Department of Psychology, Center for Visual Cognition, University of Copenhagen, Denmark.
Cortex. 2010 Feb;46(2):242-55. doi: 10.1016/j.cortex.2009.03.013. Epub 2009 Apr 16.
Whether pure alexia is a selective disorder that affects reading only, or if it reflects a more general visual disturbance, is highly debated. We have investigated the selectivity of visual deficits in a pure alexic patient (NN) using a combination of psychophysical measures, mathematical modelling and more standard experimental paradigms. NN's naming and categorization of line drawings were normal with regards to both errors and reaction times (RTs). Psychophysical experiments revealed that NN's recognition of single letters at fixation was clearly impaired, and recognition of single digits was also affected. His visual apprehension span was markedly reduced for letters and digits. His reduced visual processing capacity was also evident when reporting letters from words. In an object decision task with fragmented pictures, NN's performance was abnormal. Thus, even in a pure alexic patient with intact recognition of line drawings, we find evidence of a general visual deficit not selective to letters or words. This finding is important because it raises the possibility that other pure alexics might have similar non-selective impairments when tested thoroughly. We argue that the general visual deficit in NN can be accounted for in terms of inefficient build-up of sensory representations, and that this low level deficit can explain the pattern of spared and impaired abilities in this patient.
纯失读症究竟是一种仅影响阅读的选择性障碍，还是反映了更普遍的视觉障碍，目前仍存在高度争议。我们通过结合心理物理学测量、数学建模和更标准的实验范式，研究了一位纯失读症患者（NN）的视觉缺陷的选择性。NN 在命名和分类线条图时，无论是错误还是反应时间（RT），都表现出正常。心理物理学实验表明，NN 在固定注视时对单个字母的识别明显受损，对单个数字的识别也受到影响。他对字母和数字的视觉感知范围明显缩小。当从单词中报告字母时，他的视觉处理能力也明显降低。在一个具有碎片化图片的物体决策任务中，NN 的表现异常。因此，即使在一位纯失读症患者中，其对线图的识别完整无损，我们也发现了存在非选择性的一般视觉缺陷的证据，这种缺陷不仅限于字母或单词。这一发现很重要，因为它提出了一种可能性，即其他纯失读症患者在经过彻底测试时可能具有类似的非选择性障碍。我们认为，NN 的一般视觉缺陷可以用感官表象的低效积累来解释，而这种低级别的缺陷可以解释该患者具有受损和未受损能力的模式。
