Abstract
The purpose of this study was to investigate the visual field (VF) differences of hiragana, kanji and figure processing for normal children (NC) and mentally retarded children (MR). The subjects were 20 NC (MA=7,9, 11:10 males and 10 females) and 12 MR (MA=7, 9:4 males and 8 females). All showed right hand preference. The stimuli were hiragana (われくへ), kanji (山本大小) and figures (○ △ □ 〓). The subjects had to report both the number (2〜9) which was presented at the fixation point and either the letter or the figure which was presented on the right side or the left side of the screen. The exposure time for each task was determined for each subject during the practice session by attaining a performance level of about 70% correct responses. In both NC and MR, the mean exposure time of MA7 years was significantly longer than that of other MA years. In MR, the mean exposure time of Down's syndrome children was significantly longer than that of non-Down's syndrome children. NC showed RVF superiority for the hiragana task (t=3.65, df=3.8, p<0.001), but no VF differences for the kanji task and the figure task. For the hiragana task of NC, MA9 years showed RVF superiority (t=2.74, df=5, p<0.05) and both MA7 years and MA11 years showed an RVF advantage. NC-males showed RVF superiority (t=3.79, df=9, p<0.01), but NC-females showed a RVF advantage. On the other hand, MR showed LVF superiority both for the kanji task (t=1.63, df=20, 0.10<p<0.20) and for the figure task (t=1.98, df=24, 0.05<p<0.10), but not for the hiragana task. Thus, it is possible that the extent of hemispheric specialization of NC-males is greater than that of NC-females, or NC-females are processing the hiragana task more easily than NC-males. In addition, it seems that the extent of hemispheric specialization for verbal processing of MR is smaller than that of NC or that MR process stimuli by visiospatial strategy, and while NC process them by verbal strategy.
