Keywords event-related potentials - P300 - cochlear implantation - adult - hearing loss
Introduction
Individuals with severe to profound hearing loss are known to receive little to no
benefit with the use of hearing aids (HAs). In those cases, cochlear implants (CIs)
are an efficient alternative, which can provide a high speech recognition rate.[1 ]
This device projects sound to be received by a microphone and be sent to a speech
processor, which digitally codifies speech through different strategies that vary
according to the device's manufacturer. Signal is then sent by a transmitter to an
internal stimulator, which converts signal into electrical impulses sent to electrodes
inside of the cochlea. Thus, electrodes stimulate the cochlear nerve, and impulses
can travel along the auditory system.[2 ]
Currently, there is a need to determine audiological parameters for CI indication
and, especially, for patients' follow-up. Behavioral assessment of CI patients, through
speech perception tests and self-assessment questionnaires, has been a common procedure;
however, there is a concern presented by audiologists regarding objective assessments,
specifically electrophysiological tests, aiming to investigate the central auditory
nervous system (CANS). Auditory evoked potentials, particularly cognitive ones, which
are obtained by recording and measuring responses to sensorial stimuli captured on
the cranial surface, have been under investigation, with the purpose of investigating
possible changes in the CANS, such as neural plasticity, after CI stimulation.
Among other cognitive auditory evoked potentials, P300 provides a neurophysiological
assessment of cognitive function, since it is evoked by the conscious interaction
between the hearing system and the somatosensory cortex, and it depends on the attention
and participation of the subject to elaborate responses.[3 ]
[4 ] The P300 data are collected through random presentations of a rare acoustic stimulus
previously established among other frequent stimuli (“oddball” paradigm). The endogenous
perception of rare stimuli will provide necessary data for the elicitation of waves.
The analyzed waves can bring information on the treatment of hearing disorders and
reflect on the electrophysiological activity involved during attention, discrimination,
memory, integration and decision-making abilities.[5 ]
The P300 is included in the long latency auditory evoked potentials (LLAEPs), which
can be observed approximately between 80 and 700 ms after an acoustic stimulus presentation.[6 ] Studies show a wide variety of amplitude values for this potential, which can vary
according to task and attention.
The P300 has been tested with the CI population and is gradually being included in
clinical practice. Studies have measured P300 waves in children and adults with HAs
and CIs, showing that this kind of research is viable; however, more studies with
P300 in adult CI users are needed to demonstrate its applicability.[7 ]
[8 ]
[9 ]
[10 ] Hopefully, the results obtained in this study can contribute, along with behavioral
tests, as sensitive indicators of the processing functions in these patients and therefore
help us in the assessment of CI candidates.
Thus, the aim of this study was to analyze the auditory behavioral and electrophysiological
responses, latency and amplitude values of the P300 potential, in adults with bilateral
profound sensorineural hearing loss, HA users submitted to cochlear implantation.
Methods
The present study is a transversal prospective comparative and correlational one,
with emphasis on diagnostic research.
The project was approved by the Institutional Review Board (IRB), ethical approval
11489/2014, CAE number 32404514.9.0000.5440 (Doc. 1.255.971).
Participants
Twelve adults participated in the present study, seven male and five female. To fulfill
the inclusion criteria, subjects were required to have bilateral postlingual sensorineural
hearing loss and be submitted to CIs after bilateral HA experience.
Procedures
Data were collected in two phases. The 1st one was prior to CI surgery, when the subjects were using HAs, and the 2nd one was at least 12 months after CI activation. Both phases were performed in the
same conditions.
In the hearing health program where this study was conducted, the audiological assessment
of CI candidates investigates their hearing and language conditions, and consists
of the following procedures: pure tone audiometry and speech perception tests with
supra-aural earphones, electrophysiological assessment (brainstem evoked response
audiometry and cortical auditory evoked potentials—P300), as well as audiometry and
speech perception tests in free field, with HAs.
On the 2nd phase, participants were reevaluated with pure-tone audiometry and P300. Audiometry
was performed in free field, with the AC 40 audiometer (Interacoustics, Middelfart,
Denmark), considering frequencies from 250 to 8,000 Hz, and the subject was seated,
in an acoustically treated environment.
Mean hearing thresholds were calculated by the following frequencies: 500, 1,000,
2,000 e 4,000 Hz.
