Effect of word familiarity on visually evoked magnetic fields

摘要

This study investigated the effect of word familiarity of visual stimuli on the word recognizing function of a human brain. Word familiarity is an index of the relative ease of word perception, and is characterized by facilitation and accuracy on word recognition. We studied the effect of word familiarity, using "Hiragana" (phonetic characters in Japanese orthography) characters as visual stimuli, on the elicitation of visually evoked magnetic fields with a word-naming task. The words were selected from a database of lexical properties of Japanese. The four "Hiragana" characters used were grouped and presented in four classes of degree of familiarity. The three components were observed in averaged waveforms of the root mean square (RMS) value on latencies at about 100, 150 and 220 ms. The RMS value of the 220 ms component showed a significant positive correlation (F=(3/36); 5.501; p=0.035) with the value of familiarity. ECDs of the 220 ms component were observed in the intraparietal sulcus (EPS). Increments in the RMS value of the 220 ms component, which might reflect ideographical word recognition, retrieving "as a whole" were enhanced with increments of the value of familiarity. The interaction of characters, which increased with the value of familiarity, might function "as a large symbol"; and enhance a "pop-out' function with an escaping character inhibiting other characters and enhancing the segmentation of the character (as a figure) from the ground.