Authors:

Assadollahi, R. & PULVERMULLER, F.

Reference:

Year of publication:

2001

CBU number:

5173

Abstract:

Do neuromagnetic brain responses reflect the interaction between physical and cognitive word properties? What is the topography and timing? Four groups of written words (short/long x rare/common) were presented repeatedly in a memory task. Word-evoked fields of 15 subjects were recorded using a 148-channel MEG. Word length and frequency influenced brain responses at overlapping but distinct intervals: As early as 60-120ms after presentation, long words led to a significantly higher global field power (GFP) compared with short words. This effect was reflected in the topography at occipital sites. The physiologic manifestation of word frequency followed immediately (120-160 ms), but only for short words. An exclusive frequency effect for long words was observed slightly later (225-250 ms). Thus, there was a differential frequency effect: word frequency influenced neurophysiologic correlates of short words much earlier than that of longer words. The topography of the interactions is mainly reflected at left anterior sites. These data indicate that (a) nonphysical cognitive aspects of stimuli can have an impact on early neuromagnetic responses and (b) the latency of this impact depends on physical stimulus properties. We conclude that early steps of word processing are partly cascaded: processing of visual stimulus features (physical, word length) is followed immediately by access to forms in the mental lexicon (cognitive, word frequency)