The online processing of the ambiguous null object in Mandarin among patients with Broca’s aphasia

Background: Research on how patients with Broca’s aphasia and concomitant agrammatism process dependency structures online offers a window into the understanding of how language is organized in the mind. Previous studies have shown that patients evince differential performances on dependency structures generated at different levels of linguistic representation. The present study extends this line of research to investigate patients’ online processing of referential dependencies involving ambiguous pronominal interpretations. Aims: Mandarin, unlike English, allows the object to be missing (null) in some contexts, rendering these null pronominal forms as ambiguous between two interpretations (strict vs. sloppy), which are generated in different levels of linguistic representation. This study examined Mandarin-speaking healthy and agrammatic aphasic participants’ processing of the two interpretations of the null pronominal form such as Zhangsan qile ta de ma, Lisi ye qile e “literally: Zhangsan rode his horse and Lisi rode, too”, where Lisi rode either Zhangsan’s horse (strict) or Lisi’s horse (sloppy). Methods & Procedures: Two experiments, employing a Cross-Modal Picture Priming paradigm, manipulated three probe picture conditions (strict, sloppy, control) and two probe positions (at the verb phrase offset and 400 ms afterwards). Experiment 1 tested neurologically unimpaired controls in order to establish the time course of processing as a standard of comparison. Experiment 2 tested patients with agrammatic aphasia. Outcomes and Results: Immediately at the verb phrase offset where the null object is structurally licensed, unimpaired individuals primed both the strict and the sloppy interpretations, with no significant difference in reaction times between the two conditions. At the position 400 ms after the verb phrase offset; however, unimpaired participants did not show priming of either of the two interpretations. Patients showed the opposite pattern: at verb phrase offset, they did not show threshold-level priming of either of the two interpretations; 400 ms afterwards, they showed priming of both the strict and sloppy interpretations, with the strict interpretation eliciting significantly longer reaction times than the sloppy interpretation. Conclusions: Patients’ delay in priming both the strict and the sloppy interpretations shows that patients evince a temporal delay when processing dependency structures, which may arise from patients’ deficit with lexical integration. Additionally, patients spent significantly longer reaction times on the strict interpretation relative to the sloppy interpretation, which confirms the prediction that that the former, which is generated in the level of discourse, is computationally more costly than the latter, which is generated in the level of semantics.