White Noise Bursts Research Articles

The Effect of Hearing Loss on Localization of Amplitude-Panned and Physical Sources.

Clinics are increasingly turning toward using virtual environments to demonstrate and validate hearing aid fittings in "realistic" listening situations before the patient leaves the clinic. One of the most cost-effective and straightforward ways to create such an environment is through the use of a small speaker array and amplitude panning. Amplitude panning is a signal playback method used to change the perceived location of a source by changing the level of two or more loudspeakers. The perceptual consequences (i.e., perceived source width and location) of amplitude panning have been well-documented for listeners with normal hearing but not for listeners with hearing impairment. The purpose of this study was to examine the perceptual consequences of amplitude panning for listeners with hearing statuses from normal hearing through moderate sensorineural hearing losses. Listeners performed a localization task. Sound sources were broadband 4 Hz amplitude-modulated white noise bursts. Thirty-nine sources (14 physical) were produced by either physical loudspeakers or via amplitude panning. Listeners completed a training block of 39 trials (one for each source) before completing three test blocks of 39 trials each. Source production method was randomized within block. Twenty-seven adult listeners (mean age 52.79, standard deviation 27.36, 10 males, 17 females) with hearing ranging from within normal limits to moderate bilateral sensorineural hearing loss participated in the study. Listeners were recruited from a laboratory database of listeners that consented to being informed about available studies. Listeners indicated the perceived source location via touch screen. Outcome variables were azimuth error, elevation error, and total angular error (Euclidean distance in degrees between perceived and correct location). Listeners' pure-tone averages (PTAs) were calculated and used in mixed-effects models along with source type and the interaction between source type and PTA as predictors. Subject was included as a random variable. Significant interactions between PTA and source production method were observed for total and elevation errors. Listeners with higher PTAs (i.e., worse hearing) did not localize physical and panned sources differently whereas listeners with lower PTAs (i.e., better hearing) did. No interaction was observed for azimuth errors; however, there was a significant main effect of PTA. As hearing impairment becomes more severe, listeners localize physical and panned sources with similar errors. Because physical and panned sources are not localized differently by adults with hearing loss, amplitude panning could be an appropriate method for constructing virtual environments for these listeners.

Richardson's ground squirrel (Urocitellus richardsonii) alarm call receivers experience an auditory continuity illusion.

Auditory continuity illusions are perceptual illusions in which receivers perceive an auditory signal as continuous when part of the signal has been removed or obfuscated by a louder noise. Richardson's ground squirrels (Urocitellus richardsonii) communicate alarm acoustically in noisy natural settings. Thus, we tested whether they experience an auditory continuity illusion by presenting free-living squirrels with repeated whistle alarm calls within which every second syllable remained unmanipulated, was partially obfuscated by relatively brief (25 ms) bursts of white noise, or partially obfuscated by longer duration (100 ms) white noise bursts. Field playbacks of alarm calls with brief white noise bursts failed to elicit increased vigilance from receivers relative to unmanipulated calls, whereas calls with longer white noise bursts elicited increased vigilance relative to the other 2 call types. As with previous empirical demonstrations of the auditory continuity illusion in vertebrates, relatively short obfuscating noise resulted in receivers perceiving each syllable as a whole, while longer obfuscating noise caused receivers to perceive the beginning and end of each manipulated syllable as 2 distinct syllables, increasing the perceived syllable repetition rate. These results reveal that Richardson's ground squirrels experience an auditory continuity illusion allowing the extraction of the rate of syllable repetition from conspecific repeated alarm calls in the face of short duration environmental noise. Selection has acted upon receivers to refine the cognitive mechanisms underlying signal perception, facilitating the extraction of information masked by environmental noise. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Neural Responses to Signals for Behavior Change: Greater Within‐Person Variability is Associated With Risk Factors for Substance Dependence

An impaired ability to change behavior in the face of cues indicating a need for change is one means of defining risk for substance dependence. The present study used a cognitive task administered in a laboratory as a model of this process. It focused on 2 known and related correlates of risk (conduct disorder, borderline personality disorder) and examined their associations with reactivity to cues requesting a change in motor behavior. A total of 224 teenagers, 14 to 19years of age, performed a task during which white noise bursts were used to cue a requirement to reverse the mapping of right and left key press responses onto high- and low-frequency pure tones during a subsequent trial block. The amplitude of the P300 electroencephalographic (EEG) response to each cue was summarized by calculating its across-trial average as well as its intertrial variability (ITV). In addition, the number of motor response reversal failures (perseveration errors) was calculated. The ITV of the P300 response to cues for behavior change was superior to its average amplitude in revealing associations with risk: It was significantly greater among teenagers with more conduct problems and more borderline personality disorder symptoms in comparison with their less-affected peers. ITV was also positively correlated with perseveration errors. No group differences were found in P300 amplitude averaged over trials. The findings suggest that the measurement of intertrial variability in brain activity may be more valuable than the average level for revealing neurophysiological differences associated with impulsivity and personality risk factors for dependence. EEG measures may be particularly valuable in this context because they offer superior temporal resolution and signal-to-noise characteristics.

