Reading is the most important way for human beings to acquire knowledge. Different writing systems vary regarding their reading directions. Most writingsystems such as English and Chinese are read from left to right within a line of text, but some writing systems such as Arabic and Hebrew are written from right to left, and other writing systems such as Mongolian are written from top to bottom. Readers of these different writing systems need to use different reading mechanisms to adapt to their writing systems with different directions. Previous reading studies mainly investigated the reading mechanisms of horizontally written languages. Therefore, very little is known about the reading mechanisms of vertically writing languages. To understand how reading direction affects reading mechanisms such as visual attention deployment, perceptual span, and visual crowding effect, we conducted the present study using a rare vertically written script Mongolian.
In Study 1,two eye-tracking experiments were conducted to investigate the perceptual span and visual attention deployment when reading Mongolian. In Experiment 1,we adopted the gaze-contingent moving-window paradigm to measure the size of the perceptual span during the reading of Mongolian sentences. The results showed that the perceptual span during Mongolian reading is asymmetry downwards, extending 1 syllable above the fixation and 2 syllables below the fixation. Experiment 2 investigated the deployment of visual attention and the relationship between covert visual attention and the perceptual span. Results showed that RTs were generally shorter when the probes were presented within perceptual span than when they were presented outside perceptual span. These results provide direct evidence to the attention-biased hypothesis, which assumes that readers allocate more attention to upcoming novel information, leading to an increased perceptual span in the reading direction.
Study 2 investigated whether the effect of reading direction on visual attention is reading task-specific or is a general phenomenon that can be extended to other visual processing tasks. Specifically, we investigated whether the experience of vertical reading affects the horizontal-vertical asymmetry of the visual crowding effect. To do so, we compared experienced Mongolian readers' performance on identifying target stimuli in horizontally or vertically arranged stimulus strings. Results showed that the crowding effect was greater for horizontally arranged stimulus strings than that for the vertically arranged stimulus strings. These effects are similar to the results of the readers of horizontally writing texts such as English and Chinese. These results suggest that reading experience may not be the main cause of the horizontal-vertical asymmetry of the visual crowding effect.
In summary, the results of Study 1 clearly showed that the perceptual span in Mongolian reading is asymmetry toward the reading direction. consistent with the prediction of the attention-based hypothesis Interestingly, of perceptual span asymmetry, the results of the current study showed that more attention is deployed within the perceptual span than outside perceptual span. These results provide direct evidence to the attention-biased hypothesis. In contrast, the results of Study 2 showed that reading direction does not affect the horizontal-vertical asymmetry of another visual processing phenomenon such as crowding. The results of the present studies are important to understand how reading direction affects visual perception during reading and other visual processing tasks. These findings from Mongolian, a rare and special script that is written from top to bottom, will contribute to our understanding of the general and script-specific mechanisms of reading in different writing systems.
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