Latent inhibition (LI), poor evidence of learning following preexposure to a task-irrelevant stimulus, reflects the ability to ignore inconsequential events. Stroop interference represents a failure to inhibit processing of a task-irrelevant word when it is incongruent with the required naming of the word's print color. The apparent commonality between the two effects is in contradiction to the literature, which indicates that LI is affected by schizotypy and schizophrenia, and perhaps gender, while Stroop interference generated by the trial-to-trial procedure is unaltered by those variables. In the present experiment, low schizotypal healthy males, but not females, exhibited LI. The same groups did not differ on Stroop interference. The results are discussed in terms of different processing requirements for task-irrelevant stimuli that are an integral part of the task-relevant target stimulus (as in Stroop) or separated from it in space (as in LI).
It is generally accepted that schizophrenia, particularly when accompanied by positive symptoms, is characterized by an attentional dysfunction that can be described in terms of increased distractibility. Though impaired selective attention is not unique to schizophrenia, and some selective attention functions may also be intact in these patients (e.g., Gold et al., 2006), many writers regard a deficit in selective attention as a core psychological component of schizophrenia (e.g., Anscombe, 1987, Cadenhead and Braff, 1995 and Gray, 1998).
Not surprisingly, then, patients with schizophrenia perform poorly on experimental tasks that assess the ability to ignore irrelevant stimuli. Two such tasks, latent inhibition (LI) and Stroop, both widely used for that purpose, are the focus of the present report. By administering these tasks to the same participants, we sought to obtain data that would differentiate amongst mechanisms involved in processing irrelevant information. Furthermore, by using healthy participants divided into groups with low and high schizotypy scores (LowSz and HighSz), we hoped to identify the conditions that are responsible for the relative inability of patients with schizophrenia to ignore irrelevant stimuli, while at the same time avoiding confounding factors, such as effects of overt symptoms, hospitalization, and medication (Mednick and McNeil, 1968).
Self-report questionnaires that assess schizotypy have been widely used for this purpose. They are based on the premise that psychotic tendencies lie on a continuum, with a normal population at one extreme, and a hospitalized patient group at the other extreme, a position that is supported by a variety of evidence (for review, e.g., Vollema and van den Bosch, 1995).
