The visual system takes advantage of redundancy in the world by extracting summary statistics, a phenomenon known as ensemble perception. Ensemble representations are formed for low-level features like orientation and size and high-level features such as facial identity and expression. Whereas recent research has shown that the visual system forms intact ensemble representations even when faces are partially occluded via solid bars, how ensemble perception is impacted with the addition of naturalistic objects such as face masks or sunglasses is largely unknown. To investigate this, we conducted a series of experiments using continuous report tasks in which faces (either varying in identity or expression) were partially occluded with a surgical mask or sunglasses and participants had to report the average face using a face wheel. We found evidence that participants could still accurately extract the average even when a significant portion of it was occluded with either face masks or sunglasses. In a second experiment, however, we found performance was worse when the face wheel was variable trial to trial. Thus part of the preservation of performance in occlusion arises from the visual system learning the features of the particular face wheel being used. Overall, our results suggest that the visual system is able to establish robust ensemble representations for faces with naturalistic occlusions, but that robustness appears to be supported at least partially by learning information about the particular features that are informative for a given set of faces.
Hendley et al. (Fri,) studied this question.