Face Pareidolia in the Rhesus Monkey

Seeing Jesus in toast: Neural and behavioral correlates of face pareidolia

Understanding how the human visual system recognizes objects is one of the key challenges in neuroscience. Inspired by a large body of physiological evidence, a general class of recognition models has emerged, which is based on a hierarchical organization of visual processing, with succeeding stages being sensitive to image features of increasing complexity. However, these models appear to be incompatible with some well-known psychophysical results. Prominent among these are experiments investigating recognition impairments caused by vertical inversion of images, especially those of faces. It has been reported that faces that differ 'featurally' are much easier to distinguish when inverted than those that differ 'configurally'; a finding that is difficult to reconcile with the physiological models. Here, we show that after controlling for subjects' expectations, there is no difference between 'featurally' and 'configurally' transformed faces in terms of inversion effect. This result reinforces the plausibility of simple hierarchical models of object representation and recognition in the cortex.

Humans and Macaques Employ Similar Face-Processing Strategies

Face perception is probably the most developed visual perceptual skill in humans, most likely as a result of its unique evolutionary and social significance. Much recent research has converged to identify a host of relevant psychological mechanisms that support face recognition. In parallel, there has been substantial progress in uncovering the neural mechanisms that mediate rapid and accurate face perception, with specific emphasis on a broadly distributed neural circuit, comprised of multiple nodes whose joint activity supports face perception. This article focuses specifically on the neural underpinnings of face recognition, and reviews recent structural and functional imaging studies that elucidate the neural basis of this ability. In addition, the article covers some of the recent investigations that characterize the emergence of the neural basis of face recognition over the course of development, and explores the relationship between these changes and increasing behavioural competence. This paper also describes studies that characterize the nature of the breakdown of face recognition in individuals who are impaired in face recognition, either as a result of brain damage acquired at some point or as a result of the failure to master face recognition over the course of development. Finally, information regarding similarities between the neural circuits for face perception in humans and in nonhuman primates is briefly covered, as is the contribution of subcortical regions to face perception. WIREs Cogn Sci 2016, 7:247-263. doi: 10.1002/wcs.1388 For further resources related to this article, please visit the WIREs website.

Visual Snow (VS) syndrome is a neurological condition characterised by the constant perception of small flicking dots across the visual field. These symptoms are thought to be caused by hyperexcitability in the visual cortex. This study examined the potential link between VS and susceptibility to the face pareidolia (FP) illusion, where faces are perceived in inanimate objects. Using a self-report VS questionnaire and a standard FP sensitivity task, we collected data remotely from 132 individuals with VS and 104 age-matched controls. Results revealed higher FP sensitivity in individuals with VS, amplified in those with co-occurring migraines. Non-parametric analyses confirmed elevated face scores for VS participants, even when migraines were excluded. A rank-order analysis showed consistency in response patterns across groups, ruling out the idea that extraordinary responses to one stimulus drove the group difference. These findings suggest that individuals with VS syndrome have an increased susceptibility to the FP illusion. Future research should investigate whether hyperexcitability in the visual cortex is the cause.

The human visual system appears to process the identity of faces separately from their emotional expression, whereas the human visual system does not appear to process emotional expression separately from identity. All current explanations of this visual processing asymmetry implicitly assume that it arises because of the organization of a specialized human face perception system. A second possibility is that this finding reflects general principles of perceptual processing. Studying animals that are unlikely to have evolved a specialized face perception system may shed fresh light on this issue. We report two experiments that investigated the interaction of identity and emotional expression in pigeons' perception of human faces. Experiment 1 found that pigeons perceive the similarity among faces sharing identity and emotion, and that these two dimensions are integral according to a spatial model of generalization. Experiment 2 found that pigeons' discrimination of emotion was reliably affected by irrelevant variations in identity, whereas pigeons' discrimination of identity was not reliably affected by irrelevant variations in emotion. Thus, the asymmetry previously reported in human studies was reproduced in our pigeon study. These results challenge the view that a specialized human face perception system must underlie this effect.

