Where in the brain does visual attention select the forest and the trees?

Area of Science:

• Neuroscience
• Cognitive Psychology
• Visual Perception

Background:

• The human perceptual world is hierarchically organized, from global forms to local components.
• Neuropsychological studies suggest hemispheric specialization in visual processing: left for local, right for global.
• Temporal and parietal cortex lesions impair attentional and perceptual mechanisms.

Purpose of the Study:

• To investigate the neural mechanisms of global and local visual perception.
• To provide direct evidence for hemispheric specialization in visual attention.
• To identify the role of temporal-parietal areas in attentional control.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to measure brain activity in normal subjects.
• Two experiments involved viewing hierarchically organized figures under directed and divided attention conditions.
• Brain activity was analyzed in relation to attention directed towards global or local aspects of the figures.

Main Results:

• Directed attention to global figures activated the right lingual gyrus (prestriate cortex).
• Directed attention to local components activated the left inferior occipital cortex (prestriate cortex).
• Divided attention tasks showed temporal-parietal activation correlating with local-global attention switches.

Conclusions:

• Findings provide direct evidence for hemispheric specialization in global (right) and local (left) perception.
• Temporal-parietal areas exert attentional control over prestriate cortical processing.
• This study elucidates the neural basis of hierarchical visual attention.