Eye dominance influences triggering action: the Poffenberger paradigm revisited.

Our dominant eye (DE) is the one we unconsciously choose when performing a monocular task. Although it has been recognized for centuries, eye dominance and its behavioral consequences remain poorly understood. Here we used the simple and well-known Poffenberger paradigm (1912) in which participants press a button with the right or left index finger, in reaction to the appearance of a lateralized visual stimulus. By selecting participants according to their DE and handedness, we were able to decipher the impact of eye dominance on visuomotor transformation speed. We show, for the first time, that in right-handers simple reaction times (RT) in response to a lateralized visual target are shorter when it appears in the contralateral visual hemifield with respect to the DE. In left-handers, only those with a right DE exhibit a shorter RT with the left hand and they show no hemifield difference. Additionally, the Poffenberger paradigm has been used to estimate the interhemispheric transfer time (IHTT) in both directions, from the right to the left hemisphere or the reverse, by comparing hand RTs following stimulation of each visual hemifield. The present study demonstrates that this paradigm leads to biased estimations of these directionally considered IHTT and provides an explanation to the often reported IHTT negative values that otherwise appear implausible. These new findings highlight the need to consider eye dominance in studies investigating the neural processes underlying visually-guided actions. More generally, they demonstrate a substantial impact of eye dominance on the neural mechanisms involved in converting visual inputs into motor commands.