The non-contribution of attentional biases to visual field asymmetries for temporal discrimination

Divided visual field techniques were used to investigate hemispheric asymmetries for the threshold of fusion of two flashes in a group of right-handed adults. A right visual field (RVF) advantage was found and this was interpreted in terms of the left hemisphere's enhanced capacity for the detection of fine temporal events. This asymmetry could be the result of either (a) a structural advantage (where an asymmetry in physical access exists); or (b) an attentional bias (where attention is biased to one side). In order to assess the contribution of attentional and structural factors, attention was manipulated during the experiment by a centrally located arrow which could give neutral, valid (80%) or invalid cues (20%). Reaction time measures showed a cost for invalid trials relative to valid trials. This effective manipulation of attention for the valid and invalid trials had no effect on the RVF advantage relative to the baseline (neutral) trials. It was concluded that attentional biases play no significant role in the RVF advantage for two-flash fusion.