Unconscious Perception of Continuity During Visual Suppression

While it has been shown that accurate perception of visual features, such as orientation and color, can occur without visual awareness, it is unclear if higher-order stimulus attributes, such as continuity, can also be unconsciously discriminated. In the present study, we assessed whether perceptual grouping by continuity can be unconsciously processed during suppression of visual awareness from backward masking or transcranial magnetic stimulation (TMS). Subjects viewed briefly presented cross-shaped target patterns formed by one horizontal and one vertical set of parallel lines, with one set appearing to occlude the other based on perceptual grouping by continuity of the orientation of the center lines. We first ensured accurate perception of the stimuli in a target-only session without any awareness suppression. Perception of the target was then suppressed in two groups of subjects with backward visual masking or TMS to early visual cortex. Subjects reported their perception of target visibility and then the orientation of the continuous, non-occluded set. Detection of the target was suppressed by both visual masking and TMS, as compared to the no-suppression condition. When subjects were unaware of the target, accuracy of discrimination by continuity configuration was significantly above chance. There was no significant difference in unconscious discrimination performance between the visual masking and TMS condition. The present study reveals accurate perceptual organization with grouping by continuity in the absence of visual awareness of the stimulus, suggesting that gestalt feature segregation based on both local and global stimulus properties can occur without phenomenological impression of the visual item.