Learning to detect but not to grasp suppressed visual stimuli K Ludwig1, P Sterzer1, N Kathmann2, V H Franz3, G Hesselmann1 |
|---|
1Visual Perception Laboratory, Charité - Universitätsmedizin Berlin, Germany |
| One feature of continuous flash suppression (CFS) is its potency to render stimuli invisible for up to seconds (Tsuchiya & Koch, 2005). Here, we exploited this feature to test a central implication of the two-visual-systems hypothesis (TVSH), namely that the dorsal visuomotor system can make use of invisible information and direct grasping movements (vision-for-action), whereas the ventral system (vision-for-perception) cannot, whereby conscious reports are unaffected by invisible information (Milner & Goodale, 1995). In two experiments using CFS, subjects were asked to grasp for invisible bars of different sizes (exp. 1, N=5) or orientations (exp. 2, N=6), or to report both measures verbally. Target visibility was measured trial-by-trial using the perceptual awareness scale (PAS). We found no evidence for the use of invisible information by the visuomotor system despite extensive training (600 trials) and the availability of haptic feedback. Subjects neither learned to scale their maximum grip aperture to the size of the invisible stimulus, nor to align their hand to its orientation. Careful control of stimulus visibility across training sessions, however, revealed a robust tendency towards decreasing perceptual thresholds under CFS. We will discuss our results with respect to conflicting earlier findings and the TVSH. |
| Up Home |
|---|