7. Summary

outcomes of the predictive model accounted for more than 60% of the variance in quiet and 50% of the variance in noise for sentence recognition scores obtained at 1 month after CI activation [1]. Thus, cognitive factors play a large role in the wide variance seen in performance scores obtained by the adult CI population. Optimizing a personalized rehabilitation strategy must take into consideration the cognitive dynamics of speed of processing, working memory, and attention and executive

The input from any CI is inherently degraded compared to that available in normal-hearing individuals or, indeed, to those able to utilize a hearing aid effectively. Aging may play a role, slowing the process of learning [18] to accommodate to speech sounds presented as a new, seemingly unusual, set of sounds. Cognitive training should take into consideration the age of the CI user. In fact, it has been suggested that older CI users (>80 years) may benefit more from rehabilitation than younger users. A top-down approach may be the most appropriate approach

It is unknown to what degree the brain reorganizes speech when confronted with hearing loss [24]. We studied the dynamics of reversed cross-modal plasticity by TEP brain imaging during speech tracking before and after CI at two time points [25]. Essentially, as a result of auditory sensory deprivation, regions in the brain associated with perceiving visual input are activated during speech communication. After implantation, neuroplasticity is demonstrated as the brain recruits more auditory networks during tests of speech recognition. Olds et al. [26] confirmed these findings using the functional near-infrared spectroscopy (fNIRS) imaging technique. They observed cortical reorganization and suggested that listening effort may be involved in the cortically activated regions. They used several speech recognition tests, including sentences, with the CI turned off and on. This may account for the activated regions seen in our study, although neither of the test intervals utilized direct auditory input. We speculate that during hearing deprivation, sensitivity to voice progressively decreases. Anderson and Kraus [20] refer to this as "deprivation-induced changes in auditory mapping." Once sound is reintroduced, the more visually focused cortical regions reassert into the voice-sensitive regions. This cross-modal reactivation shows the cooperation between visual and auditory cortex. Thus, a profound aim of active rehabilitation is to take advantage, and encourage, reverse plasticity to aid in restoring cortical preference to meaningful

auditory signals. This need is also recognized by other authors [27].

training: 6-month follow-up

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6. Ongoing post-implant support, evaluations of progress, and hearing

ship between performance in quiet and in noise is highly correlated. The early performance in quiet is manifested in the 6-month scores (see Figure 1). Testing at a signal-to-noise ratio (SNR) of 10 dB creates a reasonable challenge and serves as a further indicator of who requires continued rehabilitation. We have observed that it is possible to identify CI users who have demonstrated early success or a steep learning curve. The remaining patients continue as poor users needing support and ongoing counseling to maintain their motivation. With continued exposure to auditory stimulation, they can be advised that still more progress is possible for them.

Testing speech in noise takes place at 6 months. We have seen that the relation-

function [23].

for the older population [18].

Advances in Rehabilitation of Hearing Loss

5.3 Role of plasticity

We summarize the complete rehabilitation process in Figure 5. Pre-implant counseling based on the results of the predictive modeling; surgical planning focusing on considerations to the size of cochlea and type of electrode; and intraoperative testing using X-ray findings to confirm placement and depth of insertion along with NRT to confirm neural interface via electrostimulation all take place before initial activation. This includes counseling that may need to modify expectations based on surgical outcomes and intraoperative evaluations. Two MAPs are developed at first fitting where one is based on intraoperative findings. At 1 month, observations gathered from data logging, along with comparing sentence scores in quiet to the predictive model, provide an indication as to whether a new CI user will need specialized rehabilitation. Again, counseling may need to guide and modify expectations. The type of rehabilitation is determined, usually a combination of both bottom-up and top-down approaches. At the 6-month interval, testing in noise is applied, and further adaptations to the MAPs are made. In the future, we hope to extend the predictive model to include factors for analysis of performance in noise for the long term. Continued appropriate rehabilitation after 6 months ensues, and continued counseling insures that the CI user understands the need to support hearing progress with ongoing rehabilitation, if needed.

Providing viable rehabilitation to adult poor performers lies within the realm of detective work. In the early stages, it provides affirmative counseling based on predictive modeling and effective surgical planning and its implementation. Counseling patients with realistic expectations, however, takes place throughout the entire rehabilitation process. There will always be differences in outcomes, but having a full array of options based on objective measures and individual case history will guide the specialist to advise for optimal use of their hearing abilities. Motivation is a very important component of success, and this needs to be reinforced especially for this population who, often, have unrealistic expectations (this includes the family and supporting individuals).

As CI specialists, we provide access to direct rehabilitation and rehabilitation support. Specialized rehabilitation, given the wide variability in patient outcomes,


Figure 5. Stages of the rehabilitation process.

ideally should be modeled to the specific needs of each individual CI user. To achieve the best level of performance possible, programming options will continually be investigated, supported by patient-directed auditory experience and phonologic and cognitive training, when necessary.

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We have discussed only the factors that may influence the post-implant performance of adult poor users, giving guidance on how best to examine the factors that affect performance. Our responsibility as clinicians is to offer an adult patient-user guidance that leads to an improvement in their quality of life through better hearing. We aim to utilize professional time efficiently and effectively, and we aim to concentrate on those who need post-implant therapy rather than providing standard rehabilitation strategies that may miss some and waste time for others.
