Functional imaging of the mechanisms underlying the bilateral field advantage

Visual stimulus comparisons across the vertical meridian are faster and more accurate than those restricted to a single hemifield (the bilateral field advantage). We set out to investigate the cerebral mechanisms underlying this effect using functional magnetic resonance imaging. Seven normal volunteers were presented pairs of shape stimuli bilaterally across the vertical meridian and unilaterally within a single hemifield. We found a network of additional areas activated in the unilateral condition over the bilateral condition which have been related to working memory in previous studies. The results suggest different processing strategies with different temporal characteristics in the bilateral and unilateral conditions, providing a novel explanation for the bilateral field advantage.