Canonicity of theta-role assignment

Despite sensitivity to syntactic violations and absence of overt syntactic mistakes in spontaneous speech, it was noticed that PADs show a generalized simplification of their morpho-syntactic structures (Kemper et al., 1993; Lyons et al., 1994). Based on this observation, studies attempt to look for signs of syntactic deficit in details. Their attention focuses on syntactic manipulations that might entail a certain degree of complexity.

Background literature offers a series of studies, which take into consideration two major factors: canonicity of theta-role assignment and embedding (especially in the form of

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relative clauses). The present section deals with the former, the following section deals with the latter.

In order to verify patients’ reliance on the canonicity of theta-role assignment, authors take into consideration either passive structures or verbs characterized by peculiar argument grids. For instance, Bates et al. (1985) elicit short narratives containing passive structures. The analysis of the output counts only few passives though, among which, the majority is of the periphrastic get-type. Passive is therefore underrepresented in production. However, comprehension of passive seems to be spared. Grossman & White-Devine (1998) ask comprehension questions concerning active and passive sentences, and patients answer accurately on both conditions. No difference between active and passive sentences emerges also in a sentence repetition task run by Small et al. (2000).

Bickel et al. (2000), Waters et al. (1998), and Kemper et al. (1998) test patients’

mastery of passive structures through sentence-to-picture matching tasks, and obtain rather sound results. Bickel et al. (2000)¹² do not find any significant difference between active and passive sentences. However, within the latter condition, they notice that reversible passives challenge PADs more than non-reversible passives do. That means that patients’ processing of passive structures benefits from the presence in the passive clause of an inanimate referent, which is less probable to be assigned the agent theta-role¹³.

Waters et al. (1998) gather similar results with a sentence-to-picture matching task and a video judgment task. In the latter, participants must judge whether the stimulus sentence they hear correctly describes the video content. In both tasks, PADs equally master the comprehension of active and passive sentences.

The only study to report an asymmetry between active and passive sentences is the one run by Kempler et al. (1998): their PADs are less accurate on passive sentences than on active ones. However, the asymmetry is reduced in the case of active sentences with two conjoined NPs in the object position (e.g., 'The cow chases the dog and the cat').

12 Among the reviewed studies, Bickel et al. (2000) is the only one that samples the asymmetry between active and passive sentences in a language different from English, namely German.

13 Chapter 5 includes a discussion on the reasons why passive structures with inanimate subject are processed with more ease than passive structures with two animate arguments.

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Grossman & White-Devine (1998) shift the attention towards another aspect of non-canonical theta-role assignments, namely verbs characterized by peculiar thematic grids.

In particular, Grossman & White-Devine (1998) analyse the case of causative verbs:

(4) John drowns the swimmer

In (4), the actual agent of the drowning action is the swimmer, as made explicit by the use of the verb in its intransitive form:

(5) The swimmer drowns

The same meaning as in (4) can further be conveyed by a periphrastic causative structure:

(6) John made the swimmer drown

In their study, Grossman & White-Devine (1998) sample patients’ comprehension of active sentences with transitive verbs, with causative verbs (4) and with periphrastic causative structures (6). Participants listen to the sentences and then answer Yes/No questions (e.g. 'Did the swimmer drown?' or 'Did John drown?'). Based on patients’

answers, authors claim that PADs are spared at processing transitive verbs, while they are impaired at processing lexical causative verbs. However, comprehension of causatives improves in the case of periphrastic structures, which make the peculiar theta-role distribution explicit. Authors deduce that the specific difficulties on causative verbs stem from the fact that the Agent role must be assigned to the object in the clause structure.

Manouilidou et al. (2009) further investigate non-canonical distributions of theta-roles and their effects on PADs’ processing abilities. The object of the study are psychological predicates of the 'fear' and 'frighten' kind:

(7) John fears the storm

(8) The storm frightens John

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Both kinds of verbs do not respect the thematic hierarchy, which prescribes the Agent >

Experiencer > Theme order. 'Fear' verbs entail an atypical theta-role assignment because the first element in the hierarchy (the agent) is not assigned. However, the canonical order is respected as the experiencer (John) precedes the theme (the storm). In contrast, verbs of the 'frighten' kind entail a non-canonical theta-role order as the theme (the storm) is assigned prior to the experiencer (John).

Manouilidou et al. (2009) use a sentence completion task, in which the argument structure is provided to participants, along with three alternative verbs. Participants’ task is to select the target verb that can complete the sentence in a meaningful way. Overall, PADs perform well on transitive verbs, while they have many uncertainties with contexts requiring psychological verbs (with no major asymmetries between 'fear' and 'frighten' verbs). The authors interpret the result as the manifestation of a specific deficit: PADs are impaired when theta-role assignment does not strictly respect the canonical hierarchy.

Taken together, results from the studies reviewed in the present section show that patients do not experience difficulties with thematic roles, when these are canonically realized at the deep structure level. Passive structures with a theme/agent reversed order are not problematic. This is because at the deep structure the two roles are canonically assigned: the agent corresponds to the external argument and the theme to the internal one. At the surface level, the order is reversed but patients can nonetheless process the sentences. In contrast, causative and psychological verbs entail hierarchical violations at the deep structure, which challenges PADs.