Each of our boys has Sensory Processing Disorder along with autism (the two often go together, but not always, it is possible to have one and not the other).
Sensory Processing Disorder (SPD) affects how sensory input is perceived and can lead to being over-sensitive to certain sensations and/or under-sensitive to others. For example, Bearhug and Cuddlebug are sensitive to noisy crowds and Bitty cannot tolerate mushy food textures. On the flip side, both Little Bitty and Bearhug have a very high pain threshhold, often seeming to not even notice things that would be painful for most.
SPD can also affect how the senses combine to give one a sense of balance and position in space. This is something most of us take for granted and don't even realize our brains are doing, I know I had no clue until I started learning about SPD from our sons' OT's and books like The Out of Sync Child.
Sensory Processing Disorder: Signs and symptoms
Sensory Processing Disorder: Perspectives
SPD Foundation checklist
The Out-of-Sync Child