- 學位論文
模擬內側橄欖耳蝸之遮蔽與去遮蔽效應
Simulating Masking and Anti-masking Effects of the Medial Olivocochlear Efferent Reflex
摘要
聲音的遮蔽效應發生在當背景雜訊干擾目標聲音的判斷時。本論文將藉由設計持續的雜音加上較短的音調為聲音輸入，並將此導入現有之聲學模型中，此聲學模型包含中耳、耳蝸的流體力學模型、外毛細胞、內毛細胞、聽覺神經、T型多極細胞，並以此模型模擬遮蔽效應。接著提出內側橄欖耳蝸反射之模型，並模擬去遮蔽效應。去遮蔽效應為將遮蔽效應減弱的機制，有助於聽覺辨識。本內側耳蝸橄欖迴路建立的機制參考生物實驗的外毛細胞實驗結果：將乙醯膽鹼此神經傳遞值施用於外毛細胞上，會使外毛細胞的電導上升。本模型以內側橄欖耳蝸接受刺激後增加外毛細胞的電導，減少外毛細胞的放大作用，達到去遮蔽現象。接著提出垂直細胞膜型，並觀察此模型對去如何影響遮蔽效應。垂直細胞位於背側耳蝸核，抑制位於附側耳蝸核的T型多極細胞，本垂直細胞模型以增加T型多極細胞被觸發的閾值方式模擬被抑制的機制。垂直細胞有一特性：對於雜訊的反應較小。因此垂直細胞模型加入側抑制以模擬此現象。最後設計另一組持續音調在持續雜音中為聲音輸入，並再次模擬遮蔽與去遮蔽效應。
並列摘要
The masking effect happens when the background noise influences the target sound, which is then difficult to be perceived. To simulated this effect, we constructed a tone-burst-in-noise stimulus, and then fed into the model comprised of middle ear, cochlear membrane-fluid system, outer hair cell (OHC), inner hair cell (IHC), auditory nerve (AN), T-multipolar (TM) cell. This model successfully simulated the masking effect especially in low-level region. The medial olivocochlear reflex (MOCR), a descending auditory pathway, induces the anti-masking effect to reduce the masking effect and help human to perceive sounds. Based on an experiment of the OHC which showed the conductance of OHC was increased after applying acetylcholine (ACh), we have constructed the MOC model by changing the conductance of OHC and simulated the anti-masking effect. The tuberculoventral (TUB) cell is an inhibitory interneuron in dorsal cochlear nucleus (DCN) and projects to the ventral cochlear nucleus (VCN). The TUB inhibits the interneuron in VCN, and is sensitive to tones, while not to noise. We have used these two properties to construct a TUB model and enhance the anti-masking effect in sustained tone-in-noise conditions.