Autistic people process sensory input differently on a neurological level. Most commonly, the sense of hearing is affected, effectively turning up the volume of the world.
Quiet droning or buzzing sounds such as those created by computers, which are almost inaudible to most people, may create discomfort to the point of the person being unable to focus on anything else. High-pitched or sudden noise may be experienced as physically painful. Moderate noise made by a group of people talking may feel deafening.
All senses can be involved, however, with some getting a headache from fluorescent or bright lights, some not being able to wear certain fabrics because they feel like a wire brush against their skin, some avoiding certain foods because the texture or taste cannot be tolerated, and some feeling nauseated by the smell of perfumes. Everyone is different, with thousands of possibilities of sensory issues.
'My eyes are really sensitive to light. Any kind of bright light makes them water and get red, even normal indoor lighting. That’s why I basically have to wear sunglasses all the time. I always get looks by strangers when I’m in the supermarket, and at work, half of my colleagues have told me at one point or another that they found it annoying having to talk to me without seeing my eyes. I haven’t disclosed my ASD, so it’s my fault in a way, but I just wish I didn’t have to explain myself'. (Harold, 52)
The lesser-known senses of proprioception (knowing where one’s body is in space without having to look), thermoception (sensing temperature), and nociception (sensing pain) are also often affected, explaining why some autistic people appear to be indifferent to pain, hunger, or the cold, or why they may have an odd-looking gait and stumble over their own feet.
Different sensory processing doesn’t only lead to adverse reactions. Many everyday aspects of the environment, such as running water, sunlight sparkling in dew drops, subtle smells of mown grass, the tactile experience of burying one’s hand in a bag of rice grains, clicking pebbles, etc., can be experienced as highly pleasurable, contributing immensely to the person’s happiness and sense of calm.