Memory limitations and structural forgetting: The perception of complex ungrammatical sentences as grammatical

Results from an English acceptability-rating experiment are presented which demonstrate that people find doubly nested relative clause structures just as acceptable when only two verb phrases are included instead of the grammatically required three. Furthermore, the experiment shows that such sentences are acceptable only when the intermediate verb phrase is omitted. A number of specific accounts of forgetting are considered. Two early proposed theories of this effect, the disappearing syntactic nodes hypothesis (Frazier, 1985) and the least recent nodes hypothesis (Gibson, 1991), are not consistent with the experimental results. The results, together with other acceptability patterns, suggest that the representations that are retained land subsequently forgotten) in processing sentences consist of the lexical word-strings processed thus far. Three possible accounts of the results are considered: (1) the high memory cost pruning hypothesis within the framework of Gibson (1998); (2) a recency/primacy account; and (3) a connectionist account (Christiansen & Chater, in press).