DISCUSSION
Our investigation presents data on comparison of different kinds of sound amplification technology (advanced and basic) for the first time described in a developing country. It also adds information on the short-term effect of hearing aids in attention and memory tasks and auditory evoked latencies, which should encourage further long-term studies.
The findings of the present study suggest the short-term beneficial effect of hearing-aid use in older adults who are naive to sound amplification devices, despite its level of technology [21,22].
With regard to the relationship between auditory deprivation and cognitive decline [1–5,11–19], it is believed that the use of hearing aids represents a determinant for improving the quality of life among hearing-impaired elderly [36]. To date, we have no instrument that can directly assess cognition as a whole, so we had to rely on attention and memory skills, as well as auditory evoked potentials latency to hypothesize so.
The educational level of our sample, comprising older patients who depend on the public health service, is representative of the majority of the population of the developing countries such as ours. Consequently, the findings of this study only represent those countries with a similar sociodemographic profile. Poor education is considered a potentially modifiable risk factor for dementia [10], particularly in countries such as Brazil [37]. Therefore, strategies for mitigating these risks are vital in these countries, which plays an effort to minimize cognitive impairment. Given Brazil´s rapidly aging population, auditory deprivation may constitute a factor that limits the quality of life of the elderly. Auditory deprivation is held as the main modifiable factor in adult life capable of preventing cognitive decline [10]. The role of audiologists and ENT specialists is thus to minimize hearing deprivation by diagnosing hearing loss as soon as they can.
The hearing aids we used in this study reflect the different levels of technology consistent with the devices available at the time of this clinical trial. Group A used devices of premium technology, including features of automatic asymmetric directionality, environmental acoustic gain optimizer (up to 6 dB gain for less noisy environments), and noise reduction by environment (noise reduction of up to 10 dB in noisy environments). Group B (basic technology) used hearing aids with fixed symmetric directionality (omnidirectional OR directional simultaneously), with no gain optimizer by environment, and offering maximum noise reduction of 3 dB. Both Groups A and B used default manufacturer settings (GN group) for wind-noise reduction, microphone feedback cancelation, and expansion. Group C (placebo) patients, after using their hearing aids for 12 weeks with no sound amplification, had their devices programmed according to the same protocol applied for fitting groups A and B. All the electroacoustic characteristics we mentioned here are easily found in the technical specifications of the hearing aids from the GN group (ReSound).
As shown by a previous studies [21,22,38], our results failed to show any difference between premium and basic hearing aids, which suggest that amplification plays the major role in restoring hearing abilities. It is believed that sound signal processing algorithms may reduce listening effort [16–19], but robust data supporting these theories are still lacking.
Although we chose a neuropsychological test that was not sensitive enough for detecting discrete improvements in memory and attention, the NEUPSILIN was elected for the present study because it is validated for its use in older Brazilian patients and thus could be applied in our sample. One of the tests which differed statistically between pre and post-intervention was the word recognition task. On this task, the subject hears the spoken words aloud by the examiner and must decide whether these are part of the list of words they heard earlier in the test. In this assessment, the patient must deal with phonemic distractors, thus the sound amplification itself facilitates the patient’s performance at it. A comparison of the 3 groups revealed that this difference occurred only between Groups B and C, pointing to a possible sample size effect.
The definition used by Moore et al. [39] was originally proposed by Neisser in 1967 and states that cognition is an individual´s ability to transform sensorial input into meaning. Hearing aids allow the individuals to perceive sounds again, but the reassignment of meaning to these sound stimuli is not immediate and might not take place spontaneously. In this respect, auditory training and/or speech-hearing therapy may help hearing impaired people to derive maximum benefit from sound amplification.
We believe the reassessment with auditory evoked potentials may have been carried out too early, which prevented the plasticity of the patients’ auditory system to happen. We also speculate if latency could be rapidly affected by amplification as waves amplitude were [20].
The differences we observed on the IOI-HA were more likely associated with sound amplification, regardless of the technology level. This suggests that for new users, a well-fitted hearing aid may be the main factor that guides satisfaction.