Synchronisation of Neural Oscillations and Cross-modal Influences.

At any given moment, we receive multiple signals from our different senses. Prior research has shown that signals in one sensory modality can influence neural activity and behavioural performance associated with another sensory modality. Recent human and nonhuman primate studies suggest that such cross-modal influences in sensory cortices are mediated by the synchronisation of ongoing neural oscillations. In this review, we consider two mechanisms proposed to facilitate cross-modal influences on sensory processing, namely cross-modal phase resetting and neural entrainment. We consider how top-down processes may further influence cross-modal processing in a flexible manner, and we highlight fruitful directions for further research.

Comparison of auditory spatial bisection and minimum audible angle in front, lateral, and back space

Although vision is important for calibrating auditory spatial perception, it only provides information about frontal sound sources. Previous studies of blind and sighted people support the idea that azimuthal spatial bisection in frontal space requires visual calibration, while detection of a change in azimuth (minimum audible angle, MAA) does not. The influence of vision on the ability to map frontal, lateral and back space has not been investigated. Performance in spatial bisection and MAA tasks was assessed for normally sighted blindfolded subjects using bursts of white noise presented frontally, laterally, or from the back relative to the subjects. Thresholds for both tasks were similar in frontal space, lower for the MAA task than for the bisection task in back space, and higher for the MAA task in lateral space. Two interpretations of the results are discussed, one in terms of visual calibration and the use of internal representations of source location and the other based on comparison of the magnitude or direction of change of the available binaural cues. That bisection thresholds were increased in back space relative to front space, where visual calibration information is unavailable, suggests that an internal representation of source location was used for the bisection task.

Disentangling sensorimotor and cognitive cardioafferent effects: A cardiac-cycle-time study on spatial stimulus-response compatibility

Cardiac-cycle-time effects are attributed to variations in baroreceptor (BR) activity and have been shown to impinge on subcortical as well as cortical processes. However, cognitive and sensorimotor processes mediating voluntary responses seem to be differentially affected. We sought to disentangle cardiac-cycle-time effects on subcortical and cortical levels as well as sensorimotor and cognitive processes within a spatial stimulus-response-compatibility paradigm employing startling stimuli of different modalities. Air-puffs and white noise-bursts were presented unilaterally during either cardiac systole or diastole while bilateral startle EMG responses were recorded. Modality, laterality and cardiac-cycle-time were randomly varied within-subjects. Cognitive and sensorimotor stimulus-response-compatibility was orthogonally varied between-subjects: Participants (N = 80) responded to the stimuli via left/right button-push made with either the contra- or ipsilateral hand (sensorimotor compatibility) on either the ipsi- or contralateral button (cognitive compatibility). We found that sensorimotor compatible reactions were speeded during systole whereas sensorimotor incompatible ones were prolonged. This effect was independent of cognitive compatibility and restricted to auditory stimuli. Startle was inhibited during systole irrespective of modality or compatibility. Our results demonstrate how differential cardiac-cycle-time effects influence performance in conflict tasks and further suggest that stimulus-response-compatibility paradigms offer a viable method to uncover the complex interactions underlying behavioral BR effects.

Phasic alerting enhances spatial orienting in healthy aging but not in mild cognitive impairment.

