gaze can also be seen in anxiety disorders, but poor eye contact in autistic children is not due to shyness or anxiety; rather, it is overall diminished in quantity. autistic people may struggle with both production and understanding of facial expressions. they often do not know how to recognize emotions from others' facial expressions, or may not respond with appropriate facial expressions. they may have trouble recognizing subtle expressions of emotion and identifying what various emotions mean for the conversation. a defining feature is that autistic people have social impairments and often lack intuitions about others that many people take for granted. temple grandin, an autistic woman involved in autism activism, described her inability to understand the social communication of neurotypicals, or people with typical neural development, as leaving her feeling "like an anthropologist on mars". they may also not pick up on body language or social cues such as eye contact and facial expressions if they provide more information than the person can process at that time. they struggle with understanding the context and subtext of conversational or printed situations, and have trouble forming resulting conclusions about the content. this also results in a lack of social awareness and atypical language expression. how facial expressions differ between those on the autism spectrum and neurotypical individuals is not clear. further, at least half of autistic children have unusual prosody. autistic people may also experience difficulties with verbal communication. differences in communication may be present from the first year of life, and may include delayed onset of babbling, unusual gestures, diminished responsiveness, and vocal patterns that are not synchronized with the caregiver. in the second and third years, autistic children have less frequent and less diverse babbling, consonants, words, and word combinations; their gestures are less often integrated with words. autistic children are less likely to make requests or share experiences, and are more likely to simply repeat others' words (echolalia). joint attention seems to be necessary for functional speech, and deficits in joint attention seem to distinguish autistic infants. for example, they may look at a pointing hand instead of the object to which the hand is pointing, and they consistently fail to point at objects in order to comment on or share an experience. autistic children may have difficulty with imaginative play and with developing symbols into language. some autistic linguistic behaviors include repetitive or rigid language, and restricted interests in conversation. for example, a child might repeat words or insist on always talking about the same subject. echolalia may also be present in autistic individuals, for example by responding to a question by repeating the inquiry instead of answering. language impairment is also common in autistic children, but is not part of a diagnosis. many autistic children develop language skills at an uneven pace where they easily acquire some aspects of communication, while never fully developing others, such as in some cases of hyperlexia. in some cases, individuals remain completely nonverbal throughout their lives. the cdc estimated that around 40% of autistic children don't speak at all, although the accompanying levels of literacy and nonverbal communication skills vary. restricted and repetitive behaviors a young autistic boy who has arranged his toys in a row asd includes a wide variety of characteristics. some of these include behavioral characteristics which widely range from slow development of social and learning skills to difficulties creating connections with other people. autistic individuals may experience these challenges with forming connections due to anxiety or depression, which they are more likely to experience, and as a result isolate themselves. other behavioral characteristics include abnormal responses to sensations (such as sights, sounds, touch, taste and smell) and problems keeping a consistent speech rhythm. the latter problem influences an individual's social skills, leading to potential problems in how they are understood by communication partners. behavioral characteristics displayed by autistic people typically influence development, language, and social competence. behavioral characteristics of autistic people can be observed as perceptual disturbances, disturbances of development rate, relating, speech and language, and motility. the second core symptom of autism spectrum is a pattern of restricted and repetitive behaviors, activities, and interests. in order to be diagnosed with asd under the dsm-5-tr, a person must have at least two of the following behaviors: repetitive behaviors – repetitive behaviors such as rocking, hand flapping, finger flicking, head banging, or repeating phrases or sounds. these behaviors may occur constantly or only when the person gets stressed, anxious or upset. these behaviors are also known as stimming. resistance to change – a strict adherence to routines such as eating certain foods in a specific order, or taking the same path to school every day. the individual may become distressed if there is any change or disruption to their routine. restricted interests – an excessive interest in a particular activity, topic, or hobby, and devoting all their attention to it. for example, young children might completely focus on things that spin and ignore everything else. older children might try to learn everything about a single topic, such as the weather or sports, and perseverate or talk about it constantly. sensory reactivity – an unusual reaction to certain sensory inputs such as having a negative reaction to specific sounds or textures, being fascinated by lights or movements or having an apparent indifference to pain or heat. autistic individuals can display many forms of repetitive or restricted behavior, which the repetitive