Testing contrasting accounts of word meaning activation in Broca's aphasia: Experiences from a cross-modal semantic priming study

Background: Disordered sentence comprehension in Broca's aphasia may be due in part to deficient lexical-semantic processes. Three conflicting accounts, "reduced activation" (Milberg, Blumstein, Katz, Gershberg, & Brown, 1995), "slowed activation" (Swinney, Zurif, & Nicol, 1989), and "normal activation" (Hagoort, 1993; Swaab, Brown, & Hagoort, 1998), are reviewed, and controversial issues related to testing each account are identified. Aims: Based on these considerations, we designed a cross-modal lexical decision (CMLD) experiment to test the three accounts. Methods & procedures: We auditorily presented polarised ambiguities which were embedded in sentence contexts to ten healthy older participants and seven individuals with aphasia. The contextual constraint was established by biasing towards characteristic semantic features of the alternate meanings of the ambiguous words. Lexical decision probe words were visually presented for 2750 ms, beginning at the acoustic offset of the ambiguous words. Outcomes & results: A repeated measures analysis of covariance (adjusting for lexical decision reaction times to the ambiguous words in isolation) evidenced no priming effects for the control group. Hence, no conclusions could be drawn about the performance of participants with aphasia. The surprising finding for the control group is discussed in light of potential caveats associated with the dual-task nature of the CMLD paradigm. Conclusions: Based on our findings we propose a number of parameters that should be specified in order to validly examine persons with aphasia with on-line tasks such as cross-modal lexical decision.