To obtain P300 measures, the two-channel Bio-logic equipment (Navigator® Pro from Bio-logic® Systems Corp. Auditory Evoked Potential - AEPSystem, 1.3.0 version/Natus Medical,
USA), connected to a conventional computer, was used to register the auditory evoked
potentials. Active electrodes were positioned at Cz and Fz, connected to entry 1 of
the preamplifier; channels 1 and 2. Reference electrodes were connected to entry 2
of channels 1 and 2 (jumper), from the preamplifier and placed on the left earlobe
(A1). The earth electrode was placed on the right earlobe (A2). While testing, the
individual impedance of electrodes was maintained at 5 KΩ or less, and the difference
of impedance between them at 3 KΩ or less. The time window was shown as 512 ms, with
a 50,000 μV gain, high-pass filters of 30 Hz and low pass of 100 Hz.
During the procedure, the subjects were in a semi-seated position, with their eyes
open and fixed on a target point in front of them, to avoid eye movement artifacts.
Tone bursts were chosen as auditory stimuli, with a frequency of 1,000 Hz for the
frequent stimulus and 2,000 Hz for the rare stimulus, where 80% were frequent stimuli
and 20% were rare stimuli, randomly presented, at an intensity of 90 dB. Measurements
were taken in two successive passages to allow good definition and replication.
The P300 testing took place in free field, with the loudspeaker positioned at an azimuthal
angle of 0° when subjects had bilateral HAs, and at 45° when subjects were then using
a CI, positioned next to the speech processor, at a 60 cm distance.
For both phases, subjects were asked to identify the rare stimulus by slightly raising
their index finger each time it appeared. Thus, behavioral responses in the presence
of rare stimuli were observed and registered by the researchers to be then analyzed.[6 ]
[11 ]
[12 ] Wave tracing registrations were considered when there was replication of the tracing
and when the subject identified the stimulus with a maximum of 10% stimulus deviation
(50 ± 5 stimuli). Before starting to register the responses, subjects were exposed
to the stimuli and trained so that they fully understood the task.
Behavioral registrations were made by two observers, individually, with no communication
between them and behaviors were categorized as:
Immediate response to rare stimulus;
Late response to rare stimulus (less than 2 seconds);
Incompatible response (raises finger in the absence of rare stimuli);
Cochlear implant brand and model were not variables that could be controlled, considering
the study's institutional demand of equal distribution among brands, since it is a
service accredited to the Unified Health System (SUS, in the Portuguese acronym. Public
health system that grants electronic hearing devices, equally distributed by the accredited
companies).[13 ]
[14 ]
[15 ]
Sample Profile
[Table 1 ] shows the audiological data of the 12 participants, in which we can see that 10
were unilateral CI users and 2 were binaural CI users. Six of the subjects received
CI surgery on the right ear, and six on the left ear. The average age was 46.5 years
old, considering that the lowest age was 22, and the highest, 76.
Table 1
Characterization of subjects' audiological variables without the use of electronic
hearing devices
Audiological Variables
Mean
Median
SD
Minimum
Maximum
Age at hearing loss (years)
18.08
10.00
16.78
0.00
49.00
Auditory deprivation time (years)
8.79
3.50
13.73
0.00
46.00
Age at HA fitting (years)
26.58
23.00
18.00
1.00
53.00
HA use time (years)
19.54
18.50
14.64
0.42
47.00
Average RE HT without HAs (dB HL)
110.55
112.00
9.02
85.00
118.00
Average LE HT without HAs (dB HL)
109.25
115.50
11.38
80.00
119.00
RE SPT results without HAs (%)
33.00
0.00
45.99
0.00
100.00
LE SPT results without HAs (%)
32.00
0.00
45.00
0.00
100.00
Abbreviations: dB HL, decibel hearing level; HA, hearing aid; HT, hearing thresholds;
LE, left ear; RE, right ear; SD, standard deviation; SPT, speech perception test.
[Table 2 ] contains audiological data of the subjects during both phases of the study. Mean
hearing thresholds with HAs when compared with mean hearing thresholds with CI show
a difference of 43.92 dB HL. It is noticeable that the highest mean hearing threshold
with CI was 51 dB HL, which belongs to one subject who did not perceive benefits from
CI use, unlike the rest of the group. Regarding the speech perception test (SPT) results,
higher percentage scores can be seen when subjects were in the CI phase.
