SOCIAL CHUNKING IN WORKING MEMORY 1 1 2 3 4 5 Chunking by Social Relationship in Working Memory 6 7 Ilenia Paparella and Liuba Papeo 8 Institut des Sciences Cognitives— Marc Jeannerod, UMR5229, Centre National de la 9 Recherche Scientifique (CNRS) & Université Claude Bernard Lyon1, France 10 11 12 13 14 Author Note 15 Ilenia Paparella https://orcid.org/0000-0002-7683-2503 16 Liuba Papeo https://orcid.org/0000-0003-3056-8679 17 The authors have no conflicts of interest to disclose. 18 19 Correspondence concerning this article should be addressed to Ilenia Paparella, now at 20 GIGA-Research, Cyclotron Research Center-In Vivo Imaging Unit, 8 allée du Six Août, 21 Batiment B30, University of Liège, 4000 Liège (Belgium). 22 Email: [email protected] 23 SOCIAL CHUNKING IN WORKING MEMORY 2 24 Abstract 25 Working memory (WM) uses knowledge and relations to organize and store multiple 26 individual items in a smaller set of structured units, or chunks. We investigated whether a 27 crowd of individuals that exceeds the WM is retained and, therefore, recognized more 28 accurately, if individuals are represented as interacting with one another –i.e., they form 29 social chunks. Further, we asked what counts as a social chunk in WM: two individuals 30 involved in a meaningful interaction or just spatially close and face-to-face. In three 31 experiments with a delayed change-detection task, participants had to report whether a 32 probe-array was the same of, or different from a sample-array featuring two or three dyads 33 of bodies either face-to-face (facing array) or back-to-back (non-facing array). In Experiment 34 1, where facing dyads depicted coherent, meaningful interactions, participants were more 35 accurate to detect changes in facing (vs. non-facing) arrays. A similar advantage was found 36 in Experiment 2, even though facing dyads depicted no meaningful interaction. In 37 Experiment 3, we introduced a secondary task (verbal shadowing) to increase WM load. 38 This manipulation abolished the advantage of facing (vs. non-facing) arrays, only when 39 facing dyads depicted no meaningful interactions. These results show that WM uses 40 representation of interaction to chunk crowds in social groups. The mere facingness of 41 bodies is sufficient on its own to evoke representation of interaction, thus defining a social 42 chunk in WM; although the lack of semantic anchor makes chunking fainter and more 43 susceptible to interference of a secondary task. 44 45 Keywords: working memory, chunking, perceptual grouping, social cognition, scene 46 perception. SOCIAL CHUNKING IN WORKING MEMORY 3 47 Living in a social world requires humans to process information about conspecifics and the 48 relationships between them. In scenarios that feature multiple faces or bodies, such as any 49 urban scene, vision exploits markers of interpersonal involvement to detect and recognize 50 social groups –i.e., people who engage in social relationship. One of such markers is the 51 relative positioning of bodies in space: nearby bodies in a face-to-face configuration are 52 more likely to be interpreted as interacting than bodies in other spatial configurations (Zhou, 53 Han, Liang, Hu, & Kuai, 2019); they are more likely to be attended to in a crowd (Papeo, 54 2020; Papeo, Goupil, & Soto-Faraco, 2019; Vestner, Gray, & Cook, 2020; Vestner, Tipper, 55 Hartley, Over, & Rueschemeyer, 2019) and to break into visual awareness under low- 56 visibility conditions (Papeo, Stein, & Soto-Faraco, 2017). Visual efficiency has been 57 accounted for by grouping, that is, the processing of multiple bodies as a single 58 perceptual/attentional unit, promoted by visuo-spatial cues of interaction such as spatial 59 proximity and facingness. 60 Here, we asked whether the advantage of grouping people by virtue of socially 61 relevant relations drags up to systems outside and beyond visual perception. A system that 62 might benefit from the representation of relationship between social agents is working 63 memory (WM). WM is the system that supports the temporary storage of a limited amount of 64 information for further cognitive operations (Ardila, 2003; Baddeley, 2000, 2003; Baddeley & 65 Logie, 1999). The limits of WM capacity can be exceeded through chunking, the process of 66 binding and storing multiple items into a single unit (Cowan, 2000; Mathy & Feldman, 2012; 67 Miller, 1956). Chunking in WM exploits a variety of cues, from perceptual similarity and low- 68 level perceptual features to semantic relatedness, and statistical regularities (Brady, Konkle, 69 & Alvarez, 2009; Brady & Tenenbaum, 2013; Hollingworth, 2007; Kaiser, Stein, & Peelen, 70 2014; Luck & Vogel, 1997; O’Donnell, Clement, & Brockmole, 2018). 