关键词: 聋人, 视觉功能, 缺陷理论, 补偿理论, 整合理论

Abstract: Effective use of information from multiple sensory channels is critical to explore the surroundings successfully. Hearing loss early makes deaf people rely more on visual modal and leads to changes in their visual performances. There are three theories concerning the effect of hearing impairment on visual performances of deaf people. (1) The first is the deficit theory of visual performance, which believes that visual performances of deaf people are impaired, including the auditory scaffolding hypothesis and the division of labor hypothesis. The former argues that sound is essentially a temporal and sequential signal, and a scaffolding for the development of related cognitive abilities. Therefore, lack of sound early may interfere with these visual sequencing skills. The latter believes that deaf people must rely on vision to complete the current task and monitor surrounding changes at the same time, and then hearing loss changes the way visual attention works. Compared with the highly selective and task-oriented visual attention resources of hearing people, resources of deaf people are more distributed which is harmful to foveal processing. (2) The second is the compensation theory of visual performance, which considers that visual performances of deaf people are enhanced, involving the reactivity enhancement hypothesis and the perceptual enhancement hypothesis based on behavioral outcomes, as well as the supramodal function hypothesis and the dorsal route hypothesis on the ground of physiological mechanisms. The reactivity enhancement hypothesis states that deaf people can detect stimuli in parafoveal and peripheral field more quickly, which represents a kind of compensation in time dimension. The perceptual enhancement hypothesis holds that deaf people can detect visual stimuli further away and their perceptual range is larger than typical individuals, which represents the compensation in spatial dimension. The supramodal function hypothesis suggests that supramodal functions of deaf individuals, which can be completed by multiple sensory systems instead of specific one, will become enhanced owing to the cross-modal reorganization of their auditory cortex caused by hearing loss. The dorsal route hypothesis suggests that the dorsal visual pathway of deaf people is more susceptible to hearing loss, and then visual functions associated with the dorsal route are more prone to enhancement. (3) The third is the integration theory, which suggests that the visual performances of deaf individuals could be both impaired and enhanced, depending on task requirements and ages of participants. Researches, which declare that visual functions of deaf people are impaired, usually employ experimental tasks to investigate the allocation of visual attention resources in time dimension. On the contrary, literatures verifying the enhancement of visual functions of deaf people always use tasks exploring the distribution of visual resources in spatial dimension. What’s more, deaf people's visual function deficits are mostly found in deaf children, while enhancements are obtained in deaf adults. This paper systematically reviews the three theories concerning the influence of hearing impairment on the visual functions of deaf people, but to a certain extent, they all have shortcomings. Further studies can be carried out from the following perspectives: (1) Based on this issue, construct a comprehensive theory with great explanatory power. (2) In order to overcome the large individual differences among deaf people and describe the development trajectory of deaf people's visual functions, longitudinal research is recommended. (3) Employ eye tracking technology to explore the visual performance of deaf people for the sake of the accuracy and effectiveness of data. (4) Explore the impact of visual function changes of deaf people on their reading.

Key words: deaf, visual performance, deficit theory, compensation theory, integration theory