When singular and plural are both grammatical: Semantic and morphophonological effects in agreement

• Grammatical encoding in language production is examined using subject–verb number agreement.
• We use Serbian quantified noun phrases where both singular and plural verb agreement are grammatical.
• Verb number varied with levels of individuation of the referent, and NP noun homophony with the nominative singular form.
• Four computational implementations of the Marking & Morphing model are presented to try to account for the behavioral data.
• The findings are discussed within the Marking & Morphing, competition and controller misidentification accounts.

The utterance planning processes allowing speakers to produce agreement between subjects and verbs (the catsplareplasleep) have been the topic of extensive study as a window into language production mechanisms. A key question has been the extent to which agreement processing is influenced by semantic and phonological factors. Most prior studies have found limited effects of non-syntactic, particularly phonological factors, leading to conclusions that agreement is computed by a process influenced strongly by syntactic factors and with only a minor contribution of semantics. This conclusion may have been influenced by use of agreement error data as the main dependent variable, because errors are rare, potentially reducing sensitivity to the interaction of several factors. Two studies investigate agreement processing in Serbian, which allows both singular and plural verb forms to agree with plural nouns in some constructions. We use these constructions to further investigate the contribution of semantic factors to agreement, by manipulating levels of individuation of the members of a set. In addition, we investigate the effect of morphophonological homophony onto the participants’ productions of agreeing forms. The findings are discussed in the context of three models of agreement (Marking & Morphing, competition and controller misidentification), which differ in the extent to which they allow the influence of non-syntactic factors on agreement. We also compare the behavioral findings with the predictions of four computational implementations of the Marking & Morphing account. We discuss the implications of the behavioral and computational findings for models of agreement and the language production more broadly.