Hildebrandt H, Fresenborg I, Engel A
Universität Oldenburg.
Z Exp Psychol. 1995;42(2):256-79.
Hemispheric specialization of visual imagery processes is a topic of recurrent debate. Recent theories have argued for a left postcentral center for the generation of visual images. Because of contradictory results the process of imaging has been divided into a left hemisphere component (visual imagery) and a right hemisphere component (supramodal spatial mental imagery). An alternative and more parsimonious account would be that the degree of difficulty of visual imagery tasks is responsible for hemispheric differences: easy tasks are solved faster within the left hemisphere because of a direct access to action control, whereas more difficult tasks rely on a right hemisphere specialization for spatial processing. In our experiment we varied the degree of difficulty by introducing concurrent tasks which were interspersed at random into the series of critical stimuli. Interspersing concurrent tasks prevents subjects from automatizing of critical processes and delays reaction times. For the critical visual imagery tasks we presented either upper or lower case letters to the different visual fields and asked for figural aspects of the corresponding lower or upper case letters, respectively. The interspersed stimuli concerned an estimation of the distance of the stimuli or the localization of the stimuli in the upper or lower part of the screen. We also presented upper and lower case letters in random order, thus forcing the subjects to shift between two different visual imagery tasks. In order to look for the effect of position-repetition priming upon visual field advantages we also analyzed the interaction of the position on the screen and its repetition with hemispheric advantages. In one of the visual imagery tasks, the experiments without concurrent tasks yielded a right visual field/left hemisphere advantage. On the other hand, interspersing other tasks resulted in a left visual field/right hemisphere advantage for visual imagery tasks, though none of the concurrent tasks showed a significant visual field advantage in itself. The same holds for combined and random presentation of the two different visual imagery tasks. The results therefore argue for a right hemisphere advantage for difficult visual imagery tasks, whereas easier tasks (monotonous presentation of only one visual imagery tasks) are processed faster in the left hemisphere. The random repetition of positions on the screen yielded a significant effect but had no influence on the visual field advantages found.
视觉表象过程的半球特化是一个反复争论的话题。最近的理论认为存在一个左中央后回中心用于生成视觉图像。由于结果相互矛盾，成像过程被分为左半球成分（视觉表象）和右半球成分（超模态空间心理表象）。另一种更简洁的解释是，视觉表象任务的难度程度导致了半球差异：简单任务在左半球内解决得更快，因为可以直接接入动作控制，而更困难的任务则依赖右半球在空间处理方面的特化。在我们的实验中，我们通过引入并发任务来改变难度程度，这些并发任务被随机穿插在一系列关键刺激中。穿插并发任务会阻止受试者使关键过程自动化，并延迟反应时间。对于关键的视觉表象任务，我们向不同视野呈现大写或小写字母，并分别要求对应小写或大写字母的图形特征。穿插的刺激涉及对刺激距离的估计或刺激在屏幕上部或下部的定位。我们还以随机顺序呈现大写和小写字母，从而迫使受试者在两种不同的视觉表象任务之间切换。为了寻找位置重复启动对视野优势的影响，我们还分析了屏幕上位置及其重复与半球优势之间的相互作用。在其中一项视觉表象任务中，没有并发任务的实验产生了右视野/左半球优势。另一方面，穿插其他任务导致视觉表象任务出现左视野/右半球优势，尽管没有一个并发任务本身显示出显著的视野优势。对于两种不同视觉表象任务的组合和随机呈现也是如此。因此，结果表明对于困难的视觉表象任务存在右半球优势，而较简单的任务（仅单调呈现一种视觉表象任务）在左半球中处理得更快。屏幕上位置的随机重复产生了显著效果，但对所发现的视野优势没有影响。
