Learning to detect but not to grasp suppressed visual stimuli

• Published in: Neuropsychologia 2013-11, Vol.51 (13), p.2930-2938
• Main Authors: Ludwig, K., Sterzer, P., Kathmann, N., Franz, V.H., Hesselmann, G.
• Format: Article
• Language: English
• Subjects: Activity levels. Psychomotricity; Adult; Biological and medical sciences; Biomechanical Phenomena - physiology; Blindsight; Consciousness; Dual-stream model; Female; Fundamental and applied biological sciences. Psychology; Grasping; Hand Strength - physiology; Humans; Learning - physiology; Male; Movement; Perception; Perceptual Masking - physiology; Photic Stimulation; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Psychomotor activities; Vision; Visual Perception - physiology; Young Adult
• ISSN: 0028-3932; 1873-3514
• DOI: 10.1016/j.neuropsychologia.2013.09.035

A central implication of the two-visual-systems hypothesis (TVSH) is that the dorsal visuomotor system (vision-for-action) can make use of invisible information, whereas the ventral system (vision-for-perception) cannot (Milner & Goodale, 1995). Therefore, actions such as grasping movements should be influenced by invisible information while conscious reports remain unaffected. To test this assumption, we used a dichoptic stimulation technique – continuous flash suppression (CFS) – which has the potency to render stimuli invisible for up to seconds (Tsuchiya & Koch, 2005). In two experiments using CFS, participants were asked to grasp for invisible bars of different sizes (Experiment 1) or orientations (Experiment 2), 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. Participants 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 discuss our results within the framework of the TVSH and with respect to alternative models which emphasize the close functional interaction between the dorsal and ventral visual systems. •Implication of the two-visual-systems hypothesis was tested in healthy participants.•Can the dorsal system use invisible information, whereas the ventral system cannot?•Participants grasped for invisible objects and reported their properties verbally.•Chance performance but decreasing perceptual thresholds in grasping task.•Perceptual performance possibly enhanced by concurrent visuomotor behavior.