Abstract
Continuous Flash Suppression (CFS) has become a popular tool in the study of visual processing in the absence of conscious awareness. A variety of masks have been used in CFS studies; however it remains unclear wether CFS works globally (suppressing everything equally) or feature based, possibly allowing for effects of mask-stimulus interactions. Such interactions might then severely bias the results of CFS experiments by affecting different target categories unequally. We designed a b-CFS experiment with feature-specific targets and masks in order to investigate possible effects of feature-coalignment or -orthogonality to identify mask-target interactions. Masks were pink noise patterns filtered with a narrow-orientation band pass to generate a strong directionality in the visual appearance. Target stimuli were Gabors (sinusoidal patterns in a Gaussian envelope) varying systematically in their orientational alignment with the masks. Implementing both masks and targets grayscale (luminance) patterns, the alignment between targets and masks significantly affected suppression duration (∼80% longer for perfectly aligned pairs compared to orthogonal). This effect was stronger for cardinal orientations than for oblique orientations. When implementing both targets and masks as either primary RGB patterns or isoluminant color patterns, generally there was significant suppression between mask-target pairings of both identical and different color (or color axis). The alignment effect however prevailed mostly for mask-target pairings of the same color (respectively the same color axis), but was diminished for mask-target pairings of different color. We conclude that mask-target interactions exist in Continuous Flash Suppression and appear to be feature-based. The human visual system can use orthogonality within a feature dimension or across feature dimensions to facilitate the breaking of the CFS. Further, luminance differences between masking stimuli are not required to achieve suppression, CFS therefore functions under isoluminant conditions.