For Schizophrenics, Integration—Not Attention—Is The Problem

Previous studies showing that schizophrenics have attention disorders were based on systematically exaggerated data, scientists say.

AsianScientist (May 15, 2015) – A study published in Scientific Reports has questioned the commonly held assumption that schizophrenia is related to attentional deficiencies. Instead, the team led by Professor Raymond Chan form the Institute of Psychology, Chinese Academy of Sciences, proposed that integration dysfunction is more clinically relevant, and thus should be an additional focus of research in schizophrenia.

Research on schizophrenia over the last 13 years has supported the view that schizophrenia patients have impaired temporal attention beyond and above their existing perception impairment. These studies, including those published in highly influential journals such as Schizophrenia Bulletin, all used a classic experimental paradigm called the ‘Attentional Blink’ (AB), which is designed to probe temporal attention.

In AB studies, a mathematical method is used in the post hoc analysis to remove the influence of the basic perception difference between schizophrenia patients and their controls. This method is called suppression ratio. By using this mathematical trick, researchers have claimed that the suppression ratio, which was supposed to remove the visual perception variations, should reflect the pure deficit in attention. As such, they all reported a marked decrease in attention in patients with schizophrenia.

Chan and colleagues revisited the issue, this time using a more rigorous experimental design to control for the visual perception differences between the schizophrenia patients and the controls, namely matching the perceptual difficulty of the task. In this way, they did not rely on the use of suppression ratio and found no evidence for an impaired temporal attention. Instead, an increased level of temporal binding error was associated with the schizophrenia patients.

Using a computational modeling approach and careful investigation of the mathematical methods used in the previous studies, researchers have concluded that the suppression ratio used in almost all previous studies has systematically exaggerated the degree of attentional impairment in schizophrenia. This flaw in methodology explains why the original findings were not replicated.

While this study failed to replicate the previous findings, the study however showed an unreported but expected impairments in schizophrenia, that is, the patients with schizophrenia tend to have poorer temporal binding accuracy. This is illustrated by the fact that when two visual stimuli were presented within a very short time interval (around 100 milliseconds), schizophrenia patients have greater difficulty to tell in which order the stimuli were presented.

This finding is consistent with the previous literature on temporal perception deficit in schizophrenia. The authors argue that the inability to encode sensory information in the precise order in which they are occurring in the environment can lead to serious problems in both perception and reasoning. To some extent, such a deficit contributes to many symptoms in schizophrenia, such as hallucination.

The study demonstrates how scientists could uncover important messages when their data are different from existing literature. It also reminds us of the danger of misusing post hoc data analysis methods, particularly in situations where the error ‘improves’ the results. This study also encourages students and young scientists to challenge existing theories and data by applying more rigorous methodology as well as mathematically modeling.

The article can be found at: Su et al. (2015) Temporal Perception Deficits In Schizophrenia: Integration Is The Problem, Not Deployment Of Attentions.


Source: Chinese Academy of Sciences; Photo: Shutterstock.
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