Grammatical processing load and verb argument structure effects on the production of past-tense morphology

Background: Children with language impairments often present with morphological and verb argument structure (VAS) difficulties (Leonard, 2014). Complexity of VAS (see Grela and Leonard, 2000) as well as an increase in task demand (i.e., processing load) as found in narrative production (see Thordardottir, 2008) have been shown to affect production of grammatical morphology in children. Moreover, children with SLI employ a less diverse range of verbs than their peers and are prone to inappropriate substitutions (Black and Chiat, 2008). There is a need for an ecologically valid assessment tool (e.g., narrative retell) which examines tense elicitation and VAS of a range of verbs in child-language production. Objectives: Using grammatical complexity (mean length of utterance: MLU) as a proxy measure of processing load, this study examines the effect of MLU on the production of both past-tense morphology and obligatory arguments, and of VAS on past-tense elicitation. Methods: A secondary analysis was undertaken using data from a narrative retell task undertaken with 91 typically developing children (aged 4;06 to 12;0 years). The task targeted 44 different verbs chosen based on their semantic-syntactic properties. Results: Errors in tense elicitation and VAS were rare. Cross-tabulations did not yield evidence of an inter-relationship between number of obligatory arguments and past-tense elicitation. Correlations between grammatical complexity and some verbs were found regarding omissions of obligatory arguments and tense. Grammatical complexity decreased in utterances with obligatory argument and/or tense omissions. Conclusions: At times, typically developing school-aged children present with omissions of obligatory arguments and/or past-tense morphology. These omissions correlate to a decrease in grammatical complexity in language production. The implications of processing load and age are discussed.