University of Colorado, Boulder.
J Cogn Neurosci. 1997 Mar;9(2):171-90. doi: 10.1162/jocn.1997.9.2.171.
For more than a century, it has been known that damage to the right hemisphere of the brain can cause patients to be unaware of the contralesional side of space. This condition, known as unilateral neglect, represents a collection of clinically related spatial disorders characterized by the failure in free vision to respond, explore, or orient to stimuli predominantly located on the side of space opposite the damaged hemisphere. Recent studies using the simple task of line bisection, a conventional diagnostic test, have proven surprisingly revealing with respect to the spatial and attentional impairments involved in neglect. In line bisection, the patient is asked to mark the midpoint of a thin horizontal lie on a sheet of paper. Neglect patients generally transect far to the right of the center. Extensive studies of line bisection have been conducted, manipulating-among other factors-line length, orientation, and position. We have simulated the pattern of results using an existing computational model of visual perception and selective attention called MORSEL (Mozer, 1991). MORSEL has already been used to model data in a related disorder, neglect dyslexia (Mozer & Behrmann, 1990). In this earlier work, MORSEL was "lesioned" in accordance with the damage we suppose to have occurred in the brains of neglect patients. The same model and lesion can simulate the detailed pattern of performance on line bisection, including the following observations: (1) no consistent across-subject bias is found in normals; (2) transection displacements are proportional to line length in neglect patients; (3) variability of displacements is proportional to line length, in both normals and patients; (4) position of the lines with respect to the body or the page on which they are drawn has little effect; and (5) for lines drawn at different orientations, displacements are proportional to the cosine of the orientation angle. MORSEL fails to account for one observation: across patients, the variability of displacements for a particular line length is roughly proportional to mean displacement. Nonetheless, the overall fit of the model is sufficiently good that we believe MORSEL can be used as a diagnostic tool to characterize the specific nature of a patient's deficit, and thereby has potential down the line in therapy.
一个多世纪以来，人们已经知道大脑右半球的损伤会导致患者对空间的对侧部分没有意识。这种情况被称为单侧忽略，代表了一系列临床相关的空间障碍，其特征是在自由视觉中对主要位于受损半球对侧空间的刺激没有反应、探索或定向。最近使用简单的线二分任务（一种常规的诊断测试）的研究令人惊讶地揭示了与忽视相关的空间和注意力损伤。在线二分任务中，要求患者在一张纸上标记一条细横线的中点。忽略患者通常会远远地偏向右侧。已经对线二分进行了广泛的研究，除其他因素外，还对线的长度、方向和位置进行了操纵。我们使用一种称为 MORSEL（Mozer，1991）的现有视觉感知和选择性注意计算模型来模拟结果模式。MORSEL 已经用于模拟与忽略性失读症相关的障碍的数据（Mozer & Behrmann，1990）。在这项早期工作中，根据我们假设在忽略患者大脑中发生的损伤，对 MORSEL 进行了“损伤”。同一模型和损伤可以模拟线二分的详细性能模式，包括以下观察结果：（1）在正常人中没有发现一致的跨主题偏差；（2）在忽略患者中，横切位移与线的长度成正比；（3）在正常人中和患者中，位移的可变性与线的长度成正比；（4）线相对于身体或绘制它们的页面的位置几乎没有影响；（5）对于以不同方向绘制的线，位移与方向角的余弦成正比。MORSEL 无法解释一个观察结果：对于特定线长度的位移，跨患者的可变性大致与平均位移成正比。尽管如此，模型的整体拟合度足够好，我们相信 MORSEL 可以用作诊断工具来描述患者缺陷的具体性质，从而在治疗方面具有潜在的应用。
