研究发现：人类大脑无法判断对方性别

The identical facial features might be judged male when they are viewed in one part of our field of view, but thought of as female in another location, a recent study suggests。

Researchers from the Massachusetts Institute of Technology's McGovern Institute for Brain Research in Boston showed volunteers a series of faces, ranging from highly feminine to extremely masculine, and asked to say if they were male or female. Participants were told to fix their gaze on the centre of a computer screen as the faces flashed at different locations for 50 milliseconds。

The patterns were different for different people, the scientists reported. Some individuals judged an androgynous face as female every time it appeared in the upper right corner of the screen, while others saw it as male。

"Sampling bias" is the likely explanation, say the scientists. The visual cortex, which processes images, contains cells grouped according to which part of a scene they analyze. Within each group, there is thought to be a relatively small number of neurons devoted to interpreting the gender of faces. The smaller the image, the fewer cells are activated. As a result, cells in one group might be mostly those responding to male faces, while in a different part of the visual cortex female-responding cells dominate。

In addition, in the real world the effect is not noticed because there are so many other gender clues, such as hair and clothing. And experiments using computer-generated faces stripped of all other gender-identifying features showed how hard the brain finds it to tell sexes apart。

The findings challenge a longstanding belief of neuroscientists - that how the brain sees an object should not depend on where the object is located relative to the observer。

英国《每日邮报》25日报道称，最新研究显示，同样一张面孔，从某个角度看上去是男性，而从另一个角度看上去就会变成女性。

来自波士顿麻省理工学院麦戈文脑研究所的研究人员做了这样一个实验：他们给受试者展示了一组从高度女性化到极端男性化的人脸照片，并要求受试者据此回答所见对象是男性还是女性。受试者还被告知，这些脸孔照片会在电脑屏幕的不同位置闪现出来并持续50毫秒，此时他们只能将视线落在电脑屏幕中央。

科学家们汇报研究结果时称，不同的人得出的结论是不一样的。每当一个较为中性的面孔从电脑右上角出现时，某些受试者会称该脸孔属于一个女人，而另外一些人则称这是一张男人的脸。

科学家们解释道，产生这种判断差异的可能原因是“抽样偏差”。原来，视觉皮质负责处理图片信息，其内含有分析不同视角的细胞群。每一个细胞群内，只有一小部分神经细胞负责辨别人类面孔的性别信息。而人类所看到的图片越小，被激活的神经细胞就越少。结果，细胞群内被激活的大部分是那些同辨别男性面孔相关的神经细胞，而视觉皮质的另一部分被激活的大部分是可辨别女性面孔的神经细胞。

此外，现实中这种视觉差异并不为人注意的原因在于有太多的性别线索供人类判断对方性别，比如发型和衣着。而科学家用电脑将人类面孔所有可判断性别的外在特征处理掉后，发现实际上人脑很难判断对方的性别到底是什么。

长期以来神经科学家们一直认为大脑看待物体的方式同观察视角无关，而该研究结果证明原先的理论并不成立。 （实习编辑：顾萍）