Simulations of temporal resolution and integration data with a computer model using a modulation filter bank.

Auditory temporal processing frequently appears more affected in old subjects than would be predicted by the degree of peripheral hearing loss, pointing to an age-dependent central processing deficit. In parallel, an age-dependent decline of inhibitory function has been demonstrated in the auditory pathway, suggesting a causal relationship between temporal processing and inhibition. Gabapentin has been specifically synthesized as a potential gamma-amino-butyric-acid (GABA) mimetic with the capability to cross the blood-brain barrier. Gabapentin treatment ameliorated tinnitus in a rat model and improved tinnitus annoyance in humans with acoustic trauma. Consequently, the present study evaluated the effect of gabapentin on auditory temporal processing in the gerbil model. Psychometric functions were collected for different test paradigms. (A) "Gap detection": The detection of a gap in the middle of a 800 msec broadband noise pulse was determined either at 15 or at 30 dB SL. (B) "Forward masking": The detection of a 20 msec probe stimulus following 2.5 msec after a 400 msec 40 dB SPL masker was determined with masker and probe frequency at 2.85 kHz. The effect of gabapentin was evaluated by collecting gap detection and forward masking functions before, during, and after treating gerbils with gabapentin doses of 115 or 350 mg/kg/day administered via drinking water. Data under different experimental conditions were collected for groups of 3 to 5 young (<2 years) and 6 to 10 old (>2 years) gerbils. Two-way analyses of variance for the factors age groups and treatment groups with subsequent pairwise comparisons for significant effects were used for the statistical evaluation of the data. For gap detection, mean thresholds were significantly increased in the group of old as compared with the young gerbils at 30 dB SL (young 2.0 msec; old 3.2 msec) and at 15 dB SL (young 2.9 msec; old 9.1 msec). Gabapentin had no significant effect on gap detection, and there was no significant interaction between age group and gabapentin treatment. Mean thresholds in the forward masking paradigm were significantly elevated in old (45.5 dB SPL) as compared with young (35.0 dB SPL) gerbils. Overall, gabapentin had no significant effect on masked thresholds; however, there was a significant interaction between treatment and age. Subsequent pairwise comparisons revealed no significant effect on masked thresholds in old gerbils but showed significantly elevated thresholds of young gerbils during 350 mg/kg gabapentin (38.3 dB SPL) compared with thresholds obtained in young gerbils before (32.3 dB SPL) and after (33.5 dB SPL) treatment. Gabapentin did not exert a therapeutic effect on impaired gap detection and forward masking in old gerbils. The lack of an effect of gabapentin on impaired auditory temporal processing in old gerbils and the finding of elevated masked thresholds in young gerbils can be reconciled with reports of only moderate GABAergic effects compared with other drugs (e.g., comparing elevation of GABA levels in the brain by gabapentin and vigabatrin) and effects due to binding of gabapentin to alpha-2-delta units of voltage-gated calcium channels.

When a short signal tone is presented after a noise or tone masker, the threshold for detecting the signal is raised the smaller the gap duration between the masker and the signal is. This phenomenon is termed forward masking and refers to the fact that a masker affects the signal threshold when both are presented in a non-simultaneous, consecutive manner. With increasing temporal separation, signal threshold usually drops to performance in silence when the gap is in the region of hundreds of milliseconds. As a possible explanation for forward masking, mainly two different mechanisms have been discussed in the literature: (i) continuation or persistence of neural activity (e.g., Plomp 1964; Oxenham and Moore 1994), referring to temporal integration of neural activity at presumably higher stages than the auditory nerve; (ii) neural adaptation (e.g., Duifhuis 1973; Nelson and Swain 1996), assuming adaptation at various levels of the auditory pathway (including high levels). A third possible source for interaction of masker and signal is linked to the ringing of the auditory filters but is generally assumed to be negligible for signal frequencies of 1 kHz or higher (e.g., Vogten 1978). It is still unclear whether temporal integration or adaptation can better account for forward masking in various stimulus configurations (Oxenham 2001), nor have both mechanisms been compared directly in a common modeling framework to investigate their relation. The current study compares two well established models of temporal processing in the auditory system using a unified modeling framework: (i) the temporal-window model (e.g., Oxenham and Moore 1994) representing a temporal-integration mechanism and (ii) the adaptation-loop model (e.g., Dau et al. 1996) as the representative for the adaptation mechanism. The unified modeling framework shares a compressive, non-linear auditory filter stage and a template-based (optimal detector) decision stage. The question is, whether the temporal-window model and the adaptation-loop model can be considered