Previous studies in young adults have demonstrated strong functional links between phasic alerting and exogenous orienting. The present study examined changes in the dynamic interaction between these attentional networks in healthy aging and in amnestic mild cognitive impairment. Healthy young adults, healthy older adults, and patients with amnestic mild cognitive impairment (MCI) were asked to identify as quickly as possible the color of a target stimulus that appeared within one of 2 peripheral boxes. Orienting was manipulated by a brief flashing of the same (valid cue) or opposite (invalid cue) box in which the target subsequently appeared. Alerting was manipulated by presenting an auditory white noise burst simultaneously with the visual orienting cue on half of the trials. All 3 groups displayed significant alerting and orienting effects but differed in the nature of the interaction between alerting and orienting. As expected, young adults displayed increased orienting under high alerting conditions through a selective enhancement of validly cued targets. While older adults displayed a greater effect of alerting on orienting compared to young adults, MCI patients did not display a significant interaction between attentional networks. Results provide support for the presence of increased compensatory interactions between attentional networks in healthy aging that may be no longer effective with the emergence of clinical symptoms in MCI. The demonstration of qualitatively distinct effects of healthy aging and MCI suggests that behavioral tests of attentional network interactions may serve as cognitive markers in individuals at increased risk for developing AD. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Auditory Perceptual History Is Propagated through Alpha Oscillations.

SummaryPerception is a proactive, “predictive” process, in which the brain relies, at least in part, on accumulated experience to make best guesses about the world to test against sensory data, updating the guesses as new experience is acquired. Using novel behavioral methods, the present study demonstrates the role of alpha rhythms in communicating past perceptual experience. Participants were required to discriminate the ear of origin of brief sinusoidal tones that were presented monaurally at random times within a burst of uncorrelated dichotic white noise masks. Performance was not constant but varied with delay after noise onset in an oscillatory manner at about 9 Hz (alpha rhythm). Importantly, oscillations occurred only for trials preceded by a target tone to the same ear, either on the previous trial or two trials back. These results suggest that communication of perceptual history generates neural oscillations within specific perceptual circuits, strongly implicating behavioral oscillations in predictive perception and with formation of working memory.

Age differences in electrocortical reactivity to fearful faces following aversive conditioning in youth

Although biases in the processing of affectively salient stimuli are thought to increase risk for psychopathology across the lifespan, questions remain regarding how these biases develop. The current study tested an aversive conditioning model for the development of children’s sensitivity in detecting fearful faces at varying levels of emotional intensity and their facilitated attention to fearful faces assessed via the late positive potential (LPP) event-related potential component. Participants (N = 144, ages 7–11 years) were randomly assigned to one of three conditions: an active training condition in which an 85-dB white noise burst was paired with fearful faces, an active control condition in which the white noise was presented randomly throughout the task, and a no-sound condition. Children completed a separate task in which they viewed happy, sad, and fearful child faces at varying levels of emotional intensity while electroencephalography (EEG) was recorded. Although there were no conditioning group differences in children’s sensitivity in detecting facial displays of emotion, there were group differences in LPP magnitude that were moderated by children’s age. Among younger children, those in the active conditioning group exhibited smaller LPP amplitudes to high-intensity fearful faces than children in the control groups. However, among older youth, those in the active conditioning group exhibited larger LPP amplitudes to high-intensity fearful faces than children in the control groups. These findings provide insight into how attentional biases may develop in children and how period of development may influence these patterns.

Where did that noise come from? Memory for sound locations is exceedingly eccentric both in front and in rear space.

Few studies have examined the stability of the representation of the position of sound sources in spatial working memory. The goal of this study was to verify whether the memory of sound position declines as maintenance time increases. In two experiments, we tested the influence of the delay between stimulus and response in a sound localization task. In Experiment 1, blindfolded participants listened to bursts of white noise originating from 16 loudspeakers equally spaced in a 360-degree circular space around the listener in such a way that the nose was aligned to the zero-degree coordinate. Their task was to indicate sounds' position using a digital pointer when prompted at varying delays: 0, 3, and 6s after stimulus offset. In Experiment 2, the task was analogous to Exp. 1 with stimulus-response delays of 0 or 10s. Results of the two experiments show that increasing stimulus-response delays up to 10s do not impair sound localization. Participants systematically overestimated the eccentricity of the auditory stimulus by shifting their responses either toward the 90-degree coordinate, in alignment with the right ear, or toward the 270-degree coordinate, in alignment with the left ear. Such bias was analogous in the front and in the rear azimuthal space and was only marginally influenced by the delay conditions. We conclude that the representation of auditory space in working memory is stable, but directionally biased with systematic overestimation of eccentricity.