71 Recent findings suggest that social relationship may be an effective principle of 72 chunking in WM. For example, it has been reported that body movements performed as part 73 of a meaningful interaction were more likely to be recognized in a short-delayed recognition 74 task, relative to movements performed by isolated agents (Ding, Gao, & Shen, 2017). In the SOCIAL CHUNKING IN WORKING MEMORY 4 75 authors’ interpretation, movements that gave rise to interaction were chunked and stored as 76 a single unit, thus increasing WM efficiency. In another study, infants as young as 16 months 77 showed to rely on knowledge about social relations to chunk sets of dolls in social units 78 (Stahl & Feigenson, 2014). In particular, after seeing dolls interacting in pairs, infants were 79 capable to remember two pairs, i.e. four dolls, which exceeded the three-item limit of their 80 WM. 81 The above effects have been interpreted as the result of embedding individuals into 82 the representation of a meaningful social interaction. But, can facingness alone, in the 83 absence of a semantically specified interaction, trigger chunking of bodies in WM? In visual 84 perception and attention, effects of grouping have been found for bodies postures oriented 85 toward one another without giving rise to any meaningful, coherent interaction (Papeo et al., 86 2017; 2019; Vestner et al., 2019). This circumstance raises the possibility that facingness – 87 i.e., the mutual perceptual accessibility of two bodies– is sufficient on its own to trigger the 88 representation of interaction that binds two bodies together. In other words, it is possible that 89 individuals represent face-to-face bodies as intrinsically meaningful, which would yield a WM 90 advantage, irrespective of whether the two facing bodies actually realize a semantically 91 specified interaction. 92 We addressed this in three experiments on female and male human adults, using a 93 delayed change-detection task. Participants saw static arrays of four or six bodies, which 94 approached or exceeded the WM capacity, arranged in two or three face-to-face (facing 95 arrays) or back-to-back dyads (non-facing array). Facing pairs could give rise to a coherent, 96 semantically explicit, interaction (meaningful set –MF), or not (meaningless set –ML). We 97 measured whether facing arrays were remembered better than non-facing arrays and, if so, 98 whether such advantage applied to MF as well as ML facing arrays (Experiments 1-2). 99 Finally, in Experiment 3, we asked participants to perform the same task with a concurrent 100 shadowing task (i.e., continuous word repetition). With this manipulation, we investigated the 101 effect of WM load on the performance with MF vs. ML arrays. Precisely, we tested whether 102 semantic specification provided an anchor point that made the representation of MF (vs. ML) SOCIAL CHUNKING IN WORKING MEMORY 5 103 interactions stronger and less subjected to interference in WM. Moreover, visual items can 104 be stored in WM in the form of corresponding verbal labels, when available, a strategy that is 105 especially common when items are assigned to a meaning (Donkin, Nosofsky, Gold, & 106 Shiffrin, 2015). Since verbal shadowing especially interferes with verbal retrieval and 107 rehearsal, Experiment 3 could offer insight on the format of representation of dyads in WM 108 (e.g., verbal or visuo-spatial). 109 In summary, with this study, we sought to isolate the effect of body positioning (facing 110 vs. non-facing) from the effect of representing a familiar, semantically specified interaction, in 111 promoting chunking by social relationship in WM. Given that, here, performance depended 112 on the possibility to structure a crowd in social (multiple-person) units, the results of this 113 study shed light on what counts as a social unit in WM. 114 115 Experiment 1 116 Experiment 1 tested the participants’ performance in detecting a change in a crowded array, 117 with bodies forming facing or non-facing dyads. All facing dyads depicted coherent, 118 meaningful interactions. 119 Participants 120 Twenty healthy adults (18 females; mean age 22.8 ± 3.9 standard deviation, SD) 121 participated in Experiment 1 as paid volunteers. All had normal or corrected-to-normal vision, 122 reported no history of neurological or psychiatric conditions and no assumption of 123 psychoactive substances or medications. Participants gave informed consent prior to 124 participation in the study. Experiments 1 was exploratory with respect to the sample size. 125 Sensitivity analysis (GPower 3.1) estimated a minimum detectable effect (i.e., the smallest 2 126 true effect, which would be statistically significant with alpha = 0.05, and power = 0.80) of ηp 127 0.10 for the effect of positioning (facing vs. non-facing arrays) with a sample size of 20. 128 Results of Experiment 1 were used to calculate the sample size for the following 129 experiments. The local ethics committee approved this and the following experiments. 130 SOCIAL CHUNKING IN WORKING MEMORY 6 131 Stimuli 132 Meaningful-interaction (MF) dyads. We created gray-scale images of a human body in 48 133 different poses in lateral view, using Daz3D (Daz Productions, Salt Lake City, UT) and the 134 Image Processing Toolbox in MATLAB (The MathWorks, Natick, MA).