Trains Of Noise Bursts Research Articles

Degraded inferior colliculus responses to complex sounds in prenatally exposed VPA rats

BackgroundIndividuals with autism spectrum disorders (ASD) often exhibit altered sensory processing and deficits in language development. Prenatal exposure to valproic acid (VPA) increases the risk for ASD and impairs both receptive and expressive language. Like individuals with ASD, rodents prenatally exposed to VPA exhibit degraded auditory cortical processing and abnormal neural activity to sounds. Disrupted neuronal morphology has been documented in earlier processing areas of the auditory pathway in VPA-exposed rodents, but there are no studies documenting early auditory pathway physiology. Therefore, the objective of this study is to characterize inferior colliculus (IC) responses to different sounds in rats prenatally exposed to VPA compared to saline-exposed rats.MethodsIn vivo extracellular multiunit recordings from the inferior colliculus were collected in response to tones, speech sounds, and noise burst trains.ResultsOur results indicate that the overall response to speech sounds was degraded in VPA-exposed rats compared to saline-exposed controls, but responses to tones and noise burst trains were unaltered.ConclusionsThese results are consistent with observations in individuals with autism that neural responses to complex sounds, like speech, are often altered, and lays the foundation for future studies of potential therapeutics to improve auditory processing in the VPA rat model of ASD.

Near-field discrimination of sound source distance in the rabbit.

The acoustical cues and physiological processing mechanisms underlying the perception of the distance of sound sources are not well understood. To understand the relation between physiology and behavior, a first step is to use an animal model to study distance sensitivity. The goal of these experiments was to establish the capacity of the Dutch-belted rabbit to discriminate between sound sources at two distances. Trains of noise bursts were presented from speakers that were located either directly in front of the rabbit or at a 45 ° angle in azimuth. The reference speaker was positioned at distances of 20, 40, and 60 cm from the subject, and the more distant test speaker was systematically moved to determine the smallest difference in distance that could be reliably discriminated by the subject. Noise stimuli had one of three bandwidths: wideband (0.1-10 kHz), low-pass (0.1-3 kHz), or high-pass (3-10 kHz). The mean stimulus level was 60 dB sound pressure level (SPL) at the location of the rabbit's head, and the level was roved over a 12-dB range from trial to trial to reduce the availability of level cues. An operant one-interval two-alternative non-forced choice task was used, with a blocked two-down-one-up tracking procedure to determine the distance discriminability. Rabbits were consistently able to discriminate two distances when they were sufficiently separated. Sensitivity was better when the reference distance was 60 cm at either azimuth (distance ratio = 1.5) and was worse when the reference distance was 20 cm (distance ratio = 2.4 at 0 ° and 1.75 at 45 °).

Degraded speech sound processing in a rat model of fragile X syndrome

Fragile X syndrome is the most common inherited form of intellectual disability and the leading genetic cause of autism. Impaired phonological processing in fragile X syndrome interferes with the development of language skills. Although auditory cortex responses are known to be abnormal in fragile X syndrome, it is not clear how these differences impact speech sound processing. This study provides the first evidence that the cortical representation of speech sounds is impaired in Fmr1 knockout rats, despite normal speech discrimination behavior. Evoked potentials and spiking activity in response to speech sounds, noise burst trains, and tones were significantly degraded in primary auditory cortex, anterior auditory field and the ventral auditory field. Neurometric analysis of speech evoked activity using a pattern classifier confirmed that activity in these fields contains significantly less information about speech sound identity in Fmr1 knockout rats compared to control rats. Responses were normal in the posterior auditory field, which is associated with sound localization. The greatest impairment was observed in the ventral auditory field, which is related to emotional regulation. Dysfunction in the ventral auditory field may contribute to poor emotional regulation in fragile X syndrome and may help explain the observation that later auditory evoked responses are more disturbed in fragile X syndrome compared to earlier responses. Rodent models of fragile X syndrome are likely to prove useful for understanding the biological basis of fragile X syndrome and for testing candidate therapies.

Effects of the stimulus spectrum on temporal weighting of binaural differences

The influence, or “perceptual weight” of binaural information typically varies over the duration of a brief sound, as characterized by the temporal weighting function (TWF). Here, TWFs were measured for binaural lateralization of Gabor click trains (GCT) varying in carrier frequency from 1 to 8 kHz, and of broadband noise-burst trains (NBT) with repeated (“frozen”) or newly sampled (“fresh”) noise across bursts. Interclick intervals (ICI) ranged from 2 to 10 ms. On each of many trials, human listeners judged the lateral position of a singly presented GCT or NBT, and indicated the position on a touch-sensitive display. Lateral positions varied with the overall interaural time (ITD, ranging +/− 500 µs) and level (ILD, ranging +/−5 dB) differences applied to each stimulus. Additional random variation in ITD (+/−100 µs) and ILD (+/−2dB) was applied independently to each click within a train. TWFs were calculated by multiple linear regression of normalized position judgments onto the individual click ITD and ILD values, and indicated large ICI-dependent weights on the initial click (“onset dominance”), elevated weights near offset, and lower weights for interior clicks. Flatter TWFs with reduced onset/offset weights were observed for “fresh” NBT stimuli than for GCT or “frozen” NBT stimuli. The results corroborate previous reports of temporal asymmetries in the binaural processing of periodic stimuli across frequency. [Work supported by R01 DC011548.]

