How does reading direction modulate perceptual and visuospatial attention biases?

Abstract

Left-side bias (LSB) effects have been reported in different tasks. For example, in perceptual judgments of faces, participants typically judge a face made from two left half-faces more similar to the original face than one from two right half-faces (chimeric face task). A similar effect was observed in Chinese character perception in expert Chinese readers (chimeric character task; Hsiao & Cottrell, 2009). LSB effects were also commonly observed in visuospatial attention tasks. For example, in the greyscales task with two horizontal bars, participants typically judge the bar darker on the left side to be darker overall than the one darker on the right, although they are equiluminant. In line bisection, participants tend to bisect lines slightly to the left of the real center. It remains unclear whether reading direction plays a crucial role in the bias effects. Some previous studies compared readers of languages read from left to right with those read from right to left (e.g., French vs. Hebrew); nevertheless, their differences may be due to cultural differences, for example, instead of reading direction. Although Chinese is typically read from left to right, in contrast to other languages, it can also be read from right to left. Thus, Chinese provides a unique opportunity to examine the influence of reading direction within subjects. Chinese participants performed perceptual bias (chimeric face and character tasks) and visuospatial attention bias tasks (greyscales and line bisection) once before and once after reading direction priming, in which they read Chinese passages from right to left for about 20 minutes. Participants showed significantly reduced LSB in perceptual bias tasks but not in visuospatial attention bias tasks after the priming. Thus, reading direction does not seem to influence visuospatial attention biases as much as perceptual biases, suggesting that these two forms of biases involve different underlying mechanisms.