The Effect of Contralateral Noise Stimulation on Difference Limen for Intensity

Background and Aim: Contralateral stimulation with noise can improve auditory intensity discrimination. This may be related to function of the efferent system. The purpose of this study was to determine the relationship between the auditory intensity discrimination and the efferent system function.Methods: Twenty students with normal hearing were included in this descriptive-analytic study. We examined Difference Limen for Intensity (DLI), Otoacoustic Emissions suppression and Speech In Noise. DLI was evaluated with and without contralateral noise stimulation at two different stimulus levels (20, 70 dB SL).Results: There was significant difference between mean DLI scores of with contralateral masking comparing to without it, which was more prominent as frequency increased. Mean DLI score while masking with white noise was more than mean scores when masking with narrow band noise (p<0.05). Transient evoked otoacoustic emissions responses decreased significantly in amplitude with contralateral masking. (p<0.05)Conclusion: These results suggest that medial olivocochlear bundle functions as a key role in auditory intensity discrimination

Determination of Mismatch Negativity in 4 to 9-Year-Old Children by Tonal Stimulation

Background and Aim: Mismatch negativity (MMN) is one of the auditory evoked potentials that occurs about 100-250 ms after stimulus onset. The MMN waveform is elicited by a discriminable change in a sequence of repetitive homogenous stimuli. This change can be in intensity level, frequency, or duration of auditory stimuli. The purpose of this study was to obtain MMN waveform using tonal stimuli and to investigate its changes during changes in age. Materials and Methods: The study was prescriptive-analytic cross-sectional. The participants were sixty children aged 4 to 9 year. The stimuli were at 80 dB pe SPL. A 1000Hz tone and a 1500Hz tone were used as standard and deviant stimuli, respectively. Probability of deviant stimuli was 20%. Trials were recorded using surface electrode placed at four locations on the head. Results: The MMN waveform does not exist in 22.5% of the children. Also, determining of MMN peak in 22.5% was not exactly possible. In other subjects, a significant negative correlation was observed between latency of MMN and age, but not for age and amplitude for this negativity. Conclusion: This study confirms that the MMN may not be seen in normal people. Also there are maturational changes in MMN waveform

Dichotic auditory-verbal memory in adults with cerebro-vascular accident

Background and Aim: Cerebrovascular accident is a neurological disorder involves central nervous system. Studies have shown that it affects the outputs of behavioral auditory tests such as dichotic auditory verbal memory test. The purpose of this study was to compare this memory test results between patients with cerebrovascular accident and normal subjects.Methods: This cross-sectional study was conducted on 20 patients with cerebrovascular accident aged 50-70 years and 20 controls matched for age and gender in Emam Khomeini Hospital, Tehran, Iran. Dichotic auditory verbal memory test was performed on each subject.Results: The mean score in the two groups was significantly different (p<0.0001). The results indicated that the right-ear score was significantly greater than the left-ear score in normal subjects (p<0.0001) and in patients with right hemisphere lesion (p<0.0001). The right-ear and left-ear scores were not significantly different in patients with left hemisphere lesion (p=0.0860).Conclusion: Among other methods, Dichotic auditory verbal memory test is a beneficial test in assessing the central auditory nervous system of patients with cerebrovascular accident. It seems that it is sensitive to the damages occur following temporal lobe strokes

Persian randomized dichotic digits test: Development and dichotic listening performance in young adults

Background and Aims: The dichotic listening subtest is an important component of the test battery for auditory processing assessment in both children and adults. A randomized dichotic digits test (RDDT) was created to compensate for sensitivity weakness of double digits when detecting abnormal ear asymmetry during dichotic listening. The aim of this study was the development and  intial evaluation of the Persian randomized dichotic digits test.Method: Persian digits 1-10 (except for the bisyllabic digit, 4) uttered by a native Persian language speaker were recorded in a studio. After alignment of intensity and temporal characteristics of digit waveforms, lists 1 and 2 of the RDDT were reproduced. List 1 of the test was administered at 55 dBHL on 50 right-handed normal hearing individuals (with an equal sex ratio) in the age group of 18-25 years and hearing thresholds of 15 dBHL or better in audiometric frequencies.Results: Mean (standard deviation) of percent-correct score for right and left ears and right ear advantage of the subjects was 94.3 (5.3), 84.8 (7.7), and 9.5 (7.0) percent, respectively. Sixty percent of the subjects showed normal results and unilateral and bilateral deficits were seen in 24 percent and 16 percent, respectively, of studied individuals.Conclusion: It seems the Persian version of RDDT test is the same as the original test as it is able to test ear asymmerty, unilateral and bilateral deficits in dichotic listening