A case study of the precedence effect in a sample of auditory hallucinating schizophrenics

Sammanfattning: In a reverberant environment, a direct sound is followed by several reflections. -As a result, we are often presented with multiple signals coming from different directions. Yet we are normally aware of just the first sound, the direct sound, and are able to tell the direction of it's source. This is due to a phenomenon called the precedence effect, also called the "law of the first wavefront". Earlier studies have shown that schizophrenic individuals have dysfunctions in their ability to localize sounds. The aims of this study where to contribute to the survey of sound localization by studying the precedence effect with auditory brainstem response (ABR) on hallucinating schizophrenics and healthy individuals. It was assumed that schizophrenic subjects may show aberrations in the function of the precedence effect. For this report, the precedence effect was studied in two schizophrenic individuals by recording the auditory brain stem response as a result of sound stimulation. The main finding is an increased amplitude of the precedence effect in wave V, originating from the inferior colliculus (I C), compared to the healthy subjects. The schizophrenics aberrant amplitude can perhaps be explained as dysfunctions on a psychophysiological level.