الفهرس 
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Abstract
Temporal resolution, or the ability to process rapidly changing stimuli, has been reported to be reduced in some listeners with hearing loss while being described as normal in others. Ensuring stimulus audibility by increasing stimulus levels results in near-normal temporal resolution abilities for many listeners with hearing loss, but may also result in uncomfortably loud stimulus levels. Behavioral GIN test involve a paradigm that measures the listener’s ability to identify the smallest gap interval between sounds. However, there are a variety factors such as memory, cognition, motivation, hearing loss, and attention that make it difficult to determine the underlying physiology using behavioral testing procedures alone (Lister et al., 2007). Behavioral GIN test cannot distinguish perceptual from cognitive deficits, therefore we need a method for assessing auditory temporal resolution that does not rely on behavioral measures alone (Angel, 2016). This is where electrophysiological testing may help and was the focus of our study. Cortical auditory evoked potentials (CAEPs) evoked in response to auditory change stimuli, known as acoustic change complexes (ACCs), could help as an objective measurement of auditory performance. Recording ACC to gap in noise may help in evaluating the temporal resolution. This work aimed to study the value of recording ACC in response to Gap in Noise as an objective measurement of auditory temporal resolution in normal hearing adults. Secondary objectives were to assess the effect of hearing loss on the ACC, and compare the ACC to the ‘conventional’ CAEP evoked in response to stimulus onset as well as its relation to subjective measures. This study included 2 groups: control group consisted of 50 adults with bilateral normal peripheral hearing and study group consisted of 50 adults with bilateral sensorineural hearing loss (mild and moderate degrees). The study group was further subdivided into 2 subgroups; study subgroup A (SG A) consisted of 30 adults had bilateral sensorineural hearing loss without recruitment and study subgroup B (SG B) consisted of 20 adults had bilateral sensorineural hearing loss with recruitment. In this study, behavioral and electrophysilogical Gap in Noise (GIN) test were applied to all participants. In the electrophysilogical Gap in Noise (GIN) test, broadband white noise stimuli with different silent gap durations (2, 4, 8, 12 and 20 msec) were used. The smallest gap elicited ACC was considered the threshold. The detectability of ACC response was 100% at 20 and 12 msec gap durations in normal subjects and both subgroups of SNHL. The ACC was 100% detected in normal hearing subjects down to 4 msec gap duration. For 2 msec gap duration, ACC could be detected in 90% of normal hearing subjects and 40% of subjects with SNHL with recruitment. However, it couldn’t be detected in subjects with SNHL without recruitment. Behavioral and electrophysiological GIN threshold showed statistically significant higher threshold in SNHL than NH. Moreover, there was statistically significant lower threshold in subjects with SNHL with recruitment than those without recruitment. The electrophysiological GIN threshold was better (lower) than the behavioral. As regards ACC response versus onset responses at maximum gap duration, the ACC response was delayed relative to onset response in all studied groups. However, the amplitude of ACC was larger in CG, no difference in SG A and smaller in SG B. As regards the effect of magnitude of change on ACC response, the latency was shortened and the amplitude was decreased with decreasing the magnitude of change in all studied groups. As regards the onset & ACC latency response, the latency was shortened in SG B relative to CG & SG A. Moreover, there was no statistically significant difference between CG & SG A. Furthermore, the onset amplitude of both subgroups was larger than CG. However, the amplitude of SG B was larger than SG A. On the other hand, the ACC amplitude showed variability in its components. There was a statistically significant smaller amplitude of 2P2 & 2N1P2 only in SG A than CG at all gaps. Moreover, in SG B, there was a statistically significant larger amplitude of wave 2P1 and smaller amplitude of 2N1 & 2P2 than CG at all gap durations. However, there was statistically significant smaller amplitude of waves 2P1N1 and 2N1P2 than NH at 20 & 12 msec. On the other hand, there was statistically significant larger amplitude of 2P1N1 and smaller amplitude of 2N1P2 than NH at 8 & 4 msec. Latencies and amplitudes of ACC components were variable and inconsistent across gaps durations. So, it is recommended to depend on ACC threshold rather than latencies or amplitudes. As regards correlation between behavioral and electrophysiological GIN threshold, there was strong positive correlation in all studied groups. Moreover, electrophysiological GIN threshold showed high sensitivity (84%) and high specificity (90%) in detection of temporal resolution problem. The cutoff point was found to be 4 msec, above which is considered to have temporal resolution problem. The electrophysiological GIN test could be used to evaluate temporal resolution objectively. This could help in HA selection (determining the signal processing technique), evalution of fitted HA, evaluation of CI performance and monitoring of rehabilitation. So, it will help to maximize the communication skills of the patients in various conditions.