Face masks are less effective than sunglasses in masking face identity

www.nature.com/scientificreports OPEN Face masks are less effective than sunglasses in masking face identity Charles C.‑F. Or 1*, Kester Y. J. Ng 1, Yiik Chia 1, Jing Han Koh 1, Denise Y. Lim 1 & Alan L. F. Lee 2 The effect of covering faces on face identification is recently garnering interest amid the COVID-19 pandemic. Here, we investigated how face identification performance was affected by two types of face disguise: sunglasses and face masks. Observers studied a series of faces; then judged whether a series of test faces, comprising studied and novel faces, had been studied before or not. Face stimuli were presented either without coverings (full faces), wearing sunglasses covering the upper region (eyes, eyebrows), or wearing surgical masks covering the lower region (nose, mouth, chin). We found that sunglasses led to larger reductions in sensitivity (d’) to face identity than face masks did, while both disguises increased the tendency to report faces as studied before, a bias that was absent for full faces. In addition, faces disguised during either study or test only (i.e. study disguised faces, test with full faces; and vice versa) led to further reductions in sensitivity from both studying and testing with disguised faces, suggesting that congruence between study and test is crucial for memory retrieval. These findings implied that the upper region of the face, including the eye-region features, is more diagnostic for holistic face-identity processing than the lower face region. The COVID-19 pandemic has made facial occlusions more prevalent due to mask-wearing, which covers multiple lower facial features including the entire mouth, the lower part of the nose, and the lower face outline. This has renewed interest in how facial occlusions might affect face identification, as the amount of information available in identifying faces is reduced. Since the pandemic, several studies have demonstrated that occlusion by face mask leads to general impairment to face identification. For example, Freud et al.1,2 suggested that presenting masked faces during encoding and/or retrieval stages in online Cambridge Face Memory Tests (CFMT) persistently led to poorer scores than presenting only unoccluded faces in both stages. Such impairment was also observed in another in-person face learning-and-recognition task by Hsiao et al.3. Marini et al.4 demonstrated that unoccluded faces were reidentified more accurately when unoccluded faces, rather than masked faces, were encoded. When matching two simultaneously presented faces5,6, sensitivity (d’) decreased when one or both faces were masked, while response bias varied across experiments. Pre-COVID-19 studies predicted more limited, or even an absence of, impairment to face identification, despite their focus on occluding single lower features (e.g. occluding the mouth alone). Rather than a general occlusion effect, M cKelvie7 demonstrated that face memory worsened only when presenting different (i.e. incongruent) face types, specifically, mouth-occluded faces during encoding and full faces during retrieval (and vice versa), but presenting the same (i.e. congruent) mouth occlusions in both stages did not impair face memory compared to congruently presenting full faces in both stages. The impairment, which was limited to incongruent conditions, may support the encoding specificity principle, where stimuli presented under congruent conditions across stages would lead to superior performance8,9. Encoding specificity has been demonstrated in aspects of face memory research (e.g. removing external facial a reas10; changing l ighting11), limiting generalization of encoded facial information to novel viewing conditions. Nevertheless, even under incongruent conditions, masking the nose or mouth alone might not impair face memory, in the case of familiarity judgments of masked celebrity faces that were expected to be encoded previously as unoccluded f aces12. Other studies focused on the effect of exposing only a single feature on face identification. For example, Manley et al.13 studied memory for faces covered by ski masks, leaving only the eyes visible in lineup experiments. They found that congruently masking faces led to comparable sensitivity and response bias with congruently presenting full faces, but incongruently masking faces resulted in a decline in sensitivity or a change in response 1 Division of Psychology, School of Social Sciences, Nanyang Technological University, 48 Nanyang Avenue, Singapore 639818, Singapore. 2Department of Psychology, Lingnan University, Tuen Mun, Hong Kong. *email: Scientific Reports | (2023) 13:4284 | https://doi.org/10.1038/s41598-023-31321-4 1 Vol.:(0123456789) www.nature.com/scientificreports/ bias, again in agreement with encoding specificity. Although these pre-COVID-19 studies did not have lower facial features occluded in the same way as using face masks, they demonstrate the possibility that occlusion of lower facial features may not always deteriorate face identification performance, especially under congruent conditions. In contrast, findings from multiple studies suggest that occlusion of the upper region of the face (including the eyes) impairs face identification, consistent with the notion that the eyes provide crucial diagnostic information for face identity processing (e.g.14,15). McKelvie7 suggested that masking the eyes in one or both memory test stages led to poorer face memory than congruently presenting full faces. Masking the eyes of celebrity faces was also detrimental to familiarity judgments12,16. Using sunglasses for more natural occlusions, Graham and Ritchie17 found lower sensitivities in matching two faces either or both with sunglasses than in matching two full faces. When videos of faces with or without sunglasses were encoded prior to retrieval with lineups of full faces only, Mansour et al.18 showed that encoding faces with sunglasses reduced sensitivity from encoding full faces. However, it should be noted that Hockley et al.19 only found reduced sensitivity with incongruent memory test stages, while congruently presenting faces with sunglasses resulted in little decline in sensitivity from congruently presenting full faces. Thus, they attributed the effects to encoding specificity rather than a general effect from eye occlusion. To date, few studies directly compared the effects of occluding the upper and the lower regions of the face on face identification. While earlier studies (e.g.7,12) compared the effects of occluding single features of the face and suggested the superiority of the eyes to the nose or mouth in face identification performance, more recent studies compared the effects of more natural occlusions. For example, Nguyen and P ezdek20 conducted a face memory experiment about encoding full faces or disguised faces (sunglasses covering the upper region, or bandanas covering the lower region), followed by retrieval with full faces only. 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