Ensemble coding of face identity is not independent of the coding of individual identity

Abstract

Information about a group of similar objects can be summarized into a compressed code, known as ensemble coding. Ensemble coding of simple stimuli (e.g., groups of circles) can occur in the absence of detailed exemplar coding, suggesting dissociable processes. Here, we investigate whether a dissociation would still be apparent when coding facial identity, where individual exemplar information is much more important. We examined whether ensemble coding can occur when exemplar coding is difficult, as a result of large sets or short viewing times, or whether the two types of coding are positively associated. We found a positive association, whereby both ensemble and exemplar coding were reduced for larger groups and shorter viewing times. There was no evidence for ensemble coding in the absence of exemplar coding. At longer presentation times, there was an unexpected dissociation, where exemplar coding increased yet ensemble coding decreased, suggesting that robust information about face identity might suppress ensemble coding. Thus, for face identity, we did not find the classic dissociation-of access to ensemble information in the absence of detailed exemplar information-that has been used to support claims of distinct mechanisms for ensemble and exemplar coding.

Elucidating the Neural Representation and the Processing Dynamics of Face Ensembles

“…First, we find that, behaviorally, participants are able to explicitly match summary representations across different ensembles. These results are consistent with previous work (de Fockert and Wolfenstein, 2009;Neumann et al, 2013Neumann et al, , 2017Haberman et al, 2015), which has demonstrated sensitivity to summary visual properties of face ensembles by the successful matching of ensembles to average face stimuli. However, it is possible that the sensitivity demonstrated in such studies is facilitated, or even developed, due to the availability of average faces, in their role of matching stimuli, throughout experimental testing.…”

“…This finding is consistent with the hypothesis that ensembles are largely reduced to summary representations (Haberman et al, 2015). Specifically, while information about individual constituents may not be entirely discarded (Neumann et al, 2017), summary percepts provide a convenient way of representing a wealth of information, especially when such information is only briefly available (e.g., 300 ms in our experiment). Thus, the neural signatures of individual constituent faces may be missing or considerably diminished and, hence, unable to support the decoding of distinct ensembles with the same summary representation.…”

“…However, while within-group single faces are discriminable, as seen above, it is possible that same-group ensembles are not. Specifically, if face ensembles are summarized into a single identity representation, as suggested by prior behavioral work (de Neumann et al, 2013Neumann et al, , 2017Haberman et al, 2015), same-group ensembles (e.g., Ensembles 1-1 and 1-2) may not be discriminable from each other if, though consisting of different individual faces, they are perceptually reduced to the same average identity. To evaluate this possibility, ensemble classification was evaluated separately for same-group ensembles (i.e., 2 pairs) and cross-group ensembles (i.e., 4 pairs) (Fig.…”

“…Given the limits of working memory (Luck and Vogel, 1997), a mechanism has been suggested that allows individuals to encode information, such as size Treisman, 2003, 2005), orientation (Dakin and Watt, 1997), and direction of motion (Watamaniuk et al, 1989) from similar objects into averages or "summary representations." Interest-ingly, such a mechanism also extends to the processing of more complex properties, including, in the case of faces, emotional expression Whitney, 2007, 2009), gaze (Sweeny and Whitney, 2014;Florey et al, 2016), gender (Haberman and Whitney, 2007), and even identity (de Fockert and Wolfenstein, 2009;Neumann et al, 2013Neumann et al, , 2017Leib et al, 2014;Haberman et al, 2015).…”

Independence of viewpoint and identity in face ensemble processing

“…This seems to point to different perceptual mechanisms for identity versus viewpoint processing (Haberman et al, 2015). Regarding the absence of a clear dissociation for identity, this is convergent with previous findings (Neumann, Ng, Rhodes, & Palermo, 2017) suggesting that processing a summary identity does not preclude or negate the extraction of individual identity. However, we did find that reports of single facial attributes were closer to the mean attribute than to the single-face targets which participants were instructed to report.…”