Background-Prior demonstrations of impaired attentional control in schizophrenia focused on conditions in which top-down control is needed to overcome prepotent response tendencies. Attentional control over stimulus processing has received little investigation. Here we test whether attentional control is impaired during working memory encoding when salient distractors compete with less salient task-relevant stimuli.

Although selective attention is thought to be impaired in people with schizophrenia (PSZ), prior research has found no deficit in the ability to select 1 location and withdraw attention from another. PSZ and healthy control subjects (HCS) performed a stimulus detection task in which 1, 2, or all 4 peripheral target locations were cued. When 1 or 2 locations were cued, both PSZ and HCS responded faster when the target appeared at a cued than uncued location. However, increases in the number of validly cued locations had much more deleterious effects on performance for PSZ than HCS, especially for targets of low contrast whose detection was more dependent on attention. PSZ also responded more slowly in trials with 4 cued locations relative to trials with 1 or 2 invalidly cued locations. Thus, visuospatial attention deficits in schizophrenia arise when broad monitoring is required rather than when attention must be focused narrowly.

Previous research has demonstrated deficits in pre-response motor activity in schizophrenia, as evidenced by a reduced lateralized readiness potential (LRP). The LRP deficit could be due to increased activation of the incorrect response (e.g., failure to suppress competition) or to reduced activation of the correct response (e.g., a low-level impairment in response preparation). To distinguish these possibilities, we asked whether the LRP impairment is increased under conditions of strong response competition. We manipulated the compatibility of stimulus-response mappings (Experiment 1) and the compatibility of the target with flankers (Experiment 2). In both experiments, the patient LRP was reduced as much under conditions of low response competition as under high competition. These results are incompatible with a failure of patients to suppress competition and are instead consistent with a deficit in activating the correct response.

Schizophrenia clearly involves impairments of attention, but the precise nature of these impairments has been difficult to determine. One possibility is that the deficit in attention is a secondary consequence of a deficit in goal maintenance. However, recent research suggests that people with schizophrenia (PSZ) actually focus attention more strongly on objects containing goal-relevant features. To test these competing hypotheses, we recorded event-related potentials (ERPs) from PSZ (N = 20) and healthy control subjects (HCS, N = 20) while they looked for a particular target color at fixation and tried to ignore lateral distractors that sometimes matched the target color (target-color distractors). Goal maintenance was made trivially easy by the continual presentation of a goal reminder. We found that HCS were able to successfully suppress target-color distractors (leading to a PD ERP component), whereas PSZ focused attention on these items (leading to an N2pc ERP component). This suggests that, when maintaining a task set, PSZ engage in aberrant focusing of attention, or hyperfocusing, onto goal-relevant features.

An inability to sustain attention was noted in the original clinical descriptions of schizophrenia, but the vast majority of experimental studies have failed to report a performance decrement over time, calling this observation into question. To test for such deficits when task conditions conform to basic science taxonomy for the validity of sustained attention tasks, a dynamic stimulus array was presented in which targets, differing subtly from standard stimuli, were presented infrequently and unpredictably. Both people with schizophrenia (PSZ, N=40) and healthy control subjects (HCS, N=29) displayed a reduction in hit rate and an increase in reaction time from the first to the second 5-minute period. Thereafter, the hit rate of HCS recovered and remained stable, while that of PSZ continued to decline. When performance at task onset was equated between groups, the decrement over time in PSZ remained of the same robust magnitude. Thus, when the nature of the task challenges sustaining attention over time, PSZ display a clear deficit in this ability.