual and acoustical analyses of vocal quality and analyses of maximum performance tasks of vocal function (voice range profile) were performed. Results showed a significant deterioration of the acoustic voice signal as well as increased ratings on vocal roughness judged by experts after the time period of 5 years. An increase of self-reported voice instability and the tendency to avoid social parties supported these findings. Smoking males had a lower speaking fundamental frequency compared with nonsmoking males, and this seemed reversible for males who stop smoking. This study suggests a normal gradual vocal aging process with clear consequences in daily life, which should be taken into consideration in clinical practice as well as in studies concerning communication in social life.     

Online aging study of a high rate MRPC

With the constant increase of accelerator luminosity, the rate requirements of MRPC detectors have become very important, and the aging characteristics of the detector have to be studied meticulously. An online aging test system has been set up in our lab, and in this paper the setup of the system is described and the performance stability of a high-rate MRPC studied over a long running time under a high luminosity environment.The high rate MRPC was irradiated by X-rays for 36 days and the accumulated charge density reached 0.1 C/cm~2.No obvious performance degradation was observed for the detector.     

Auditory temporal resolution in normal-hearing preschool children revealed by word recognition in continuous and interrupted noise

The purpose of this study was to examine temporal resolution in normal-hearing preschool children. Word recognition was evaluated in quiet and in spectrally identical continuous and interrupted noise at signal-to-noise ratios (S/Ns) of 10, 0, and -10 dB. Sixteen children 4 to 5 years of age and eight adults participated. Performance decreased with decreasing S/N. At poorer S/Ns, participants demonstrated superior performance or a release from masking in the interrupted noise. Adults performed better than children, yet the release from masking was equivalent. Collectively these findings are consistent with the notion that preschool children suffer from poorer processing efficiency rather than temporal resolution per se.     

Age-dependent plasticity in the superior temporal sulcus in deaf humans: a functional MRI study

Background  

Sign-language comprehension activates the auditory cortex in deaf subjects. It is not known whether this functional plasticity in the temporal cortex is age dependent. We conducted functional magnetic-resonance imaging in six deaf signers who lost their hearing before the age of 2 years, five deaf signers who were >5 years of age at the time of hearing loss and six signers with normal hearing. The task was sentence comprehension in Japanese sign language.     

Auditory processing of real and illusory changes in frequency modulation (FM) phase

Auditory processing of frequency modulation (FM) was explored. In experiment 1, detection of a tau-radians modulator phase shift deteriorated as modulation rate increased from 2.5 to 20 Hz, for 1- and 6-kHz carriers. In experiment 2, listeners discriminated between two 1-kHz carriers, where, mid-way through, the 10-Hz frequency modulator had either a phase shift or increased in depth by deltaD% for half a modulator period. Discrimination was poorer for deltaD = 4% than for smaller or larger increases. These results are consistent with instantaneous frequency being smoothed by a time window with a total duration of about 110 ms. In experiment 3, the central 200-ms of a 1-s 1-kHz carrier modulated at 5 Hz was replaced by noise, or by a faster FM applied to a more intense 1-kHz carrier. Listeners heard the 5-Hz FM continue at the same depth throughout the stimulus. Experiments 4 and 5 showed that, after an FM tone had been interrupted by a 200-ms noise, listeners were insensitive to the phase at which the FM resumed. It is argued that the auditory system explicitly encodes the presence, and possibly the rate and depth, of FM in a way that does not preserve information on FM phase.     

Dual mechanisms in the perceptual processing of click train temporal regularity

Two experiments measured human sensitivity to temporal jitter in 25-click trains with inter-click intervals (ICIs) between 5 and 100 ms. In a naturalistic experiment using wideband clicks, jitter thresholds were a nonmonotonic function of ICI, peaking for ICIs near 40-60 ms. In a subsequent experiment, clicks were high-passed and presented against a low-frequency noise masker. Jitter threshold vs ICI functions lost the positive slope over short ICIs but retained the negative slope at long ICIs. The same behavior was seen in click rate discrimination tasks. Different processes mediate regularity analysis for click trains with ICIs above and below 40-60 ms.