Contextual Coherence Increases Perceived Numerosity Independent of Semantic Content

Number perception emerges from multiple stages of visual processing. Understanding how systematic biases in number perception occur within a hierarchy of increasingly complex feature representations helps uncover the multistage processing underlying our visual number sense. Recent work demonstrated that reducing coherence of low-level visual attributes, such as color and orientation, systematically reduces perceived number. Here, we ask when in the visual processing hierarchy coherence affects numerosity perception and specifically whether the coherence effect is exclusive to low-level visual features or instead whether it can be driven by contextual or semantic relationships. We tested adults in an ordinal numerical comparison task with contextual coherence mathematically manipulated using a statistical model of visual object co-occurrence. Across several experiments, we found that arrays with high contextual coherence were perceived as numerically larger than arrays with low contextual coherence. This contextual coherence effect was not attenuated even when we reduced objects to texforms (unrecognizable images that preserve midlevel visual features) or removed semantic content from the images through box scrambling and diffeomorphic warping. Together, these results suggest that visual coherence derived from natural statistics of object co-occurrence systematically alters perceived numerosity at low-level visual processing, even before later stages at which items can be explicitly categorized and identified. Public Significance Statement While humans possess a number sense that allows the perception of abstract number, perceived number can be systematically biased by irrelevant features. In the previously described coherence illusion, arrays of items that are similar to each other in color or line orientation, are perceived as more numerous than arrays of items that are heterogeneous. In this series of studies, we explore whether abstract features such as semantic relatedness can drive the coherence illusion. We demonstrate that the coherence effect emerges via low level visual processing stages that are independent of categorical or semantic information.