Past and present: electrophysiological differences in processing time reference
Recent studies have shown that reference to the past is more problematic in aphasic individuals than reference to the present (Anjarningsih et al. 2009; Bastiaanse, 2008). A fundamental issue concerns the extent to which past time reference difficulties are specific to aphasia. The present experiment was aimed at testing universal differences in processing present and past reference. We hypothesized that if past time reference problems are specific to aphasia, the same ERP effects should be observed while healthy individuals process verbs referring to the present and verbs referring to the past. However, if differences between present and past are more universal, non-similar ERP effects should be found.
Processing present and past time reference expressed through verbs is different in healthy individuals. Violation of the previously set time frame with a present tensed verb elicits a clear P600 response time locked to the critical verb. It means that present time reference is started being decoded and integrated into the preceding time context as soon as such it is presented. In contrast, there is no response time locked to the target verb when time frame is violated with a past tensed verb. This could be due to the fact that the proper decoding of time frame from verbal morphology does not happen right after a past tensed verb is presented. Instead, processing past time reference is delayed. These findings are in line with aphasiological data and suggest that problems with past in aphasia are based on more universal differences between processing present and past time reference.