The perceptual span in Tibetan reading

Tibetan script differs from other alphabetic writing systems in that word forms can be composed of horizontally and vertically arrayed characters. To examine information extraction during the reading of this script, eye movements of native readers were recorded and used to control the size of a window of legible text that moved in synchrony with the eyes. Letters outside the window were masked, and no viewing constraints were imposed in a control condition. Comparisons of window conditions with the control condition showed that reading speed and oculomotor activity matched the control condition, when windows revealed three letters to the left and seven to eight letters to the right of a fixated letter location. Cross-script comparisons indicate that this perceptual span is smaller than for English and larger than for Chinese script. We suggest that the information density of a writing system influences the perceptual span during reading.