Auditory training in hearing care practice
The most common method of rehabilitation for people with hearing loss is the timely hearing aid fitting. However, even correct hearing aids are not always a one-size-fits-all solution in terms of speech intelligibility. One of the reasons for this is the changes in the central auditory system, which is especially common with the elderly people. A decrease in neuronal synchrony with age, a slowdown in the refractory period, as well as a deterioration in temporal processing and interhemispheric transmission of auditory information lead to degradation of acoustic stimuli neural coding and impaired speech intelligibility. This is most pronounced when perceiving speech in a noisy environment. Furthermore, with age the auditory cortex activity decreases and auditory absent-mindedness increases, while selective attention is required to process auditory information. Decreased working memory function further exacerbates difficulty of listening in noise and selecting relevant information.
At the same time, it is common knowledge that there is the effect of neuroplasticity: ability to reorganize, to change, form new and restore lost neural connections. Although neuroplasticity is most common at young age, the ability to reorganize the central parts of the auditory system in response to learning remains throughout all life. This fact served as a theoretical basis for the use of special training as a way to improve speech comprehension.
Auditory training — is a set of special acoustic tasks to activate the auditory cortex. The concept of auditory training as sound stimulation has been known since as early as the VI century. Doctors used the sound of a large bell in an attempt to activate the hearing of the deaf persons. In 1800 Itard at a Paris school for the deaf taught the students to identify and distinguish between vowels and consonants as well as different pitches of tonal stimuli which improved their auditory perception. Similar work was carried out by English researchers. In the United States audiology achieved great success after the Second World War when there were many military personnel with hearing loss and the basic principles of auditory training also developed. In the 1950s and 60s, it was used to ease the patients with hearing loss into using hearing aids. In the 1960-70s, interest in auditory training decreased due to the lack of evidence and theoretical justification for its effectiveness. However, in the late 1990s the first evidence of the auditory deprivation effect on the auditory system appeared, followed by evidence of neuroplasticity, after which the principles of auditory training were re-developed. It had been shown that with the special training it was possible to achieve better speech intelligibility when using hearing aids due to improvements in the central auditory system even with the older people.
Currently existing approaches to the rehabilitation of patients with central auditory disorders through auditory training can be divided into two types.
1. The "bottom-up" approach (from the periphery to the central parts, i.e. conditioned by the incoming sound signal) includes increasing the intensity of the sound stimulus, improving its quality through the use of hearing aids and induction loop systems and improving acoustics environment. In addition, this approach includes special classes with a speech therapist (teacher of the deaf) using a set of acoustic tasks aimed at correcting the identified auditory deficit (rhythm perception, temporal resolution, binaural interaction, dichotic listening, etc.)
2. The "top-down" approach integrates language, cognitive, and metacognitive teaching strategies that focus on activating central nervous system resources through exercises to develop auditory attention, active memory, language, and cognitive functions. There is data showing the benefits of learning foreign languages and playing musical instruments. In addition, there is a whole system of exercises for the brain under the general name "neurobics" the main principle of which is the constant replacement of habitual and patterned actions with unusual ones which allows to use the senses in a new way and in different combinations to create new neural connections in the brain [Katz L.C., Rubin M., 2014].
These two approaches complement one another and to achieve the best results should be used in combination. Developing a rehabilitation plan should always be carried out individually depending on the specifics of the auditory deficits, the patient’s lifestyle, their social and communicative needs, as well as any concomitant diseases.
The Laboratory of Hearing and Speech of PSPbSMU named after. I. P. Pavlov with the participation of the Laboratory of Psychophysiology of Speech Institute of Physiology RAS named after. I. P. Pavlov has developed an auditory training program that includes speech and non-speech exercises of varying degrees of complexity with an emphasis on activating auditory-verbal memory and attention [Certificate of state registration of the software No. 2021662786: Hearing and the Ability to Understand Natural Speech (SUPER)]. The training software includes six categories of tasks: "Sounds", "Syllables", "Words", "Phrases", "Dialogue", and "Memory", each of which is further divided into several subcategories containing tasks of different levels of complexity for training certain functions. Thus, the category "Sounds" contains three subcategories: 1) "Non-speech sounds" (including four task groups: to determine the rhythmic pattern of a sequence of signals; to distinguish signals by pitch; to distinguish signals by volume; to detect a pause between two signals of different spectrum ); 2) "Speech sounds" (includes tasks for distinguishing isolated vowels and consonants in the Russian language, pronounced by a male and female voice in silence or with a background noise); 3) "Localization" (includes tasks to determine the source of the sound and assess the direction of movement of the sound signal). The figure below shows the screen when selecting the "Words" category, the "Similar words" subcategory: if the patient correctly recognizes and picks the word they think they heard, a cheerful emoticon appears with the inscription "correct!" If the patient picks a wrong answer, a sad emoticon appears on the screen; if the patient finds it difficult to answer, they can choose the option "?" (Don't know).
Different tasks involve not only hearing but also related functions (like attention or memory), varying speech and non-speech stimuli involved in the auditory training software helps maintain the patient’s interest. The stimuli used should be quite difficult but not impossible while gradually increasing in complexity as training progresses. An appropriate ratio of correct to incorrect answers should be maintained: a 100% success rate means that the task is too easy, while a task that is too difficult will reduce the patient's motivation. A score of 70% can be considered a good indicator for moving to the next difficulty level. Patient's progress tracking provided by the software shows the professional if the current training plan is correct and helps increase the patient's motivation.
The described program was tested on young and elderly patients using hearing aids with chronical bilateral sensorineural hearing loss of degree 2–3 [Boboshko M.Y. et al., 2021]. Based on the results of an in-depth audiological examination, an individual training program was drawn up for each patient with an emphasis on training the identified auditory deficit. Auditory training sessions were conducted at least twice a week for 30–60 minutes within 4–8 weeks. Data from a repeat examination after a course of classes indicated significant improvements in auditory perception of both non-speech and speech signals in both patient groups. The improvement was manifested in an increase in the percentage of correct answers and in a decrease in reaction time when performing test tasks, as well as in an increase in general speech comprehension when using hearing aids.
Thus the auditory training program shows to be highly effective. The exercise results were largely determined by the training intensity with a gradual transition from simple to more complex tasks, the duration of auditory training, as well as the patient’s motivation.
