Autism is a condition that was first
described by Leo Kanner (1943) and Hans Asperger
(1944). The predominant features of autism are impairments in
communication, social interaction and patterns of repetitive behaviours,
interests, or activities; which present on a continuum of severity (Lord et
al., 2000). Autism may be connected to abnormalities including epilepsy, mental
handicap and a variety of brain pathologies (Williams, Whiten, Suddendorf &
Perrett, 2001). Linked to neurological function and early development
differences, studies indicate the pathology of autism is one of the most
complex amid neurodevelopmental disorders (Koyama, 2009).
Facial recognition is one of four core domains
of the social impairments, together with joint attention, responses to the
emotional displays of others, and social orientation (Dawson et al.,
2002b). Social
development can be severely affected by facial processing abilities; with face
identification and emotion recognition essential to accessing important social
cues (Nomi & Uddin, 2015). In a social-focused world, an
impeded capacity to socialise with others can be an isolating challenge for
autistic individuals (Poliakova, Palkhivala, & Johnson, 2008). Although diagnosis of autism is generally achieved
using behavioural measurements, these behavioural traits have been associated with
structural and functional anomalies in the autistic brain. This essay aims to
discuss the findings of neuroimaging studies and relevant neurocognitive
theories to explain facial recognition impairments in autism.
The ability to understand the actions and
emotions of other human beings relies on the capacity to use one’s own motor,
cognitive, and emotional expressions to understand another human’s observed
actions and internal states (Oberman &
Ramachandran, 2007). This ability is compromised in individuals
with autism, whose behavioural impairments, such as eye contact, body language,
imaginative play and understanding of gestures and facial expressions (American
Psychiatric Association, 2013), are key to social interaction.
A deficit in facial recognition affects
autistic individuals overall social interaction skills as recognising faces is
implemented in social engagement (Nomi &
Uddin, 2015). As facial recognition is a social interaction skill evident very
early in life, initial Functional Magnetic Resonance Imaging (fMRI) studies focused
on autistic individuals’ failures to attend to faces (Dawson et al., 2002a;
Schultz et al., 2000). Studies have discovered abnormal facial perception in
autism, with autistic individuals struggling to judge the emotions (Ashwin
et al., 2007), or trustworthiness (Adolphs, Sears & Piven, 2001) of
others. Additionally, studies show autistic deficits include poor memory of
faces (Boucher et al., 1998), and a lack of attention to the eyes of others (Sterling et
al., 2008).
Dawson et al.,
(2002a) utilised electroencephalographic (EG)
recordings to observe the high-density brain event-related potentials (ERPs) of
children with autism when seeing photographs of faces (an unfamiliar and the
mother’s) and toys (favourite and new). In comparison to the control groups,
children with autism did not show ERP amplitude differences during facial
recognition. However, object differentiation was observed. This contributes to
the growing evidence indicating an impairment in recognition that is specific
to faces. Following sections will discuss some of the predominant research and
theories that have attempted to understand the pathology of this impairment.
There are many theories that attempt to
explain the social impairments in autism. Two significant cognitive theories
include the Executive Dysfunction theory (see Hill, 2004 for
a review), and the Weak Central Coherence theory (WCC: Hermelin &
O’Connor, 1967). However, it may be argued that the most relevant theory to the
facial recognition impairments of autism is the Theory of Mind (ToM: Rajendran
& Mitchell, 2007). ToM
hypothesises that the social impairments observed in autism is due to an
inability to take into account the mental states of others, or mentalise (Frith, 2001; Castelli
et al, 2002) and is sometimes used synonymously with
social intelligence (Baron-Cohen
et al., 2000).
A lack of
attention to the eyes of others has been discussed as a possible influence on the
difficulties of mentalizing that are characteristic of autism. A study
utilizing eye tracking investigated patterns of attention to faces found
evidence suggesting individuals with autism have atypical gaze patterns when
viewing faces, although face recognition reaction time and accuracy was typical
(Sterling et al., 2008). Such studies suggest the
facial recognition impairments of autistic individuals could be due to not
focusing on areas of the face, such as the eyes, that express emotions and
characterise an individual.