Table 2
Characterization of Subjects' Audiological Variables with the Use of HA and CI
Audiological variables
Mean
Median
SD
Minimum
Maximum
Average HT with HAs (dB HL)
75.25
73.50
16.33
50.00
96.00
Average HT with CIs (dB HL)
31.33
29.00
8.85
17.00
51.00
Average SPT result with HAs (%)
28.20
9.00
34.49
0.00
80.00
Average SPT result with CIs (%)
68.42
81.50
34.54
0.00
100.00
Abbreviations: CI, cochlear implant; dB HL, decibel hearing level; HA, hearing aid;
HT, hearing thresholds; LE, left ear; RE, right ear; SD, standard deviation; SPT,
speech perception test.
The non-identification of hearing loss etiology represents 50% of the 12 subjects,
and otosclerosis is the most frequent etiology, whereas other causes (mumps, bacterial
meningitis, ototoxicity and mechanical trauma) appeared only once.
About the CI brands used in this study, Med-El (Innsbruck, Austria) was the most frequent
one, followed by Cochlear (Sydney, Australia) and Advanced Bionics (Norwest, Australia),
each with 3 subjects. Lastly, there were 2 subjects with Neurelec (Vallarius, France)
Advanced Bionics (Los Angeles, USA). Each device has its own functional characteristics,
which are described in [Table 3 ].
Table 3
Characterization of cochlear implant devices used by the subjects of this sample (n = 12)
Subject
Device brand
Number of channels (n )
Speech coding strategies
Pulse rate per channel (pps)
Current (Hz)
1
Med-El
11
FS4
802
87.08
2
Cochlear
22
ACE
900
25
3
Neurelec
24
Crystalis XDP
500
−
4
Med-El
12
FS4
705
17.92
5
Cochlear
22
ACE
900
25
6
Ad. Bionics
16
Hires PWI Fidelity 120
3,712
18
7
Ad. Bionics
16
Hires S/Fidelity 120
3,712
18
8
Ad. Bionics
16
Hires P/Fidelity 120
2,652
26.9
9
Cochlear
22
ACE
1,200
25
10
Med-El
11
FS4
802
40
11
Neurelec
24
Crystalis
500
−
12
Med-El
12
FS4
750
50.42
Abbreviations: Ad., Advanced; CI, Cochlear implant; Hz, hertz; n, number; pps, pulses
per second.
Data Analysis
An exploratory analysis took place, to summarize values, organize and describe data
in two ways: through tables with descriptive measures and through graphs. Continuous
variables were expressed as basic descriptive statistics and categorical variables
were expressed as frequency and percentage. To reach the established aims, a linear
mixed-effects regression model and Pearson correlation coefficient (r) were used.
A significance level of 5% (p ≤ 0.05) was adopted for all analyses and adjustments were obtained in the SAS software,
version 9.2 (SAS Institute Inc., Cary, NC, USA).
Results
To verify the correlation between two quantitative variables, an analysis was performed
through Pearson correlation coefficient (r), as we can see in [Table 4 ]. There was a strong positive correlation when the following variables were correlated:
subject's current age and age at hearing loss, current age and age when starting to
use Has, and hearing loss onset age with the start of HA use. There was also a moderately
negative relation between subject's age and mean hearing thresholds with CI after
at least 12 months of use.
Table 4
Correlation between audiological variables
Pearson correlation coefficient
Parameter
Age at hearing loss
Auditory deprivation time
Age at HA fitting
Average HT with HA
Average HT with CI
Current age
Corr
0.6526[a ]
0.0611
0.6450[a ]
0.3062
−0.5912[a ]
p -value
0.0214[b ]
0.8502
0.0235[b ]
0.3329
0.0429[b ]
Age at hearing loss
Corr
−
−0.2025
0.6816[a ]
−0.1095
−0.5220
p -value
−
0.6304
0.0146[b ]
0.7346
0.0817
Auditory deprivation time
Corr
−
−
0.4778
0.4289
−0.0102
p -value
−
−
0.1161
0.1641
0.9748
Age at HA fitting
Corr
−
−
−
0.1971
−0.5078
p -value
−
−
−
0.5391
0.0919
Abbreviations: CI, cochlear implant; Corr, correlation; HA, hearing aid; HT, hearing
threshold.
a Corr ≥ 40%.
b
p < 0.05.
In the analysis of potentials N1, P2, N2 and P300, when correlated to the subject's
gender, age, time of auditory deprivation, CI current (Hz), pulses per second (pps)
and mean hearing thresholds with HAs, there was no significant value. However, P300
latency values in both phases, when analyzed and related to CI's current, show an
increase in latency (p = 0.0545).
