The time-course of lexical activation during sentence comprehension in people with aphasia

Abstract

Purpose: To investigate the time-course of processing of lexical items in auditorily presented canonical (subject-verb-object) constructions in young, neurologically unimpaired control participants and participants with left-hemisphere damage and agrammatic aphasia.

Method: A cross modal picture priming (CMPP) paradigm was used to test 114 control participants and 8 participants with agrammatic aphasia for priming of a lexical item (direct object noun) immediately after it is initially encountered in the ongoing auditory stream and at 3 additional time points at 400-ms intervals.

Results: The control participants demonstrated immediate activation of the lexical item, followed by a rapid loss (decay). The participants with aphasia demonstrated delayed activation of the lexical item.

Conclusion: This evidence supports the hypothesis of a delay in lexical activation in people with agrammatic aphasia. The delay in lexical activation feeds syntactic processing too slowly, contributing to comprehension deficits in people with agrammatic aphasia.

FIGURE 1

(a) A sample sentence and corresponding probe pictures from the online cross modal picture priming task in Experiments 1 and 2. The sentence was presented auditorily at a normal speech rate. Probe pictures were presented at the offset of the direct object noun in each sentence (italics) and at three subsequent test points at 400-ms intervals. Approximate probe positions in each sentence are indicated by *. Probe pictures for the related and control conditions are depicted, though only one probe picture was presented on each individual trial. (b) The paired sentence that had the same probe pictures to depict counterbalancing of related and control probes. In this matched sentence design, the pictures related to the direct object noun for one sentence were used as the unrelated control pictures for the direct object noun of another sentence (e.g., as indicated by the dashed box around animal trainer), so that over all items, the related and control sets of pictures were identical, avoiding response time confounds due to differences between pictures.

FIGURE 2

Priming effects (control – related reaction times) for unimpaired control participants (from Experiment 1) and participants with aphasia (from Experiment 2) across four probe positions (PP). *p < .05.