Measures of the inability to mentalise
include The Revised Eyes Test (Baron-Cohen et al, 1999), which boasts an
ability to detect subtle deficits in social cognitive functions. Despite the role of ToM in
autism research being irrefutable, definition and theoretical foundation of the
theory remains debated, and continues to be reconceptualised (Rajendran
& Mitchell, 2007). Hypothesises such as Klin, Jones, Schultz
and Volkmar’s (2003) enactive mind (EM) evolve the original theory. The EM
approach is a developmental hypothesis discussing the social cognition of
autism as related to a lack of social stimuli that is salient. Nevertheless, despite
developments, the ToM is often at the core of explanations behind the social
deficits in autism.
Various
brain regions have been associated with the social impairments of autism
(Diagram 1). Functional magnetic resonance imaging (fMRI) studies such as Schultz et al., (2000) reveal abnormal activity in
the ventral temporal cortex during face discrimination. The ventral temporal
cortex is associated with visual categorisation (Grill-Spector & Weiner, 2014), meaning autistic individuals’
visual categorisation abilities may be impaired, which in turn affects their
ability to distinguish faces and emotions.
The Social
Brain theory (SB: Brothers, 1990) proposes a network of neural regions
(including the orbitofrontal cortex (OFC), superior temporal gyrus (STG) and
amygdala) that make up the “social brain”. These areas have been implicated in influencing
drive-based emotions and behaviour (amygdala: Baron-Cohen et al., 2000); such as emotional memory (amygdala:
Amunts et al., 2005), decision making and emotional processing, (the OFC: Bechara,
Damasio & Damasio, 2000; Berntson, Bechara, Damasio, Tranel, & Cacioppo,
2007) and speech
perception (the STG: Chang
et al., 2010).
Emotional
processing and speech perception are especially important for the social brain
and social interaction (Dolan, 2002).
They refer not only to understanding or expressing one’s own emotions or
speech, but also other peoples, and therefore reading people in order to
interact. Additionally, the tone of speech is an important element of
perceiving speech (Belin, Bestelmeyer, Latinus, & Watson, 2011). Consequently, not being able
to process the emotions and tones behind spoken words makes social interaction
extremely difficult and confusing. Such difficulties in processing and
perception are typical in autistic individuals’ behaviours (Klin et al.,
1999). As discussed, brain regions in the “social brain” related to
these processing functions have been found to be abnormal or impaired in
autistic individuals, which could explain autistic behavioural traits of a
difficulty to mentalise, and the disinterest in, and attention to faces.
Atypical brain growth (Courchesne et al,
2001), and cerebellar vermis and brain stem abnormalities (Hashimoto et al,
1995) have been the most consistently reported in individuals with autism (Fatemi et al., 2012). Abnormalities in the
cerebellum could explain some of the more general social impairments in autism.
Operating closely with the prefrontal cortex (Pinel, 2006), which
has a significant function in executive processes (Luna,
Padmanabhan, & O’Hearn, 2010) the
cerebellum is involved in motor functions and cognitive functions such as
verbal working memory, sequence learning (Paul et al., 2009) and emotional function (Wolf
et al., 2009). Abnormalities in the cerebellum affecting cognitive functions, such
as emotional function, could be affecting autistic individuals’ ability to understand
their own emotions, and the emotions of others.
As abnormalities
in the amygdala and hippocampus have been revealed in autistic individuals (Aylward et al., 1999), the amygdala theory of autism
has emerged, which implicates the amygdala in the deficits of autism (Baron-Cohen
et al., 2000). With the amygdala and hippocampus associated with memory, (Banich & Compton, 2011) facial recognition
could be related to a recognition memory deficit (Blair et al., 2002).
Baron-Cohen
et al., (1999) test the
Social Brain theory with high-functioning autistic individuals in an fMRI
study. Findings of increased activation in the superior temporal gyrus (STG),
amygdala and the prefrontal cortex in typically developing subjects when
applying social intelligence supported the Social Brain theory. The
fronto-temporal regions of the autistic participants were activated, but not
the amygdala, when attempting to infer emotions from a person’s eyes. Additionally,
studies have found the right anteromedial temporal lobe, including the
amygdala, to have a role in comprehending emotions from faces, (Adolphs, Tranel
& Damasio, 2001) suggesting abnormality in the amygdala in individuals with
autism could relate to the difficulties responding to emotional displays of
others.
