线分法试验中反转效应机制的探讨

Cross-over in line bisection among stroke patients

目的探讨线分法试验中反转效应的可能机制。方法首先根据偏侧忽略行为量表筛选出存在左侧偏侧忽略的脑卒中患者25例，另外选取20例年龄与之相匹配的正常人纳入对照组。所有入选者均进行以下线分作业：在2张A4纸的左侧、中央及右侧各画3条水平直线，直线的长度分别为100mm和20mm，让受检者用右手执笔在每条线段中央划一条垂直短线；然后在另外2张A4纸上同样画3条水平直线，让受检者标出所看到线段的两端点。结果偏侧忽略（左侧）患者在进行线分法试验时出现了长度反转效应，对线段两端均有忽略，不仅低估了100mm线段长度，也低估了20mm线段长度。结论偏侧忽略患者在进行线分法试验时，进入中心视野的线段不被忽略，即所谓的“中心凹忽略回避”理论，该理论可用于解释线分法试验中的反转效应。

Objective To explore possible mechanisms of the cross-over observed in stroke patients completing a line bisection test. Methods Twenty-five stroke patients with left neglect and twenty normal subjects were studied. In the ordinary linebisection test, there are two papers presenting 20 mm and 100 mm lines respectively. On each paper, three lines with the same length are presented at the left, middle and right of the paper. In the line image test, the two papers are the same as in line bisection test, but here subjects are asked to set endpoints of each real line. Results Replicating earlier findings, length cross-over was observed in the patients with neglect. In the line image test, those patients neglected lines on both sides but with a much larger proportion on the left. The patients underestimated long lines as in previous studies, but they also underestimated very short lines in contrast to earlier findings. Conclusion Foveal neglect sparing may explain these observations. For very short lines, the left end of the line falls into foveal vision and the left part of the line was not neglected. As a result, the crossover effect of line length occurs.