[Figs. 1 ] and [2 ] show mean latency distributions for the N1 and P2 potentials (exogenous) and N2
and P300 (endogenous), respectively, in the different fixation positions of the electrodes
(Cz and Fz) related to the two phases of the research, while [Figs. 3 ] and [4 ] show the mean distributions of the amplitude. Due to the objective of this study,
there was an emphasis on the P300 cognitive potential. Therefore, we can observe that
P300 mean latency values at Cz and Fz increase in the CI phase. Amplitude levels decreased
at Cz and increased at Fz during the transition from HA to CI.
Fig. 1 Distribution of latency measurements of the N1 and P2 waves in the pre- (using HA)
and postphases (using CI), in the Cz and Fz electrode positions.
Fig. 2 Distribution of latency measurements of the N2 and P3 waves in the pre- (using HA)
and postphases (using CI), in the Cz and Fz electrode positions.
Fig. 3 Distribution of amplitude measurements of the N1 and P2 waves in the pre- (using
HA) and postphases (using CI), in the Cz and Fz electrode positions.
Fig. 4 Distribution of amplitude measurements of the N2 and P3 waves in the pre- (using
HA) and postphases (using CI), in the Cz and Fz electrode positions.
For both phases, wave morphology at Cz benefited the components' tracing ([Fig. 5 ]).
Fig. 5 Example of a record (with repetition) of the P300 test, about the present study,
in the prephase (with HA) and post (with CI). Letters A, B E and F are frequent registers.
Letters C, D, G and H are infrequent registers, with electrode position in Cz and
Fz, respectively.
It is important to note that during training, before starting to effectively register
potentials, some individuals showed more difficulty to detect the rare stimulus in
the HA phase, needing more training time. Still in this phase, a few subjects could
not distinguish two rare stimuli when presented in sequence, with a reduced time gap,
that is, two or more rare stimuli in a row. In the meantime, that did not occur when
they were in the CI phase, since they started to promptly respond and identify the
rare stimuli even when presented with short time gaps.
Regarding the behavioral task during the exam, in the HA phase, five subjects showed
immediate response to the onset of rare stimuli, six showed late response to the onset
of rare stimuli, and one showed an incompatible response, that is, he raised his index
finger in the absence of a rare stimulus. During the CI phase, 11 subjects showed
immediate response to the onset of rare stimuli and only 1 showed late response, which
indicates an overall better performance in the CI phase.
Discussion
Cochlear implantation is known to be the best option for profound hearing loss,[16 ] as many studies show its effectiveness on the development of oral language and speech
perception.[17 ]
[18 ]
[19 ] Cochlear implant centers establish as one of the audiological criteria for candidates
that, although they have effectively experienced using HAs, they are not benefitted
by such device. Besides, if mean hearing thresholds in free field with HAs reveal
no access to speech sounds, that indicates that those patients are CI candidates.[20 ] With that being said, audiometry results from the first phase show correct indication
of those subjects as CI candidates, with male predominance (58.33%), which is also
seen in other studies[21 ]
[22 ] that show hearing loss is more frequent in male patients.
When correlating social and demographical variables related to hearing loss, it was
verified that there is a strong positive correlation between the subject's current
age and age at hearing loss (0.6526), current age and age when starting to use HAs
(0.6450), and hearing loss onset age with age at the start of HA use (0.6816). Such
result shows that this group of subjects received auditory stimulation through HAs,
after hearing loss onset, and that is a crucial factor to consider for central auditory
system activity maintenance. There was also a moderate negative correlation between
the subject's age and mean hearing thresholds after at least 12 months of use (0.5912)
([Table 4 ]). This finding is also addressed in the literature, describing that an increased
time of CI use results in an improved hearing ability (identified by decreased hearing
threshold results) and performance in patients with postlingual hearing loss. Even
at CI activation, the ability to detect sounds is already noticeable and auditory
recognition improves progressively, as well as speech comprehension, around 18 months
after implantation.
We can verify that the data shown at [Table 1 ] reflect what has been happening in most audiological centers in Brazil, that is,
individuals with early onset hearing loss (18.08 years old on average) waiting for
a significant amount of time receive the intervention process (8.79 years of hearing
deprivation on average) and an even bigger time when the time of HA adaptation is
considered (26.58 years old on average).[23 ]
[24 ] Those findings are probably explained by the demand of patients within the observed
age range, who now represent ∼ 50% of individuals who seek treatment and electronic
hearing devices in the study's country (Brazil). This demand conflicts with financial
difficulties of public health programs.
