Deficits in auditory object localization in schizophrenia and their relation with auditory verbal hallucinations

ALBA FERRARA, L.; HAUSMANN, M.; LEWALD, J.; DE ERAUSQUIN, G.

Nueva Orleans

Congreso; Society for Neuroscience Annual Meeting; 2012

Society for Neuroscience

Schizophrenia patients often perceive hallucinations as located "outside their heads"; spatial location and emotional tone of the voices define these abnormal perceptions. Auditory verbal hallucinations (AVH) may seem to originate in the external space due to a failure in the neural path responsible for spatial location of speech sources. Thus, schizophrenia patients perform poorly in sound localization tasks. However, whether such a disturbance relates to schizophrenia in general or to AVH in particular still remains unclear. We studied sound localization in patients with AVH to test whether difficulties in processing audiospatial cues underlie misidentification of the location of the source. 15 patients with history of AVH, 12 patients without history of hallucinations (NAVH) and 16 controls (CG) participated in a combined paradigm of sound localization (Task A) and internal/external perception of prosody (Task B). Task A consisted of tunes presented in either the right or the left ear in two conditions (located close to or far from the listener). Task B consisted of numbers spoken in either angry or neutral tones in two conditions (inside/outside the head). Angry/neutral numbers, of which one was virtually inside and the other outside the head, were presented simultaneously and monaurally via headphones. Modification of acoustic stimuli using virtual acoustic space techniques (width manipulation and convolution with HRTF) creates the illusion that the sound is "inside the head" or "outside the head". Inside the head, stimuli were created by inter-aural amplitude radio adjustment; and outside the head, stimuli were created by convolution with a generic HRTF. Patients responded in both tasks by a keypress.Tasks A and B were analyzed in two separate 2 x 3 factorial ANOVAs. In Task A accuracy was above chance level (M=75% ± SE= 2.7), but without effects of Presentation side (left/right) or Group (AVH, NAVH, CG). In Task B, stimuli presented to the left ear were located more accurately than to the right (F(1,40)=14.19, p<.001). Additionally, CG located the source more accurately than patients regardless of AVH traits (F(1,40)=12.19, p<.001). Both patient groups did not differ from each other and there was no significant interaction.Although a general deficit in sound location was not found, schizophrenia patients have difficulties to distinguish between virtually located inside/outside auditory objects loaded with emotional prosody. Albeit it was proposed that impairments in recognizing inner voices in auditory space was a contributing mechanism of hallucination's formation, our data suggest that such deficit is associated with schizophrenia itself and not hallucinations in particular.