Auditory false perceptions are mediated by psychosis risk factors

Introduction. Auditory hallucinations exist in psychotic disorders as well as the general population. Proneness to hallucinations, as measured by positive schizotypy, predicts false perceptions during an auditory signal detection task (Barkus, Stirling, Hopkins, McKie, & Lewis, 2007). Our aim was to replicate this result and extend it by examining effects of age and sex, both important demographic predictors of psychosis.

Method. A sample of 76 healthy volunteers split into 15-17 years (n = 46) and 19 years plus (n = 30) underwent a signal detection task designed to detect propensity towards false perceptions under ambiguous auditory conditions. Scores on the Unusual Experiences subscale (UE) of the O-LIFE schizotypy scale, IQ, and a measure of working memory were also assessed.

Results. We replicated our initial finding (Barkus et al., 2007): High scores on positive schizotypy were associated with false perceptions. Younger participants who scored highly on positive schizotypy reported significantly more false perceptions compared to other groups (p = .04). Older participants who had had an imaginary friend reported more false perceptions during the signal detection task (p <. 01).

Conclusions. Younger participants seem most vulnerable to the effects of positive schizotypal traits in terms of a signal detection deficit that underlies auditory hallucinations. Schizotypy may have greatest impact closer to the risk period for development of psychotic disorders.

Rapid formation of robust auditory memories: Insights from noise

Before a natural sound can be recognized, an auditory signature of its source must be learned through experience. Here we used random waveforms to probe the formation of new memories for arbitrary complex sounds. A behavioral measure was designed, based on the detection of repetitions embedded in noises up to 4 s long. Unbeknownst to listeners, some noise samples reoccurred randomly throughout an experimental block. Results showed that repeated exposure induced learning for otherwise totally unpredictable and meaningless sounds. The learning was unsupervised and resilient to interference from other task-relevant noises. When memories were formed, they emerged rapidly, performance became abruptly near-perfect, and multiple noises were remembered for several weeks. The acoustic transformations to which recall was tolerant suggest that the learned features were local in time. We propose that rapid sensory plasticity could explain how the auditory brain creates useful memories from the ever-changing, but sometimes repeating, acoustical world. © 2010 Elsevier Inc.

Informational masking in young and elderly listeners for speech masked by simultaneous speech and noise

Three experiments measured the effects of age on informational masking of speech by competing speech. The experiments were designed to minimize the energetic contributions of the competing speech so that informational masking could be measured with no large corrections for energetic masking. Experiment 1 used a "speech-in-speech-in-noise" design, in which the competing speech was presented in noise at a signal-to-noise ratio (SNR) of -4 dB. This ensured that the noise primarily contributed the energetic masking but the competing speech contributed the informational masking. Equal amounts of informational masking (3 dB) were observed for young and elderly listeners, although less was found for hearing-impaired listeners. Experiment 2 tested a range of SNRs in this design and showed that informational masking increased with SNR up to about an SNR of -4 dB, but decreased thereafter. Experiment 3 further reduced the energetic contribution of the competing speech by filtering it into different frequency bands from the target speech. The elderly listeners again showed approximately the same amount of informational masking (4-5 dB), although some elderly listeners had particular difficulty understanding these stimuli in any condition. On the whole, these results suggest that young and elderly listeners were equally susceptible to informational masking. © 2009 Acoustical Society of America.

An analysis of the masking of speech by competing speech using self-report data (L)

Many of the items in the “Speech, Spatial, and Qualities of Hearing” scale questionnaire [S. Gatehouse and W. Noble, Int. J. Audiol.43, 85–99 (2004)] are concerned with speech understanding in a variety of backgrounds, both speech and nonspeech. To study if this self-report data reflected informational masking, previously collected data on 414 people were analyzed. The lowest scores (greatest difficulties) were found for the two items in which there were two speech targets, with successively higher scores for competing speech (six items), energetic masking (one item), and no masking (three items). The results suggest significant masking by competing speech in everyday listening situations.

Auditory gist: Recognition of very short sounds from timbre cues

Sounds such as the voice or musical instruments can be recognized on the basis of timbre alone. Here, sound recognition was investigated with severely reduced timbre cues. Short snippets of naturally recorded sounds were extracted from a large corpus. Listeners were asked to report a target category (e.g., sung voices) among other sounds (e.g., musical instruments). All sound categories covered the same pitch range, so the task had to be solved on timbre cues alone. The minimum duration for which performance was above chance was found to be short, on the order of a few milliseconds, with the best performance for voice targets. Performance was independent of pitch and was maintained when stimuli contained less than a full waveform cycle. Recognition was not generally better when the sound snippets were time-aligned with the sound onset compared to when they were extracted with a random starting time. Finally, performance did not depend on feedback or training, suggesting that the cues used by listeners in the artificial gating task were similar to those relevant for longer, more familiar sounds. The results show that timbre cues for sound recognition are available at a variety of time scales, including very short ones.

