Implicit redundant-targets effect in visual extinction.

Patients with left visual extinction as a result of unilateral right hemisphere damage were tested on a redundant-targets effect paradigm (RTE). LED-generated brief flashes were lateralized either to the left or to the right visual hemifield or presented bilaterally. Subjects were asked to press a key as fast as possible following either unilateral or bilateral stimuli and immediately afterwards to report on the number of stimuli presented. As previously found in normal subjects, bilateral stimuli were responded to faster than unilateral ones, and this was evidence of a RTE. The main thrust of this study was that extinction patients showed a RTE not only for correctly perceived bilateral stimuli but also in trials in which they extinguished the stimulus on the field contralateral to the lesion. This result is compatible with a preserved processing of the extinguished input at least up to the stage at which it may interact with the input from the normal side to yield a speeded motor response. Interestingly, the implicit redundancy gain of extinction patients was found to fit a coactivation (i.e. neural) rather than a probabilistic model.