Impaired distracter inhibition on a selective attention task in unmedicated, depressed subjects

Background. Impaired distracter inhibition may contribute to the selective attention deficits observed in depressed patients, but studies to date have not tested the distracter inhibition theory against the possibility that p rocesses such as transient memory review processes may account for the obse rved deficits. A negative priming paradigm can dissociate inhibition from s uch a potentially confounding process called object review. The negative pr iming task also isolates features of the distracter such as colour and loca tion for independent examination. Method. A computerized negative priming task was used in which colour, iden tification and location features of a stimulus and distracter were systemat ically manipulated across successive prime and probe trials. Thirty-two unm edicated subjects with DSM-IV diagnoses of non-psychotic unipolar depressio n were compared with 32 age, sex and IQ matched controls. Results. Depressed subjects had reduced levels of negative priming for cond itions where the colour feature of the stimulus was repeated across prime a nd probe trials but not when identity or location was the repeated feature. When both the colour and location feature were the repeated feature across trials, facilitation in response was apparent. Conclusions. The pattern of results supports studies that found reduced dis tracter inhibition in depressed subjects, and suggests that object review i s intact in these subjects. Greater impairment in negative priming for colo ur versus location suggests that subjects may have greater impairment in th e visual stream associated with processing colour features.