Background. Impaired distractor inhibition may contribute to the selective attention deficits
observed in depressed patients, but studies to date have not tested the distractor inhibition theory
against the possibility that processes such as transient memory review processes may account for the
observed deficits. A negative priming paradigm can dissociate inhibition from such a potentially
confounding process called object review. The negative priming task also isolates features of the
distractor such as colour and location for independent examination.
Method. A computerized negative priming task was used in which colour, identification and
location features of a stimulus and distractor were systematically manipulated across successive
prime and probe trials. Thirty-two unmedicated subjects with DSM-IV diagnoses of non-psychotic
unipolar depression were compared with 32 age, sex and IQ matched controls.
Results. Depressed subjects had reduced levels of negative priming for conditions where the colour
feature of the stimulus was repeated across prime and 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 distractor inhibition in
depressed subjects, and suggests that object review is intact in these subjects. Greater impairment
in negative priming for colour versus location suggests that subjects may have greater impairment
in the visual stream associated with processing colour features.