It was evident in this research that mean hearing thresholds were better with CI than
with HA. The comparison shows difference between averages of 43.92 dB HL and a considerable
difference in word recognition of 40.22%, equivalent to speech recognition improvement
of over 10 words, showing there is a bigger benefit with the use of CIs ([Table 2 ]).[20 ]
[25 ] One study from 2004[26 ] reported that, in the time between 6 and 12 months of CI use, some patients achieve
their maximum hearing performance, while others keep evolving after 12 months.
Regarding etiology investigation, 50% of the subjects had an unknown cause of hearing
loss and are under investigation, which agrees with previous researches.[21 ]
[22 ]
[26 ]
[27 ] Those studies indicate the need for genetic studies in cases of hearing loss with
no apparent cause, so that we can get to a real etiological profile. Otosclerosis
(16.67%) showed the highest frequency among other etiologies (mumps, bacterial meningitis,
ototoxicity, and mechanical trauma), which were present only once each (8.33%). It
was also noted that, when comparing average hearing thresholds with those of subjects
with HAs and with CIs, only the subject with meningitis did not benefit from CIs and
that is due to a reduction in the amount of spiral ganglion cells, which is a characteristic
of the auditory system lesion caused by meningitis.[28 ]
[29 ]
At the time of data collection, there was an equal distribution of CI brands indicated
to the patients, in a way that did not allow for a quantitative statistical comparison
that could evaluate the association between the device brand and the subjects' responses
to the tests.
Variables related to CI ([Table 3 ]), such as number of channels, pulse rate by channel and current (Hz) did not present
any significant difference when correlated to P300 amplitude and latency measurements,
except for latency values correlated to HA and CI phases, which were increased. The
latency of P300 does not depend on the physical characteristic of the acoustic stimulus,
such as duration and intensity, but rather on proprieties related to the event, such
as its probability, discrimination difficulty and stimulus novelty. Nonetheless, it
is believed that there is a physiological P300 latency increase from the age of 15
years.[30 ]
[31 ]
[32 ]
[33 ] In this study, comparisons of latency measures were made between the same individuals
in different situations, over a short period of less than a decade. Therefore, it
is believed that variations are related to the use of the electronic device.
P300 mean latency values increased at Cz and Fz during the CI phase ([Fig. 2 ]), which wasn't initially expected, since the auditory benefit provided by CIs, verified
through behavioral evaluations, is bigger than the benefit provided by HAs. Even with
that increase, it was observed that mean latency values are within normality, with
348.80 ms at Cz and 344.42 ms at Fz during the HA phase and 375.37 ms at Cz and 363.02 ms
at Fz during the CI phase.[6 ]
This increase can reflect on the applied stimulus situation, which would activate
more the parietal lobe region (P3b—250–500 ms component). This region is activated
by the “oddball” stimulus and is connected to the activity of performing a task while
receiving a stimulus.[6 ] The P300 amplitude can be more related to the number of attention resources allocated
to the stimulus and memory performance involved and represents brain's perception
while receiving an important information.
The P300 amplitude can have a bigger association with the amount of attentional resources
allocated to the stimulus and memory performance involved and represents brain's perception
when receiving an important information. It is originated from different regions of
the CANS that process different types of information, such as the frontal and central
regions (P3a—250–280 ms), and are related to the detection of stimulus novelty. The
P300 latency reflects the time spent during stimulus cognitive processing and its
amplitude is related to the amount of attention resources allocated during the stimulus.[34 ]
It is worth pointing out that some patients who had absent P300 responses in the HA
phase started to show responses in the CI phase. A few studies also found an increase
in P300 latency, justifying that the difficulty to discriminate stimuli can cause
this latency increase, even if they respond correctly to the behavioral task.[9 ]
[35 ] One of those studies reports that patients who always presented better sound discrimination
also presented better latency values, that is, shorter latencies.[9 ] Those findings suggest the possibility that direct electrical stimulation of the
cochlea may not function as effectively as the auditory system does in conditions
in which the cochlea is in its normal state, that is, not working simultaneously with
an electric device.
