The sensory system enables us to take in information from the world; the processing aspect of that system enables us to interpret that information.  The motor system is what enables us to respond.  When a baby snuggles easily, when we laugh at a joke, when we run to catch a ball that’s flying toward us, and when we answer a question that has been posed, we are using our motor system to form our response.  The use of the trunk to cuddle, of the mouth and tongue to form words, of arms and legs to run and catch, of muscles in the face to smile or frown or look away—all these are motor activities that permit us to respond to the world.

In children with developmental delays we often observe problems of muscle tone or motor planning.  Muscle tone refers to the ability of our muscles to support our bodies without effort.  Children with low tone, whose muscles are very loose, have to put great effort into holding their heads up and walking.  Muscle tone in part influences the ability of individual muscle groups to respond the way we want them to.  Motor planning refers to the ability of a person to plan and execute a series of muscle movements.  Sound muscle tone enables a person to flex and contract muscles on command; poor muscle tone means that those muscles will be too tight or too loose, resistant to the person’s effort to control them.  Sound motor planning means a person will be able to figure out what action is needed and then execute it; he will be able to put one foot in front of the other and shift his weight from left to right while counterbalancing with his arms in order to walk across a room.  Poor motor planning means a person may be unable to figure out which foot to start with, which one to move next, and which way to lean to keep her balance.

Problems with motor planning can make even the simplest tasks difficult.  Acknowledging Daddy when he leans over the crib means turning to face him, making eye contact, and responding with gestures or a smile—sequencing numerous motions together.  Many unimpaired infants can do that on automatic pilot, but a child with motor-planning difficulties has to work through each step.  It’s easy to see how he might get distracted along the way!  Any activity that requires sequencing actions or behaviors presents similar challenges.  Hence eating, exploring toys, playing games, and interacting socially are made more difficult for children with motor-planning or sequencing challenges. Later in life, complex social sequences—greeting new people, engaging in give-and-take behaviors such as two-way conversations, sports—require skills in motor planning and sequencing.  Even our ability to sequence ideas into a logical flow may be related in part to this ability.

Sensory reactivity, processing, and motor planning and sequencing affect how a child functions in the world—how well he relates to the people around him; how well he communicates his wishes and ideas; how well he thinks and navigates the often bumpy world of emotions.  When we look at a child’s individual differences, these are among the abilities we examine.  When a child is considered to have special needs, often one or more of these abilities is not developing or functioning optimally.