Accuracy of measured auditory memory may be negatively impacted by deficient functioning of the auditory system in the form of a hearing loss or an auditory processing disorder

Vasiliki (Vivian) Iliadou¹, Nikolaos Moschopoulos¹, Aikaterini Eleftheriadou², Ioannis Nimatoudis^1
1Clinical Psychoacoustics Lab, 3rd Department of Psychiatry, Neuroscience Sector, Medical School, Aristotle University of Thessaloniki, Thessaloniki, Greece
²Department of Occupational Therapy, Metropolitan College, Thessaloniki, Greece

Measurement of Cognition -a psychiatric paradigm

One of the most frequently assessed cognitive skills in medical practice is that of short-term and working memory. When presented with cognition results we often think that they are an accurate representation of abilities. This short article will provide rationale and evidence as to why this might not always be true. Psychologists evaluate cognitive skills. Digit span test is most commonly used either as a standalone tool or as part of Intelligence Quotient (IQ) assessment (Woods et al., 2011). The digit span test is administered through the auditory modality and consists of repetition of increasing numbers of digits with the same (forward) and reverse (backward) order as they are being heard. It is easy to understand that if a person’s hearing is impaired the depicted cognitive skill will be inaccurately evaluated. The hypothesis in this case is that the psychologist will measure poorer memory than if the hearing impairment is corrected. The problem is that psychologists as well as medical practitioners not involved with the auditory system usually think that it is straightforward to understand the presence of a hearing impairment. While this might be so in severe forms of hearing loss, it might not be the case in mild to moderate hearing loss, unilateral hearing loss or auditory processing disorder. A hearing test is needed prior to cognitive evaluation for the measured cognition to be accurate. In the case of auditory processing disorder which depends on the acoustic characteristics of the environment an individual may “miss” an uttered number and then score lower in the memory test. Keeping in mind that there is a documented high frequency of occurrence (around 50%) of speech in noise/babble difficulties in psychiatric patients (McKay et al, 2000; in Iliadou et al, 2013) the possibility that this might interfere with an auditory memory test cannot be ruled out. There is a higher probability for an inaccurate measurement of auditory memory if the psychologist is not aware of APD or of the individual possibly having APD. It is advisable to evaluate auditory processing before a cognitive evaluation. This would be of benefit if the cognitive testing is entirely based on the auditory modality but also if other senses (i.e. vision) are involved since in most cases instructions are given orally. It is time to translate research into clinical practice and recognise that (i) hearing is more than a pure tone audiogram and (ii) hearing impairment (hearing loss and/or auditory processing disorder) should be addressed before any accurate cognitive evaluation can take place.

Hearing Test

A hearing test usually consists of a pure tone audiogram. The information provided only partially represents efficient everyday hearing ability. Hearing includes much more than hearing sensitivity. It includes speech perception in competing sounds, dichotic listening, temporal processing and resolution through gap detection, frequency discrimination and localisation among other auditory processing components. These basic skills of communication may be deficient at variable degrees depending on type and degree of hearing impairment (hearing loss & APD) as well as the current acoustic environment. This is valid for any individual or patient suffering from a specific disorder but is rarely recognised and used in the clinical practice.

Clinical Psychoacoustic Lab

In the Clinical Psychoacoustics Lab of the 3rd Psychiatric Department we have often found hearing loss in stable patients. The interesting fact is that the patient is often unaware of the hearing difficulty and that significant others attribute any misunderstandings in communication to the psychiatric disorder. The percent of psychiatric patients with abnormal hearing threshold has been found to be around 25% with 53% having speech in babble deficits (Iliadou et al, 2013). A complete thorough central auditory processing evaluation is rarely implemented in psychiatric patients. This may be due to (i) lack of on APD clinic, (ii) lack of knowledge, (iii) lack of an APD clinic that will reliably assess psychiatric patients or (iv) thinking that psychiatric patients do not provide stable and repeatable results. There are data showing that stable psychiatric patients can be reliably tested for both hearing sensitivity and auditory processing disorder (McKay et al, 2000; Iliadou et al, 2013) and that neuroscience-informed auditory training will enhance their verbal cognitive abilities (Fisher et al, 2009 & 2016).

There are also available data showing that adjusting sound intensity of administration of the digit span test in psychiatric patients improves their measured memory. This improvement is mainly focused on the backwards measured short-term and working memory. This memory component is thought to reflect executive functioning and yet it looks like it is sensitive to hearing sensitivity. Our results of a study (Iliadou et al, under review) controlling for hearing sensitivity shows that (i) repeatability of memory testing in this patient group is high and (ii) even mild to moderate hearing losses may negatively impact on memory testing. The latter results in inaccurately poorer cognitive abilities. This is an indication that cognitive results of individuals that are about to be evaluated for hearing impairment should be cautiously handled as the possibility of underestimating cognitive abilities is high. This is well known when referring to mild cognitive impairment or Alzheimer’s disease (Dupuis et al, 2015;  Davies, 2017). It is recognised for mental disorder (Iliadou et al, 2018) and should extend to any individual of any age, as cognitive testing is influenced by the sensory input. The auditory system is the one mostly conveying information to hear and perceive instructions and handle stimuli in the required way during cognitive testing.​

References

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