Estimating the true cost of garden-pathing: A computational model of latent cognitive processes

What is the processing cost of being garden-pathed by a temporary syntactic ambiguity? We argue that comparing average reading times in garden-path versus non-garden-path sentences is not enough to answer this question. Trial-level contaminants such as inattention, the fact that garden-pathing may occur non-deterministically in the ambiguous condition, and “triage” (rejecting the sentence without reanalysis; Fodor Inoue, 2000) lead to systematic underestimates of the true cost of garden-pathing. Furthermore, the pure garden-path effect due to encountering an unexpected word needs to be separated from the additional cost of syntactic reanalysis. To get more realistic estimates for the individual processing costs of garden-path surprisal and syntactic reanalysis, we implement a novel computational model that includes trial-level contaminants as probabilistically occurring latent cognitive processes. The model shows good predictive fit to existing reading-time and judgment data. Furthermore, the latent-process approach captures differences between NP/Z garden-path sentences and RRC garden-path sentences: The NP/Z garden path occurs nearly deterministically but can be mostly eliminated by adding a comma. By contrast, the RRC garden path occurs with a lower probability, but disambiguation via semantic plausibility is not always effective.