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Abstract:
What is the impact of physical and cognitive word properties
on the neuromagnetic brain response? Are the physiological
correlates of these properties dissociable and if so, at which
latencies? A group of 15 subjects performed a memory task while
brain responses were recorded using a 148 channel MEG. Four groups
of written words (short/long x rare/common) were presented
repeatedly. Word length and frequency influenced brain responses at
overlapping but distinct intervals: Already 90-120 ms after
presentation long words led to a significantly higher global field
power (GFP) compared to short words. The physiological
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 (240-290 ms). Thus, there was a
differential frequency effect: word frequency influenced
neurophysiological correlates of short words much earlier than that
of longer words. These data indicate (I) that non-physical
cognitive aspects of stimuli can have an impact on early
neuromagnetic responses, and (II) that the latency of this impact
may depend on physical stimulus properties. We conclude that early
steps of word processing are partly cascaded: processing of visual
stimulus features (physical, word length) is immediately followed
by access to word forms in the mental lexicon (cognitive, word
frequency).
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