Journal of Cognitive Neuroscience
Common blood flow changes across visual tasks: Ii. decreases in cerebral cortex
Journal of Cognitive Neuroscience
Order Information in Working Memory: fMRI Evidence for Parietal and Prefrontal Mechanisms
Journal of Cognitive Neuroscience
Attention Mechanisms in Visual Search - An fMRI Study
Journal of Cognitive Neuroscience
Journal of Cognitive Neuroscience
Contribution of Hand Motor Circuits to Counting
Journal of Cognitive Neuroscience
Neural correlates of symbolic number comparison in developmental dyscalculia
Journal of Cognitive Neuroscience
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Visual object enumeration is rapid and accurate for four or fewer items but slow and error-prone for over four items. This dichotomy has recently been linked to visual attentional phenomena by findings suggesting that ''subitizing'' of small sets of objects is preattentive whereas ''counting'' of over four items demands spatial shifts of attention. We evaluated this link at a neural level, using H215O positron emission tomography to measure changes in regional cerebral blood flow while subjects enumerated the number of target vertical bars that ''popped out'' of a 16-bar visual display consisting of both horizontal and vertical bars. Relative to a condition with a single target, subi tizing (one to four targets) activated foci in the occipital extrastriate cortex, consistent with involvement of early,preattentive visual processes. Relative to subitizing, counting (five to eight targets) activated a widespread network of brain regions, including multiple foci implicated in shifting visual attention- large regions of the superior parietal cortex bilaterally and a focus in the right inferior frontal cortex.These results offer the first direct neural support for mapping the subitizing-counting dichotomy onto separable processes mediating preattentive vision and shifts of visual attention.