认知与发展心理学研究室知识库

为揭示发展性阅读障碍的成因，越来越多的研究者开始关注基础的言语感知。范畴感知(categorical perception)是言语感知的一个显著特征，指人们能够将连续变化的语音信号感知为一个个离散的语音范畴，把无数语音分类成有限的语音范畴。采用音段信息，研究发现相比正常阅读者，阅读障碍者对范畴间刺激表现出低敏感缺陷，以及对范畴内刺激表现出过度敏感缺陷。综合范畴间和范畴知缺陷，研究者认为阅读障碍者不但没有建立有效的言语感知信号，反而形成了异常的感知信号。汉语是声调语言，且声调是一种超音段信息。声调不仅具有范畴感知特征，还具有独特的神经加工基础。在汉语阅读中，声调加工发挥着独立且重要的作用。虽然现有研究关注了汉语发展性阅读障碍儿童的声调感知，但基本只考察了阅读障碍儿童的声调范畴间感知。而根据音段信息的研究，阅读障碍者的言语感知异常不仅与范畴间刺激属性有关，还与范畴内刺激属性有关。只有结合范畴间和范畴内的表现，才能全面揭示阅读障碍者的声调范畴感知。因此，本研究采用声调连续体为实验刺激，从行为研究及电生理研究两个水平，全面考察汉语发展性阅读障碍儿童的声调范畴感知。

研究招募北京市5-6年级汉语发展性阅读障碍儿童及同年龄对照组儿童为被试。研究一采用了识别任务和区分任务，在行为层面考察了汉语发展性阅读障碍儿童的声调范畴感知。研究二采用被动oddball范式，以1VLVIN和LDN成分为生理指标，考察了汉语发展性阅读障碍儿童声调范畴感知的神经机制。结果表明:

1、阅读障碍儿童对范畴间刺激表现出低敏感缺陷。在行为上，阅读障碍儿童的识别曲线斜率绝对值更小以及区分范畴间刺激的正确率更低。在神经机制上，阅读障碍儿童感知范畴间刺激诱发的LDN波幅小于对照组儿童，且这一缺陷在大脑左侧、中部以及右侧均可观察到。

2、阅读障碍儿童对范畴内刺激表现出过度敏感缺陷。当阅读障碍儿童感知范畴内刺激时，其诱发的1V}VIN波幅大于对照组儿童，且这一缺陷只在大脑右侧可观察到。

综上，本研究首次从行为水平和神经机制水平全面地考察了汉语发展性阅读障碍儿童的声调范畴感知。研究不仅发现阅读障碍儿童对声调范畴间刺激表现出低敏感缺陷，而且还对声调范畴内刺激表现出过度敏感缺陷。这加深了研究者对汉语阅读障碍缺陷本质的理解，为汉语发展性阅读障碍儿童未来的干预与治疗提供了一定启示。

More and more researchers have focused on the underlying speech perception to reveal the aetiology of developmental dyslexia. Categorical perception is a significant characteristic of speech perception, indicating that people are able to perceive the continuously changing speech signals as discrete speech categories, and classify the countless speech signals into limited speech categories. Studies with segmental information have found that dyslexics are hyposensitive to the between-categorical stimuli and oversensitive to the within-categorical stimuli compared with typical readers. Combining the between-categorical and within-categorical perception deficits researchers proposed that dyslexics formed the abnormal perception signals instead of establishing the effective speech perception signals. Chinese is a tonal language, and tone is a kind of suprasegmental information. Tone has not only the characteristics of categorical perception, but also the unique neural mechanism. Tone processing plays an independent and crucial role in Chinese reading. Although previous studies have examined the tone perception in Chinese children with developmental dyslexia, these studies mainly focused on between-categorical perception of tone in individuals with dyslexia. According to the studies with segmental information, nonetheless, the perception deficit in individuals with dyslexia is not only related to the between-categorical attribute, but also the within-categorical attribute. Only combining the between- and within-categorical performance, can we systematically reveal the categorical perception of tone in individuals with dyslexia. In this study, hence, we adopted the tonal continua as stimuli, and systematically investigated categorical perception of tone from the behavioral and neural levels in Chinese children with developmental dyslexia.

Children with developmental dyslexia and the corresponding chronological-age control group were recruited as participants. All participants are primary school students at 5th or 6th grade in Beijing. Adopting identification and discrimination tasks, study 1 examined the categorical perception of tone in Chinese children with developmental dyslexia at the behavioral level. Using passive oddball paradigm, study 2 examined the categorical perception of tone in Chinese children with developmental dyslexia at the neural level, with MMN and LDN as the neural markers. We have two important findings.

First, dyslexic children were hyposensitive to the between-categorical stimuli. At the behavioral level, dyslexic children exhibited smaller absolute value of identification slope and lower accuracy in discriminating between-categorical stimuli. At the neural level, compared with chronological-age children, smaller LDN amplitude was found for dyslexic children on the left, middle and right side of the brain. Second, dyslexic children were oversensitive to the within-categorial stimuli. When dyslexic children perceived the within-categorical stimuli, they exhibited larger LVLVIN than chronological-age children on the right side of the brain.

In conclusion, the present study systematically examined the categorical perception of tone in Chinese children with developmental dyslexia from behavioral and neural levels for the first time. The findings showed both the deficit of hyposensitive perception in between-categorical stimuli and the deficit of oversensitive perception in within-categorical stimuli for Chinese children with developmental dyslexia. This study deepens the understanding of the nature of Chinese dyslexia, and provides inspiration for the future intervention and remediation in Chinese children with developmental dyslexia.