Hamburger Kai, Hansen Thorsten
Justus Liebig University Giessen, Giessen, Germany.
Atten Percept Psychophys. 2010 May;72(4):1045-52. doi: 10.3758/APP.72.4.1045.
In the horizontal-vertical illusion (HVI), the length of the vertical line is overestimated, whereas in the bisection illusion (BI), the horizontal bisecting line is expected to be overestimated. Here, only half of our 22 observers showed the expected BI, whereas the other half underestimated the bisecting line. Observers also differed in their judgments of the strength of the HVI: The HVI was stronger for observers showing the classical bisection effect, and weaker or absent for those underestimating the bisecting line. To account for these results, we used a linear model to individually estimate the strength of two putative factors underlying both illusions. Whereas the strength of the HVI and BI were highly correlated, the estimated factors were uncorrelated. Therefore, in two control experiments, we then measured the pure horizontal-vertical (pHVI) and bisection (pBI) illusions. A significant correlation between the estimated factors and the measured illusion variants was found. Results were robust against variations of contrast, repetitive presentations, and choice of adjusted line. Thus, the classical HVI as an additive combination of two independent factors was confirmed, but we found considerable interindividual variations in the strength of the illusions. The results stress the importance of analyzing individual data rather than taking sample means for understanding these illusions.
在横竖错觉（HVI）中，垂直线的长度被高估，而在平分错觉（BI）中，水平平分线预计会被高估。在此，我们的22名观察者中只有一半表现出预期的BI，而另一半则低估了平分线。观察者对HVI强度的判断也存在差异：对于表现出经典平分效应的观察者，HVI更强，而对于低估平分线的观察者，HVI较弱或不存在。为了解释这些结果，我们使用线性模型分别估计两种错觉背后两个假定因素的强度。虽然HVI和BI的强度高度相关，但估计的因素不相关。因此，在两个对照实验中，我们随后测量了纯横竖（pHVI）和平分（pBI）错觉。发现估计因素与测量的错觉变体之间存在显著相关性。结果对于对比度变化、重复呈现以及调整线的选择具有稳健性。因此，经典的HVI作为两个独立因素的加性组合得到了证实，但我们发现错觉强度存在相当大的个体差异。结果强调了分析个体数据而非采用样本均值来理解这些错觉的重要性。
