Face Perception in Autism Spectrum Disorder

Human beings are a highly social species. In order to survive and thrive, we rely on social exchanges in which we constantly keep track of others’ faces (Leopold & Rhodes, 2010). Since the majority of people spend a bigger portion of their days looking at faces than at other objects (Haxby et al., 2000), fluency with faces is the core of our everyday social interactions (Leopold & Rhodes, 2010). This fluency enables us to predict others’ future behavior, choose who to interact with, and build social connections (Hugenberg & Wilson, 2013). Differences in understanding facial cues and the inability to preferentially attend to faces can result in social and developmental irregularities deficits, including Autism or Autism Spectrum Disorder (ASD) (Hugenberg & Wilson, 2013).

Faces are the center of our social exchanges and are likely among the most important visual stimuli, requiring highly developed facial perception skills that rely on specialized cortical networks (Haxby et al., 2000). There are patches in the human visual stream that specifically respond to faces as opposed to other stimulus categories, such as tools, places, and body parts. The essence of the face-selective regions in the human cortex are the Occipital Face Area (OFA) within the inferior occipital gyrus and the Fusiform Face Area (FFA) within the lateral fusiform gyrus. These regions are located in the occipitotemporal visual extrastriate cortex along the ventral stream (Haxby et al., 2000).

Difficulty understanding facial cues and preferentially attending to faces correlate with social and developmental challenges (Hugenberg & Wilson, 2013; Yardley et al., 2008; Baron-Cohen et al., 1997). ASD is a developmental condition involving difficulties with social skills, repetitive behaviors, speech, and nonverbal communication. The social-communicative difficulties in ASD include the use of information from faces, such as eye gaze, facial expression, and speech (American Psychiatric Association, 2013). Some behavioral differences in face perception have been reported between autistic and non-autistic individuals. Several studies show that ASD individuals tend to look less at the features of the faces, especially the eyes, both in toddlers (Chawarska & Shic, 2009) and adults (Pelphrey et al., 2002) with ASD. Furthermore, it has been shown that compared to non-autistic controls, ASD individuals show less of a face inversion effect, which describes the phenomenon of decreased efficiency when identifying faces that are presented upside down (Falck‐Ytter, 2008). This effect does not hold for non-facial objects. The fact that those with ASD show neither a face inversion effect nor a deficit in object perception might suggest that they use different strategies for face perception compared to those without ASD.

Presumably, such differences between autistic and non-autistic individuals are the result of observable structural and functional brain alterations. This idea has triggered a line of research investigating the neural correlates of differences in the face-selective network, namely the FFA and OFA. In one study, the Schultz team used the brain imaging technique functional magnetic resonance imaging (fMRI) to investigate brain responses of non-autistic and ASD individuals when viewing faces versus objects or patterns. Where participants had to press a button to discriminate between stimulus categories, experimenters found significant differences between the brain activation patterns of the two groups in the temporal lobe structures. To be more specific, they found decreased activation in fusiform gyrus and increased activation in inferior temporal gyri (Schultz et al., 2000), which are implicated in the face and object processing, respectively.

Further investigations by Pierce et al. (2001) have shown that during a face perception task those with autism had reduced activation in the fusiform gyrus and left amygdala compared to the control group. One autistic individual was found to have no activation in the fusiform gyrus at all. Their findings are supported by previous studies that reported reduced amygdala activation during a social intelligence task and an emotion processing task (Baron‐Cohen et al. 1999; Critchley et al. 2000). The amygdala, a pair of small almond-shaped regions deep in the brain, has been recognized as the center of emotion and fear conditioning in the brain (Andrewes, 2015). However, its function goes beyond emotional processing and includes memory, decision making, and face perception (Andrewes, 2015; Bechara, 2003; Haxby & Gobbini, 2011). The amygdala is proposed to play a role in eye gaze perception, directing attention toward faces, and emotional responses to being looked at (Kawashima et al., 1999; Haxby & Gobbini, 2011). Thus, it is expected that reduced volume of the amygdala may result in irregularities in gaze and face perception. The amygdala is a deep brain structure, while the FFA and occipital face area are cortical areas. Amygdala activation is observed as early as infancy, as opposed to cortical activations that become specialized for a cognitive task such as face perception as a result of experience later on in life (Graham et al., 2016; Kadosh & Johnson, 2007). Thus, the cascade of atypical social development in ASD individuals may be a result of the malfunction of the amygdala from birth (Pierce et al., 2001).

It should be noted that the accuracy and response times were not significantly different between the two groups. Thus, ASD individuals show intact accuracy and reaction time despite the lack or reduced activations in face-selective areas during face perception task. This may be a sign of compensatory mechanisms that evolved to perform face perception. However, this mechanism might not lead to a fully successful face perception.

These findings showing intact object recognition and a lack of an inversion effect for faces suggest that ASD individuals may treat faces as if they are objects. That is to say, autistic individuals utilize different neural systems than the non-autistic groups when seeing faces (Pierce et al., 2001). This also justifies why autistic individuals are not generally prosopagnosic. A huge difference between face and object perception is that face perception is holistic and relies on spatial configurations of the features in the face, while object recognition relies on the detection of individual features of the object as opposed to the overall configuration. It is evident that the pattern of brain activity in individuals with ASD resembles that of feature-based strategies that are common for object perception as opposed to face perception. It could be assumed that the irregular pattern of activation, along with the reduced volume of the amygdala, underly the behavioral differences of ASD individuals (Schultz et al., 2000). Moreover, it is highly likely that the atypical neurofunctional responses to faces extend to the fusiform gyrus and the amygdala and includes higher-order areas such as frontoparietal networks that are involved in attention (Pierce et al., 2001).

Although findings are not entirely consistent about the exact regions and dynamics of irregularities, they are informative in two main ways. First, the lack of behavioral differences in autistic individuals performing a face perception task, even in the absence of FFA activation, suggests that multiple regions in addition to the fusiform gyrus can support face processing. This is in line with the domain-general view that the fusiform gyrus is an experience-dependent neural region. In this view, subordinate levels of familiar categories of objects, such as faces for non-autistic individuals, are processed in the FFA. Consequently, since autistic individuals show differences in how they process gaze (Baron-Cohen et al., 1997) and recognize emotional expressions (Celani et al., 1999), and thus may have altered processing of subordinate-level facial features, lack or absence of activation in the FFA is expected within the domain-general view (Pierce et al., 2001). The fact that FFA is not innately dedicated to process faces but is an experience-dependent region can inspire new rehabilitation strategies for individuals with lesions of face-selective regions in the brain.

Second, observing different patterns of brain activations between non-autistic and autistic individuals while the behavioral results are similar shows a great constraint on a one-to-one mapping between behavior and brain regions. That is to say, a specific cognitive process cannot be inferred solely from the observed brain activations. It also points to the necessity of studying possible compensatory mechanisms in the autistic brain. This is crucial since it allows for a full understanding of the scope of irregularities that are not necessarily disadvantages, but can be advantages to some aspects of our modern life.

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Written by Elaheh Akbarifathkouhi.

Illustrated by Gil Torten.

Edited by Melis Cakar and Zoe Guttman.

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