Do hatchmarks affect the use of the benchmark strategy in number line estimation tasks with fractions? An eyetracking study

Abstract The number line is frequently used to represent number magnitudes, including fractions. Visual hatchmarks can enhance performance in number line estimation tasks, but their effectiveness may depend on specific item features. It remains unclear how hatchmarks influence individuals’ use of the benchmark strategy, in which reference points are used for orientation. This study addresses this gap using eye tracking. We recorded 63 adults’ eye movements while they solved fraction number line estimation tasks on a computer. Line segments were marked with 0 and 1 at the endpoints and were presented in three hatchmark conditions: no hatchmarks, third hatchmarks (at 1/3 and 2/3), and quarter hatchmarks. Participants were asked to find the correct position of a symbolic fraction shown above the line. Measures of accuracy, reaction time, and fixation duration suggest that participants used mental benchmarks regardless of whether the number line included visual hatchmarks. When hatchmarks were available, participants looked at them and were, overall, more accurate than without hatchmarks. The beneficial effect of hatchmarks was more pronounced when hatchmarks corresponded to fraction denominators (e.g., 5/9 in the third-hatchmark condition) compared to when they did not (e.g., 5/9 in the quarter-hatchmark condition). However, hatchmarks led to longer reaction times, especially when they did not correspond to fraction denominators. This study provides a nuanced picture of the effects of hatchmarks on number line estimation. Hatchmarks can increase accuracy but can also make participants less efficient. In instruction, support measures such as hatchmarks should be carefully selected to achieve the intended effects.