Neuroimaging evidence for shared lemma representations in speech production and comprehension

Abstract

Lemma representations are thought to map the meaning of words to their sounds and vice-versa (Levelt et al., 1999). There is evidence using different methodologies that suggests that lemmas are localised in the middle portion of the left middle temporal gyrus (Indefrey & Levelt, 2004). However, according to another view, sound to meaning mapping occurs bilaterally in the posterior inferior and middle temporal gyri (Hickok & Poeppel, 2007). No previous study has attempted to use neuroimaging to find evidence for lemmas being shared across production and comprehension and for their localisation in the brain. We conducted an fMRI study with four tasks that comprised two modalities (speech production and comprehension) and targeted different levels of representation (phonological, conceptual, syntactic) to which the lemma connects. We found common activation across all four tasks in the middle part of left middle temporal gyrus as well as in the left posterior inferior temporal gyrus and in bilateral posterior middle temporal gyrus, regardless of the modality and the targeted level of representation. This evidence supports theories that claim lemma representations underlie both production and comprehension, and it supports both claims regarding the localisation of lemmas.