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Learning to detect but not to grasp suppressed visual stimuli.
K Ludwig1, P Sterzer, N Kathmann
1Visual Perception Laboratory, Department of Psychiatry and Psychotherapy, Campus Charité Mitte, Charité - Universitätsmedizin Berlin, Germany; Department of Psychology, Humboldt-Universität zu Berlin, Germany.
Neuropsychologia
|October 8, 2013
Summary
The two-visual-systems hypothesis suggests actions use invisible information, but this study found no evidence for this. Even with training, grasping movements were not influenced by invisible visual stimuli.
Area of Science:
- Cognitive Neuroscience
- Visual Perception
- Motor Control
Background:
- The two-visual-systems hypothesis (TVSH) posits distinct dorsal (vision-for-action) and ventral (vision-for-perception) pathways.
- A key TVSH tenet is that the dorsal system can utilize invisible information, while the ventral system cannot.
Purpose of the Study:
- To investigate whether the visuomotor system (dorsal pathway) can use invisible visual information for action, as predicted by the TVSH.
- To test if grasping movements are influenced by invisible stimuli while conscious perception remains unaffected.
Main Methods:
- Utilized continuous flash suppression (CFS) to render visual stimuli invisible.
- Participants performed grasping tasks with invisible bars of varying sizes and orientations, alongside verbal reports.
- Target visibility was assessed using the perceptual awareness scale (PAS) on a trial-by-trial basis.
Main Results:
- No evidence was found that the visuomotor system used invisible information for grasping, even after extensive training and with haptic feedback.
- Participants did not adjust grip aperture for invisible bar sizes or hand orientation for invisible bar orientations.
- A significant decrease in perceptual thresholds was observed under CFS conditions across training sessions.
Conclusions:
- The findings challenge the strict interpretation of the TVSH regarding the dorsal system's use of invisible information for action.
- Results suggest a more integrated interaction between dorsal and ventral visual systems than previously proposed.
- Alternative models emphasizing functional coupling between visual processing streams may better explain observed phenomena.
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