Interactions between egocentric and allocentric spatial coding of sounds revealed by a multisensory learning paradigm

Although sound position is initially head-centred (egocentric coordinates), our brain can also represent sounds relative to one another (allocentric coordinates). Whether reference frames for spatial hearing are independent or interact remained largely unexplored. Here we developed a new allocentric spatial-hearing training and tested whether it can improve egocentric sound-localisation performance in normal-hearing adults listening with one ear plugged. Two groups of participants (N = 15 each) performed an egocentric sound-localisation task (point to a syllable), in monaural listening, before and after 4-days of multisensory training on triplets of white-noise bursts paired with occasional visual feedback. Critically, one group performed an allocentric task (auditory bisection task), whereas the other processed the same stimuli to perform an egocentric task (pointing to a designated sound of the triplet). Unlike most previous works, we tested also a no training group (N = 15). Egocentric sound-localisation abilities in the horizontal plane improved for all groups in the space ipsilateral to the ear-plug. This unexpected finding highlights the importance of including a no training group when studying sound localisation re-learning. Yet, performance changes were qualitatively different in trained compared to untrained participants, providing initial evidence that allocentric and multisensory procedures may prove useful when aiming to promote sound localisation re-learning.

Self-Resemblance Modulates Processing of Socio-Emotional Pictures in a Context-Sensitive Manner

Abstract. Relevance of emotional information varies with self-involvement. The current study was undertaken to test whether subtle facial self-resemblance is sufficient to affect attentional and affective processing of complex socio-emotional pictures. Faces digitally manipulated to resemble the participants’ (final sample: N = 21) own versus unfamiliar control faces (form and color morphs) were presented in pictures of emotionally evocative social interactions, that is, threat versus sex scenes. At stimulus onset asynchronies (SOAs) of either 300 ms or 3,000 ms after picture onset, startle responses were elicited by acoustic white noise bursts (50 ms, 105 dB), and recorded at the orbicularis oculi via electromyography (EMG). The majority of participants remained unaware of the morphing manipulation, and awareness did not affect the principal results. As indexed by inhibition of startle at short lead intervals and by picture-evoked heart rate deceleration, facial self-resemblance modulates effects of motivational salience in a context-sensitive way, increasing prepulse inhibition with threat-related, but not erotic cues. Overall, the present study suggests that visual cues of general motivational significance and of self-relevance are integrated in a fast, presumably automatic manner.

Search for Transient Gravitational-wave Signals Associated with Magnetar Bursts during Advanced LIGO’s Second Observing Run

Abstract We present the results of a search for short- and intermediate-duration gravitational-wave signals from four magnetar bursts in Advanced LIGO’s second observing run. We find no evidence of a signal and set upper bounds on the root sum squared of the total dimensionless strain (h rss) from incoming intermediate-duration gravitational waves ranging from 1.1 × 10−22 at 150 Hz to 4.4 × 10−22 at 1550 Hz at 50% detection efficiency. From the known distance to the magnetar SGR 1806–20 (8.7 kpc), we can place upper bounds on the isotropic gravitational-wave energy of 3.4 × 1044 erg at 150 Hz assuming optimal orientation. This represents an improvement of about a factor of 10 in strain sensitivity from the previous search for such signals, conducted during initial LIGO’s sixth science run. The short-duration search yielded upper limits of 2.1 × 1044 erg for short white noise bursts, and 2.3 × 1047 erg for 100 ms long ringdowns at 1500 Hz, both at 50% detection efficiency.

Developmental changes in the perception of audiotactile simultaneity

We charted the developmental trajectory of the perception of audiotactile simultaneity by testing three groups of children (aged 7, 9, and 11 years) and one group of adults. A white noise burst and a tap to the index finger were presented at 1 of 13 stimulus onset asynchronies (SOAs), and the participants were asked to report whether the two stimuli were simultaneous. Compared with adults, 7-year-olds made significantly more simultaneous responses at 9 of the 13 SOAs, whereas 9-year-olds differed from adults at only 2 SOAs. The precision of simultaneity perception was lower, and response errors were higher, in younger children than in adults. The 11-year-olds were adult-like on all measures, thereby demonstrating that judgments about simultaneity for audiotactile stimuli are mature by 11 years. This developmental pattern is similar to that for simultaneity perception for visuotactile stimuli but later than that for audiovisual stimuli. The longer developmental trajectories of the perception of simultaneity between touch and vision and between touch and audition may arise from the need to coordinate and recalibrate between different reference frames and different neural transmission times in each sensory system during body growth; in addition, the ubiquity of audiovisual experience in everyday life may accelerate the development of that modality pairing.

