The Effects of Blur and Inversion on the Recognition of Ambient Face Images

Abstract

When viewing unfamiliar faces that vary in expressions, angles, and image quality, observers make many recognition errors. Specifically, in unconstrained identity-sorting tasks, observers struggle to cope with variation across different images of the same person while succeeding at telling different people apart. The use of ambient face images in this simple card-sorting task reveals the magnitude of these face recognition errors and suggests a useful platform to reexamine the nature of face processing using naturalistic stimuli. In the present study, we chose to investigate the impact of two basic stimulus manipulations (image blur and face inversion) on identity sorting with ambient images. Although these manipulations are both known to affect face processing when well-controlled, frontally viewed face images are used, examining how they affect performance for ambient images is an important step toward linking the large body of research using controlled face images to more ecologically valid viewing conditions. Briefly, we observed a high cost of image blur regardless of blur magnitude, and a strong inversion effect that affected observers’ sensitivity to extrapersonal variability but did not affect the number of unique identities they estimated were present in the set of images presented to them.

Contrast Negation Impairs Sorting Unfamiliar Faces by Identity: A Comparison With Original (Contrast-Positive) and Stretched Images

“…Replicating previous findings, we found sorting photo-cards of unfamiliar faces by identity is a difficult task (Balas et al., 2019; Balas & Pearson, 2017; Jenkins et al., 2011; Kramer, Manesi, et al, 2018; Zhou & Mondloch, 2016). For example, we observed fragmentation of cards in all conditions into more groups than necessary for the two identities across all conditions for most participants.…”

“…To the extent that our results might generalize to other face tasks, we suggest future research considers the relative role of shape and surface properties in face learning, recognition, and verification by using naturally occurring (ambient) images (cf. Balas et al., 2019) or emulating realistic contexts (cf. Kramer et al., 2017).…”

“…Card-sorting tasks are typically used to examine the influence of variability inherent to naturally occurring (or uncontrolled) photographs on dependent variables (e.g., Balas & Pearson, 2017; Jenkins et al., 2011; Kramer, Manesi, et al., 2018; Zhou & Mondloch, 2016) or explore differences on performance measures between different stimulus conditions (e.g., various levels of blur) that vary as between-subjects factors (Balas et al., 2019; see also Kramer, Manesi, et al., 2018 for a report of card-sorting performance with full faces vs. internal features only vs. external features only). In Experiment 2A, we presented all three sets of images viewed across participants of Experiments 1A and 1B with each stimulus set allocated to a stimulus condition.…”

“…This is easily demonstrated if one searches for a reasonably well-known individual (e.g., celebrity) on the internet where multiple different images likely will be returned. Typically, researchers download 20 images of a number of identities (two or four) and ask participants to sort the images into piles or groups where each pile/group represents one identity (e.g., Balas et al., 2019; Balas & Pearson, 2017; Jenkins et al., 2011; Kramer, Manesi, et al., 2018; Zhou & Mondloch, 2016). This task has successfully replicated the superiority of discriminating known identities over unknown identities (Jenkins et al., 2011; Kramer, Manesi, et al., 2018; Zhou & Mondloch, 2016) and has shown certain informational content that is either useful (i.e., internal features) or relatively unhelpful (i.e., external features) for the identification of familiar and unfamiliar faces (Kramer, Manesi, et al., 2018).…”

“…While imposition of image blur (unqualified by degree of blur imposed) and picture-plane inversion has been shown to generalize from other face identification tasks to the card-sorting task (Balas et al., 2019), it is currently unknown whether previous evidence suggesting relative roles for shape and surface properties also generalizes to card-sorting tasks. We opted for card-sorting tasks in this study because the recently introduced fine-grained analyses employed in card-sorting tasks (more in the following sections) allow us to examine the relative utility of these two broad types of properties for discriminating facial identity where observers sort photo-cards that collectively represent instances of within- and between-person variability.…”