Generally speaking, auditory processing disorder is a term for a group of conditions in which the parts of a child's brain tasked with turning sound into language and hearing into listening don't do their jobs right. How this issue develops and at what age it most often does so is little understood—we'll discuss this more below—but it is estimated that between 1.5 million and 2.5 million children a year are diagnosed with this disorder. Because auditory pathways leading from the ear into the brain and the auditory processing centers within the brain itself are continuously developing throughout infancy and early childhood, it's not possible to screen for and definitively establish the presence of an APD in a child until she or he is six or seven years old. A specific diagnosis detailing the magnitude of the APD as well as any related or concurrent problems such as ADD or ADHD and the right course of therapy and treatment cannot in turn be made until the child is seven or eight. But there are clearly many, many more younger children dealing with these listening difficulties. We think some children are even born with this issue. Unfortunately, because the development of auditory processing skills is linked with a growing child's use of language and increasingly complex communications and social interactions and cannot be accurately measured until those skills develop, parents have to go without formal diagnosis and intervention for too long. The ideas in this book will help you understand what's at stake in your child's listening development and in turn help your child from the moment you begin to suspect that there may be a problem. You don't need to wait for a formal diagnosis to begin to help.
THE ABCS OF APD
In broad strokes, it's easiest to understand hearing—the process of experiencing sound—as a two-stage phenomenon. First, sound vibrations are collected by the outer ear, funneled to the inner ear, where they become physical vibrations, and then sent on to the cochlea, where they are transformed into electrical impulses. Then these impulses travel along the eighth cranial nerve into the brain.
As the electrical impulses enter and go deeper into the brain, they pass through a series of relay stations in which the auditory information they carry is analyzed for timing (duration), intensity (volume), and frequency (pitch). The sound signals from each ear also get switched over like railcars changing tracks and are rerouted to the opposite side of the brain. Sound received in the right ear is sent to the left auditory cortex, while sound from the left ear goes to the right auditory cortex. The auditory cortex is a specialized area within the cerebral cortex that organizes, analyzes, and transforms sound information into the sensations and reactions that we recognize as language and speech. For most people the left cortex does the lion's share of the work.
Once inside these brain centers, sound impulses are put through a highly sophisticated and detailed battery of analyses and examinations contoured by memory, instinct, thought, and various voluntary and involuntary reactions into the sensation we experience as hearing. It's a complex process—one that simultaneously incorporates multiple locations of brain geography, a system of feedback to the cochlea to help narrow the focus of hearing, and a myriad of other analyses, impulses, gateways, functions, and processes. All this happens in a fraction of a second.