Dyslexia Research Trust
Maki Koyama
I am interested in sensory and cognitive processing underlying reading
mechanisms in Japanese. The Japanese writing system uses both phonetic
“Kana” and logographic “Kanji” script. Kana is a phonetic script that is both
visually simple and orthographically regular, whereas Kanji is visually complex
and orthographically irregular. Thus Kanji are somewhat like English irregular
words; you have to learn their whole visual form to recognize them. I hope that
my studies on Japanese will help to elucidate the processing necessary for
reading across all scripts. My preliminary studies have shown that both visual
and auditory skills are needed for both Kana and Kanji, but to different extents.
Kana literacy skills rely particularly on auditory and phonological short-term
memory, but NOT visual short-term memory, while Kanji literacy skills are
uniquely explained by phonological short-term memory, orthographic processing,
and visual-short-term memory. These results suggest that phonological shortterm memory plays an important role for both Kana and Kanji, but learning Kanji
depends largely on visual-orthographic processing skills relative to learning Kana
and alphabetic scripts. Interestingly, orthographic processing skills that are
required for both Kana and Kanji reading are highly dependent on visual motion
sensitivity. This result implies that visual magnocellular system, which is
responsible for dynamic visual sensory processing, may be a general underlying
mechanism for the development of literacy skills, irrespective of the writing
system or the script.
I will also start brain imaging studies to determine the possible function(s) of two
brain regions in reading Japanese. One is called “the Visual Word Form Area”
located in the left fusiform gyrus (underneath the occipital lobe of the brain),
which is suggested to be sensitive to abstract representations of visual word form.
The other is the left middle frontal gyrus, whose activation is thought to be
especially important for reading logographs as in Kanji and Chinese. The
advantage of using Japanese is that Kana and Kanji can sound the same but be
completely different visually. I believe that by combining cognitive and imaging
studies I will be able to contribute to a deeper understanding of reading
mechanisms. Furthermore, elucidating normal reading in Japanese will help us
better understand Japanese dyslexia, which manifests itself differently from
dyslexia in English.