Robust sound source localization is performed by the human auditory system even in challenging acoustic conditions and in previously unencountered, complex scenarios. Here a computational binaural localization model is proposed that possesses mechanisms for handling of corrupted or unreliable localization cues and generalization across different acoustic situations. Central to the model is the use of interaural coherence, measured as interaural vector strength (IVS), to dynamically weight the importance of observed interaural phase (IPD) and level (ILD) differences in frequency bands up to 1.4 kHz. This is accomplished through formulation of a probabilistic model in which the ILD and IPD distributions pertaining to a specific source location are dependent on observed interaural coherence. Bayesian computation of the direction-of-arrival probability map naturally leads to coherence-weighted integration of location cues across frequency and time. Results confirm the model's validity through statistical analyses of interaural parameter values. Simulated localization experiments show that even data points with low reliability (i.e., low IVS) can be exploited to enhance localization performance. A temporal integration length of at least 200 ms is required to gain a benefit; this is in accordance with previous psychoacoustic findings on temporal integration of spatial cues in the human auditory system.

A critical review of studies of temporal resolution in listeners with cochlear hearing impairment is presented with the aim of assessing evidence for suprathreshold deficits. Particular attention is paid to the roles of variables-such as stimulus audibility, overall stimulus level, and participant's age-which may complicate the interpretation of experimental findings in comparing the performance of hearing-impaired (HI) and normal-hearing (NH) listeners. On certain temporal tasks (e.g., gap detection), the performance of HI listeners appears to be degraded relative to that of NH listeners when compared at equal SPL (sound pressure level). For other temporal tasks (e.g., forward masking), HI performance is degraded relative to that of NH listeners when compared at equal sensation level. A relatively small group of studies exists, however, in which the effects of stimulus audibility and level (and occasionally participant's age) have been controlled through the use of noise-masked simulation of hearing loss in NH listeners. For some temporal tasks (including gap-detection, gap-duration discrimination, and detection of brief tones in modulated noise), the performance of HI listeners is well reproduced in the results of noise-masked NH listeners. For other tasks (i.e., temporal integration), noise-masked hearing-loss simulations do not reproduce the results of HI listeners. In three additional areas of temporal processing (duration discrimination, detection of temporal modulation in noise, and various temporal-masking paradigms), further studies employing control of stimulus audibility and level, as well as age, are necessary for a more complete understanding of the role of suprathreshold deficits in the temporal-processing abilities of HI listeners.

Temporal integration in the A1 acoustic receptor cell of noctuid moths (Lepidoptera: Noctuidae) was studied. This was done by recording from the auditory nerve of Spodoptera littoralis and Noctua pronuba while stimulating with short-duration tone pulses. Consistent with previous experiments of the same kind, a decrease in threshold was observed with increasing stimulus duration. These threshold improvements, however, were larger than expected from an energy detector model of the receptor based on previous experiments with double clicks. This difference was analysed and could be attributed to a bias introduced by the choice of threshold criterion. If a fixed number of spikes elicited per stimulation is used as criterion, this will tend to lower the measured thresholds for long durations because for long stimuli, more time is available for accumulation of the spikes needed to exceed the criterion. It appears that temporal integration in the noctuid ear can be characterised by different time constants. One, termed the intrinsic time constant, is measured in the double-click experiments and provides information about the temporal integration and resolution within the receptor cell. Behavioural time constants, on the other hand, characterise the temporal integration reflected in the behaviour of the animals.

The present study investigated whether and to which extent temporal integration in bats is influenced by echolocation behavior. One way to quantify temporal integration is to measure the detection threshold for a pair of short tone pips as a function of the temporal separation between the pips. To asses the effect of preceding sonar emission on temporal integration in the bat, Megaderma lyra, the detection thresholds of identical subjects were measured in a passive as well as in an active paradigm. In the passive paradigm, the presentation of the pip pairs was independent of the bats' sonar emissions; in the active paradigm, the presentation was triggered by the bats' sonar emissions. In both cases, the bats showed a very short integration time in the range of 100-200 micros. Moreover, the comparison of the active and passive results within each bat revealed no systematic differences in the two measuring paradigms. These results indicate that temporal integration is not influenced by echolocation. Simulations with a computer model of cochlear filtering based on measurements of M. lyra cochlear tuning suggest that the perceptual temporal integration is dominated by the integration of the cochlear filters.

