Auditory verbal hallucinations in schizophrenia as aberrant lateralized speech perception: Evidence from dichotic listening Kenneth Hugdahl a, b, ⁎, Else-Marie Løberg a, b , Liv E. Falkenberg a , Erik Johnsen b, e , Kristiina Kompus a , Rune A. Kroken b , Merethe Nygård a , René Westerhausen a, b , Koksal Alptekin c , Murat Özgören d a Department of Biological and Medical Psychology, University of Bergen, Norway b Division of Psychiatry, Haukeland University Hospital, Bergen, Norway c Dokuz Eylül University, Faculty of Medicine Department of Psychiatry, Izmir, Turkey d Dokuz Eylül University, Faculty of Medicine Department of Biophysics, Izmir, Turkey e Department of Clinical Medicine, University of Bergen, Norway abstract article info Article history: Received 27 February 2012 Received in revised form 29 May 2012 Accepted 18 June 2012 Available online 15 July 2012 Keywords: Auditory hallucinations Schizophrenia Dichotic listening Speech processing Left hemisphere Perceptual model Lateralization We report evidence that auditory verbal hallucinations (AVH) in schizophrenia patients are perceptual distortions lateralized to the left hemisphere. We used a dichotic listening task with repeated presentations of consonant– vowel syllables, a different syllable in the right and left ear. This task produces more correct reports for the right ear syllable in healthy individuals, indicative of left hemisphere speech processing focus. If AVHs are lateralized to the left hemisphere language receptive areas, then this should interfere with correct right ear reports in the dichotic task, which would result in significant negative correlations with severity of AVHs. We correlated the right and left ear correct reports with the PANSS hallucination symptom, and a randomly selected negative symptom, in addition to the sum total of the positive and negative symptoms, in 160 patients with schizophrenia. The results confirmed the predictions with significant negative correlations for the right ear scores with the PANSS hallucination item, and for the sum total of positive symptoms, while all other correlations were close to zero. The results are unambiguous evidence for AVHs as aberrant speech perceptions originating in the left hemisphere. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Auditory verbal hallucinations (AVHs) are a key symptom in schizophrenia (Wing et al., 1974; David, 1999) which directs at- tention inwards towards the "voice", with consequences for social interaction and reality orientation. It is estimated that about 70% of diagnosed patients experience auditory hallucinations (Wing et al., 1974; Shergill et al., 1998). Auditory verbal hallucinations are the subjective experience and conviction of someone speaking to the patient despite the absence of an acoustic signal (Hugdahl et al., 2009). The "voices” are commonly characterized as having an out-of-head origin, often having a negative and commanding emotional valence, and not possible to cognitively control and to avoid for the patient. Patients also often struggle with complying with the demands and requirements imposed by the "voices" (cf. Daalman et al., 2011). There is an ongoing discussion in the literature regarding the underlying mechanisms for AVH, and whether these can best be described as inner speech (e.g. Blakemore et al., 1998; Allen et al., 2007), traumatic memory (e.g. Badcock et al., 2005; Waters et al., 2006), or as aberrant speech perceptions (e.g. Fiszdon et al., 2005; Spencer et al., 2009, see also Jones, 2010 for a thorough review and discus- sion of existing theoretical models for AVH). What is lacking, however, are hypothesis-driven empirical tests of the different models. In this study we aimed at an empirical test of a speech perception model, with the hypoth- esis that if AVHs are aberrant speech perceptions, then they should impli- cate the left hemisphere receptive language areas (Binder et al., 1996; van den Noort et al., 2008), and interfere with the processing of an external speech sound, that is processed in the same brain areas. Such a hypothesis is derived from previous functional neuroimaging studies showing that the language regions in the brain are in a hyper-excited state during AVHs (Spencer et al., 2009), and that neuronal activation in the left speech perception area is correlated negatively with frequency and severity of AVHs (Plaze et al., 2006). Such a prediction would also follow from the findings by Woodruff et al. (1997) that patients with severe hallucina- tions showed reduced left temporal cortex response sensitivity to exter- nal speech sounds. Adding to this, Aleman and Vercammen (2012) concluded after a review of the existing activation literature that "if audi- tory hallucinations share a processing system with auditory sense percep- tion, one would not expect an increase in activity upon external auditory stimulation in the auditory areas of patients actively experiencing AVH" (p. 272). A disadvantage with imaging data is however that it is not clear whether an implicated brain region is necessary and sufficient for Schizophrenia Research 140 (2012) 59–64 ⁎ Corresponding author at: Department of Biological and Medical Psychology, University of Bergen, Jonas Lies vei 91, N-5009 Bergen, Norway. E-mail address: Hugdahl@psybp.uib.no (K. Hugdahl). 0920-9964/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.schres.2012.06.019 Contents lists available at SciVerse ScienceDirect Schizophrenia Research journal homepage: www.elsevier.com/locate/schres