Abby's reaction to being lightly touched is similar to a person being threatened, while John's reaction to his uncle's visit is similar to a person being terrified and cries to be put down.
Sensory defensiveness is a low neurological threshold that can affect a child's vestibular, proprioception, visual and motor planning. This can lead to gravitational insecurity, which affects their development of gross and fine motor skills. This can create opportunities for higher learning in school.
Sensory defensiveness is caused by a disconnection in the CNS and a retained primitive reflex called the Tonic Labyrinthine Reflex (TLR). Sally Goddard explains that if the TLR is not inhibited at the correct time, it will interfere with vestibular system interactions.