Abstract
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.
Highlights
Understanding emotional content of facial expression is a critical skill for social interaction and communication
The simple effect of facial expression in the inverted-negative condition revealed a narrower range of emotion judgments, which was similar to that of upright-positive faces: happy faces (M = 4.681, SD = .993) were judged more positively than neutral faces (M = 4.094, SD = .477, p < .01), which were judged more positively than fearful faces (M = 3.712, SD = 0.779, p < .05)
We found that b-continuous flash suppression (CFS) time was correlated with emotion judgment in the upright-positive face condition, suggesting that emotional content could determine the breakthrough times of facial expression
Summary
Understanding emotional content of facial expression is a critical skill for social interaction and communication. We adopted the breaking continuous flash suppression (b-CFS) [1,2] paradigm to examine whether emotional content can influence breakthrough times under CFS when different facial expressions were presented and masked. When using the bCFS technique, a series of dynamic high-contrast masks are presented to one eye, and due to the interocular suppression, this renders a critical stimulus presented to the other eye invisible. By manipulating the contrasts of the critical stimulus on one eye and the flashing mask on the other eye, eventually the interocular suppression from the mask would break and the critical stimulus would become visible. The reaction time required for b-CFS is usually considered as an index of how efficiently a stimulus breaks through interocular suppression and becomes visible [3]
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