Depth-Dependent Temporal Response Properties in Core Auditory Cortex

The computational role of cortical layers within auditory cortex has proven difficult to establish. One hypothesis is that interlaminar cortical processing might be dedicated to analyzing temporal properties of sounds; if so, then there should be systematic depth-dependent changes in cortical sensitivity to the temporal context in which a stimulus occurs. We recorded neural responses simultaneously across cortical depth in primary auditory cortex and anterior auditory field of CBA/Ca mice, and found systematic depth dependencies in responses to second-and-later noise bursts in slow (1-10 bursts/s) trains of noise bursts. At all depths, responses to noise bursts within a train usually decreased with increasing train rate; however, the rolloff with increasing train rate occurred at faster rates in more superficial layers. Moreover, in some recordings from mid-to-superficial layers, responses to noise bursts within a 3-4 bursts/s train were stronger than responses to noise bursts in slower trains. This non-monotonicity with train rate was especially pronounced in more superficial layers of the anterior auditory field, where responses to noise bursts within the context of a slow train were sometimes even stronger than responses to the noise burst at train onset. These findings may reflect depth dependence in suppression and recovery of cortical activity following a stimulus, which we suggest could arise from laminar differences in synaptic depression at feedforward and recurrent synapses.

Lateralization of noise-burst trains based on onset and ongoing interaural delays

The lateralization of 250-ms trains of brief noise bursts was measured using an acoustic pointing technique. Stimuli were designed to assess the contribution of the interaural time delay (ITD) of the onset binaural burst relative to that of the ITDs in the ongoing part of the train. Lateralization was measured by listeners' adjustments of the ITD of a pointer stimulus, a 50-ms burst of noise, to match the lateral position of the target train. Results confirmed previous reports of lateralization dominance by the onset burst under conditions in which the train is composed of frozen tokens and the ongoing part contains multiple ambiguous interaural delays. In contrast, lateralization of ongoing trains in which fresh noise tokens were used for each set of two alternating (left-leading/right-leading) binaural pairs followed the ITD of the first pair in each set, regardless of the ITD of the onset burst of the entire stimulus and even when the onset burst was removed by gradual gating. This clear lateralization of a long-duration stimulus with ambiguous interaural delay cues suggests precedence mechanisms that involve not only the interaural cues at the beginning of a sound, but also the pattern of cues within an ongoing sound.

Auditory stimulus repetition effects on cortical hemoglobin oxygenation: a near-infrared spectroscopy investigation

The cortical response to repeated sensory stimuli plateaus (or declines) as repetition frequencies increase beyond 2-8 Hz. This study examined the underlying changes in cortical oxygenated and deoxygenated hemoglobin associated with this phenomenon using near-infrared spectroscopy. The optical signal was measured from 11 healthy volunteers listening to noise-burst trains presented at 2, 10, and 35 Hz. In a bilateral region consistent with the posterior superior temporal gyrus there was an inverse relationship between deoxyhemoglobin concentration change and stimulus frequency: greatest at 2 Hz, intermediate at 10 Hz, and smallest at 35 Hz. These findings provide preliminary support for a relationship between the perceptual characteristics of auditory stimuli and modulation of cortical oxygenation as measured via an emerging neuromonitoring technique.

Onset dominance in lateralization.

Saberi and Perrott [Acustica 81, 272-275 (1995)] found that the in-head lateralization of a relatively long-duration pulse train could be controlled by the interaural delay of the single pulse pair that occurs at onset. The present study examined this further, using an acoustic pointer measure of lateralization, with stimulus manipulations designed to determine conditions under which lateralization was consistent with the interaural onset delay. The present stimuli were wideband pulse trains, noise-burst trains, and inharmonic complexes, 250 ms in duration, chosen for the ease with which interaural delays and correlations of select temporal segments of the stimulus could be manipulated. The stimulus factors studied were the periodicity of the ongoing part of the signal as well as the multiplicity and ambiguity of interaural delays. The results, in general, showed that the interaural onset delay controlled lateralization when the steady state binaural cues were relatively weak, either because the spectral components were only sparsely distributed across frequency or because the interaural time delays were ambiguous. Onset dominance can be disrupted by sudden stimulus changes within the train, and several examples of such changes are described. Individual subjects showed strong left-right asymmetries in onset effectiveness. The results have implications for understanding how onset and ongoing interaural delay cues contribute to the location estimates formed by the binaural auditory system.

Sudden changes in simulated room acoustics influence echo suppression

Listeners seated in an anechoic chamber discriminated the direction of the lag noise burst within a lead-lag pair. The lead loudspeakers were 42° or 48° left of midline, and the lag loudspeakers were 35° or 55° right. A train of noise bursts, during which the lag was always 45° right, preceded the test noise in some conditions. In the first experiment the lead was broadband (‘‘B’’) and lag was either high-(‘‘H’’) or low-pass (‘‘L’’) filtered. Discrimination of the test noise location was poorer when the B-L (lead-lag) test was preceded by a B-L train than when the test noise was presented in isolation, suggesting that echo suppression built up during the repetitious train. By comparison, discrimination of the B-L test was unaffected by a B-H train, indicating that any buildup of suppression during the train was broken when the lag’s frequency shifted from H to L, which simulated a change in absorption of echoes by room surfaces. A second experiment in which the intensity of the lag varied between train and test produced similar results. The data are consistent with an interpretation in which echo suppression is temporarily broken when listeners’ built-up expectations about room acoustics are violated. [Work supported by NIH DC01625.]