Vertical scanning biases and their possible influence on reading direction: celtic wisdom or folly?

The reason people read from top to bottom is unknown, but could be related to brain-mediated directional biases or environmental factors. To learn if there is a brain-mediated directional bias responsible for top-down reading direction, we evaluated the directional scanning in the vertical dimension by using directional letter and face cancellation tasks. Twenty participants were instructed to cancel either target letters or faces using either an up-down or down-up direction, with the stimuli located in left, right, and center hemispace. The results indicated significant differences in completion time between the search direction (up vs. down) and spatial position for the letter cancellation task, with a faster completion time for the bottom-up scan in right space and top-down in left space. Because the left hemisphere primarily attends to contralateral right hemispace our results suggest that, when attending to letter stimuli, the left hemisphere is biased to scan in a proximal to distal (upward) direction. Although the reasons why this is reversed in left hemispace and why we did not see directional biases in the face condition remains unclear, these results do suggest that the direction in which we learn to read is inconsistent with the brain's intrinsic directional bias.