Good Vibes Shrink Numbers: Positive Emotions Bias the Brain’s Number Sense

When you are in a good mood, the world may literally look smaller than it is. A new behavioral study published in BMC Psychology by Xingyuan Xue and Yuan Yao of Suzhou University of Science and Technology reports that positive-valence stimuli, whether they arrive as pleasant emotional images or as the promise of monetary reward, systematically bias the human number sense toward underestimation. The finding challenges a long-standing assumption in cognitive psychology: that our ability to rapidly perceive quantities operates as a relatively independent perceptual module, insulated from the emotional and motivational states of the observer.

Number sense, sometimes called the approximate number system, is the capacity to quickly recognize quantities, estimate magnitudes, and infer relationships between numbers without counting each item one by one. It is what allows you to glance at a parking lot and roughly gauge how many cars are present, or to compare two crowds at a party without tallying heads. Because this ability emerges early in development, is shared with many animal species, and functions quickly and automatically, researchers have traditionally treated it as a foundational perceptual attribute that sits largely outside the reach of top-down cognitive processing, such as attention, expectation, and mood.

Xue and Yao set out to test whether that independence survives contact with positive valence. Their reasoning drew on a well-documented feature of positive affect: pleasant emotional states and rewarding outcomes tend to enhance both the frequency and the intensity of the actions they reinforce. If positive valence changes how we act, the authors asked, might it also change how we perceive, even at the apparently objective level of judging how many dots are on a screen? To answer this, the researchers ran three behavioral experiments, each built around a numerical comparison task in which participants judged the quantities of dot arrays.

The experimental design was elegantly simple. Participants viewed arrays of dots and compared the numerosity they perceived against a reference. Crucially, some of the dot arrays were constructed from positive-associated stimuli, meaning the individual units carried pleasant emotional associations or were linked to monetary reward, while others were built from neutral stimuli. The two types of arrays were presented randomly across trials, allowing the researchers to isolate the effect of valence from any general difficulty or fatigue effects that might accumulate over the course of the session.

The results were consistent across all three experiments. Both positive emotion and monetary reward elicited a measurable underestimation effect in number sense: when the dot arrays were made of positive-valence units, participants systematically judged the quantities to be smaller than they actually were. The same bias did not appear when the arrays were composed of neutral stimuli, whose numerosity judgments remained comparatively accurate. In other words, it was not that participants became generally worse at estimating quantities when they were in a positive state; rather, the positive valence of the stimuli themselves pulled their perceptual estimates downward in a specific and reproducible way.

This dissociation matters because it rules out several mundane explanations. If positive mood simply made participants careless or less motivated, the error should have appeared across all stimulus types, including neutral ones. Instead, the underestimation was tied to the valence of the material being judged, which points to a perceptual mechanism rather than a general performance decrement. The authors describe this as evidence for a perceptual underestimation bias in number sense associated with positive-valence stimuli, a bias that operates below the level of deliberate judgment and shapes the raw estimate before any conscious decision is made.

To explain the effect, the researchers turn to predictive processing theory, an influential framework in modern neuroscience that recasts perception as a process of prediction rather than passive reception. According to this view, the brain constantly generates hypotheses about the causes of its sensory input and uses incoming signals mainly to correct those hypotheses. Perception, on this account, is a controlled hallucination constrained by data, and the priors, or expectations, that feed the predictive machinery can be shaped by emotion, motivation, and reward. Positive-valence stimuli, the theory suggests, may activate priors associated with abundance, safety, or reward, and those priors could tilt the interpretation of ambiguous perceptual evidence toward smaller quantities.

The predictive processing account also helps explain why the bias is directional rather than random. Under this framework, affective states are not noise injected into perception; they are signals that adjust the weighting of evidence and the precision assigned to prediction errors. A rewarding or pleasant stimulus may lead the brain to allocate processing resources differently, effectively changing the gain of the neural populations that encode numerosity. If positive valence reduces the effective resolution or salience of the quantity signal, the perceptual system would settle on a lower estimate, producing exactly the kind of systematic underestimation that Xue and Yao observed in their dot-comparison tasks.

The study’s implications extend beyond the laboratory bench. Numerical estimation underlies a surprising range of everyday and high-stakes judgments, from assessing crowd sizes and inventory quantities to evaluating financial figures and risk statistics. If positive emotional contexts and reward cues reliably shrink our sense of quantity, then environments saturated with pleasant imagery or monetary incentives, such as advertising, gambling interfaces, and marketing displays, may be quietly distorting the numerical judgments people make within them. A shopper estimating how many items constitute a good deal, or an investor gauging figures presented alongside rewarding imagery, could be operating with a systematically biased perceptual baseline without any awareness of the distortion.

As with any behavioral study, the findings invite further questions. The experiments demonstrate the bias for dot-array comparison, and future work will need to determine how far it generalizes to other magnitude domains, such as time, size, and distance, which are known to share neural resources with numerosity. It also remains to be tested whether negative-valence stimuli produce a compensating overestimation, which would clarify whether the effect reflects a general valence-driven scaling of magnitude or a specific property of positive affect. What is already clear, however, is that the number sense is not the emotion-proof perceptual module it was long assumed to be. The study, funded by the Social Science Foundation of Jiangsu Province and approved by the ethics committee of Suzhou University of Science and Technology, adds a striking data point to a growing body of research showing that even our most basic perceptions are colored, and in this case literally diminished, by the emotional value of what we perceive. The next time a pleasant scene makes a crowd look sparse, it may not be your eyes that are deceived, but the ancient quantity sense quietly bending to your good mood.

Subject of Research: The influence of positive-valence stimuli on the approximate number system and numerical estimation bias

Article Title: The underestimation bias of the number sense in positive-valence stimuli

Article References: Xue, X., & Yao, Y. (2026). The underestimation bias of the number sense in positive-valence stimuli. BMC Psychology. https://doi.org/10.1186/s40359-026-05747-0

Image Credits: AI Generated

DOI: 10.1186/s40359-026-05747-0

Keywords: number sense, numerical cognition, approximate number system, positive emotion, monetary reward, predictive processing theory, perception, underestimation bias, valence, cognitive psychology, visual perception, BMC Psychology