二次元手動ポインティングにおける左端数字バイアス

The left-digit bias (LDB) is a tendency to estimate differences between numbers sharing the same leftmost digit (e.g., 47 and 49) as smaller than between numbers with different leftmost digits (e.g., 49 and 51) in nonspatial evaluations and number-to-position tasks. In the present study, we examined motoric consequences of LDB by measuring angles of spatial-localization responses in circular space as participants localized spoken numbers (1-12.5 in 0.5-unit increments; e.g., "two point five") on a clock-face arrangement. To test the role of visual feedback, the task was performed either with (N = 27) or without vision (N = 23). After correcting for cyclical errors in angular localization, we found that targets sharing the same leftmost digit were indeed placed closer together in angular space than equidistant targets with different leftmost digits, regardless of visual feedback. This LDB manifested as compression of decimal targets toward the lower boundary of their leftmost digit category. Our findings demonstrate the robustness of LDB signatures across task settings, extend them to angular measures, and point to cognitive rather than perceptual origins. They are consistent with the overweighting of leftmost digits during number processing, which asymmetrically compresses representational space toward lower same-digit boundaries. (PsycInfo Database Record (c) 2026 APA, all rights reserved).