A time-efficient multi-deviant paradigm to determine the effects of gap duration on the mismatch negativity

The insertion of a silent period (or gap) in a frequently occurring standard stimulus elicits a negative-going event-related potential (ERP), called the Deviant-Related Negativity (DRN). This is often studied using a single-deviant paradigm. To study the effects of gaps with multiple durations, a different sequence would be required for each gap. A more time-efficient multi-deviant paradigm has been developed in which stimuli of various gap widths are included in a single sequence. In the present study, 14 young adults watched a silent video while ignoring an auditory sequence. A single run of a multi-deviant sequence was presented in which 6 different rare deviants alternated with a standard stimulus. The standard was a 200-ms white noise burst. The deviants were constructed by inserting a gap in the standard. The duration of the 6 gaps ranged from 2 to 40 ms. Participants were also presented with multiple runs of single-deviant sequences. Each of the 3 deviants was run in a separate sequence. The amplitude of the DRN elicited by the deviant increased as gap duration became longer, although it did plateau for the longer duration gaps. The amplitudes of the DRNs were larger in the single-deviant paradigm than in the multi-deviant paradigm. However, the difference was only significant when the mastoid reference was used. Behavioural data showed a mean d’ of 2.1 for the 5-ms gap. None of the participants were able to detect the 2-ms gap. There was no correlation between d’ and the DRN amplitude. Still, the effects of gap duration on the amplitude of the DRN were similar between the single and multi-deviant sequences. This makes the multi-deviant paradigm a possible time-saving alternative to the single-deviant paradigm.

Relationship between localization acuity and spatial release from masking

Spatial Release from Masking (SRM) is defined as the ability to obtain better Speech Recognition Thresholds (SRTs) when the masking sounds are spatially separated from the target sound. Localization refers our ability identify the direction of the sound and localization acuity is measured as the difference in locations between the actual and perceived locations. SRM and localization share many common cues on how the task is performed. Here, we present data from young normal hearing on SRM task using Coordinate Response Measure (CRM) sentences and localization acuity using three different noise Gaussian white noise bursts: low pass (1/3 octave wide centered at 500 Hz), high pass (1/3 octave wide centered at 3150 Hz), and broadband (200–5000 Hz). Thirteen loudspeakers (Orb Mod 1), separated by 15 deg in the frontal plane were used to present the stimuli. Initial analyses of the results indicated that, as expected, all the listeners obtained substantial spatial release from masking consistent with the literature, filtering the broadband noise had little effect on localization acuity for listeners with normal hearing. Finally, the relationship between SRM and localization acuity will be discussed.Spatial Release from Masking (SRM) is defined as the ability to obtain better Speech Recognition Thresholds (SRTs) when the masking sounds are spatially separated from the target sound. Localization refers our ability identify the direction of the sound and localization acuity is measured as the difference in locations between the actual and perceived locations. SRM and localization share many common cues on how the task is performed. Here, we present data from young normal hearing on SRM task using Coordinate Response Measure (CRM) sentences and localization acuity using three different noise Gaussian white noise bursts: low pass (1/3 octave wide centered at 500 Hz), high pass (1/3 octave wide centered at 3150 Hz), and broadband (200–5000 Hz). Thirteen loudspeakers (Orb Mod 1), separated by 15 deg in the frontal plane were used to present the stimuli. Initial analyses of the results indicated that, as expected, all the listeners obtained substantial spatial release from masking consistent with the litera...

Evidence of P3a During Sleep, a Process Associated With Intrusions Into Consciousness in the Waking State.

The present study examines processes associated with intrusions into consciousness during an unconscious state, natural sleep. The definition of sleep is still much debated. Almost all researchers agree that sleep onset represents a gradual loss of consciousness of the external environment. For sleep to be beneficial, it needs to remain as undisturbed as possible. Nevertheless, unlike other unconsciousness states, sleep is reversible. For purposes of survival, it is critical that the sleeper be able to “detect” and perhaps become conscious of highly relevant biological or personal information. Therefore, even in sleep, the brain must decide whether a new incoming stimulus is relevant and if so, may require an arousal to wakefulness, or whether it is irrelevant and can be gated to prevent disruption of sleep. Event-related potentials (ERPs) were used to measure the extent processing of auditory stimuli some of which elicited an ERP component, the P3a, in the waking state. The P3a is associated with processes resulting in the interruption of frontal central executive, leading to conscious awareness. Very little research has focused on the occurrence of the P3a during sleep. A multi-feature paradigm was used to examine the processing of a frequently occurring “standard” stimulus and six rarely occurring different “deviant” stimuli during wakefulness, NREM, and REM sleep. A P3a was elicited by novel environmental sounds and white noise bursts in the waking state, replicating previous studies. Other deviant stimuli (changes in pitch, intensity, duration) failed to do so. The ERPs indicated that processing of the stimuli that did not elicit a P3a in wakefulness were much inhibited during both NREM and REM sleep. Surprisingly, those deviants that did elicit a P3a in wakefulness continued to do so in stage N2 and REM sleep. The subject did not, however, awaken. These results suggest processes leading to consciousness in wakefulness may still remain active during sleep possibly allowing subjects to act on potentially highly relevant input. This may also explain how sleep can be reversed if the stimulus input is sufficiently critical.

