Not all reading is alike: MEG study of the task effect during verb generation

The word can be read in different ways: a reader can pronounce the written word out loud, in response to another word, or even scan through the word without conscious access to its meaning. Does the brain activation during reading depend on the purpose of the reading? In the series of experiments we examined how the task to produce a related word modifies the recognition process of a visually presented word compared to its plain reading. Using MEG and magnetic source imaging, we found that the task demands penetrated into early (200-400 ms) and late (450-800 ms) stages of written word processing. The brain response to the presented noun was stronger when the participants were required to generate an associated verb (verb generation task) rather than to read the noun silently. Moreover, the spatial pattern of brain activation under the verb generation task was bilateral, suggesting involvement of the right hemisphere in the elaborate linguistic processing (Fig.1).

Fig. 1. Reconstructed cortical response evoked by visually presented nouns.
The subject had to either simply read the word or read the word and generate a related verb.
The red color denotes the areas that show greater response
during the verb generation task than during silent reading.

Notably, difficulty of the verb generation, i.e. the strength of association between the noun and the potential ‘verb responses’ (compare a sun – to shine and paper – to crumble, to tear apart, to burn,...), affected the period between 250 and 400 ms after the noun presentation. When the noun was strongly associated with the verb, the noun-evoked response was greater in the left temporal pole and left ventro-lateral prefrontal cortex - the regions previously implicated in semantic retrieval. We suggest that this early brain response reflects the automatic access to the verb's semantic representation, which occurs simultaneously with the lexico-semantic analysis of the noun due to the strong noun-verb associative links.

This research is carried out in cooperation with Professor B.M. Velichkovsky, Department of Neurocognitive and Socio-Humanitarian Sciences of National Research Center ‘Kurchatov Institute’.