Earlier research has shown that schizophrenic individuals process complex sound in aberrant ways (Olsson.O., Dissertation, Lund, 2000). It has also been shown that they abnormally perceive forward and backward masking (Källstrand et al., Psychiatry Res. 2002 Dec 15; 11 (1-2); 115-25). Experiments described in those studies indicate that in schizophrenia, brain-stem activity is involved, where primitive sorting of sound elements takes place. Brain Stem Response Audiometry (BSRA) shows that e.g. dissimilar spectra significantly separates schizophrenics from healthy subjects (Nielzén.S., 15th AEP Congress, March 2007, p. S86). The present study aims at demonstrating effects of loudness change of complex sound stimulation.

Eighteen paranoid schizophrenic patients were compared with 25 healthy volunteers regarding BSRA recordings from 2048 sweeps of loud noise stimuli (76 dB) and 2048 quieter ones (73 dB). Analysis of latencies in ms and amplitudes in micro-volts of the peaks and troughs was performed.

The amplitude of the highest peak of the region 1-4 ms was significantly lower with quiet noise for the schizophrenic group (P=.0002).

The schizophrenics showed significantly prolonged latencies of the highest peak during 4,5-9 ms with the quiet noise (P=.046); they had a significant longer latency from left than from right electrode (P=.049).

The results corroborate earlier cumulative BSRA results. These have been collected in a model – S-Detect – which is used as an objective decision support for the diagnosis of schizophrenia.