Word form encoding is under attentional demand: evidence from dual-task interference in aphasia

Although speakers can go on producing utterances while doing concurrent tasks, language planning is affected in conditions of divided attention. It is however unclear whether a concurrent task impacts only lexical selection, or if post-lexical processing is also impacted. To elucidate this question, we reasoned that if an encoding process is under attentional control, this should be even more the case when the planning process is disrupted due to brain damage: increased error rates in left-hemisphere damaged participants under dual-task conditions should therefore shed light on which encoding processes need attentional resources. Twelve participants producing either predominantly lexical or phonological errors following left-hemisphere stroke and eleven matched healthy controls underwent a dual-task picture naming paradigm with a concurrent auditory verbal and non-verbal task. The results indicate an impact of active dual-tasks on word production in both controls and aphasic participants, but a magnified effect on errors in aphasic participants with an overall increase of phonological errors under dual-task conditions. These results suggest that post-lexical encoding processes are under attentional demand.