Auditory observation of stepping actions can cue both spatial and temporal components of gait in Parkinson's disease patients

Objectives: A common behavioural symptom of Parkinson’s disease (PD) is reduced step length (SL). Whilst sensory cueing strategies can be effective in increasing SL and reducing gait variability, current cueing strategies conveying spatial or temporal information are generally confined to the use of either visual or auditory cue modalities, respectively. We describe a novel cueing strategy using ecologically-valid ‘action-related’ sounds (footsteps on gravel) that convey both spatial and temporal parameters of a specific action within a single cue.
Methods: The current study used a real-time imitation task to examine whether PD affects the ability to re-enact changes in spatial characteristics of stepping actions, based solely on auditory information. In a second experimental session, these procedures were repeated using synthesized sounds derived from recordings of the kinetic interactions between the foot and walking surface. A third experimental session examined whether adaptations observed when participants walked to action-sounds were preserved when participants imagined either real recorded or synthesized sounds.
Results: Whilst healthy control participants were able to re-enact significant changes in SL in all cue conditions, these adaptations, in conjunction with reduced variability of SL were only observed in the PD group when walking to, or imagining the recorded sounds.
Conclusions: The findings show that while recordings of stepping sounds convey action information to allow PD patients to re-enact and imagine spatial characteristics of gait, synthesis of sounds purely from gait kinetics is insufficient to evoke similar changes in behaviour, perhaps indicating that PD patients have a higher threshold to cue sensorimotor resonant responses.

Representations of specific acoustic patterns in the auditory cortex and hippocampus

Previous behavioural studies have shown that repeated presentation of a randomly chosen acoustic pattern leads to the unsupervised learning of some of its specific acoustic features. The objective of our study was to determine the neural substrate for the representation of freshly learnt acoustic patterns. Subjects first performed a behavioural task that resulted in the incidental learning of three different noise-like acoustic patterns. During subsequent high-resolution functional magnetic resonance imaging scanning, subjects were then exposed again to these three learnt patterns and to others that had not been learned. Multi-voxel pattern analysis was used to test if the learnt acoustic patterns could be 'decoded' from the patterns of activity in the auditory cortex and medial temporal lobe. We found that activity in planum temporale and the hippocampus reliably distinguished between the learnt acoustic patterns. Our results demonstrate that these structures are involved in the neural representation of specific acoustic patterns after they have been learnt.

Isolating Informational Masking in Both Pure and Complex Tone Sequences

Objectives: Interference between a target and simultaneous maskers occurs both at the cochlear level through energetic masking and more centrally through informational masking (IM). Hence, quantifying the amount of IM requires a strict control of the energetic component. Presenting target and maskers on different sides (i.e., dichotically) reduces energetic masking but provides listeners with important lateralization cues that also drastically reduce IM. The main purpose of this study (Experiment 1) was to evaluate a "switch" manipulation aiming at restoring most of the IM despite dichotic listening. Experiment 2 was designed to investigate the source of the difficulty induced by this switching dichotic condition.

Design: In Experiment 1, the authors presented 60 normal-hearing young adults with a detection task in which a regularly repeating target was embedded in a randomly varying background masker. The authors evaluated spatial masking release induced by three different dichotic listening conditions in comparison with a diotic baseline. Dichotic stimuli were presented in either a nonswitching or a switching condition. In the latter case, the presentation sides of dichotic target and maskers alternated several times throughout 10 sec sequences. The impact of the number of switches on IM was investigated parametrically, with both pure and complex tone sequences. In Experiment 2, the authors compared performance of 13 young, normal-hearing listeners in a monotic and dichotic version of the rapidly switching condition, using pure-tone sequences.

Results: When target and maskers switched rapidly within sequences, IM was significantly stronger than in nonswitching dichotic sequences and was comparable with the masking effect induced by diotic sequences. Furthermore, Experiment 2 suggests that rapidly switching target and maskers prevent listeners from relying on lateralization cues inherent to the dichotic condition, hence preserving important amounts of IM.

Conclusions: This paradigm thus provides an original tool to isolate IM in signal and maskers having overlapping spectra.

