Background. Inhibitory functioning is assumed to be deficient in some psychiatric disorders, most notably in patients with schizophrenia and obsessive–compulsive disorder (OCD). In order to investigate inhibitory functioning, priming tasks are commonly used. The present paradigm offers the opportunity to isolate specific distractor features (identity, location) for independent examination.

Methods. Negative priming (NP) for stimulus identity and location was examined in patients with schizophrenia (N = 16), patients with OCD (N = 15) and matched controls (N = 16). All groups performed a referent size-selection task in which they were instructed successively to select the larger one of two cardinal numbers. The deeper processing of both stimuli was expected to yield large NP effects that allow the detection of subtle group differences.

Results. Large NP effects were found for stimulus identity in all three groups. Schizophrenic patients differed from normal controls with respect to the amount of incidental location priming. Subgroup analyses of OCD patients showed NP impairments for checkers when the response–stimulus interval (RSI) was short, but large identity NP when the RSI was long. OCD non-checkers showed normal NP patterns with short RSI, but reduced identity NP with longer RSI.

Conclusions. Schizophrenic patients do not show the ability to use spatial selective attention in order to guide their actions as shown by normal controls. Information processing was differentially impaired in OCD subgroups (checkers and non-checkers) dependent on RSI variation. This result supports those studies that found reduced NP in OCD patients and points to the necessity of differential subgroup studies.