General introduction 11 Yet, in case of sensorineural hearing loss, an additional effect is that the distorted conversion of sounds to the brain often causes sounds to be perceived as blurred (Dillon, 2008). Also, discomfort can be experienced when loud sounds are heard, even at levels that are not perceived as annoying by normally-hearing individuals (Levitt, 2001). Consequently, sensorineural hearing loss is characterized by a reduced dynamic range of hearing, meaning that the range between the weakest sound that can be heard and the most intense sound that can be tolerated is often smaller when sensorineural hearing loss is present (Dillon, 2008). Sensorineural hearing loss involves problems with multiple auditory functions that contribute to further distortionof sounds (Dillon, 2008; Plomp, 1978).These auditory functions – specifically spectral, temporal, and spatial resolution – partly share their cause, but affect auditory functioning in different ways. Decreased spectral resolution causes difficulties with recognizing two separate sounds of a different frequency that are presented simultaneously. Decreased spectral and temporal resolution cause the distortion of sounds and difficulties with listening selectively, for example with understanding speech in noise. Lastly, decreased spatial resolution causes a higher sensitivity for loud sounds and causes difficulties with spatial hearing. The impact of hearing loss on hearing function depends on whether one (unilateral hearing loss) or both ears (bilateral hearing loss) are affected. Bilateral hearing loss is most common and results in reduced hearing function as described above. When normal hearing is present in one ear, the reduced sensitivity of sounds is rather modest. Unilateral hearing loss often results in no more than a small attenuation of sounds presented at the affected side, since sounds need to travel around the head to the opposite ear. However, unilateral hearing loss may lead to specific difficulties in case of adverse listening situations. When information of only one ear can be used, it can become more difficult to recognize the meaningful sounds and to filter out the environmental noise (Sargent et al., 2001). Also, unilateral hearing loss causes difficulties with locating a sound source, since the brain needs input of two ears to accurately determine the direction where a signal originates. Personal and environmental factors Many personal and environmental factors interact with hearing loss and its impact on hearing functions, everyday activities, and participation in life situations (Granberg,
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