Development of a Time-Efficient Approach to Measure the Acoustic Impedance of Industrial Insulating Materials

This study presents a development on a time efficient approach to measure the Acoustic Impedance of Industrial Insulating materials using an impedance tube with single moveable microphone and a white noise generator. The standing wave method is used to measure the acoustic properties (absorption coefficient and acoustic impedance) of sound absorbing materials. In order to use a burst of white noise instead of individual stationary sine waves, a signal processing technique was developed. The algorithm is based on the equation of simple harmonic motion, but uses distance as a variable, instead of time. This innovative method allows measuring at frequency resolutions as low as 5 Hz in a reasonably short amount of time. This is an advantage, as the classical standing wave method uses frequency resolutions of one-third of octaves for measurements, as otherwise time would be prohibitive. Experimental results are validated with those measured with the sine wave generator using one-third of octave frequencies by comparing their behaviours.

Elevated physiological arousal is associated with larger but more variable neural responses to small acoustic change in children during a passive auditory attention task

Little is known of how autonomic arousal relates to neural responsiveness during auditory attention. We presented N = 21 5-7-year-old children with an oddball auditory mismatch paradigm, whilst concurrently measuring heart rate fluctuations. Children with higher mean autonomic arousal, as indexed by higher heart rate (HR) and decreased high-frequency (0.15-0.8 Hz) variability in HR, showed smaller amplitude N250 responses to frequently presented (70%), 500 Hz standard tones. Follow-up analyses showed that the modal evoked response was in fact similar, but accompanied by more large and small amplitude responses and greater variability in peak latency in the high HR group, causing lower averaged responses. Similar patterns were also observed when examining heart rate fluctuations within a testing session, in an analysis that controlled for between-participant differences in mean HR. In addition, we observed larger P150/P3a amplitudes in response to small acoustic contrasts (750 Hz tones) in the high HR group. Responses to large acoustic contrasts (bursts of white noise), however, evoked strong early P3a phase in all children and did not differ by high/low HR. Our findings suggest that elevated physiological arousal may be associated with high variability in auditory ERP responses in young children, along with increased responsiveness to small acoustic changes.

Establishing a Critical Framework for the Appraisal of “Noise” in Contemporary Sound Art with Specific Reference to the Practices of Yasunao Tone, Carsten Nicolai and Ryoji Ikeda

Yasunao Tone, Carsten Nicolai and Ryoji Ikeda are three practitioners representative of electronic music and sound-art practices that emerged in the 1990s where sound materials not normally considered musical, such as digital clicks, glitches and bursts of white noise, are prevalent. It is notable that the origins of this body of work lay outside of the established music institutions of academia and the mainstream popular music industry. Practitioners such as these are often associated with particular record labels including Mille Plateaux or Raster-Noton and attempts to coalesce these practices into a single, unified genre have been made by Cascone (2000), Sangild (2004) and Kelly (2009). These assessments however, tend to critique work mainly in technological terms. In contrast, this thesis draws out deeper philosophical concerns relevant to these practices through a critical analysis of materials produced by and about these practitioners, including commercial releases, works, writings and interviews. What emerges from this is that Heidegger's notion of truth as `revealing' and Derrida's critique of phonocentrism can provide a clearer philosophical framework for a consideration of this work. This framework, by extension could be used to critique other sound art or music practices. Moreover, ideas found in Attali's (1985) telling of economic history through music are applied to these practices in order to argue that the use of materials reflects a wider cultural shift away from the notion of value as something quantified, abstract and intrinsic, predominant since the Age of Enlightenment, towards one concerned with the qualitative, contextual and extrinsic. This is related to Kim-Cohen's (2009) advocacy of a conceptual sound art to argue that noise practices represent forms of practice that challenge both notions of absolute music - music primarily understood 'as a numerical sign system' (Kim-Cohen 2009: 40) - and prevailing political-economic structures.