On the interdependency between attentional biases and visual field effects with bilateral presentations of stimuli.

Previous research indicates that bilateral presentations of visual stimuli yield greater visual field differences than unilateral ones. Although this fact has generally been interpreted by reference to functional models of hemispheric specialization, an alternative explanation has been offered, which suggests that it is artifactually caused by an attentional bias (AB). Indeed, consistent positive correlations between the direction of ABs and that of visual field effects have been reported. However, this relationship remains uncertain since different tasks, presented at different moments, have been used in order to document it. We report on a bilateral presentation task which controlled this potential discrepancy by mixing trials measuring ABs with those assessing visual field effects. We showed that, in a group of dextrals, the direction of the visual field effect is intimately correlated with that of the AB; subjects with a right AB showed a right visual field advantage, whereas subjects with a left AB showed a left visual field advantage; moreover, subjects with no overall AB did not show any visual field advantage. The results of this experiment confirm the fact that the formally reported correlations between the direction of ABs and visual field effects are determined by individual differences in ABs rather than by the task being used to assess them. This observation points to the necessity for further research on variables affecting the between-subjects variability in ABs with the use of bilateral presentations of visual stimuli.