Cortical activations for symmetry effect on visual word form perception in developmental dyslexia

Area of Science:

• Neuroscience
• Developmental Psychology
• Cognitive Science

Background:

• The human visual system's ability to generalize across symmetric views is crucial.
• Developmental dyslexia (DD) is often associated with difficulties in distinguishing mirror-symmetric stimuli, like 'b' and 'd'.
• Overcoming mirror generalization is vital for acquiring proficient reading skills.

Purpose of the Study:

• To investigate the impact of symmetry on visual word form perception in individuals with developmental dyslexia.
• To compare visual processing and brain activity related to symmetry in dyslexic and typical juvenile readers.

Main Methods:

• Utilized real, non-, jiagu-, and scrambled Hanzi characters with symmetric and asymmetric compositions as stimuli.
• Conducted behavioral experiments to assess accuracy in distinguishing character compositions.
• Employed block-design functional magnetic resonance imaging (fMRI) to examine brain activity, focusing on the visual word form area (VWFA).

Main Results:

• Both typical and dyslexic groups showed improved accuracy with symmetric over asymmetric character compositions (the "symmetry effect").
• The visual word form area (VWFA) was identifiable in typical readers but not consistently in dyslexic readers.
• Typical readers exhibited greater sensitivity to visual word forms in the lingual and fusiform areas.
• Dyslexic readers displayed heightened occipitotemporal activity when analyzing symmetry, especially with visual word forms.

Conclusions:

• Typical readers effectively suppress mirror generalization during literacy acquisition.
• Persistent mirror generalization in developmental dyslexia may negatively affect reading performance.
• The findings highlight differences in visual processing and neural activation patterns between dyslexic and typical readers concerning symmetry and visual word forms.