Availability of unconscious information in human visual cortex: behavioural and neuroimaging experiments with graspable objetcs
Final Report Abstract
According to a very influential theory of human vision, the visual system is divided into a ventral "vision-for-perception" pathway, and a dorsal "vision-for-action" pathway. The theory proposes that information in the dorsal stream can be processed without reaching awareness, while in the ventral stream it cannot. This differential link to awareness (or, consciousness) in the two pathways has long been under debate. In this research project, we found no evidence for a strong differential link. In a grasping study - designed and optimized to trigger information processing along the "vision-for-action" pathway - neurologically intact human participants did not learn to grasp objects that they did not consciously see. Surprisingly, however, we did observe training effects over time, such that the interocular suppression method – used for rendering the to-be-grasped stimuli invisible – became less effective across sessions, possibly due to the involvement of haptic feedback during grasping. In a neuroimaging study, we found evidence for shape-selective neural processing under interocular suppression in both dorsal and ventral stream areas. This result is in disagreement with the notion that dorsal “vision-foraction” processing is exclusively preserved when interocular suppression is applied. Overall, our data from funding period 1 strongly support alternative vision models emphasizing the close functional interaction between the dorsal and ventral visual pathways. Future research efforts must bring the human and primate data from neuroimaging, neuropsychology and behavioral studies together in an effort to formulate an updated “standard model” of human vision. In funding period 2, we were able to show that while the ventral and the dorsal visual stream are indeed linked to visual awareness, neural activity in ventral areas more closely reflects graded differences in awareness compared to dorsal areas. Importantly, this result may reconcile some divergent previous findings, and thus might become a significant contribution to an updated vision model. Inspired by the heterogeneity of published findings, we also placed a stronger focus on the interocular suppression method itself. In the last couple of years, this method (also referred to as continuous flash suppression, CFS) has been widely used to study visual information processing in the absence of awareness. Based on our results from a series of unconscious priming experiments, we have formulated a list of technical recommendations for future CFS research. In a comprehensive review of our findings and data from other labs, we conclude that there is no evidence for a “dorsal stream processing bias” under CFS. In close collaboration with colleagues from the KU Leuven (Belgium), we conceived the “stimulus fractionation model” of CFS that provides a highly plausible picture of the current literature. We are confident that this model will inspire new research, and lead to a more reproducible literature with respect to the scope and limitations of visual processing under CFS.
Publications
- (2014) Neural processing of visual information under interocular suppression: a critical review. Frontiers in psychology 5 453
Sterzer, Philipp; Stein, Timo; Ludwig, Karin; Rothkirch, Marcus; Hesselmann, Guido
(See online at https://doi.org/10.3389/fpsyg.2014.00453) - (2015) Investigating category- and shape-selective neural processing in ventral and dorsal visual stream under interocular suppression. Human brain mapping 36 (1) 137–149
Ludwig, Karin; Kathmann, Norbert; Sterzer, Philipp; Hesselmann, Guido
(See online at https://doi.org/10.1002/hbm.22618) - (2018) Investigating masked priming along the "vision-for-perception" and "vision-for-action" dimensions of unconscious processing. Journal of experimental psychology. General 147 (11) 1641–1659
Hesselmann, Guido; Darcy, Natasha; Rothkirch, Marcus; Sterzer, Philipp
(See online at https://doi.org/10.1037/xge0000420) - (2012). What visual information is processed in the human dorsal stream? Journal of Neuroscience 32: 8107-8109
Hebart, M., & Hesselmann, G.
(See online at https://doi.org/10.1523/JNEUROSCI.1462-12.2012) - (2013) Dissecting visual awareness with fMRI. The Neuroscientist 19: 495-508
Hesselmann, G.
(See online at https://doi.org/10.1177/1073858413485988) - (2013). Learning to detect but not to grasp suppressed visual stimuli. Neuropsychologia 51: 2930-2938
Ludwig, K., Kathmann, N., Sterzer, P., Franz, V.H., & Hesselmann, G.
(See online at https://doi.org/10.1016/j.neuropsychologia.2013.09.035) - (2014). No conclusive evidence for numerical priming under interocular suppression. Psychological Science 25:2116-2119
Hesselmann, G., & Knops, A.
(See online at https://doi.org/10.1177%2F0956797614548876) - (2015). Exploring the boundary conditions of unconscious numerical priming effects with continuous flash suppression. Consciousness & Cognition 31:60-72
Hesselmann, G., Darcy, N., Sterzer, P., & Knops, A.
(See online at https://doi.org/10.1016/j.concog.2014.10.009) - (2015). Weighing the evidence for a dorsal processing bias under continuous flash suppression. Consciousness & Cognition 35:251-259
Ludwig, K., & Hesselmann, G.
(See online at https://doi.org/10.1016/j.concog.2014.12.010) - (2016). Priming in a shape task but not in a category task under continuous flash suppression. Journal of Vision 16:17
Hesselmann, G., Darcy, N., Ludwig, K., & Sterzer, P.
(See online at https://doi.org/10.1167/16.3.17) - (2016). Stimulus visibility differentially modulates response patterns in dorsal and ventral visual stream. Cortex 83:113-123
Ludwig, K., Sterzer, P., & Hesselmann, G.
(See online at https://doi.org/10.1016/j.cortex.2016.07.002) - (2017). Continuous Flash Suppression: Stimulus Fractionation rather than Integration. Trends in Cognitive Sciences 21:719–721
Moors, P., Hesselmann, G., Wagemans, J., & van Ee, R
(See online at https://doi.org/10.1016/j.tics.2017.06.005)
