Auditory processing disorder (APD), rarely known as King-Kopetzky syndrome or auditory disability with normal hearing (ADN), is an umbrella term for a variety of disorders that affect the way the brain processes auditory information. Individuals with APD usually have normal structure and function of the outer, middle, and inner ear (peripheral hearing). However, they cannot process the information they hear in the same way as others do, which leads to difficulties in recognizing and interpreting sounds, especially the sounds composing speech. It is thought that these difficulties arise from dysfunction in the central nervous system.

SIGNS AND SYMPTOMS

Many people experience problems with learning and day-to-day tasks with difficulties over time. Adults with this disorder can experience the signs and symptoms below:

• talk louder than necessary
• talk softer than necessary
• have trouble remembering a list or sequence
• often need words or sentences repeated
• have poor ability to memorize information learned by listening
• interpret words too literally
• need assistance hearing clearly in noisy environments
• rely on accommodation and modification strategies
• find or request a quiet work space away from others
• request written material when attending oral presentations
• ask for directions to be given one step at a time

CAUSES

Acquired

Acquired APD can be caused by any damage to or dysfunction of the central auditory nervous system and can cause auditory processing problems.For an overview of neurological aspects of APD, see Griffiths.

Genetics

Some studies indicated an increased prevalence of a family history of hearing impairment in these patients. The pattern of results is suggestive that Auditory Processing Disorder may be related to conditions of autosomal dominant inheritance. The ability to listen to and comprehend multiple messages at the same time is a trait that is heavily influenced by our genes say federal researchers. These "short circuits in the wiring" sometimes run in families or result from a difficult birth, just like any learning disability.Auditory processing disorder can be associated with conditions affected by genetic traits, such as various developmental disorders. Inheritance of Auditory Processing Disorder refers to whether the condition is inherited from your parents or "runs" in families.Central auditory processing disorder may be hereditary neurological traits from the mother or the father.

Developmental

In the majority of cases of developmental APD, the cause is unknown. An exception is acquired epileptic aphasia or Landau-Kleffner syndrome, where a child's development regresses, with language comprehension severely affected.The child is often thought to be deaf, but normal peripheral hearing is found. In other cases, suspected or known causes of APD in children include delay in myelin maturation, ectopic (misplaced) cells in the auditory cortical areas,or genetic predisposition.In a family with autosomal dominant epilepsy, seizures which affected the left temporal lobe seemed to cause problems with auditory processing.In another extended family with a high rate of APD, genetic analysis showed a haplotype in chromosome 12 that fully co-segregated with language impairment.

Hearing begins in utero, but the central auditory system continues to develop for at least the first decade.There is considerable interest in the idea that disruption to hearing during a sensitive period may have long-term consequences for auditory development.One study showed thalamocortical connectivity in vitro was associated with a time sensitive developmental window and required a specific cell adhesion molecule (lcam5) for proper brain plasticity to occur. This points to connectivity between the thalamus and cortex shortly after being able to hear (in vitro) as at least one critical period for auditory processing. Another study showed that rats reared in a single tone environment during critical periods of development had permanently impaired auditory processing.‘Bad’ auditory experiences, such as temporary deafness by cochlear removal in rats leads to neuron shrinkage. In a study looking at attention in APD patients, children with one ear blocked developed a strong right-ear advantage but were not able to modulate that advantage during directed-attention tasks.