**1. Introduction**

Approximately 25% of French adults are affected by hearing loss, of which 4% are at a disabling level [1]. A weak but significant correlation between hearing loss and cognitive performance has been reported [2]. Elderly people with hearing loss show an accelerated cognitive decline compared to their peers without hearing impairment [3–6] and thus a higher risk of dementia. In fact, according to the Lancet Commission, hearing loss is the largest potentially modifiable risk factor for dementia [7]. Several studies have shown promising results on the positive effects of hearing aid use on cognitive decline [8–10]. However, in cases of severe to profound hearing loss, the only reliable option for auditory rehabilitation is cochlear implantation [11].

At the cognitive level, cochlear implantation leads to improved performance in attention, memory [12,13] and inhibition [13]. Improvements in executive function tasks are greater in patients with lower baseline cognitive abilities [14].

**Citation:** Baranger, M.; Manera, V.; Sérignac, C.; Derreumaux, A.; Cancian, E.; Vandersteen, C.; Gros, A.; Guevara, N. Evaluation of the Cognitive Function of Adults with Severe Hearing Loss Pre- and Post-Cochlear Implantation Using Verbal Fluency Testing. *J. Clin. Med.* **2023**, *12*, 3792. https://doi.org/ 10.3390/jcm12113792

Academic Editor: Tatsuya Yamasoba

Received: 10 May 2023 Revised: 27 May 2023 Accepted: 29 May 2023 Published: 31 May 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Verbal fluency tests are regularly used to assess lexical access [15,16]. They provide information on memory storage capacity, the ability to retrieve stored information, the ability to organize thought and the strategies used to search for words [17]. These tests require that the participant produces as many words as possible from a specific category/condition in a limited period of time. Verbal fluency tests are performed under two main types of conditions: the phonemic condition (the subject is asked to produce words beginning with a certain given letter) and the semantic condition (the subject is asked to produce words from a certain given category). Verbal fluency tests reflect multiple high and low level cognitive abilities [16]. Both fluency tests require the integrity of lexical and semantic representations and of executive functions [15].

Semantic and phonemic fluencies depend on distinct neural systems. For phonemic verbal fluency, it can be seen with Functional Magnetic Resonance Imagining (fMRI) that the posterior regions of the left inferior frontal gyrus are more activated. On the other hand, for semantic fluency there is greater activation of the more anterior regions of the frontal and posterior regions of the temporal cortex [18,19].

Adults with severe to profound post-lingual hearing loss have a deterioration of phonological memory and its dorsal (fronto-parietal) pathway. The longer the subjects are exposed to this hearing loss, the more they use the ventral semantic (occipitotemporal) pathway to compensate for the lack of elementary phonological decomposition [20]. Phonological decomposition is an initial auditory step that enables secondary semantic analysis. Individuals who fail phonological decomposition lack linguistic analysis and correspondence between perceived and memorized phonology. This then limits the extraction of meaning from speech.

These difficulties with internal phonological representations and the degradation of auditory information worsen with the duration of auditory deprivation [21]. For postlingual cochlear implant recipients, phonemic reconstruction is a more difficult cognitive task than semantic processing because of the degradation of auditory information delivered by the cochlear implant [22].

This study aims, firstly, to establish the phonemic and semantic lexical access abilities of adult subjects with bilateral severe to profound hearing loss and, secondly, to evaluate the impact of the cochlear implantation on phonemic and semantic lexical access.

#### **2. Study 1**

#### *2.1. Materials and Methods*
