Abstract
When the eyes view separate and incompatible images, the brain suppresses one image-removing it from visual awareness. A popular paradigm for doing this is continuous flash suppression (CFS). One eye views a static 'target', the other is presented with a complex dynamic stimulus which very effectively suppresses the target. Measuring the time needed for the suppressed target to break suppression as it slowly increases in contrast (bCFS) has been widely used to investigate unconscious processing and the results have generated controversy regarding the scope of visual processing without awareness. In particular, upright faces and fearful faces have been claimed to have priority access to awareness. Here, we address this controversy with a new 'CFS tracking' paradigm (tCFS) in which the suppressed monocular target steadily increases in contrast until breaking into awareness (as in bCFS) after which it decreases until it becomes suppressed again (reCFS), with this cycle continuing for many reversals. Unlike bCFS, tCFS provides measures of breakthrough thresholds as well as suppression thresholds, and the difference between breakthrough and suppression thresholds defines the important metric of 'suppression depth'. The suppression depth results over two experiments are consistent in showing no face inversion effects (i.e. no priority for upright faces relative to inverted) and no effect of emotion (no priority for fearful faces relative to happy or neutral). Given this consistent non-selectivity, we conclude that CFS elicits a strong suppression in early visual cortex at a level preceding face processing.