Parsing Modifiers: The Case of Bare NP Adverbs

Current models of Human Sentence Processing fall into two broad categories: Constraint Satisfaction accounts, which emphasise the immediate access of the comprehension processes to detailed linguistic information as parsing progresses (e.g., MacDonald et al., 1994), and Syntax First accounts, which hold that parsing is essentially a two-stage process, with initial decisions being made on the basis of a subset of available information (see, e.g., Frazier, 1995). In this paper, we examine evidence from Mitchell (1987) which seems strongly to favour a syntax £rst position, suggesting that basic lexical information about verbs may have little in¤uence on the early stages of sentence processing. We provide experimental evidence to show (a) that detailed linguistic information is available early, but (b) that bare NP adverbs (a type of modi£er) are read surprisingly fast, a £nding which appears dif£cult to reconcile with many current accounts of sentence processing. Constraint Satisfaction models of Human Sentence Processing rely heavily on detailed information about the combinatorial possibilities and probabilities associated with each word of a sentence. For example, MacDonald et al. (1994) suggest that the reading of a sentence such as (1a) is affected by lexico-syntactic factors including the frequencies with which the word raced is used in each of its senses (for example, as a past participle or as a past tense verb), as well as thematic factors such as how good an agent or patient horse is of raced. (1a) The horse raced past the barn fell.1 (1b) The landmine buried in the sand exploded. This type of account can be contrasted with Syntax First positions, according to which initial parsing decisions are made on the basis of a subset of available linguistic information (generally comprising category information and phrase structure rules, e.g., Frazier, 1979). These decisions may later be revised in the light of further (syntactic, thematic or pragmatic) evidence, but these revisions have an associated processing cost. According to such accounts, (1b) should be as hard to understand as (1a), since they are syntactic homomorphs. The constraint satisfaction view, on the other hand, predicts the intuitively observable difference between the two, by pointing out that (thematically) landmine makes a poor agent (but a good patient) of buried, as well as (syntactically) the statistical facts that buried is typically used as a passive past participle (in comparison to raced which is typically used as an active past tense verb). However, evidence from a study by Mitchell (1987) appears highly incompatible with constraint-based accounts. According to Mitchell, the most basic form of information associated with a verb—that of whether a verb is transitive or intransitive, or in other words the verb’s subcategorisation information—may not be available during the initial stages of sentence comprehension. Using materials like those in (2), he found that readers of (2a) were typically slow (relative to a control with a disambiguating adverbial phrase such as during surgery after visited or sneezed) at reading the word wrote. This is to be expected within almost any framework, since it is syntactically permissible (as well as thematically acceptable) for the doctor to be initially interpreted as the direct object of visited. (2a) After the child visited the doctor wrote him a prescription. (2b) After the child sneezed the doctor wrote him a prescription. Crucially, Mitchell also showed that readers were slow to read the doctor in (2b). Since sneezed is a (typically) intransitive verb,2 Mitchell interpreted these £ndings as suggesting that information about the subcategorisation of sneezed was not initially available to the parsing process (but was made available as soon as later processes could check the plausibility of the doctor as an object of sneezed). Mitchell’s £ndings are clearly problematic for constraintbased accounts of sentence processing. If the differences between (1a) and (1b) are to be accounted for in terms of information about the (probabilistic) ‘goodness of £t’ between a verb and its arguments (including the relative frequencies with which particular subcategorisation frames of a given verb are used), an account must be made of the apparent insensitivity of the human parser to the fact that sneezed is rarely, if ever, used as a transitive verb. Less often remarked upon is the dif£culty that Mitchell’s results may pose for many syntax £rst theories. Although the 1Regions of example sentences where more than one interpretation is (potentially) available are typeset in italics, and disambiguating regions are set in bold. 2Almost every ‘intransitive’ verb, as Adams et al. (1998) note, can be used in some transitive senses, if only in highly stylised phrases such as He sneezed a tiny sneeze, She yawned a big yawn, etc. details of models differ, a number of current positions converge on the importance of (potential) argumenthood, with incoming constituents being preferentially attached to the current phrase marker as arguments rather than as modi£ers or adjuncts (e.g., Crocker, 1992; Frazier & Clifton, 1996). In order to adjudicate between the attachment of a constituent as a modi£er or as an argument, the human parser must be aware that a potential site for argument attachment exists. If this information is unavailable at the time a verb is encountered, then an argument attachment strategy would provide a poor account, at least at the explanatory level, of the parser’s behaviour. Interpretations of Mitchell’s £ndings tend to assume that detailed information about the verb is initially available, but that either linguistic or experimental factors give rise to the results obtained. For example, Tanenhaus and Trueswell (1995) observe that there may be a residual bias to interpret a noun phrase following a verb as its object, lexical biases notwithstanding. This has the advantage of providing a straightforward account of Mitchell’s £ndings within a constraint satisfaction framework, but the disadvantage that it damages the predictive power of the theory (if dif£culty in reading (1a) is accounted for in terms of information associated with a particular verb, but Mitchell’s £ndings are interpreted in the light of the behaviour of verbs in general, how are we to know which factors are likely to in¤uence the interpretations of hitherto untested sentences? ). Critics of Mitchell’s experimental design have noted that he used a self-paced reading paradigm in his initial study. Due to the way that the materials were segmented (such that participants saw the words . . . sneezed the doctor in a single display before pressing a key to view the matrix verb of which the doctor was the subject), participants may have been misled into ‘strategically’ attempting to interpret the doctor as the object of sneezed. This criticism (effectively of the ecological validity of the self-paced reading paradigm) was addressed by Adams, Clifton, and Mitchell (1998), who replicated Mitchell’s experiment using an eyetracker, so that materials did not have to be arti£cially segmented. Although their £ndings contradict Mitchell’s, they remain unconvinced that subcategorisation information is initially available. One argument that they make is that Mitchell’s £ndings must still be accounted for: even if segmentation affects the way in which subjects read Mitchell’s materials, it is clear that it does not cause subjects to violate phrase-structure rules (when attaching adverbials in control materials), whereas subcategorisation information appears to be easily overridden. In this paper, we offer a different interpretation of Mitchell’s £ndings. This rests on the observation that although intransitive verbs such as sneezed do not subcategorise for object NPs, there is a class of NPs which can legitimately follow them: namely, bare NP adverbs (Larson, 1985). For example, the sentence in (3) is a perfectly acceptable sentence in English. (3) After the child sneezed the other day, the doctor wrote him a prescription. The other day serves an adverbial function; that is, it seems to modify, rather than serve as an argument of, the verb sneezed. If participants are initially aware of the subcategorisation properties of verbs, the delay in reading the doctor in (2b) relative to its control might be accounted for by a system which was working on the assumption that any NP following an intransitive verb such as sneezed would be a bare NP adverb; the delay re¤ects the fact that the doctor must be rejected in this case.