Evidence indicates that faces are rapidly detected and prioritized in visual processing due to their social relevance. Crucially, research has shown that faces capture attention even when they are task-irrelevant, suggesting the existence of an automatic, domain-specific attentional mechanism. This prioritization appears to extend to face pareidolia—the illusory perception of faces in objects—indicating that face detection may rely on a broadly tuned mechanism that classifies stimuli as faces or non-faces based on relatively minimal information, such as the T-shaped configuration common to all faces. To explore whether such a configuration is sufficient to automatically capture attention, we conducted three behavioral experiments using a visual search paradigm. In Experiments 1A (online) and 1B (lab-based), participants searched for a butterfly target while either a real or an illusory face appeared among object distractors. Contrary to expectations, neither real nor illusory faces captured attention. In Experiment 2, in different blocks, participants were asked to search for a real face, an illusory face, or a butterfly presented among object distractors. The results showed that real faces were detected more efficiently than illusory faces or butterfly targets. Crucially, illusory faces showed a search disadvantage even compared to butterflies. Overall, these findings challenge the assumption that a minimal face configuration automatically captures attention. More importantly, these findings challenge the notion that attentional capture by irrelevant faces is entirely automatic, suggesting instead that such capture may be influenced by contextual factors or task demands.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00426-025-02211-3.

Face pareidolia, the perception of illusory faces in everyday objects, often includes social characteristics such as gender, age and emotion. However, it is unclear whether the characteristics of object face pareidolia are influenced by selection bias and/or the semantic characteristics of object images. The current study uses static and dynamic synthetic visual noise—an evocative but minimal stimulus—to examine the social characteristics associated with pareidolic faces in an unbiased way. Experiment 1 (N = 40) directly compared face pareidolia in objects and static, vertically symmetrical noise, finding social traits in both. Faces in synthetic noise appeared older and angrier than those seen in objects. Experiment 2 (N = 30) examined pareidolia in symmetrical and random dynamic noise, showing similar results to static noise. Our results provide ‘context-free’ insight into the perceptual and cognitive biases that influence the processing of ambiguous stimuli in human vision.

Dogs have a rich social relationship with humans. One fundamental aspect of it is how dogs pay close attention to human faces in order to guide their behavior, for example, by recognizing their owner and his/her emotional state using visual cues. It is well known that humans have specific brain regions for the processing of other human faces, yet it is unclear how dogs’ brains process human faces. For this reason, our study focuses on describing the brain correlates of perception of human faces in dogs using functional magnetic resonance imaging (fMRI). We trained seven domestic dogs to remain awake, still and unrestrained inside an MRI scanner. We used a visual stimulation paradigm with block design to compare activity elicited by human faces against everyday objects. Brain activity related to the perception of faces changed significantly in several brain regions, but mainly in the bilateral temporal cortex. The opposite contrast (i.e., everyday objects against human faces) showed no significant brain activity change. The temporal cortex is part of the ventral visual pathway, and our results are consistent with reports in other species like primates and sheep, that suggest a high degree of evolutionary conservation of this pathway for face processing. This study introduces the temporal cortex as candidate to process human faces, a pillar of social cognition in dogs.

Beyond the FFA: Brain-behavior correspondences in face recognition abilities

The human brain is specialized for face processing, yet we sometimes perceive illusory faces in objects. It is unknown whether these natural errors of face detection originate from a rapid process based on visual features or from a slower, cognitive re-interpretation. Here we use a multifaceted approach to understand both the spatial distribution and temporal dynamics of illusory face representation in the brain by combining functional magnetic resonance imaging and magnetoencephalography neuroimaging data with model-based analysis. We find that the representation of illusory faces is confined to occipital-temporal face-selective visual cortex. The temporal dynamics reveal a striking evolution in how illusory faces are represented relative to human faces and matched objects. Illusory faces are initially represented more similarly to real faces than matched objects are, but within ~250 ms, the representation transforms, and they become equivalent to ordinary objects. This is consistent with the initial recruitment of a broadly-tuned face detection mechanism which privileges sensitivity over selectivity.

