Abstract
Number line estimation (NLE) tasks are widely employed in research and pedagogical contexts. For both children and adults, leftmost digits disproportionately influence number line placements—a phenomenon known as a left digit effect or left digit bias. Here, we ask whether left digit bias is limited to literal leftmost digits. In Study 1, adults completed a standard 0 to 1000 number line task and a leading zero version in which target numerals began with leftmost zeros (e.g., 0398). Study 2 used the leading zero task (placing numbers like 0398 on a range up to 1000) and a leading one-zero task (placing numbers like 10398 on a 10000–11000 number line). A robust “left digit” bias was observed for the hundreds digits in all cases, showing that left digit effects are deeply context-dependent. Task conditions can lead to strong left-digit-like biases for digits that are not the literal leftmost digits in the target numerals.
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