Department of Neurosciences, KU Leuven, ExpORL, Leuven, Belgium.
Ear Hear. 2017 Sep/Oct;38(5):e305-e315. doi: 10.1097/AUD.0000000000000429.
Auditory stimuli modulated by modulation frequencies within the 30 to 50 Hz region evoke auditory steady state responses (ASSRs) with high signal to noise ratios in adults, and can be used to determine the frequency-specific hearing thresholds of adults who are unable to give behavioral feedback reliably. To measure ASSRs as efficiently as possible a multiple stimulus paradigm can be used, stimulating both ears simultaneously. The response strength of 30 to 50Hz ASSRs is, however, affected when both ears are stimulated simultaneously. The aim of the present study is to gain insight in the measurement efficiency of 30 to 50 Hz ASSRs evoked with a 2-ear stimulation paradigm, by systematically investigating the binaural interaction effects of 30 to 50 Hz ASSRs in normal-hearing adults.
ASSRs were obtained with a 64-channel EEG system in 23 normal-hearing adults. All participants participated in one diotic, multiple dichotic, and multiple monaural conditions. Stimuli consisted of a modulated one-octave noise band, centered at 1 kHz, and presented at 70 dB SPL. The diotic condition contained 40 Hz modulated stimuli presented to both ears. In the dichotic conditions, the modulation frequency of the left ear stimulus was kept constant at 40 Hz, while the stimulus at the right ear was either the unmodulated or modulated carrier. In case of the modulated carrier, the modulation frequency varied between 30 and 50 Hz in steps of 2 Hz across conditions. The monaural conditions consisted of all stimuli included in the diotic and dichotic conditions.
Modulation frequencies ≥36 Hz resulted in prominent ASSRs in all participants for the monaural conditions. A significant enhancement effect was observed (average: ~3 dB) in the diotic condition, whereas a significant reduction effect was observed in the dichotic conditions. There was no distinct effect of the temporal characteristics of the stimuli on the amount of reduction. The attenuation was in 33% of the cases >3 dB for ASSRs evoked with modulation frequencies ≥40 Hz and 50% for ASSRs evoked with modulation frequencies ≤36 Hz.
Binaural interaction effects as observed in the diotic condition are similar to the binaural interaction effects of middle latency responses as reported in the literature, suggesting that these responses share a same underlying mechanism. Our data also indicated that 30 to 50 Hz ASSRs are attenuated when presented dichotically and that this attenuation is independent of the stimulus characteristics as used in the present study. These findings are important as they give insight in how binaural interaction affects the measurement efficiency. The 2-ear stimulation paradigm of the present study was, for the most optimal modulation frequencies (i.e., ≥40 Hz), more efficient than a 1-ear sequential stimulation paradigm in 66% of the cases.
在 30 到 50 Hz 区域内调制频率调制的听觉刺激在成年人中引发具有高信噪比的听觉稳态反应（ASSR），并且可用于确定无法可靠地提供行为反馈的成年人的频率特异性听力阈值。为了尽可能高效地测量 ASSR，可以使用多刺激范式同时刺激双耳。然而，当双耳同时受到刺激时，30 到 50 Hz ASSR 的响应强度会受到影响。本研究的目的是通过系统研究正常听力成年人中 30 到 50 Hz ASSR 的双耳相互作用效应，深入了解使用双耳刺激范式测量 30 到 50 Hz ASSR 的效率。
在 23 名正常听力成年人中使用 64 通道 EEG 系统获得 ASSR。所有参与者均参加了单耳、双耳、双耳刺激实验。刺激由中心频率为 1 kHz 的调制一倍频程噪声带组成，强度为 70 dB SPL。单耳刺激条件下，双耳均呈现 40 Hz 调制的刺激。在双耳刺激条件下，左耳刺激的调制频率保持在 40 Hz，而右耳的刺激为未调制或调制载波。在调制载波的情况下，调制频率在不同条件下以 2 Hz 的步长在 30 到 50 Hz 之间变化。单耳刺激条件包括双耳和双耳刺激条件中包含的所有刺激。
对于单耳刺激条件，所有参与者的调制频率≥36 Hz 时均产生明显的 ASSR。在双耳刺激条件下观察到显著的增强效应（平均：~3 dB），而在双耳刺激条件下观察到显著的降低效应。刺激的时间特征对降低量没有明显影响。对于调制频率≥40 Hz 的 ASSR，33%的情况下的衰减量>3 dB，对于调制频率≤36 Hz 的 ASSR，50%的情况下的衰减量>3 dB。
在双耳刺激条件下观察到的双耳相互作用效应与文献中报道的中潜伏期反应的双耳相互作用效应相似，表明这些反应具有相同的潜在机制。我们的数据还表明，当双耳呈现时，30 到 50 Hz ASSR 会被衰减，并且这种衰减与本研究中使用的刺激特征无关。这些发现很重要，因为它们深入了解了双耳相互作用如何影响测量效率。与 1 耳顺序刺激范式相比，本研究的双耳刺激范式在最优化调制频率（即≥40 Hz）下，在 66%的情况下更有效。
