The Visual Crowding Effect In Chinese-Speaking Children With Developmental Dyslexia

Although the causes of developmental dyslexia are still debated, most researchers agree that visual cognition plays a vital role during reading. Research shows that flanking English letters strongly interfere with letter identification for dyslexics due to their visual deficits. Unlike English, Chinese is a densely-packed language and readers maybe more rely on visual processing to recognize characters, it’s possible that Chinese dyslexics might exhibit more pronounced visual crowding effect (VCE). Based on the previous studies, we tried to investigate the relationship between the visual crowding effect and developmental dyslexia.Three studies including eight experiments were carried out. Developmental dyslexia (DD), chronological age (CA) and reading level (RL) matched children were selected to take part in all studies. In study 1, we used the experimental paradigm of Bouma(1970) to examine whether Chinese children with developmental dyslexia are more influenced by VCE than chronological age and reading level matched children. In study 2, on the basis of Study 1, we used the same paradigm as study 1 to test the character and spatial properties of target and flanker characters. In study 3, whether the character font and character-spacing influenced the VCE while reading the complexity and un-complexity text. The more detailed contents and main findings were shown as follows.In study 1, in a character recognition task, three types of children’s accuracy rates were recorded. There were two conditions of stimuli:1) a single character showed randomly on the left/right 5 visual degree of retinal eccentricity, and 2) triple characters with a middle target character and two flanker characters showed on the left and right of 1 visual degree away from the target. The target and flanker characters had no semantic correlations. In both conditions, the target characters were presented on the same position of the screen.In study 2, five experiments were included to explore the properties of character and spatial of target and flanker which influence the VCE of DD. In experiment 2, we manipulated the constructions of character. In experiment 3, characters complexity were defined as strokes were examined as the property of target and flanker. In experiment 4, the font size of flanker character were tested. Based on Bouma’s law, we test the critical gap of character in experiment 5. In experiment 6, eccentricity was investigated as one of factors which influence the DD’s VCE.In study 3, two experiments were included to explore whether the character font size and character-spacing influence the VCE of DD during different visual complexity text reading. In experiment 7, We manipulated character font size with visual angel (0.75°、1°、1.25°、1.5°、1.75°) to examine whether it modulated the VCE during text reading. In experiment 8, We manipulated character-spacing (default、±3pt、±6pt、±12pt) to examine whether it modulated the VCE in sentence reading.To summarize, following conclusions were made.(1) Chinese developmental dyslexia children did experience more difficulty by visual crowding effect than normal children. And the character constructions、the size of flanker character and gap between target-flanker did not work for VCE difference of dyslexics and control.(2)Character complexity can improve the VCE of children. DD experience the same difficulty as the normal by VCE while the target and flanker were both low-complexity characters. The VCE by character constructions of DD was less than control.(3) As the faulty-integration model, the VCE of dyslexics and controls was much bigger as the font size of flanker characters much bigger. The VCE of DD experienced more cost.(4) The critical gap of Bouma’s law did not work for character recognition task. Character’s critical distance maybe bigger, and the Chinese dyslexics need larger critical gap of target and flankers. Larger gap can reduce the VCE, and the same as eccentricity.(5)Visual complexity play a vital role on VCE during text reading both for dyslexics and control. Character font size can influence the VCE of dyslexics, especially in small size (0.75°). Both DD and normal controls’ eyemovents were indeed modulated by characters font size.(6) Character-spacing can also influence the VCE of dyslexics. There were longer time and more fixations during reading the low-visual-complexity text with +6pt character-spacing, while spacing with +12pt didn’t, indicating that enlarging character-spacing facilitates reading performances. However, the quantity relationship of character-spacing and the VCE need to be further studied.