||A negative test of the sensorimotor dissociation with saccades perturbed by close to threshold distractors
In a dual task participants first made a saccade toward a suprathreshold target presented on the extinction of the fixation point and then decided whether a close to threshold distractor (d'~2) displayed on 50% of the trials was present/absent. Distractors were displayed for 17 - 80 ms at þ5° from fixation on the horizontal meridian. Targets were presented at 10° eccentricity either on the same meridian and side as the distractor (Experiment 1) or on the vertical upper meridian (Experiment 2). Distractor - target stimulus onset asynchrony (SOA) was -80 ms or 0 ms (ie distractor first or concurrent with target; Experiment 1) or -100 ms (Experiment 2). In Experiment 1, saccade endpoints were shifted toward the distractor ('global effect') only on trials entailing perceptual Hits for both SOAs. In Experiment 2 the curvature of saccades (but not their endpoints) was biased toward the distractor, once again only on Hit trials (suggesting an excitatory rather than inhibitory perturbation). The data provide further evidence that the motor program is unaffected by 'invisible' (missed) stimuli.