Slowing and stopping in schizophrenia

Professional Doctorate - Doctor of Clinical Psychology (DCP)Background: Individuals with Schizophrenia have been described to have extensive cognitive impairments that span across several domains and can significantly impact functional outcomes and quality of life. Slowing in reaction time paradigms has been consistently documented in Schizophrenia such as in simple and choice reaction time tasks. In addition to slowing, the performance by individuals with Schizophrenia in choice reaction time tasks has also been documented to be more variable and error prone relatively to healthy participants. Executive functioning deficits in Schizophrenia are profound and as a result, response inhibition difficulties have been reported across various paradigms. Model-based analysis have not yet been conducted in regards to choice reaction time performance in Schizophrenia, and this method has the potential of uncovering further underlying cognitive processes in decision-making. Method: A meta-analysis was conducted to extend and expand the investigations by Schatz (1999) to include information of accuracy and standard deviation as well as reaction time, and performance of participants with Schizophrenia and health control groups was compared. An experiment was also conduced that took place across two sessions on separate days. Nineteen participants with Schizophrenia or Schizoaffective disorder, as well as control participants matched by age and gender were recruited. In the first session, participants completed a choice reaction task, completed measures of working memory and premorbid intelligence, and participants with Schizophrenia also completed a clinical interview. The second session included a stop-signal task, data from which was not analysed further in the research manuscript due to the time-frame limitations of the project. The data from the choice reaction time task were fit by two cognitive models of choice processes: the Drift-Diffusion model (DDM, Ratcliff & McKoon, 2008) and the Linear Ballistic Accumulator model (LBA, Brown & Heathcote, 2008). Results: The meta-analysis revealed a consistent pattern of control groups performing faster and more accurately relative to participants with Schizophrenia in choice reaction time tasks. Reaction time and accuracy comparisons from the experiment indicated that participants with Schizophrenia were slower and less accurate in their responding, however this finding was not significant. Model-based analyses revealed that the LBA fit the data better than the DDM and produced a greater number of significant results, which are described in further detail. Sequential effects were found in the Schizophrenia group and model-based analyses further confirmed a bias towards participants with Schizophrenia repeating the immediately past response. A positive correlation was found between mean reaction time and negative symptoms in the Schizophrenia group. Furthermore, the combined effects of the threshold and rate parameters in the model-based analysis suggested a differential response strategy occurring in the group of participants with Schizophrenia relative to controls. Conclusions: The findings in the present study echo previous reports of slower and less accurate performance in Schizophrenia in choice reaction time tasks. A more in-depth discussion is provided regarding the possible interpretations of the threshold and rate parameter results. Relevant research findings regarding perseveration, flexibility in responding, as well as motion perception deficits in Schizophrenia are described and integrated with the results obtained. Finally, the strengths and limitations of the present study are highlighted and recommendations for future research and the potential implications of the present study are proposed