Near-infrared Spectroscopic Analysis of Orthographic Sentences' Differential Effects on Verbal Working Memory

Abstract

Verbal working memory for different orthographic sentences in Japanese was investigated using near-infrared spectroscopy (NIRS). 12 participants were asked to read aloud three sentences presented sequentially on a CRT display in the Reading task. The participants also memorized an underlined target word in each sentence in the Reading Span Test (RST) task. Four conditions were presented to the participants: (1) A sentence with spaces using only Kana characters (Kana-S); (2) A sentence with spaces using Kanji and Kana characters (Kanji-S); (3) A sentence without spaces using only Kana characters (Kana-NS); and (4) A sentence without spaces using Kanji and Kana characters (Kanji-NS). Oxy-Hb waveforms in frontal areas increased significantly when reading the sentences aloud in the RST task, compared to the Reading task. In the RST task, Oxy-Hb waveforms in the right dorsolateral prefrontal cortex during the recall of target words in Kana-NS and Kanji-S (i.e., unfamiliar orthography) increased significantly, compared to Kana-S and Kanji-NS (i.e., familiar orthography). These results suggest that increased attention control is necessary to working memory for orthographically unfamiliar sentences.