Say what you please? Really?

Gennari and MacDonald (2009) presented evidence that reading times in comprehension are influenced by the likelihood of a speaker choosing a particular structure in production. It’s an important and interesting paper. From this they propose the PDC (Production Distribution Comprehension): choices made to ease planning in production give rise to distributional patterns in the input, which in turn influence comprehension. The present paper suggests maybe everything (language production, acquisition, parsing, and language typology) works this way and seems to imply that therefore we might not need abstract syntactic representations, recursion, a language acquisition device, etc., at least not to explain processing difficulty. Maybe, but we might want more evidence. In addition to the subjectvs. object-relative clause distinction that motivated the PDC, a second case is discussed in the current paper: modifiers that may attach low or high. But the argumentation only shows that a production account is in principle possible, it doesn’t say why it’s any better than available comprehension accounts. PDC is usually discussed as a “view” or “perspective.” But when the author suggests it’s mechanistic, it sounds more like an empirical claim. If it is an empirical claim, then one might want to know how distributional patterns are discovered in the input, how general they are, how they are stored, and how they are utilized. After all, on the PDC model, that’s where all the action is, at least for the comprehension system. It might also be germane to figure out whether the statistics are gathered separately for different speakers, different dialects, different registers. Also, it might be good to provide evidence that it IS the statistics themselves that guide expectations in comprehension, and not implicit knowledge of how the production system works. As for the PDC perspective, let’s endorse it. Let’s look for production-based explanations, and any other explanations we can construct, if they are precise enough to make predictions. Does the PDC make predictions? It might if speakers can say what they please. But in fact the grammar of the language will dictate what constitutes a phrase, what order is permitted or required, whether ellipsis is possible, and so forth. And the grammar demonstrably is NOT just the summation of past favored production choices but, in addition to whatever constraints acquisition or comprehension may impose, convention and historical accident also come into play, and these various factors interact in complex ways. So, at best, PDC applies when the grammar offers more than one option for the same message. To take a well-known example, in sentences containing a dative verb, Double Object structures (DO) and Prepositional Object structures (PO) are largely synonymous. Maybe in such cases principles like Easy First apply. Although Easy First is not well-defined, clearly on any tenable version of it, phrases already “given” in discourse will count as “easy.” So the prediction is that given should appear before new, listeners should store these statistics, and comprehenders should find these structures easier when given appears before new. So there is a prediction. The problem in this case, however, concerns the facts. For DO, the prediction appears to be correct. But for PO, it is not (Clifton and Frazier, 2004; Brown et al., 2012). What should we conclude from this? That PDC is confirmed (by DO structures)? That PDC is disconfirmed (by PO structures)? That in precisely the case of interest, where the grammar permits more than one option, whatever is going on is more complex than PDC countenances? Let’s take another example. Perhaps the dative alternation is misleading for some reason. Take extraposition from subject (1b) and from object (2b). Apparently we could explain the ease of (1b) with “Easy First”— the most important of the three core production planning principles since “Plan reuse/priming” will depend on context, and Reduce interference will depend on lexical choices. But “Easy First” would seem to predict no advantage for extraposition from object (2b) since the object is last regardless of whether the object is extraposed, as in (2b), or not extraposed (2a). Nevertheless, intuitively, and in pilot data of Emily Westland (2012), (2b) is markedly better than (2a). Like the dative alternation example, this suggests a PDC approach may be a bit too simple.