Abstract
According to the salient-features coding hypothesis, the S-R translation is fast when the salient stimulus and response alternatives correspond in an experimental task (Weeks & Proctor, 1990). When a stimulus set is spatially orthogonal to a response set (e.g., vertical stimulus and horizontal response configurations), an up-right/down-left mapping has an advantage over the reverse mapping. This is termed an orthogonal S-R compatibility (SRC), and interpreted that “above” and “right” are the salient features in horizontal and vertical axes, respectively. However, in the previous studies about the orthogonal SRC, all the stimulus sets were displayed above the response keys. It means that, in above-below spatial representation, the relative “aboveness” of the stimulus set might determine the saliency. In our experiment, two response keys were set on the right and the left of a fixation point (green LED), respectively. The fixation was at the midpoint and intersection of both stimulus and response sets. Each trial began with the display of the fixation LED for 1s that was followed by the stimulus (red LED) appeared above or below it 100ms later. Each participant engaged in both up-right/down-left and up-left/down-right mapping conditions. If the relative position of each S-R pair determines the saliency, there would be no mapping preference in this configuration. However, as a result, mean RT was significantly shorter with the up-right/down-left mapping than with the reverse mapping. This shows that the saliency of “above” in orthogonal SRC is not due to the stimulus pair's “aboveness” but to the fact that “above” is the spatially salient feature in a vertical axis. In the following experiment, we investigate the relationship between salient features and spatial axes.