J.J.M. van Hoof

Psychomotor slowing and planning deficits in schizophrenia

The relative contribution of cognitive and motor processing to psychomotor slowing in schizophrenia was investigated using three tasks: a simple line-copying task and a more complex figure-copying task, both following a reaction paradigm, and a standard psychomotor test, the Digit Symbol Test (DST). Various movement variables of the task performances were derived from recordings made with the aid of a digitizing tablet. The patients with schizophrenia appeared to be about one-third slower in their total performance time on all three tasks when compared with healthy controls, which suggests a general psychomotor slowing in this group. When itemized over the various movement variables, this slowing was found in both initiation time and movement time in the copying tasks and in the DST in the time to match the symbol and the digit, but not in writing the digit. Furthermore, in the figure-copying task it was found that increased figure complexity or decreased familiarity prolonged the initiation time. These latency increases were not significantly larger for the schizophrenia group as a whole, but only for a subgroup of patients with higher scores on negative symptoms. Regarding reinspection time, the effects of familiarity were larger in the schizophrenia group as a whole. These group findings suggest that patients tend to plan their actions less in advance, which, in the case of the more complex or unfamiliar task conditions, is a less sophisticated planning strategy. Given the longer latencies in patients with more severe negative symptoms, it seems that these patients have problems with turning a plan into action. The present study provides evidence of psychomotor slowing and planning deficits in schizophrenia.

Fine motor retardation and depression

New computerized techniques allow the precise measurement of psychomotor retardation in patients with a major depressive episode (MDE). One such technique is the analysis of writing and drawing behaviour during figure copying tasks. In the present study, 22 inpatients with an MDE were compared to 22 normal controls. Three tasks were used: the drawing of lines and simple figures, the copying of complex figures and a task in which figures had to be rotated. Objectives were to provide support for earlier findings that the patients were slower than the controls and to explore the cognitive and motor processes involved. Two strategies were applied: analysis of the reaction time and movement time and their different components, and manipulation of the cognitive and motor demands. Patients showed considerable retardation with most of the kinematic variables. Motor deficits and cognitive slowing down contributed to this retardation. Cognitive difficulties increased with increasing complexity of the task.

Differentiation of cognitive and motor slowing in the Digit Symbol Test (DST): differences between depression and schizophrenia

Abstract Schizophrenia and depression have an overlap in symptomatology, namely a slowing in both motor and mental activities, denoted in depression as ‘psychomotor retardation’ and in schizophrenia as ‘psychomotor poverty’. By means of a new technique that allows the measurement of psychomotor speed and the computerized analysis of writing movements recorded during the performance of the Digit Symbol Test, it indeed proved to be possible to observe a slowing in both disorders. In addition, a different structure of slowing in the two patient groups could be identified.