Legge Gordon E, Cheung Sing-Hang, Yu Deyue, Chung Susana T L, Lee Hye-Won, Owens Daniel P
University of Minnesota, 75 East River Road, Minneapolis, MN 55455, USA.
J Vis. 2007 Mar 7;7(2):9.1-15. doi: 10.1167/7.2.9.
The visual span for reading is the number of letters, arranged horizontally as in text, that can be recognized reliably without moving the eyes. The visual-span hypothesis states that the size of the visual span is an important factor that limits reading speed. From this hypothesis, we predict that changes in reading speed as a function of character size or contrast are determined by corresponding changes in the size of the visual span. We tested this prediction in two experiments in which we measured the size of the visual span and reading speed on groups of five subjects as a function of either character size or character contrast. We used a "trigram method" for characterizing the visual span as a profile of letter-recognition accuracy as a function of distance left and right of the midline (G. E. Legge, J. S. Mansfield, & S. T. L. Chung, 2001). The area under this profile was taken as an operational measure of the size of the visual span. Reading speed was measured with the Rapid Serial Visual Presentation (RSVP) method. We found that the size of the visual span and reading speed showed the same qualitative dependence on character size and contrast, reached maximum values at the same critical points, and exhibited high correlations at the level of individual subjects. Additional analysis of data from four studies provides evidence for an invariant relationship between the size of the visual span and RSVP reading speed; an increase in the visual span by one letter is associated with a 39% increase in reading speed. Our results confirm the visual-span hypothesis and provide a theoretical framework for understanding the impact of stimulus attributes, such as contrast and character size, on reading speed. Evidence for the visual span as a determinant of reading speed implies the existence of a bottom-up, sensory limitation on reading, distinct from attentional, motor, or linguistic influences.
阅读的视觉广度是指像在文本中那样水平排列的、无需移动眼睛就能可靠识别的字母数量。视觉广度假说认为，视觉广度的大小是限制阅读速度的一个重要因素。基于这一假说，我们预测，阅读速度随字符大小或对比度的变化是由视觉广度大小的相应变化所决定的。我们在两项实验中对这一预测进行了检验，在实验中我们测量了五人小组的视觉广度大小和阅读速度，它们分别是字符大小或字符对比度的函数。我们使用一种“三字母组方法”将视觉广度表征为字母识别准确率随中线左右距离变化的曲线（G.E.莱格、J.S.曼斯菲尔德和S.T.L.钟，2001年）。该曲线下的面积被用作视觉广度大小的操作性度量。阅读速度通过快速序列视觉呈现（RSVP）方法进行测量。我们发现，视觉广度大小和阅读速度在字符大小和对比度方面呈现出相同的定性依赖关系，在相同的临界点达到最大值，并且在个体受试者层面表现出高度相关性。对四项研究数据的进一步分析为视觉广度大小与RSVP阅读速度之间的不变关系提供了证据；视觉广度增加一个字母与阅读速度提高39%相关。我们的结果证实了视觉广度假说，并为理解对比度和字符大小等刺激属性对阅读速度的影响提供了一个理论框架。视觉广度作为阅读速度决定因素的证据意味着存在一种自下而上的、对阅读的感觉限制，这与注意力、运动或语言影响不同。
