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The left digit effect in an unbounded number line task.

Kelsey Kayton¹, Greg Fischer¹, Hilary Barth¹

¹Department of Psychology, Wesleyan University, 207 High Street, Middletown, CT, 06459, USA.

Psychonomic Bulletin & Review

|March 26, 2024

Summary

The left digit effect, where numbers like 19 and 22 seem farther apart than they are, persists in unbounded number line tasks. This suggests the effect isn't solely due to specific task strategies.

Keywords:

Left digit effect Number line estimation Numerical cognition

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Area of Science:

Cognitive Psychology
Numerical Cognition

Background:

The left digit effect describes the overestimation of distance between numbers with different leading digits (e.g., 19 vs. 22).
Previous research primarily utilized bounded number line tasks to study this phenomenon.

Purpose of the Study:

To investigate the presence and robustness of the left digit effect in an unbounded number line task.
To determine if the effect is dependent on task-specific strategies employed in bounded number line tasks.

Main Methods:

A preregistered study involving 58 college students.
Participants completed an unbounded number line task with target numerals between 0 and 100 across multiple blocks.
Data collection focused on numeral estimation accuracy and response patterns.

Main Results:

A statistically reliable medium-sized left digit effect was observed (d = 0.70).
The findings indicate the left digit effect is not exclusive to bounded number line tasks.
Evidence suggests the effect is independent of strategies unique to bounded line estimation.

Conclusions:

The left digit effect is a reliable phenomenon in unbounded number line estimation.
This challenges the notion that the effect is solely an artifact of bounded number line tasks.
Further research is needed to explore alternative explanations, such as symbol-to-magnitude conversion processes.