Tuesday, November 06, 2007

Schizophrenia: sensory gating and extracting meaning from noise

I have blogged extensively in the past regarding schizophrenia and how people that are on that end of the cognitive thinking style are marked by a propensity to abstract meaning from apparent noise and meaningless or coincidental events. This, I have contrasted with Autistic thinking style which does not endow meaning even where it is legitimate.

It is also well known that Schizophrenics have a deficit with sensory gating and thus have loose attention/ loose associations etc. and are generally marked by less focal attention. This may lead to lowered filtering of irrelevant stimuli, which may lead to unusual experiences.

It is my contention that these two aspects may be independent of each other and when they come together may lead to psychosis. The deficits in sensory gating give rise to unusual experiences, while the normal confabulating left-brain mechanisms would try to explain the unusual experiences or noise in terms of a coherent narrative. If the first propensity to endow more meaning to even meaningless stimuli gets conjuncted with sensory gating, one may strew together a narrative that is not in touch with reality and thus lead to full blown psychosis, including delusions and hallucinations.

A recent study has just demonstrated that Schizophrenics have a propensity to derive meaning out of what is auditory noise for other normal people. I think there are two issues involved here- first more words were extracted from the auditory noise signal by the schizophrenics, and second they gave meaning to those words by strewing them together as 'phrases'. The length of the phrases heard for prodormant schizophrenics, indicated whether they were likely to suffer from schizophrenia in the future, if not on medication. thus both sensory gating deficits and meaning-endowing deficits seem to be at work.

A tendency to extract messages from meaningless noise could be an early sign of schizophrenia, according to a study by Yale School of Medicine researchers.

The study this month in the British Journal of Psychiatry reported on 43 participants diagnosed with "prodromal symptoms"- meaning they exhibited early warning signs of psychosis such as social withdrawal, mild perceptual alterations, or misinterpretation of social cues.

Participants in the study were randomly assigned to take the anti-psychotic medication olanzapine or a placebo, and then symptoms and neuropsychological function were assessed for up to two years.

During the "babble task," participants listened with headphones to overlapping recordings of six speakers reading neutral texts, which made the words virtually incomprehensible. The participants were asked to repeat any words or phrases that they heard. Only four words-"increase," "children," "A-OK," and "Republican"-were consistently reproduced.

Eighty percent of the participants who "heard" phrases of four or more words in length went on to develop a schizophrenia-related illness during times that they were not taking olanzapine, said the lead author, Ralph Hoffman, M.D., associate professor of psychiatry. In contrast, only six percent of those in the study converted to schizophrenia-related illness if the phrases "heard" were less than three words in length.

"A tendency to extract message-like meaning from meaningless sensory information can, over time, produce a 'matrix of unreality' that triggers the initial psychotic phase of schizophrenia-spectrum disorders," Hoffman said.

To me, this is further support for my hypothesis that Schizophrenic thinking style is marked by extracting too much meaning and it also supports the popular attention-arousal model of schizophrenia that considers the sensory gating deficits leading to hyperarousal and that in turn leading to loose and defocussed attention and this feeding on itself in a downward spiral. you can learn more about the theory by watching this excellent video.

Note related, though relevant to schizophrenia, is a new study that finds that Schizophrenics are more 'theoretically ' rational as compared to normal people.

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