Voice identity discrimination and hallucination-proneness in healthy young adults: a further challenge to the continuum model of psychosis?

INTRODUCTION: Auditory hallucinations occur in schizophrenia and also in the general population. However, evidence points to differences in the nature and the mechanisms of clinical and non-clinical hallucinations, challenging the dominant assumption that they represent the same phenomenon. The current study extended this evidence by examining voice identity perception in hallucination-prone individuals. In schizophrenia, deficiencies discriminating between real (external) voices have been linked to basic acoustic cues, but voice discrimination has not yet been investigated in non-clinical hallucinations. METHODS: Using a task identical to that employed in patients, multidimensional scaling of voice dissimilarity judgements was used to examine how healthy individuals differing in hallucination-proneness (30 high and 30 low hallucination-prone individuals) distinguish pairs of unfamiliar voices. The resulting dimensions were interpreted with reference to acoustic measures relevant to voice identity. RESULTS: A two-dimensional "voice space", defined by fundamental frequency (F0) and formant dispersion (Df), was derived for high and low hallucination-prone groups. There were no significant differences in speaker discrimination for high versus low hallucination-prone individuals on the basis of either F0 or Df. CONCLUSIONS: These findings suggest voice identity perception is not impaired in healthy individuals predisposed to hallucinations, adding a further challenge to the continuum model of psychotic symptoms.

Symptom dimensions of the psychotic symptom rating scales in psychosis: a multisite study.

The Psychotic Symptom Rating Scales (PSYRATS) is an instrument designed to quantify the severity of delusions and hallucinations and is typically used in research studies and clinical settings focusing on people with psychosis and schizophrenia. It is comprised of the auditory hallucinations (AHS) and delusions subscales (DS), but these subscales do not necessarily reflect the psychological constructs causing intercorrelation between clusters of scale items. Identification of these constructs is important in some clinical and research contexts because item clustering may be caused by underlying etiological processes of interest. Previous attempts to identify these constructs have produced conflicting results. In this study, we compiled PSYRATS data from 12 sites in 7 countries, comprising 711 participants for AHS and 520 for DS. We compared previously proposed and novel models of underlying constructs using structural equation modeling. For the AHS, a novel 4-dimensional model provided the best fit, with latent variables labeled Distress (negative content, distress, and control), Frequency (frequency, duration, and disruption), Attribution (location and origin of voices), and Loudness (loudness item only). For the DS, a 2-dimensional solution was confirmed, with latent variables labeled Distress (amount/intensity) and Frequency (preoccupation, conviction, and disruption). The within-AHS and within-DS dimension intercorrelations were higher than those between subscales, with the exception of the AHS and DS Distress dimensions, which produced a correlation that approached the range of the within-scale correlations. Recommendations are provided for integrating these underlying constructs into research and clinical applications of the PSYRATS.

Voices to reckon with: perceptions of voice identity in clinical and non-clinical voice hearers.

The current review focuses on the perception of voice identity in clinical and non-clinical voice hearers. Identity perception in auditory verbal hallucinations (AVH) is grounded in the mechanisms of human (i.e., real, external) voice perception, and shapes the emotional (distress) and behavioral (help-seeking) response to the experience. Yet, the phenomenological assessment of voice identity is often limited, for example to the gender of the voice, and has failed to take advantage of recent models and evidence on human voice perception. In this paper we aim to synthesize the literature on identity in real and hallucinated voices and begin by providing a comprehensive overview of the features used to judge voice identity in healthy individuals and in people with schizophrenia. The findings suggest some subtle, but possibly systematic biases across different levels of voice identity in clinical hallucinators that are associated with higher levels of distress. Next we provide a critical evaluation of voice processing abilities in clinical and non-clinical voice hearers, including recent data collected in our laboratory. Our studies used diverse methods, assessing recognition and binding of words and voices in memory as well as multidimensional scaling of voice dissimilarity judgments. The findings overall point to significant difficulties recognizing familiar speakers and discriminating between unfamiliar speakers in people with schizophrenia, both with and without AVH. In contrast, these voice processing abilities appear to be generally intact in non-clinical hallucinators. The review highlights some important avenues for future research and treatment of AVH associated with a need for care, and suggests some novel insights into other symptoms of psychosis.

Voice identity discrimination in schizophrenia.

Voices provide a wealth of socially-relevant information, including cues to a speaker's identity and emotion. Deficits recognising emotion from voice have been extensively described in schizophrenia, and linked specifically to auditory hallucinations (AH), but relatively little attention has been given to examining the ability to analyse speaker identity. Hence, the current study assessed the ability to discriminate between different speakers in people with schizophrenia (including 33 with and 32 without AH) compared to 32 healthy controls. Participants rated the degree of perceived identity similarity of pairs of unfamiliar voices pronouncing three-syllable words. Multidimensional scaling of the dissimilarity matrices was performed and the resulting dimensions were interpreted, a posteriori, via correlations with acoustic measures relevant to voice identity. A two-dimensional perceptual space was found to be appropriate for both schizophrenia patients and controls, with axes corresponding to the average fundamental frequency (F0) and formant dispersion (D(f)). Patients with schizophrenia did not differ from healthy controls in their reliance on F0 in differentiating voices, suggesting that the ability to use pitch-based cues for discriminating voice identity may be relatively preserved in schizophrenia. On the other hand, patients (both with and without AH) made less use of D(f) in discriminating voices compared to healthy controls. This distorted pattern of responses suggests some potentially important differences in voice identity processing in schizophrenia. Formant dispersion has been linked to perceptions of dominance, masculinity, size and age in healthy individuals. These findings open some interesting new directions for future research.