Recent research on temporal resolution indicates that a person can listen using a temporal window with a time constant of less than 10 ms. A basic question is how information from these brief “looks” is combined and processed. The initial focus is on the old problem of temporal integration and data are reported from an experiment similar to Zwislocki's two-click experiment [J. Zwislocki, J. Acoust. Soc. Am. 32, 1046–1059 (1960)]. The data are well described by assuming true integration for brief click separations and by assuming two independent looks for separations longer than approximately 10 ms. Thus the data are more consistent with multiple looks than with true, long-duration temporal integration. To account for more general “integration” phenomena, a simple multiple-look strategy is compared with neural summation using spike data recorded from the auditory nerve of chinchilla for CF tones. The decision statistic is either an optimally weighted combination of the spike count from contiguous short bins (looks) or the total spike count summed over the duration of the tone. The time-intensity trading functions (threshold for d′ = I versus duration) for these schemes are very similar. This demonstrates, consistent with intuition, that a multiple-look scheme can show integration-like behavior and that such behavior does not imply true integration. [Work supported by NS12125.]

Previous research in the visual domain suggests that exogenous attention in form of peripheral cueing increases spatial but lowers temporal resolution. It is unclear whether this effect transfers to other sensory modalities. Here, we tested the effects of exogenous attention on temporal and spectral resolution in the auditory domain. Eighteen young, normal-hearing adults were tested in both gap and frequency change detection tasks with exogenous cuing. Benefits of valid cuing were only present in the gap detection task while costs of invalid cuing were observed in both tasks. Our results suggest that exogenous attention in the auditory system improves temporal resolution without compromising spectral resolution.

The visual system is known to integrate sensory information across both space and time, but these dimensions are often studied separately. Here we provide novel behavioural evidence for an early integration over space and time, and propose a computational model of this integration that is biologically plausible. We designed a controlled task that forces human participants to integrate information over both space and time to perform well. Stimuli were temporally segmented rings of oriented elements and participants had to detect a missing element in the ring. We found that temporal integration was enhanced when successive visual events were temporally proximate, spatially aligned to form a continuous contour, but also, and more surprisingly, when they were brief. Notably, the spatial effects on integration are temporally asymmetric: integration is facilitated when more events are presented earlier in the sequence, and even more so when they form a collinear contour. These findings indicate that temporal integration is sensitive to both the spatial configuration and the number of visual events presented over time, supporting a continuous rather than discrete process at early visual stages. All of these results are well accounted for by a computational model in which temporal integration arises from the overlap of internal signals generated by individual visual events. These signals are shaped by a spatially and temporally tuned divisive normalisation mechanism and integrated via coincidence detection. Predictions from this model match human performance in seminal past work as well as novel stimulus displays, offering an account of how spatio-temporal interactions determine what we perceive and when.

Subjects judged the loudness of tones (Experiment 1) and of bursts of noise (Experiment 2) that varied in intensity and duration as well as in mode of presentation (monaural vs. binaural). Both monaural and binaural loudness, for both types of signals, obeyed the bilinear-interaction prediction of the classic temporal integration model. The loudness of short tones grows as a power function of both intensity and duration with different exponents for the two factors (.2 and .3, respectively). The loudness of wide-band noises grows as a power function of duration (with an exponent of approximately .6) but not of sound pressure. For tones, binaural summation was constant but fell short of full additivity. For noises, summation changed across level and duration. Temporal summation followed the same course for monaural and binaural tonal stimuli but not for noise stimuli. Notwithstanding these differences between tone and noise, we concluded that binaural and temporal summation are independently operating integrative networks within the auditory system. The usefulness of establishing the underlying metric structure for temporal summation is emphasized.

