To plan or to listen? The trade-off between comprehension and production in conversation.

Bögels, S., Casillas, M., & Levinson, S. C. (2016). To plan or to listen? The trade-off between comprehension and production in conversation. Poster presented at the Eighth Annual Meeting of the Society for the Neurobiology of Language (SNL 2016), London, UK.
Transitions between speakers in conversation are usually smooth, lasting around 200 milliseconds. Such rapid response latencies suggest that, at least sometimes, responders must begin planning their response before the ongoing turn is finished. Indeed, evidence from EEG suggests that listeners start planning their responses to questions as soon as they can, often midway through the incoming turn [1]. But given substantial overlap in the neural hardware for language production and comprehension, early response planning might incur a cost on participants’ concurrent comprehension of the ongoing turn. Do early responses come at the expense of less careful listening? We performed an EEG study in which participants played an interactive game with a confederate partner. Participants saw two pictures on their screen (e.g., a banana and a pineapple), then heard a (prerecorded) question from their partner, and then responded verbally by naming the correct picture. Participants were made to believe that their partner spoke to them live. Examples of the conditions in the experiment: 1. Early planning: 'Which object is curved and is considered to be fruit/healthy?'; 2. Late planning: 'Which object is considered to be fruit/healthy and is curved?' (response: 'the banana'). The questions were designed such that participants could start planning their response early (Example 1) or late (Example 2) in the turn. Crucially, in another part of the turn, we included either an expected word (e.g., 'fruit') or an unexpected one (e.g., 'healthy') to elicit a differential N400 effect. Our aims were two-fold: replicating the prior planning effect [1] and testing the effect of planning on comprehension. First, our results largely replicated the earlier study [1], showing a large positivity in the ERPs and an alpha/beta reduction in the time-frequency domain, both immediately following the onset of the critical information when participants could have first started planning their verbal response (i.e., 'curved'). As before [1], we interpret these effects as indicating the start of response planning. Second, and more importantly, we hypothesized that the N400 effect (the ERP difference between 'fruit' and 'healthy') would be attenuated when participants were already planning a response (i.e., in early vs. late planning). In contrast, we found an N400 effect of similar size in both the early and late planning conditions, although a small late positivity was only found in the late planning condition. Interestingly, we found a positive correlation between participants' overall response time and the size of the N400 effect after planning had started (i.e., in early planning), illustrating a trade-off between comprehension and production during turn taking. That is, quick responders showed a smaller N400 effect. We argue that their focus on production planning reduced their attention to the incoming audio signal and probably also their predictive processing, leading to a smaller N400 effect. Slow responders focused instead on the audio signal, preserving their N400 effect but delaying their response. Reference [1]: Bögels, S., Magyari, L., & Levinson, S. C. (2015). Neural signatures of response planning occur midway through an incoming question in conversation. Scientific Reports, 5: 12881. Topic Area: Meaning: Discourse and Pragmatics
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