Summary: New research from Tokyo Metropolitan University shows that numbers displayed in our visual field can subtly bias how we judge spatial positions. In classic line-bisection tasks, small numbers shift perceived centers leftward while large numbers shift them rightward, consistent with the idea of a left-to-right mental number line. However, when the same numerical information appears inside two-dimensional shapes such as squares, that numerical effect disappears and is replaced by a prominent upward bias linked to object-recognition processes. The findings reveal that spatial-numerical associations interact with deeper visual pathways, demonstrating that perception integrates symbolic magnitude and object-based processing.
Researchers asked volunteers to mark the perceived midpoint of lines, vertical bars and squares filled with strings of Arabic numerals. The deviations from the veridical centers exposed subtle, systematic biases. Results indicate that numerical magnitude alone is not the only driver of spatial attention: the brain’s object-processing streams can dominate and reshape spatial perception.
Key Facts
- Number magnitude shifts perceived center: Small numbers moved perceived horizontal midpoints leftward; larger numbers produced opposite shifts depending on orientation.
- Two-dimensional shapes alter the effect: When numbers were embedded in squares, magnitude-driven biases disappeared and a strong upward bias emerged.
- Object-based processing can dominate: Visual recognition mechanisms (ventral stream) appear to override numerical magnitude signals and redirect attention, especially in 2D object contexts.
Source: Tokyo Metropolitan University
Overview of the study
A research team led by Professor Masami Ishihara, with doctoral student Ryo Hishiya, used perceptual bisection tasks to examine how numbers influence spatial attention. Participants, all neurologically and psychiatrically healthy Japanese speakers, were asked to identify the subjective center of horizontally or vertically oriented bars and of square shapes composed of aligned numeral strings. The numerals used were either relatively small (1 or 2) or large (8 or 9).
In horizontal stimuli, participants placed their subjective midpoint farther to the left when smaller numerals were present compared with larger numerals—behavior consistent with the long-documented left-to-right “mental number line.” For vertical bars, however, larger numbers shifted responses downward and smaller numbers produced upward shifts, a pattern not aligned with a simple bottom-to-top mental magnitude representation.
When the researchers tested two-dimensional square stimuli, the pattern changed more dramatically. Numerical magnitude effects essentially vanished within squares. Instead, squares containing numeral strings elicited a pronounced upward bias and a weaker leftward bias. Squares without numbers exhibited a stronger horizontal (leftward) bias, likely reflecting the well-known phenomenon of pseudoneglect—an attentional preference for the left side of space.
The authors interpret the upward bias for number-filled squares as evidence that object-based processing—mediated by the ventral visual stream involved in recognizing shapes and symbolic strings—can dominate over the cognitive mapping of magnitude onto space. In other words, recognizing the numerals as object-like entities appears to redirect attention upward, overpowering the spatial influence of numerical magnitude.
Key Questions Answered:
A: Numbers shift perceived midpoints of stimuli according to their magnitude: smaller numbers bias judgments leftward in horizontal displays and influence vertical placement in oriented stimuli, reflecting an internal mapping between magnitude and space.
A: In two-dimensional shapes, object-based visual processing appears to take precedence, generating a vertical attentional bias that overwhelms magnitude-driven effects.
A: The results suggest multiple interacting mechanisms shape spatial perception: symbolic numerical processing interacts with—and can be overridden by—ventral stream object recognition, so spatial bias depends on stimulus format as well as numerical magnitude.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal article was reviewed in full by editorial staff.
- Additional context and clarification were added by the editorial team.
About this vision and perception research news
Author: GO TOTSUKAWA
Source: Tokyo Metropolitan University
Contact: GO TOTSUKAWA – Tokyo Metropolitan University
Image: The image is credited to Neuroscience News
Original Research: Open access. “Numerically induced attentional biases in horizontal, vertical, and two-dimensional shapes” by Masami Ishihara et al., Scientific Reports. DOI: 10.1038/s41598-025-21167-3
Abstract
Numerically induced attentional biases in horizontal, vertical, and two-dimensional shapes
Previous research has shown that numerical magnitude often induces attentional biases along the horizontal axis. This study compared spatial-numerical associations across horizontal, vertical, and two-dimensional square stimuli made from aligned strings of relatively smaller (1 or 2) or larger (8 or 9) Arabic numerals. Healthy Japanese-speaking participants judged the veridical center of each stimulus.
For horizontal stimuli, participants placed subjective midpoints further left when smaller numbers were present, supporting a left-to-right mental number line. For vertical stimuli, however, smaller numbers produced upward biases—contrary to a simple bottom-to-top magnitude mapping. In square stimuli, the presence of number strings produced a stronger vertical bias, whereas squares without numeral strings showed a stronger horizontal bias. The upward tendency for number-filled squares is consistent with activation of object-based processing rather than purely numerical cognition.
Overall, these findings indicate that different neural mechanisms can predominate over spatial-numerical associations in two-dimensional contexts, highlighting how the brain integrates symbolic magnitude and structural object-processing in shaping spatial attention.