Left-Corner Parsing And Psychological Plausibility

It is well known that even extremely limited centerembedding causes people to have difficulty ill comprehension, but that leftand right-branching constractions produce no such effect. If the difficulty in comprehension is taken to be a result of processing load, as is widely assumed, then measuring the processing load induced by a parsing strategy on these constructions may help determine its plausibility as a psychological model. On this basis, it has been ~rgued [A J91, JL83] that by identifying processing load with space utilization, we can rule out both top-down and bottom-up parsing as viable candidates for the human sentence processing mechanism, attd that left-corner parsing represents a plausible Mternative. Examining their arguments in detail, we find difficulties with each presentation. In this paper we revise the argument and validate its central claim. In so doing, we discover that the key distinction between the parsing methods is not the form of prediction (top-down vs. bottom-up vs. leftcorner), but rather the ability to iastantiate the operation of composition.