When an individual is using HAs, a device that basically amplifies sound, the remaining
cells are stimulated and the cochlea itself generates a nervous impulse, which is
then transmitted to the CANS. This case is different from CI users, where there is
an electricity transducer inserted in the cochlea to allow electric stimulation. This
thought might explain latency delay at 12 months of CI use, and there is still the
possibility that the cochlea needs more time to adjust to electrodes, which could
bring different results in the future. Previous studies suggest there is information
that codified sound delivered through CIs is different from the sound delivered by
the normal cochlea, so it is likely that CI recipients' brains need highly charged
auditory processing and, consequently, a higher effort during cognitive processing.[35 ]
In terms of amplitude, a decrease at Cz and an increase at Fz were observed from the
HA phase to the CI phase. Amplitude values found were relatively low in both phases
(HA phase = 5.13 µV at Cz and 3.71 µV at Fz; CI phase = 3.68 µV at Cz and 4.71 µV
at Fz), and those values may be justified by the fact that the CI provides a lower
discrimination field when compared with the cochlea itself. One study suggests P300's
amplitude in CI patients is related to individual differences in their ability to
discriminate, that is, patients with low discrimination capacity show lower amplitude
levels.[7 ]
Although there was no significant difference between latency and amplitude results,
it was noticeable that the wave morphology of frequent and rare stimuli during the
test was more favorable to the tracing of the N1-P2-N2 complex and especially of the
P300, in the rare register during the CI phase ([Figs. 1 ], [2 ], [3 ], and [4 ]).
Considering the age factor, many studies suggest there is a variation of latency and
amplitude measurements according to age; some studies show latency increase at around
1 to 2 ms/year, and amplitude decrease with an average rate of 0.2 µV/year.[36 ]
[37 ] In adults over 45 years old, latency increases 10 ms for each decade.[38 ] One hypothesis is that participants in this research were 46.5 years old on average,
which is a factor to consider concerning latency increase. However, in this study,
the results' comparison was obtained in a single-subject manner, which is considered
the most stable situation and, therefore, it should not be a considerable variable.
It is also worth highlighting that there was a time span of 12 months between tests,
so the age variable alone could not interfere in the difference found, that is, the
latency increase ([Fig. 2 ]).[6 ]
[39 ]
[40 ]
Another factor that could affect the results could be the fact that this research
was conducted on the same patient at different time intervals, which is not a strong
consideration, since literature has shown that latency variations are small under
those circumstances. One study found mean retesting values of 10.50 ms (Fz) and 15.25 ms
for female gender and 6.00 ms (Fz) and 5.83 ms (Cz) for male gender.[37 ] Equivalent results were found in studies that demonstrated P300 latency measures
test-retest reliability in normal adults[41 ]
[42 ] suggesting that those patterns, observed for a long time, can reflect on the habituation
of certain processes in the central nervous system.[41 ]
Early responses are usually related to the presented stimulus' sensation, perception
and discrimination, while delayed responses are usually related to cognition and memory.
The exogenous complex, N1, P2 and N2, in a qualitative analysis, also presented increased
latency values, especially at the Fz position, with a 35.53 ms difference for N2,
11.80 ms difference for P2 and 12.00 ms difference for N1. Amplitude values, as described
in the literature,[6 ] did not produce significant variations.
Statistical analysis showed that there was no relation between P300 and other variables;
however, when related to latency values, in both phases, the result was p = 0.0545. Although this result shows no significance, the number of participants
in this study could lead to a bias, so one hypothesis is that a larger sample could
give the result a different tendency.
Once the aim of the evaluation was to identify the P300 wave, the fact that the response
procedure (raising the index finger instead of mentally counting) was modified did
not interfere in the type of response. Some studies have concluded that, when comparing
long latency potentials evaluation procedures, with different instructions regarding
the perception of rare stimuli, the complex N1, P2, N2 did not change, although P300
showed a slight modification, which is precocious in the lower cognitive complexity
process.[12 ]
[43 ]
[44 ]
A longitudinal assessment is important so that CANS changes in adults with CIs can
be evaluated in an extended period and compared with CANS development in adults with
normal hearing. Thus, studies with larger samples and longer time of observation are
necessary for a better understanding of hearing disorders.
Conclusion
Behavioral and electrophysiological assessments have contributed to a better understanding
of hearing performance in CI users. The participants showed a remarkable improvement
of their hearing thresholds after 12 months of CI use, except for the patient with
meningitis. Mean P300 latency levels increased after 12 months of CI use at Cz and
Fz, while mean amplitude levels decreased at Cz and increased at Fz. There was a moderate
negative association between age and mean hearing thresholds with CIs.