Face perception in humans is governed more by right-hemispheric than left-hemispheric neural correlate. Some but not all neurophysiological studies depict a right-side dominance for face responsive neurons in the brains of macaques. Hence, it is an open question whether and to what extent a right-hemisphere preference of processing faces exists across primate brains. We investigated chimpanzees discriminating chimeric faces of chimpanzees and humans, i.e., the combination of either left or right sides of a face vertically flipped and merged into a whole face. We found an effect of choosing the left-chimeric face more often than the right-chimeric face as being the one of the two that is closer to the original face, reflecting an advantage for the right side of the brain to process faces, as reported in humans. Moreover, we found a modulation by age of the participants, suggesting that the exposure history with a particular category shapes the right-hemispheric neural correlate to a configural/holistic processing strategy. In other words, the findings in chimpanzee participants parallel those in human participants and are suggestive for similar neural machineries in the occipital-temporal cortices in both species.

The ability to recognize faces accurately and rapidly is an evolutionarily adaptive process. Most studies examining the neural correlates of face perception in adult humans have focused on a distributed cortical network of face-selective regions. There is, however, robust evidence from phylogenetic and ontogenetic studies that implicates subcortical structures, and recently, some investigations in adult humans indicate subcortical correlates of face perception as well. The questions addressed here are whether low-level subcortical mechanisms for face perception (in the absence of changes in expression) are conserved in human adults, and if so, what is the nature of these subcortical representations. In a series of four experiments, we presented pairs of images to the same or different eyes. Participants' performance demonstrated that subcortical mechanisms, indexed by monocular portions of the visual system, play a functional role in face perception. These mechanisms are sensitive to face-like configurations and afford a coarse representation of a face, comprised of primarily low spatial frequency information, which suffices for matching faces but not for more complex aspects of face perception such as sex differentiation. Importantly, these subcortical mechanisms are not implicated in the perception of other visual stimuli, such as cars or letter strings. These findings suggest a conservation of phylogenetically and ontogenetically lower-order systems in adult human face perception. The involvement of subcortical structures in face recognition provokes a reconsideration of current theories of face perception, which are reliant on cortical level processing, inasmuch as it bolsters the cross-species continuity of the biological system for face recognition.

Face recognition in humans is a complex cognitive skill that requires sensitivity to unique configurations of eyes, mouth, and other facial features. The Thatcher illusion has been used to demonstrate the importance of orientation when processing configural information within faces. Transforming an upright face so that the eyes and mouth are inverted renders the face grotesque; however, when this "Thatcherized" face is inverted, the effect disappears. Due to the use of primate models in social cognition research, it is important to determine the extent to which specialized cognitive functions like face processing occur across species. To date, the Thatcher illusion has been explored in only a few species with mixed results. Here, we used computerized tasks to examine whether nonhuman primates perceive the Thatcher illusion. Chimpanzees and rhesus monkeys were required to discriminate between Thatcherized and unaltered faces presented upright and inverted. Our results confirm that chimpanzees perceived the Thatcher illusion, but rhesus monkeys did not, suggesting species differences in the importance of configural information in face processing. Three further experiments were conducted to understand why our results differed from previously published accounts of the Thatcher illusion in rhesus monkeys.

Faces are valuable signals for efficient social interaction. Yet, social cognition including the sensitivity to a coarse face scheme may be deviant in schizophrenia (SZ). Tuning to faces in non-face images such as shadows, grilled toasts, or ink blots is termed face pareidolia. This phenomenon is poorly investigated in SZ. Here face tuning was assessed in 44 male participants with SZ and person-by-person matched controls by using recently created Face-n-Thing images (photographs of non-face objects to a varying degree resembling a face). The advantage of these images is that single components do not automatically trigger face processing. Participants were administered a set of images with upright and inverted (180° in the image plane) orientation. In a two-alternative forced-choice paradigm, they had to indicate whether an image resembled a face. The findings showed that: (i) With upright orientation, SZ patients exhibited deficits in face tuning: they provided much fewer face responses than controls. (ii) Inversion generally hindered face pareidolia. However, while in neurotypical males, inversion led to a drastic drop in face impression, in SZ, the impact of orientation was reduced. (iii) Finally, in accord with the signal detection theory analysis, the sensitivity index (d-prime) was lower in SZ, whereas no difference occurred in decision criterion. The outcome suggests altered face pareidolia in SZ is caused by lower face sensitivity rather than by alterations in cognitive bias. Comparison of these findings with earlier evidence confirms that tuning to social signals is lower in SZ, and warrants tailored brain imaging research.