APD Testing
Testing
The American Speech-Language and Hearing Association (ASHA) designates audiologists as the professionals who diagnose auditory processing disorders. Speech-language pathologists (SLPs) provide information about speech and language abilities that helps with the diagnosis, and they are often in charge of remediation plans for children diagnosed with APD. A complete APD examination involves first, the verification that the peripheral hearing system is functioning as expected, and second, tests that stress the auditory system to evaluate how it deals with hearing in difficult listening situations. APD testing includes:
1. Audiogram. A regular hearing test is performed to decide if the first three parts of the ear are working properly.
The audiologist tests the outer ear to make sure that there is no earwax or other matter that is simply blocking the canal that opens to the middle ear. The eardrum movement is measured (the test is called “tympanometery”) to be sure that there is no problem with fluid in the middle ear and that the three little bones in the middle ear are free to move as they should. Then the hair cells of the inner ear are tested indirectly by determining how soft a sound the person being tested can perceive. (That is what the “audiogram” tests.) We also measure the ability of the person tested to understand single words in a very quiet environment by testing first one ear, then the other.
If hearing is normal, or there is only a small hearing loss that is equal in the two ears, the examiner can proceed to Auditory Processing testing.
2. Auditory Processing tests. After the regular hearing test has been done, the Auditory Processing testing comes next. It usually focuses upon three main areas: how efficiently the two ears work together, how well the nerves in the Auditory Pathways pass the signals from the ear upward to the cortex of the brain, and how well the person is able to understand distorted auditory signals.
A. Dichotic Listening. The ability to find sounds in space and to single out a certain speaker when there are multiple auditory things happening in the environment is heavily dependent upon how well the two ears coordinate. Much of our spatial hearing ability depends on the two ears comparing the time differences or loudness differences of the sounds they take in. The ear can make sense of timing differences as little as 3 milliseconds (that is 3/1000th of a second) to decide if a sound comes from the right or left side.
The first set of tests in an APD evaluation are focused on determining how efficiently a person’s ears coordinate. This is done by presenting one sound (such as a single word) to the right ear and a second sound (such as a different word) to the left ear at the exact same moment. If the ears are working efficiently, the person being tested should be able to repeat back both of the words.
B. Temporal Processing. The efficiency and balance of the Auditory Pathways (nerves) to pass timing cues from the inner ear to the cortex of the brain. If the ears are not balanced for timing cues, it will be hard for the cortex to make sense of what is heard. The brain might be receiving “smeared” cues from one or both ears. Instead of clear input, the auditory part of the cortex may be receiving imbalanced input.
C. Monaural Low-Redundancy tasks. The Auditory Pathways (nerves) that connect the inner ear to the cortex are also responsible for “filling in” auditory input that has been distorted. Distorted cues are common in noisy situations where a speaker’s voice might be covered up by other voices talking at the same time.
It is crucial to anyone’s understanding of speech in noise that the auditory pathways be able to take a partial signal, compare it to previous knowledge of the language, and “fill in” the missing portions. Your brain does this for all kind of signals. For example, when you look at a large dog behind a picket fence, there are portions of the dog that you do not see because they are blocked out by the picket fence. But, because of much practice looking at the world and understanding how things happen, your brain sees the outline of the dog as one thing and the picket fence as a second object. The pattern they make tells you that the picket fence is in front, and the dog is behind the fence. The ability to understand auditory signals that are not perfect is something that our ears do every day.
After these three areas have been tested, the audiologist compares the results to how a large sample of children or adults of the same age have performed on the tests. Conclusions are then drawn to decide if the processing of auditory signals that is happening in the Auditory Pathways is typical or not.
Other points to note:
Auditory Processing tests are difficult because we are “stressing the system”. We make the auditory inputs very challenging because we want to see how the auditory pathways function under pressure.
Because of this, it is important that anyone being tested for an Auditory Processing problem come to the evaluation fully rested and not hungry. There are frequent breaks in the testing, though, and sometimes we do the testing over multiple days. How long the testing takes depends on the person being tested. It could be two hours or three hours, or sometimes more.