Numerosity adaptation partly depends on the allocation of implicit numerosity-contingent visuo-spatial attention

Grasso, Paolo A.; Anobile, Giovanni; Arrighi, Roberto · 2021 · Crossref

DOI: 10.1167/jov.21.1.12

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Summary

This study investigates whether numerosity adaptation—the perceptual underestimation or overestimation of item counts following prolonged exposure—is purely perceptual or influenced by visuo-spatial attention. While numerosity adaptation is well-documented, its underlying mechanisms remain debated, with some evidence suggesting it relies on low-level texture processing and others indicating a dedicated numerical system. The authors hypothesize that automatic, implicit allocation of attentional resources during adaptation may significantly shape the magnitude of the aftereffect. To test this, they conducted three experiments manipulating the spatial distribution of numerical and non-numerical stimuli during adaptation periods. In Experiment 1, participants underwent adaptation with either a single adaptor presented unilaterally or two adaptors presented bilaterally, where the second adaptor was "neutral" (matched in numerosity to the subsequent reference stimulus). Results showed that the magnitude of numerosity adaptation was significantly reduced in the double-adaptor condition compared to the single-adaptor condition. This reduction occurred despite the neutral adaptor being theoretically incapable of inducing perceptual adaptation, suggesting that the presence of a second numerical stimulus diverted attentional resources away from the adapting location. Experiment 2 replicated this design but replaced the neutral numerical adaptor with non-numerical bars of equivalent aggregate area. The reduction in adaptation magnitude disappeared in this condition, indicating that the attentional effect observed in Experiment 1 was specific to numerosity-contingent attentional capture rather than general spatial attention or low-level visual features. Experiment 3 examined the role of exogenous visuo-spatial cues by briefly flashing rings around the test, reference, or both stimuli after the adaptor offset. The results demonstrated that these uninformative cues significantly shifted numerosity discrimination judgments at both baseline and during adaptation. However, the cues did not differentially modulate the magnitude of the adaptation effect itself, suggesting that while attention influences baseline perception, the specific reduction in adaptation seen in Experiment 1 stems from attentional allocation during the adaptation period rather than post-adaptation cueing. The findings collectively indicate that numerosity adaptation is not solely a perceptual phenomenon but is partly dependent on the implicit allocation of visuo-spatial attention tuned to numerical information. The study concludes that the magnitude of the adaptation aftereffect is shaped by how attentional resources are distributed among numerical stimuli in the visual field. This challenges the view of numerosity adaptation as a purely low-level perceptual process, highlighting the integral role of cognitive attentional mechanisms in numerical perception.

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• multisensory crossmodal