Temporal integration at equiluminance and chromatic adaptation

Psychometric functions were determined for the detection of temporal gaps in sinusoidal signals at center frequencies between 0.2 and 2.0 kHz. A continuous notched-noise masker was used to restrict listening to the signal frequency region. The gap always started when the signal was at a positive-going zero crossing. There were three different conditions for the starting phase of the signal at the termination of the gap. In the standard-phase condition the signal restarted at a positive-going zero crossing, in the reversed-phase condition at a negative-going zero crossing, and in the preserved-phase condition at the phase the signal would have had if the gap had not been present. In the standard-phase and reversed-phase conditions the psychometric functions were nonmonotonic, showing oscillations with a period equal to that of the signal; maxima in the functions for the standard-phase condition coincided with minima in the functions for the reversed-phase condition, and vice versa. In the preserved-phase condition the psychometric functions were monotonic and the 75% points were roughly independent of center frequency, having a value of about 5 ms. The general form of the results can be modeled by a filter bank followed by a square-law device and a temporal integrator, but good agreement between the data and the model could not be attained across the whole range of gap durations. The deviations between data and model suggest that subjects are sensitive to the brief transitions in phase (or, equivalently, in frequency) in some conditions.

Two successful noise maskers, A and B, are presented prior to a click signal. In two separate forward masking experiments each of these maskers is presented alone in the same temporal relationship to the click as in the two masker condition. The levels of the single maskers are adjusted so that each alone produces the same amount of masking of the click. How much need the signal be increased to achieve threshold when the noises are presented in succession? If the auditory system were both additive and linear, a 3‐dB increment would be required. If the effects of the maskers are additive at the time the signal occurs but single intensity is compressed, the signal level at threshold must be more than doubled. Empirically we find that the signal increases by about 10 dB. Additivity is shown in a separate experiment by adding a third masker C and finding that A and C produce the same masking effect as B and C. The results of these experiments are consistent with the hypothesis that the auditory system is additive but nonlinear. [Work supported by NIH.]

Factors affecting predicted speech intelligibility with cochlear implants in an auditory model for electrical stimulation

A Brief History of SHAR.- Structures, Mechanisms and Energetics in Temporal Processing.- The Human Auditory Cortex: In Search of the Flying Dutchman.- From Cajal to the Connectome: Building a Neuroanatomical Framework for Understanding the Auditory System.- Recording from Hair Cells.- Three Decades of Tinnitus Related Research.- The Sense of Hearing in Fishes.- A Quarter-Century's Perspective on a Psychoacoustical Approach to Loudness.- Nonsyndromic Deafness: It Ain't Necessarily So.- Evolving Mechanosensory Hair Cells to Hearing Organs by Altering Genes and Their Expression.- The Implications of Discharge Regularity-My Forty-Year Peek into the Vestibular System.- Aging, Hearing Loss and Speech Recognition: Stop Shouting, I Can't Understand You.- Cochlear Mechanics, Otoacoustic Emissions and Medial Olivocochlear Efferents: 20 Years of Advances and Controversies Along with Areas Ripe for New Work.- Examining Fish in the Sea: A European Perspective on Fish Hearing Experiments.- The Behavioral Study of Mammalian Hearing.- Hearing in Insects: The Why, When and How.- The Cognitive Auditory System.- Fundamentals of Hearing in Amniote Vertebrate.- Directional Hearing in Insects and Other Small Animals: The Physics of Pressure-Difference Receiving Ears.- Cortical Representation of Sound Locations: Distributed Representation by Magnitude and Timing of Neural Spike Patterns.- Mechanisms Underlying the Pitch of Pure and Complex Tones.- Unavoidably Delayed: A Personal Perspective of Twenty Years of Research on a Sound Localization Cue.- Size Matters in Hearing: How the Auditory System Normalizes the Sounds of Speech and Music for Source Size.- A Changing View of the Auditory System Obtained from the Ears of Bats.- From Cave Fish to Pile Driving: A Tail of Fish Bioacoustics.- Current Topics in the Study of Sound Conduction to the Inner Ear.- From Degenerative Debris to Neuronal Tracing: An Anterograde View of Auditory Circuits.- Adventures in Bionic Hearing.- My Dull Deaf Ears: Four Millennia of Acquired Hearing Loss.- What's the Use of Genetics?.- Advances in the Understanding of Binaural Information Processing: Consideration of the Stimulus as Processed.- Temporal Processing: Observations on the Psychophysics and Modeling of Temporal Integration and Temporal Resolution.- Psychoacoustics and Auditory Perception.- APPENDIX: Table of Contents from SHAR volumes 1-49.