Self-Organization in Sentence Processing: Evidence
from Local Ambiguities

Whitney Tabor
University of Connecticut

Bruno Galantucci
University of Connecticut

Daniel Richardson
Cornell University

Several recent parsing models (Kim, 2000; Stevenson, 1994, 1998; Vosse & Kempen, 2000) assume that lexically anchored pieces of syntactic trees are activated by the words in a sentence as they are encountered, with each tree-fragment attempting to combine with other activated tree fragments to form a bigger tree. These models share properties of self-organizing systems, in that systemic behaviors arise through the interactions of small, autonomously-acting but interconnected parts. In contrast to current incremental, grammar-driven processing accounts, self-organizing models predict that locally coherent fragments will be computed even when they are ruled out by information the parser has
already encountered. Three self-paced reading experiments tested this prediction. In Experiment 1, reading times in sentences of the form (1) on the words "drivers without consulting" were greater when the verb was "fire" than when it was "hire", in keeping with the hypothesis that the irrelevant compound noun interpretation of "fire truck" was computed, although it was inconsistent with the preceding modal verb, "would".

(1) We did not believe the company would fire/hire truck drivers without consulting the union.

In (2), the self-organization theory predicts that the locally coherent active reading of "the player tossed the frisbee" will interfere with the globally coherent (reduced relative) parse.

(2) The coach chided the player (who was) tossed/thrown the frisbee.

Indeed, Experiment 2 showed that reading times on "tossed" and the following words with "who was" absent were elevated compared to the other three cases, indicating that clausal structures can also produce distraction. Finally, Experiment 3 replicated the syntactic aspects of Experiment 2 and found evidence for early use of semantic information in the formation of local subparses.

(3) The bandit worried about the prisoner/gold (which was) transported the whole way.

Reading times on the verb "transported" and following words were elevated when the manipulated noun was animate ("prisoner") and "who was" was absent, compared to the other three cases, indicating that the semantic coherence of the active sense of "prisoner transported" created a local distraction. In addition to the empirical support just noted,
self-organization offers a unified treatment of classic garden path sentences (e.g., "the horse raced past the barn fell") and center embedded structures ("the dog the rat the cat chased bit ran"): all difficulty stems from competition from errant
combinations, as shown by Kempen & Vosse, 2000. We show that a model similar to theirs unifies all three kinds of effects.

References

Kim, A. E. (2000). The grammatical aspects of word recognition. PhD Dissertation, Department of Psychology, University of Pennsylvania.

Stevenson, S. (1994). Competition and recency in a hybrid network model of syntactic disambiguation. Journal of Psycholinguistic Research, 23(4):295-322.

Stevenson, S. (1998). Parsing as Incremental Restructuring. In Fodor, J. D. & Ferreira, F. (Eds.) Reanalysis in Sentence Processing, (pp. 327-364). Dordrecht: Kluwer Academic Publishers.

Vosse, T. & Kempen, G. (2000). Syntactic structure assembly in human parsing: a computational model based on competitive inhibition and a lexicalist grammar. Cognition, 75: 105-143.