Summary: New research reveals that numbers in our visual field can subtly distort the way we judge spatial positions, demonstrating that perception is determined by both numerical magnitude and object-based processing. In traditional line bisection tasks, smaller numbers shifted the perceived centers to the left, supporting the idea of a mental number line.
But when shapes became more complex, such as squares, the number effect disappeared, replaced by strong bottom-up biases linked to object recognition systems in the brain. These findings show that spatial-numerical association interacts with deeper visual pathways rather than acting alone. The work offers new insight into how the brain integrates symbolic and spatial information.
Key facts
The size of the numbers altered perception: smaller numbers shifted the centers of the perceived lines to the left, while larger numbers shifted them to the right or down depending on orientation. The 2D shapes break the pattern: in squares, the magnitude effects disappeared and an object-driven upward bias emerged in their place. Master object-based processing: Visual recognition pathways can override numerical magnitude cues, reshaping spatial attention.
Source: Tokyo Metropolitan University
Researchers at Tokyo Metropolitan University have studied the relationship between numerical information in our vision and how it affects our perception of space.
Volunteers were asked to identify the center of lines and squares filled with numbers; how far they were from the true center revealed unexpected biases.
Crucially, his work with squares showed how our perception of space is a complex interplay between “object-based” processing and our processing of numerical information.
The numbers in our vision can affect the way we see the world in unexpected ways. Known as spatial-numerical association, the way our brain processes numbers can introduce “attentional biases.”
For example, for people from a left-to-right writing culture, a simple game in which players press one of two lower-numbered buttons reveals a faster response when the lower number is to the left; The opposite occurs when larger numbers are used.
Sometimes the information doesn’t need to be numbers, but rather something that indicates magnitude, such as a brighter light or a louder noise. In fact, similar trends have been observed in animals and insects.
This suggests that a “mental number line,” some left-to-right mapping of magnitude-related information in space, might be a deeply rooted feature in nature. Understanding how these biases work is crucial not only to get a better idea of how our brain works, but also to optimize how information is presented in the real world.
A team of researchers at Tokyo Metropolitan University led by Professor Masami Ishihara and PhD student Ryo Hishiya have been using “bisection tasks” to investigate spatial-numerical association. Standard bisection tasks ask volunteers to estimate the center of a line or bar.
When painting the bar with smaller numbers, they found that volunteers consistently put the center further to the left than with larger numbers. This confirms the left-to-right “mental number line” found in previous work.
However, when they tried the same exercise with vertical bars, the volunteers lowered the score for larger numbers, contrary to the “bottom-up” association expected from previous work. There’s clearly more at play than just the mental number line.
In a new approach, the team proceeded to repeat the experiment with squares, that is, two-dimensional shapes. Interestingly, they found that the effect of number magnitude disappeared.
Instead, the presence of figures was enough to induce a strong upward bias and a weak leftward bias; the absence of numbers led to a stronger bias in the horizontal direction, probably due to pseudoneglect, a known natural bias in attention to the left.
The team proposes that this vertical bias reflects the impact of the ventral visual stream, the part of our brain that tries to recognize objects (in this case, numerical strings) that also tends to drive attention upward. In this case, “object-based” processing seems to show a dominant effect on our processing of the value of numbers.
While future work remains, the team’s experiments offer new insight into the subtle asymmetries that color our view of the world.
Key questions answered:
A: The perceived centers of the lines change depending on the numerical magnitude, reflecting an internal mental number line.
A: Object-based processing took over, producing strong vertical biases that dominated the numerical effects.
A: The brain integrates symbolic numbers with structural streams of object processing, meaning that spatial perception is determined by multiple interacting systems.
Editorial notes:
This article was edited by a Neuroscience News editor. Magazine article reviewed in its entirety. Additional context added by our staff.
About this vision and perception research news.
Author: GO TOTSUKAWA
Source: Tokyo Metropolitan University
Contact: GO TOTSUKAWA – Tokyo Metropolitan University
Image: Image is credited to Neuroscience News.
Original research: Open access.
“Numerically induced attention biases in horizontal, vertical, and two-dimensional ways” by Masami Ishihara et al. Scientific Reports
Abstract
Numerically induced attentional biases in horizontal, vertical, and two-dimensional ways.
Previous studies have shown that numerical magnitudes can induce attentional biases primarily in horizontal space.
The present study aimed to clarify the spatial-numerical association in horizontal, vertical, and two-dimensional square stimuli composed of visually aligned strings of relatively smaller Arabic numerals (i.e., 1 or 2) or larger numbers (i.e., 8 or 9).
Neurologically and psychiatrically healthy participants, all Japanese speakers, were asked to identify the veridical center of the stimuli.
Results indicated that, with horizontal stimuli, participants placed their subjective midpoint further to the left when smaller numbers were presented compared to larger numbers, in accordance with the predicted left-to-right mental number line.
However, with vertical stimuli, smaller numbers induced upward biases, which is inconsistent with the intended bottom-up representation.
For the square, stimuli with number strings elicited biases with a stronger vertical component, whereas stimuli without number strings elicited biases with a stronger horizontal component.
The upward biases of square stimuli with number strings may reflect the activation of object-based processing rather than the cognitive function of number processing.
These findings suggest that different mechanisms may predominate over spatial-numerical associations with respect to biases in the two-dimensional plane.
