A recent study by our group showed that the scaling of reach trajectories to target size is independent of conscious visual awareness of that intrinsic target property (Binsted et al. in Proc Natl Acad Sci USA 104:12669-12672, 2007). The present investigation sought to extend previous work and determine whether unconscious target information represents a temporally durable or evanescent visuomotor characteristic. To accomplish that objective, we employed Di Lollo et al's (J Exp Psychol Gen 129:481-507, 2000) object substitution masking paradigm and asked participants to complete verbal reports and reaching responses to different sized (1.5, 2.5, 3.5, 4.5, 5.5 cm) targets under masked and non-masked target conditions. To determine whether visuomotor networks retain unconscious target information, reaching trials were cued concurrent with target presentation or 1,000 or 2,000 ms after target presentation. For the perceptual trials, participants readily identified the size of non-masked trials but demonstrated only chance success identifying target size during masked trials. Interestingly, however, reaches directed to non-masked and masked targets exhibited comparable and robust scaling with target size; that is, lawful speed-accuracy relations related to movement planning and execution times were observed regardless of whether participants were aware (i.e., non-masked trials) or unaware (i.e., masked trials) of target size. What is more, the length of the visual delay period used here did not differentially influence the scaling of reach trajectories. These results indicate that a conscious visual percept is not necessary to support motor output and that unconscious visual information persists in visuomotor networks to support the kinematic parameterization of action.
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