Researchers from Cardiff University report that anomalies of sensation and perception are common in the general population, with more than 1 in 10 reporting higher levels than the average of patients diagnosed with psychosis.
The research project was inspired by a need for a comprehensive measure of anomalous sensory experience and perceptual distortion, as the majority of existing measures are derived from psychiatric assessment techniques.
Consequently, they often focus on specific forms of perceptual distortion, such as ‘visions’ or ‘voices’, and do not always cover other types of anomalous experience.
To tackle this problem the researchers designed, tested and validated, a new measure of anomalous perceptual experience that specifically uses non-clinical language to ask about a wide range of phenomena, including unusual touch sensations, changes in time perception and being unable to distinguish one sensation from another.
Sensory distortions are traditionally associated with mental or neurological illness, although recent work is now suggesting that unusual experiences are distributed throughout the population (this is known as the ‘continuum model of psychosis’).
Perhaps unsurprisingly, when patients with psychosis completed the measure high levels of unusual experience were reported.
It is not clear, however, why some people with high levels of unusual experiences become distressed and impaired by their experiences, often leading to a diagnosis of mental illness, while others are able to function and remain untroubled by them.
One possibility is that there might be different sources for different types of unusual experience. When the types of experiences reported by healthy individuals in the study were analysed for how they clustered together, three themes emerged.
One cluster was associated with relatively benign smell and taste experiences, another with experiences potentially related to temporal lobe disturbance and another with experiences traditionally linked to psychosis.
This suggests that the distribution of perceptual distortions found in the population may be driven by a number of underlying processes, all which might contribute to producing strange experiences in the individual.
The research is published as an open-access paper in the journal Schizophrenia Bulletin.
Disclaimer: This paper is from my own research group.