When we make sense of visual stimuli, we rely on a seamless combination of sensory information and knowledge about the world. However, a recent study led by researchers from Cardiff University and the University of Cambridge suggests that this process of interpreting the world is shifted in psychosis.
Eighteen subjects with psychotic symptoms and 16 healthy volunteers were recruited from CAMEO, an NHS service based in Cambridgeshire for early intervention in psychosis. The participants viewed two-tone pictures like the one on the right. While these pictures may resemble meaningless patterns of black and white patches, they were made from coloured photographs of people, like the one on the bottom left. The experimenters also created control images that were not based on real photographs. Subjects had to decide whether or not the picture included a person – a task that has been proven to be particularly challenging without knowing anything about the original image.
Afterwards, the participants saw the original coloured images in 3 blocks of 10. Finally, they were presented with the two-tone images again and were asked to decide once more whether or not a person was included in the image. The researchers found that both groups did better after seeing the original images, but intriguingly, this improvement was bigger for patients with early psychosis.
The two-tone images were the same in the first and last block, so the visual information did not change. In contrast, viewing the original images contributed to prior knowledge. The findings suggest that patients with psychotic symptoms rely more strongly on such knowledge when they process visual stimuli.
However, the authors note that the patients differed from controls on a range of measures, including the occurrence of unusual thoughts, depression and anxiety symptoms. To better understand the relationship between psychotic symptoms and information processing, they conducted a second study. This time, 40 healthy volunteers were recruited. The extent of experienced hallucinations (anomalous perceptions) and delusions (bizarre beliefs) varies in the general population and can be quantified with schizotypy scales. Many experience hallucinations or delusions without qualifying for psychosis, and it is thought that this schizotypy personality measure might be related to information processing.
The 40 healthy volunteers completed a similar process to that described above and their performance was correlated with their schizotypy scores. Essentially, higher schizotypy scores were associated with a greater performance improvement after seeing the original images. Healthy volunteers who are more prone to psychosis and patients with psychotic symptoms seem to show a similar shift in information processing: favouring prior knowledge over sensory information.
The fact that these shifts were also seen in healthy volunteers could change the way we think about mental illness. Professor Paul Fletcher from the University of Cambridge, who is the senior author of the study, said:
“It’s important to remember that there has been something of a tendency to treat psychotic experiences like hallucinations and delusions as though they are completely separate from normal experiences. Our data suggest that we can appeal to normal mechanisms of perception in trying to explain them. We do not necessarily have to invoke some gross derangement of brain function but rather an exaggeration of normal processes.”
These shifts in information processing seem to be related to the risk of developing psychosis or related mental health problems. The first author of the study, Dr Christoph Teufel, who is affiliated with Cardiff University and the University of Cambridge, explained how this effect could be used for early detection:
”We are currently conducting a similar experiment as part of a very large cohort study. The hope is that this might contribute to the development of neurocognitive biomarkers that help to identify individuals who are at a risk of developing a psychotic illness and might profit from early targeted interventions.”
Written by Julia Gottwald.