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Hemispheric specialization for global and local processing: the effect of stimulus category
G R Fink1, J C Marshall, P W Halligan
1Wellcome Department of Cognitive Neurology, Institute of Neurology, London, UK. g.fink@fil.ion.ucl.ac.uk
Proceedings. Biological Sciences
|April 22, 1997
Summary
Brain processing of visual scenes shows hemispheric differences. Object-based stimuli, unlike letter-based ones, reverse the typical left/right brain activation patterns for global and local visual features.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Neuroimaging
Background:
- Neuropsychological studies suggest right hemisphere dominance for global visual processing and left hemisphere dominance for local processing.
- Previous research using letter-based stimuli (Navon figures) showed left prestriate cortex activation for local processing and right prestriate cortex activation for global processing.
- Limited understanding exists regarding how different stimulus categories influence hemispheric lateralization in visual processing.
Purpose of the Study:
- To investigate brain activity using positron emission tomography (PET) during local and global processing of object-based hierarchical stimuli.
- To determine if stimulus category influences hemispheric lateralization in prestriate cortex activation.
- To compare findings with previous studies using letter-based stimuli.
Main Methods:
- Positron emission tomography (PET) scans were performed on normal subjects.
- Subjects engaged in tasks requiring local or global processing of object-based hierarchical stimuli.
- Attentional modulation of neural activity in the prestriate cortex was assessed.
Main Results:
- Attentional modulation of neural activity was observed in the prestriate cortex.
- Greater right-sided activation occurred during local processing of object-based stimuli.
- Greater left-sided activation occurred during global processing of object-based stimuli, a reversal of findings with letter-based stimuli.
Conclusions:
- The category of visual stimuli significantly modifies hemispheric lateralization in prestriate areas during global and local processing.
- Object-based stimuli elicit opposite lateralization patterns compared to letter-based stimuli for global and local visual features.
- This highlights the dynamic nature of brain lateralization influenced by stimulus characteristics.