Physiological assessments have a simple approach, measure the function of the anatomical parts in question. In our case this would mean the parts that make up the auditory pathway. The pros and cons of this approach with the tools available can be seen in the previous article, Physiological Assessment of the Auditory System.
Behavioral assessments are more complex in terms of the varied perspectives this task can be approached with and even the assessments available to test a given function. Assessing how well a person can understand speech in noise is one such function where there are many tests available and no gold standard as to which is best.
As this is an article and not a book, this discussion is just the tip of the iceberg regarding behavioral assessments. In future articles we will discuss some of the other considerations in choosing a behavioral test battery.
Norman Erber identified a listening hierarchy for auditory training. This was designed to teach hearing impaired children to learn to listen in an organized progressive fashion.
These steps are:
- Auditory awareness – recognizing that a sound was present
- Auditory discrimination – recognizing same vs. different. For example bat/pat or bat/bat
- Auditory identification – correctly identifying what was heard. For example, retrieving an item or pointing to the correct picture.
- Auditory comprehension – interpret and understand what was heard. For example, understanding speech in less than ideal conditions or understanding sarcasm.
There was a strong interest with a lot of disagreement regarding a neurological perspective on auditory functions. Theoretically, one could suggest using a behavioral assessment for each anatomical area. When the correlation between the anatomical area and its function is clear it is certainly a commendable approach to take. For instance, we know that binaural function requires the corpus callosum’s involvement specifically. However, we cannot say with certainty that when binaural function is poor that the issue lies at the corpus callosum’s doorstep. A lot more research using behavioral testing in combination with imaging, that demonstrates a statistically significant correlation between the behavioral result and the anatomical area, would be needed to make such a claim of a behavioral test alone with confidence.
The wealth of EEG research, in addition to a better understanding of acoustics helped us recognize that differences could be seen, and thus assessment should look at:
- The timing of the brain’s response, as marked by the latency of the EEG wave as well as the timing of gaps in speech and the ability to perceive them → temporal processing
- The strength of the response, as marked by the wave’s amplitude → organization and/or fatigue
- Between hemispheres, particularly the T-complex → speech vs non-speech processing
- The collaboration process when both ears are engaged → binaural processing
- Where the energy of a speaker’s speech was, informing listener of gender, age, emphasis and intonation → prosody/pitch processing
- Comprehension of degraded speech, whether in competition to other talkers in the background, filtered speech or compressed speech → auditory closure
This led to a view of different types of APD and also resulted in commercially available tests for the clinical audiologist.
We understand that no one model accurately captures the complexity of the auditory system. We need a blend of the approaches discussed here. Temporal processing requires awareness, identification, discrimination and comprehension in a quick time frame (300 ms) of all the acoustical components of the sound. So does binaural processes. Additionally, there are other tasks to consider assessing. This includes such tasks as spatial awareness and localization, whose functions are crucial to your safety. I am sure you can understand the value of being able to identify just where the sound of that car honking at you is coming from.
This brings us to the crux of the issue.
The value of an assessment is in the treatment plan it drives.
So while the SLP may address intonation in a compensatory manner, the audiologist would directly rehabilitate the pitch recognition.
Anatomically based assessments largely leave you with a yes or no diagnosis i.e. yes you have APD or no you don’t. The value is rather limited. This type of diagnostic approach allows you to utilize tests that may leave people more comfortable in knowing that it “really” is APD. However, you are left not knowing specifically what the deficits are. Therefore, the treatment plan cannot directly rehabilitate the deficits, as they are unknown. In school a child may qualify for service as OHI (other health impaired), but the services provide can only be compensatory rather than mitigating the issue. You are forced to manage the condition rather than strengthen the weak area, this is more work and not as functional as minimizing or alleviating the handicap . The SLP will help you understand what people are trying to communicate, which will be a good thing when you want to understand why they are covering their ears or wincing when you sing off-key 😉