It remains unknown to what extent the human visual system interprets information about complex scenes without conscious analysis. Here we used visual masking techniques to assess whether illusory contours (Kanizsa shapes) are perceived when the inducing context creating this illusion does not reach awareness. In the first experiment we tested perception directly by having participants discriminate the orientation of an illusory contour. In the second experiment, we exploited the fact that the presence of an illusory contour enhances performance on a spatial localization task. Moreover, in the latter experiment we also used a different masking method to rule out the effect of stimulus duration. Our results suggest that participants do not perceive illusory contours when they are unaware of the inducing context. This is consistent with theories of a multistage, recurrent process of perceptual integration. Our findings thus challenge some reports, including those from neurophysiological experiments in anaesthetized animals. Furthermore, we discuss the importance to test the presence of the phenomenal percept directly with appropriate methods.

11 12It remains unknown to what extent the human visual system interprets information 13 about complex scenes without conscious analysis. Here we used visual masking 14 techniques to assess whether illusory contours (Kanizsa shapes) are perceived when 15 the inducing context creating this illusion does not reach awareness. In the first 16 experiment we tested perception directly by having participants discriminate the 17 orientation of an illusory contour. In the second experiment, we exploited the fact 18 that the presence of an illusory contour enhances performance on a spatial 19 localization task. Moreover, in the latter experiment we also used a different 20 masking method to rule out the effect of stimulus duration. Our results suggest that 21 participants do not perceive illusory contours when they are unaware of the 22 inducing context. This is consistent with theories of a multistage, recurrent process 23 of perceptual integration. Our findings thus challenge some reports, including those 24 from neurophysiological experiments in anaesthetized animals. Furthermore, we 25 discuss the importance to test the presence of the phenomenal percept directly with 26 appropriate methods. CC-BY-NC 4.0 International license not peer-reviewed) is the author/funder. It is made available under aThe copyright holder for this preprint (which was . http://dx.doi.org/10.1101/050526 doi: bioRxiv preprint first posted online Apr. 27, 2016; 2 33Introduction 34 35What role does conscious processing of the environment fulfill and how much 36 processing occurs in the absence of awareness? It is self-evident that much of the 37 internal bodily functions and the learned motor behaviors, such as walking or 38 driving, operate mostly without awareness. But for processing through the classical 39 senses, like vision, there have been widely discrepant findings on how much stimulus 40 processing can occur and how it affects decision-making when the subject is 41 unaware of the stimulus. Moreover, the approach to be used when studying 42 unconscious stimulus processing has also been subject of controversy [1]. 43 44Several experiments suggest that the effect of contextual stimuli within a target, 45 such as the percept of visual illusions or adaptation effects, persists even when 46 participants are unaware of the presented contextual information [2][3][4][5][6]. The use of 47 continuous flash suppression (CFS), in which a dynamic, high-contrast stimulus is 48 presented to one eye to suppress the stimulus in the other eye from awareness, has 49 become a popular way to probe unconscious stimulus processing [7]. Using this 50 procedure it has been claimed that the perception of physical facial attributes [8], 51 the complex analysis of naturalistic scenes [9], and even linguistic processing and 52 arithmetic can be performed without awareness [10]. However, several of these 53 findings have recently failed to be replicated and were challenged on theoretical 54 grounds [11][12][13]. 55 56Neuroimaging experiments showed that wh...