The more crowded an acoustic environment is, the more brain capacity is needed to hear someone talking – and the less there is left for understanding, interpreting and planning an answer.
For people with a hearing disability, following a conversation is an arduous task, even if they use a hearing aid. Fatigue is a big problem for many people with hearing disabilities. And of course the more mental capacity devoted to hearing what someone is saying, the less cognitive spare capacity is left over to understand and interpret the content.
This means that many sufferers withdraw both from working life and social situations.
In a new thesis from Linköping University, audiologist Sushmit Mishra has found a method – a test – that can measure the cognitive spare capacity: the Cognitive Spare Capacity Test, or CSCT.
“The test was developed for research, but a simplified version may be useful when planning for rehabilitation in connection with hearing impairment.
Mr Mishra has investigated how cognitive spare capacity is affected by memory load, background noise and visual information. He has studied both younger and older people, with and without hearing impairments.
The tests consisted of the subject listening to a series of two-digit numbers being spoken. The test subjects had to recall numbers according to certain criteria; for example the odd numbers given by the male speaker, or the highest number the female and the male voice mentioned.
The findings showed that cognitive spare capacity is sensitive to memory load. It is reduced by background noise, increases when given visual information – especially when there is background noise – and is reduced in older people with age-related hearing loss, particularly in the absence of visual information, when memory load is increased and when background noise consists of several other people speaking.
“The main finding was that visual information, in the form of the test subject being able to see the person speaking, frees up spare capacity and thereby helps older people with impaired hearing,” says Mr Mishra.
This means that in order to completely understand a person's hearing impairment, an audiological assessment should be carried out with the aid of audio-visual tests.
A modern hearing aid provides many opportunities for modifying the sound signal.
“And it is possible to find the optimum modification by using the CSCT to measure the cognitive spare capacity,” says Mr Mishra.Sushmit Mishra defended his thesis in Disability Studies on 21 March. His thesis is titled: “Exploring Cognitive Spare Capacity: Executive Processing of Degraded Speech”.