Moving with Beats and Loops: The Structure of Auditory Events and Sensorimotor Timing

Traditionally, audio-motor timing processes have been understood as motor output from an internal clock, the speed of which is set by heard sound pulses. In contrast, this paper proposes a more ecologically-grounded approach, arguing that audio-motor processes are better characterized as performed actions on the perceived structure of auditory events. This position is explored in the context of auditory sensorimotor synchronization and continuation timing. Empirical research shows that the structure of sounds as auditory events can lead to marked differences in movement timing performance. The nature of these effects is discussed in the context of perceived action-relevance of auditory event structure. It is proposed that different forms of sound invite or support different patterns of sensorimotor timing. Hence, the temporal information in looped auditory signals is more than just the interval durations between onsets: all metronomes are not created equal. The potential implications for auditory guides in motor performance enhancement are also described.

A new comparator account of auditory verbal hallucinations: how motor prediction can plausibly contribute to the sense of agency for inner speech

The comparator account holds that processes of motor prediction contribute to the sense of agency by attenuating incoming sensory information and that disruptions to this process contribute to misattributions of agency in schizophrenia. Over the last 25 years this simple and powerful model has gained widespread support not only as it relates to bodily actions but also as an account of misattributions of agency for inner speech, potentially explaining the etiology of auditory verbal hallucination (AVH). In this paper we provide a detailed analysis of the traditional comparator account for inner speech, pointing out serious problems with the specification of inner speech on which it is based and highlighting inconsistencies in the interpretation of the electrophysiological evidence commonly cited in its favor. In light of these analyses we propose a new comparator account of misattributed inner speech. The new account follows leading models of motor imagery in proposing that inner speech is not attenuated by motor prediction, but rather derived directly from it. We describe how failures of motor prediction would therefore directly affect the phenomenology of inner speech and trigger a mismatch in the comparison between motor prediction and motor intention, contributing to abnormal feelings of agency. We argue that the new account fits with the emerging phenomenological evidence that AVHs are both distinct from ordinary inner speech and heterogeneous. Finally, we explore the possibility that the new comparator account may extend to explain disruptions across a range of imagistic modalities, and outline avenues for future research.

Bringing sounds into use: Thinking of sounds as materials and a sketch of auditory affordances

We live in a richly structured auditory environment. From the sounds of cars charging towards us on the street to the sounds of music filling a dancehall, sounds like these are generally seen as being instances of things we hear but can also be understood as opportunities for action. In some circumstances, the sound of a car approaching towards us can provide critical information for the avoidance of harm. In the context of a concert venue, sociocultural practices like music can equally afford coordinated activities of movement, such as dancing or music making. Despite how evident the behavioral effects of sound are in our everyday experience, they have been sparsely accounted for within the field of psychology. Instead, most theories of auditory perception have been more concerned with understanding how sounds are passively processed and represented or how they convey information of world, neglecting how this information can be used for anything. Here, we argue against these previous rationalizations, suggesting instead that information is instantiated through use and, therefore, is an emergent effect of a perceiver’s interaction with their environment. Drawing on theory from psychology, philosophy and anthropology, we contend that by thinking of sounds as materials, theorists and researchers alike can get to grips with the vast array of auditory affordances that we purposefully bring into use when interacting with the environment.

Auditory cueing in Parkinson's patients with freezing of gait. What matters most: action-relevance or cue-continuity?

Gait disturbances are a common feature of Parkinson’s disease, one of the most severe being freezing of gait. Sensory cueing is a common method used to facilitate stepping in people with Parkinson’s. Recent work has shown that, compared to walking to a metronome, Parkinson’s patients without freezing of gait (nFOG) showed reduced gait variability when imitating recorded sounds of footsteps made on gravel. However, it is not known if these benefits are realised through the continuity of the acoustic information or the action-relevance. Furthermore, no study has examined if these benefits extend to PD with freezing of gait. We prepared four different auditory cues (varying in action-relevance and acoustic continuity) and asked 19 Parkinson’s patients (10 nFOG, 9 with freezing of gait (FOG)) to step in place to each cue. Results showed a superiority of action-relevant cues (regardless of cue-continuity) for inducing reductions in Step coefficient of variation (CV). Acoustic continuity was associated with a significant reduction in Swing CV. Neither cue-continuity nor action-relevance was independently sufficient to increase the time spent stepping before freezing. However, combining both attributes in the same cue did yield significant improvements. This study demonstrates the potential of using action-sounds as sensory cues for Parkinson’s patients with freezing of gait. We suggest that the improvements shown might be considered audio-motor ‘priming’ (i.e., listening to the sounds of footsteps will engage sensorimotor circuitry relevant to the production of that same action, thus effectively bypassing the defective basal ganglia).