Can emotional content be extracted under interocular suppression?

Previous studies showed that emotional faces break through interocular suppression more easily compared to neutral faces under the continuous flash suppression (CFS) paradigm. However, there is controversy over whether emotional content or low-level properties contributed to the results. In this study, we directly manipulated the meaningfulness of facial expression to test the role of emotional content in breaking CFS (b-CFS). In addition, an explicit emotion judgment for different facial expressions (happy, neutral, and fearful) used in the b-CFS task was also conducted afterwards to examine the relationship between b-CFS time and emotion judgment. In Experiment 1, face orientation and luminance polarity were manipulated to generate upright-positive and inverted-negative faces. In Experiment 2, Asian and Caucasian faces were presented to Taiwanese participants so that these stimuli served as own-race and other-race faces, respectively. We found robust face familiarity effects in both experiments within the same experimental framework: upright-positive and own-race faces had shorter b-CFS times than inverted-negative and other-race faces, respectively. This indicates potential involvement of high-level processing under interocular suppression. In Experiment 1, different b-CFS times were found between emotional and neutral faces in both upright-positive and inverted-negative conditions. Furthermore, with sufficient duration (1000 ms) participants could still extract emotional content in explicit valence judgment even from inverted-negative faces, though with a smaller degree than upright-positive faces. In Experiment 2, differential b-CFS times were found between emotional and neutral faces with own-race but not other-race faces. Correlation analyses from both experiments showed that the magnitude of emotion judgment was correlated with b-CFS time only for familiar (upright-positive / own-race) but not unfamiliar (inverted-negative / other-race) faces. These results suggest that emotional content can be extracted under interocular suppression with familiar faces, and low-level properties in unfamiliar faces may play a major role in the b-CFS time.