Semantic hyperpriming in schizophrenia

Impairment of memory is one of the principal cognitive symptoms of schizophrenia. Pomarol-Clotet et al ¹ reported on a meta-analysis in which they evaluated the results of studies on semantic priming in schizophrenia. Semantic priming is a component of long-term implicit memory. They argued that hyperpriming (i.e. greater semantic priming in patients than healthy controls) could be an artefact of a general slowing in schizophrenia. As a consequence, these authors aimed to consider general slowing as a moderator variable in their statistical analysis. The measure of general slowing that they chose corresponded to the difference in response time between controls and patients, when prime and target were unrelated. In our opinion, this measure is not the most suitable as it reflects other cognitive processes. Individuals need to inhibit the prime so as to be able to process the target, since prime and target do not share any semantic relationship. Consequently, response time in an unrelated condition could be the expression of an accurate inhibitory process rather than of a general slowing as proposed by the authors. Some arguments support this view. First, we evaluated slowing in a simple reaction task in two different studies. ^2,3 Values were included as covariates in the analyses of covariance of priming effects. Despite confirming general slowing, there was evidence of significant increased priming in patients with schizophrenia compared with controls. Consequently, hyperpriming can be demonstrated even if general slowing is taken into account and controlled. Second, we demonstrated that the time required to inhibit an unrelated prime was significantly enhanced in patients with schizophrenia compared with healthy controls. General slowing was also controlled. Consequently, we demonstrated that the increased priming effect in patients compared with controls was mainly induced by increased time required to inhibit the unrelated prime. Our results support impairment of the inhibition of semantically unrelated information in patients with schizophrenia. Pomarol-Clotet et al suggested that ‘the greater the slowing, the greater the amount of priming’. Given our results, an alternative explanation has to be considered. We suggest that hyperpriming in patients with schizophrenia could reflect decreased abilities to inhibit irrelevant information such as semantically unrelated information.