Do readers use character information when programming return-sweep saccades?

TL;DR

This study investigates whether readers use character size information when programming return-saccades across lines, finding that font size influences saccade landing positions regardless of visual acuity, indicating reliance on global text properties.

Contribution

It demonstrates that font size affects return-sweep saccades independently of visual acuity, highlighting the role of global typographic cues in eye movement control during reading.

Findings

Larger font size leads to further right saccade landings.

Return-sweeps are guided by font size regardless of line length.

Saccadic undershoot increases with larger saccades, unaffected by font size.

Abstract

Reading saccades that occur within a single line of text are guided by the size of letters. However, readers occasionally need to make longer saccades (known as return-sweeps) that take their eyes from the end of one line of text to the beginning of the next. In this study, we tested whether return-sweep saccades are also guided by font size information and whether this guidance depends on visual acuity of the return-sweep target area. To do this, we manipulated the font size of letters (0.29 vs 0.39 deg. per character) and the length of the first line of text (16 vs 26 deg.). The larger font resulted in return-sweeps that landed further to the right of the line start and in a reduction of under-sweeps compared to the smaller font. This suggests that font size information is used when programming return-sweeps. Return-sweeps in the longer line condition landed further to the right of the line start and the proportion of under-sweeps increased compared to the short line condition. This likely reflects an increase in saccadic undershoot error with the increase in intended saccade size. Critically, there was no interaction between font size and line length. This suggests that when programming return-sweeps, the use of font size information does not depend on visual acuity at the saccade target. Instead, it appears that readers rely on global typographic properties of the text in order to maintain an optimal number of characters to the left of their first fixation on a new line.