Kleinhans et al., (2009) conducted an fMRI study
measuring activation of the amygdala and fusiform gyrus over time in response
to neutral facial stimuli. The findings show amygdala hyperarousal in response
to social stimuli in individuals with autism, and the authors propose that the
social deficits observed may be linked to sustained amygdala arousal. Schultz, (2005) states that deficits in the
amygdala-fusiform system affect social cognitive skills such as face perception
and thus proposes that the early developmental issues in autism are linked to
the amygdala and the fusiform (an area linked to visual social perception) of
the ventral temporal lobe. These
findings support the amygdala theory of autism, and contribute to the research
implicating these regions in the social impairments of autism.
The
complexity of autism’s pathophysiology is highlighted in more recent advances
in genetics (Persico & Napolioni, 2013), with some studies suggest
infants with an older sibling with autism are significantly more likely to be
diagnosed with autism (Ozonoff et al., 2011). Research into the molecular genetics and the
underlying neurobiological processes of autism indicates that autism
transmitted familialy is a more diverse phenotype of the deficits of autism (Volkmar et
al., 2004). However,
genetic contributions to understanding the contributing factors of autism are
extremely heterogeneous (Persico & Napolioni, 2013), with more research required
to identify the genetic foundation of autism. Nevertheless, genetic research
could enable improved diagnosis methods, reveal unique insights into autism,
and refine the current understanding of autism’s biological underpinnings
(State & Sestan, 2012).
Development of innovative developmental
models to explain autism’s triad of impairments have been aided by
psychological research (Volkmar et
al., 2004). Reliable
diagnosis of autism spectrum disorder in children as young as two has been
achieved, with conversational skills remaining impaired when reassessed aged
4-5 (Moor and Goodson, 2003), contributing to the current understanding of the
pervasive nature of these deficits (Ciaranello & Ciaranello, 1995), and
giving hope to early diagnosis of autism being possible in the future. However,
despite accumulating research evidencing structural and functional abnormalities,
diagnosis is generally achieved using behavioural measurements. One issue with the definition of
autism involves the fact that diagnosis measures are based on restrictive
conceptualisations of autism as social, communication and behavioral
difficulties.
Due to its
heterogeneous nature, autism is unlikely to be the result of a single cognitive
(or genetic) cause (Happé, Ronald & Plomin, 2006). While the diagnosis of
autism becomes more consistent, the definition simultaneously becomes broader (Volkmar et al., 2004). These developments impede one
another. The picture of autism we use to diagnose individuals is rapidly
developing, potentially meaning the increasing diagnosis of autism is not
representative of the broadening concept of autism. The current classifications
of autism may not be reliable measurements of autism and research is now
beginning to explore beyond the boundaries of the three domains of difficulty,
looking at individuals who do not fit into these restricted classifications (Volkmar et al., 2004). Nevertheless, using the triad
of impairments as a basis for diagnosing autism provides a foundation for
researchers to expand from.
Current
research has a limited overview of the autistic spectrum, with research
predominantly focusing on high-functioning individuals, and a limited
demographic (Harms, Martin, & Wallace, 2010). This produces difficulties for establishing
links between brain and behaviour in autism, due to anatomical studies being
predominantly based on low-functioning individuals, while most behavioural
studies focusing on proficient or high-functioning individuals (Hill &
Frith, 2003). Additionally, a
lack of sensitivity in behavioural measures to detect group differences could
explain the mixed findings evident in behavioural studies (Harms et al., 2010).
Despite
limitations of current research, structural findings and cognitive theories
have implicated abnormalities in the frontal lobes to the social and cognitive
features of autism, and thus facial recognition; meanwhile, an important role
of genetic and environmental factors in autism is emerging (Koyama, 2009). Early
diagnosis of autism could be an important element in implementing early
interventions to help support individuals with autism. Better understanding of the face-recognition
deficits of autism could help research into the developmental elements of the
pathobiology, thereby enabling more
suitable support for autistic individuals with social impairments. Studies such as Moor and Goodson
(2003) show possibilities for earlier diagnosis, and there is growing evidence
of successful interventions (Matson & LoVullo, 2009). I believe future research must
expand to concentrating on developing assessments and treatments that are
better suited to low-functioning individuals to better gage the full scale of
the spectrum of autism and the pathology behind the attributed facial recognition
impairments.
