Behavioural Science Institute, Radboud University Nijmegen, The Netherlands.
Clin Neurophysiol. 2013 Jun;124(6):1151-62. doi: 10.1016/j.clinph.2012.12.044. Epub 2013 Feb 9.
A growing body of evidence suggests that individuals with dyslexia perceive speech using allophonic rather than phonemic units and are thus sensitive to phonetic variations that are actually irrelevant in the ambient language. This study investigated speech perception difficulties in adults with dyslexia using behavioural and neural measurements with stimuli along a place-of-articulation continuum with well-defined allophonic boundaries. Adults without dyslexia served as control participants.
Categorical perception of a /bə - də/ place-of-articulation continuum was evaluated using both identification and discrimination tasks. In addition to these behavioural measures, mismatch negativity (MMN) was recorded for stimuli that came from either similar or different phoneme categories.
The adults with dyslexia exhibited less consistent labelling than controls, but no heightened sensitivity to allophonic contrasts was observed at the behavioural level. Neural measurements revealed that stimuli from different phoneme categories elicited MMNs in both the adults with dyslexia and controls, whereas stimuli from the same category elicited an MMN in the adults with dyslexia only.
The finding that adults with dyslexia have heightened sensitivity to allophonic contrasts in the form of neural activation supports the allophonic explanation of dyslexia.
Sensitivity to allophonic contrasts may be a valuable marker for dyslexia.
越来越多的证据表明，诵读困难个体在感知言语时使用的是变音而非音位单位，因此他们对语音变化很敏感，而这些语音变化在环境语言中实际上是无关紧要的。本研究使用行为和神经测量方法，以具有明确变音边界的发音位置连续体为刺激，调查了诵读困难成年人的言语感知困难。不患有诵读困难的成年人作为对照组参与了研究。
使用识别和辨别任务评估了 /bə - də/ 发音位置连续体的范畴感知。除了这些行为测量外，我们还记录了来自相似或不同音位类别的刺激所诱发的失匹配负波（MMN）。
与对照组相比，诵读困难组的成年人表现出较少的一致性标记，但在行为水平上并未观察到对变音对比的敏感性增强。神经测量结果显示，来自不同音位类别的刺激在诵读困难组和对照组中都能诱发 MMN，而来自同一类别的刺激仅在诵读困难组中能诱发 MMN。
诵读困难成年人在神经激活形式上对变音对比的敏感性增强的发现支持了诵读困难的变音解释。
对变音对比的敏感性可能是诵读困难的一个有价值的标志物。
