Auditory Localization in Schizophrenia

Auditory Perception

Localization, Auditory perception, Source monitoring, Virtual reality

Auditory sound localization is the ability to identify the position of a sound source in space. It is defined into 3 dimensions: by its position in azimuth, elevation and distance. If it is difficult to localize a sound source, it is possible to remove the localization ambiguity by interacting with the environment, in particular by changing one's position in relation to the source (e.g. by changing the orientation of the head). Patients with schizophrenia have difficulties to localize and discriminate sounds in space but it is still poorly explored. Additionally, deficits in auditory localization could underlie difficulties in source-monitoring (i.e., distinguish the source/origin of the information) reported in schizophrenia or deficits in auditory externalization (i.e., perception of sound outside the head). Furthermore, schizophrenia is characterized by cerebral abnormalities in the auditory cortex, manifesting as auditory processing disorders at different stages of the pathology. Auditory localization may therefore be impaired from the onset of a first psychotic episode (FEP). This early phase of the disease is also referred to as the critical period, as the chances of remission are highest and the response to treatment is best. However, the three-dimensional aspect of auditory perception and the behavioral exploration strategies used to localize a sound in the early stages of schizophrenia are still little studied.

The main objective of this study is to study the auditory localization performance on the horizontal and vertical planes (sound direction) in patients with a first episode psychosis (FEP) compared to healthy control subjects. This study will: * evaluate the role of head movement on auditory localization abilities in patients with FEP compared with healthy control subjects; * evaluate the localization abilities of sounds in a noisy environment in patients with FEP compared with healthy control subjects; * evaluate the repercussions of poor auditory localization performance on the ability to distinguish between what comes from an internal source and what comes from an external source (source-monitoring abilities); * evaluate the repercussions of poor auditory localization performance on the ability to externalize an external auditory source compared with an internal source (auditory externalization abilities); * evaluate the relationships between auditory localization performance and auditory discrimination performance (pitch, volume, length); * evaluate the repercussions of the severity of symptoms in patients with FEP on auditory localization performance. Subjects will undergo several auditory and cognitive tasks. The duration of the entire experiments will be 2.30 hours: * An auditory localization task in virtual reality with the SPHERE paradigm: the subject is immerged into a room and sounds are delivered through loudspeakers in different localization on the horizontal and vertical planes. Sounds are delivered in two experimental blocks: silent and noisy background. Each block is divided into two listening conditions: fixed head and active head movement (i.e., with the possibility of moving the head). Subjects have to localize each sound. * A source monitoring task divided into two parts: one part that will evaluate the reality-monitoring performances ('hear-imagine' task). Subjects either have to listen to words or imagine themselves listening to words; Another part evaluating internal source-monitoring performances ('say-imagine' task). Subjects either have to pronounce words or imagine themselves pronouncing words. * An auditory externalization task: Nonverbal sounds are delivered through headphones and processed to be perceived inside or outside the head. Subjects will have to discern whether a sound is perceived as coming from inside or outside the head. * A battery of psychoacoustic tests including the Tone Matching Task (TMT) which evaluates the capacity of discriminating static pitch.

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