Bacon Michael Patrick, Bridgeman Bruce, Ramachandran Vilayanur S
Department of Psychology, Social Sciences 2 UCSC, Santa Cruz, CA 95064, USA.
Atten Percept Psychophys. 2013 Jan;75(1):5-9. doi: 10.3758/s13414-012-0401-1.
We investigated the physiological mechanism of grapheme-color synesthesia using metacontrast masking. A metacontrast target is rendered invisible by a mask that is delayed by about 60 ms; the target and mask do not overlap in space or time. Little masking occurs, however, if the target and mask are simultaneous. This effect must be cortical, because it can be obtained dichoptically. To compare the data for synesthetes and controls, we developed a metacontrast design in which nonsynesthete controls showed weaker dichromatic masking (i.e., the target and mask were in different colors) than monochromatic masking. We accomplished this with an equiluminant target, mask, and background for each observer. If synesthetic color affected metacontrast, synesthetes should show monochromatic masking more similar to the weak dichromatic masking among controls, because synesthetes could add their synesthetic color to the monochromatic condition. The target-mask pairs used for each synesthete were graphemes that elicited strong synesthetic colors. We found stronger monochromatic than dichromatic U-shaped metacontrast for both synesthetes and controls, with optimal masking at an asynchrony of 66 ms. The difference in performance between the monochromatic and dichromatic conditions in the synesthetes indicates that synesthesia occurs at a later processing stage than does metacontrast masking.
我们使用元对比掩蔽研究了字形-颜色联觉的生理机制。一个元对比目标会被延迟约60毫秒的掩蔽物变得不可见；目标和掩蔽物在空间或时间上不重叠。然而，如果目标和掩蔽物同时出现，则几乎不会发生掩蔽。这种效应一定是皮层性的，因为它可以通过双眼分别呈现获得。为了比较联觉者和对照组的数据，我们设计了一种元对比实验，其中非联觉对照组表现出比单色掩蔽更弱的双色掩蔽（即目标和掩蔽物颜色不同）。我们为每个观察者设置了亮度相等的目标、掩蔽物和背景来实现这一点。如果联觉颜色影响元对比，那么联觉者应该表现出与对照组中较弱的双色掩蔽更相似的单色掩蔽，因为联觉者可以将他们的联觉颜色添加到单色条件中。用于每个联觉者的目标-掩蔽物对是能引发强烈联觉颜色的字形。我们发现，联觉者和对照组的单色U形元对比都比双色U形元对比更强，在66毫秒的异步时达到最佳掩蔽效果。联觉者在单色和双色条件下表现的差异表明，联觉发生在比元对比掩蔽更晚的加工阶段。