behavior scale-revised (rbs-r) categorizes as follows. stereotyped behaviors: repetitive movements, such as hand flapping, head rolling, or body rocking. compulsive behaviors: time-consuming behaviors intended to reduce anxiety, that an individual feels compelled to perform repeatedly or according to rigid rules, such as placing objects in a specific order, checking things, or handwashing. sameness: resistance to change; for example, insisting that the furniture not be moved or refusing to be interrupted. ritualistic behavior: unvarying pattern of daily activities, such as an unchanging menu or a dressing ritual. this is closely associated with sameness and an independent validation has suggested combining the two factors. restricted interests: interests or fixations that are abnormal in theme or intensity of focus, such as preoccupation with a single television program, toy, or game. self-injury: behaviors such as eye-poking, skin-picking, hand-biting and head-banging. self-injury self-injurious behaviors (sib) are relatively common in autistic people, and can include head-banging, self-cutting, self-biting, and hair-pulling. some of these behaviors can result in serious injury or death. following are theories about the cause of self-injurious behavior in children with developmental delay, including autistic individuals: frequency and/or continuation of self-injurious behavior can be influenced by environmental factors (e.g. reward in return for halting self-injurious behavior). however this theory is not applicable to younger children with autism. there is some evidence that frequency of self-injurious behavior can be reduced by removing or modifying environmental factors that reinforce this behavior.: 10–12 higher rates of self-injury are also noted in socially isolated individuals with autism. studies have shown that socialization skills are related factors to self injurious behavior for individuals with autism. self-injury could be a response to modulate pain perception when chronic pain or other health problems that cause pain are present.: 12–13 an abnormal basal ganglia connectivity may predispose to self-injurious behavior.: 13 other features autistic individuals may have symptoms that do not contribute to the official diagnosis, but that can affect the individual or the family. some individuals with asd show unusual or notable abilities, ranging from splinter skills (such as the memorization of trivia) to rare talents in mathematics, music or artistic reproduction, which in exceptional cases are considered a part of the savant syndrome. one study describes how some individuals with asd show superior skills in perception and attention, relative to the general population. sensory abnormalities are found in over 90% of autistic people, and are considered core features by some. more generally, autistic people tend to show a 'spiky skills profile', with strong abilities in some areas contrasting with much weaker abilities in others. differences between the previously recognized disorders under the autism spectrum are greater for under-responsivity (for example, walking into things) than for over-responsivity (for example, distress from loud noises) or for sensation seeking (for example, rhythmic movements). an estimated 60–80% of autistic people have motor signs that include poor muscle tone, poor motor planning, and toe walking; deficits in motor coordination are pervasive across asd and are greater in autism proper. pathological demand avoidance can occur. people with this set of autistic symptoms are more likely to refuse to do what is asked or expected of them, even to activities they enjoy. unusual or atypical eating behavior occurs in about three-quarters of children with asd, to the extent that it was formerly a diagnostic indicator. selectivity is the most common problem, although eating rituals and food refusal also occur. there is tentative evidence that gender dysphoria occurs more frequently in autistic people (see autism and lgbt identities). as well as that, a 2021 anonymized online survey of 16–90 year-olds revealed that autistic males are more likely to identify as bisexual, while autistic females are more likely to identify as homosexual. possible causes main article: causes of autism exactly what causes autism remains unknown. it was long mostly presumed that there is a common cause at the genetic, cognitive, and neural levels for the social and non-social components of asd's symptoms, described as a triad in the classic autism criteria. but it is increasingly suspected that autism is instead a complex disorder whose core aspects have distinct causes that often cooccur. while it is unlikely that asd has a single cause, many risk factors identified in the research literature may contribute to asd development. these include genetics, prenatal and perinatal factors (meaning factors during pregnancy or very early infancy), neuroanatomical abnormalities, and environmental factors. it is possible to identify general factors, but much more difficult to pinpoint specific ones. given the current state of knowledge, prediction can only be of a global nature and therefore requires the use of general markers. biological subgroups research into causes has been hampered by the inability to identify biologically meaningful subgroups within the autistic population and by the traditional boundaries between the disciplines of psychiatry, psychology, neurology and pediatrics. newer technologies such as fmri and diffusion tensor imaging can help identify biologically relevant phenotypes (observable traits) that can be viewed on brain scans, to help further neurogenetic studies of autism; one example is lowered activity in the fusiform face area of the brain, which is associated with impaired perception of people versus objects. it has been proposed to classify autism using genetics as well as behavior. (for more, see brett abrahams) genetics main article: heritability of autism