Separating hierarchical relations and word order in language production: is proximity concord syntactic or linear?

In this paper we address the question whether hierarchical relations and word order can be separated in sentence production. In two experiments, we assess whether subject-verb agreement errors (such as 'The time for fun and games are over') require linear proximity of a so-called 'local' noun ('games' in the example) to the verb. In the first experiment, we found a proximity effect when participants were asked to complete sentential beginnings of the kind: 'The helicopter for the flights'. In the second experiment, we asked participants to produce a question such as 'Is the helicopter for the flights safe?'. The syntactic relation between the subject noun and the local noun is the same in the two experiments, but the linear position of the local noun is different. The distribution of agreement errors was similar in the two experiments. We argue that these data provide evidence for a stage in language production in which a syntactic structure is built prior to a stage in which words are assigned to their linear position. Agreement is computed during the first stage.