Early Numerosity Encoding in Visual Cortex Is Not Sufficient for the Representation of Numerical Magnitude

Abstract

Recent studies have demonstrated that the numerosity of visually presented dot arrays is represented in low-level visual cortex extremely early in latency. However, whether or not such an early neural signature reflects the perceptual representation of numerosity remains unknown. Alternatively, such a signature may indicate the raw sensory representation of the dot-array stimulus before becoming the perceived representation of numerosity. Here, we addressed this question by using the connectedness illusion, whereby arrays with pairwise connected dots are perceived to be less numerous compared with arrays containing isolated dots. Using EEG and fMRI in two independent experiments, we measured neural responses to dot-array stimuli comprising 16 or 32 dots, either isolated or pairwise connected. The effect of connectedness, which reflects the segmentation of the visual stimulus into perceptual units, was observed in the neural activity after 150 msec post stimulus onset in the EEG experiment and in area V3 in the fMRI experiment using a multivariate pattern analysis. In contrast, earlier neural activity before 100 msec and in area V2 was strictly modulated by numerosity regardless of connectedness, suggesting that this early activity reflects the sensory representation of a dot array before perceptual segmentation. Our findings thus demonstrate that the neural representation for numerosity in early visual cortex is not sufficient for visual number perception and suggest that the perceptual encoding of numerosity occurs at or after the segmentation process that takes place later in area V3.

Challenging the neurobiological link between number sense and symbolic numerical abilities

“…Behavioral evidence comparing monoptic versus dichoptic presentation of numerical stimuli even suggests that numerical information is processed in subcortical structures, before the integration of visual information from both eyes occurs . Still, even if numerical information is processed in early visual areas, debate remains about where in the processing hierarchy perception of number emerges . Frequently, the methods used to demonstrate number processing in the parietal lobe have also been used to show number‐related processing in other parts of the brain.…”

“…105 Still, even if numerical information is processed in early visual areas, debate remains about where in the processing hierarchy perception of number emerges. 106,107 Frequently, the methods used to demonstrate number processing in the parietal lobe have also been used to show number-related processing in other parts of the brain. For example, when the same method used to identify number-sensitive topographic maps in the superior parietal lobe, receptive field mapping, was applied across much of the rest of the brain, a widespread network of regions showed sensitivity to number (Fig.…”

Similarly oriented objects appear more numerous

“…Connectedness affects numerosity representations in extrastriate cortical areas and operates on signals associated with perceived numerosity rather than lower level representations in primary visual cortex. For example, connectedness affects numerosity adaptation and is detectable in neural responses to stimulus arrays after 150 ms in visual area V3, but not in lower cortical areas (Fornaciai, Cicchini, & Burr, 2016;Fornaciai & Park, 2018). Connectedness and grouping of objects also affects numerosity signals in the intraparietal areas (He, Zhou, Zhou, He, & Chen, 2015).…”

Serial dependence in numerosity perception

“…Numerosity represents one of the fundamental attributes of the external environment, and it has been shown to be underpinned by largely dedicated processing mechanisms (e.g., Anobile, Cicchini, & Burr, 2016 ; Cicchini, Anobile, & Burr, 2016 ; Burr, Anobile, & Arrighi, 2017 ), generalized across different sensory modalities (Arrighi, Togoli, & Burr, 2014 ) and between perceptual and motor systems (Anobile, Arrighi, Togoli, & Burr, 2016 ). Recent studies further highlight the visual processing pathway subserving numerosity perception, showing that numerical information is represented at multiple levels in the visual hierarchy, starting from very early visual areas such as V2 or V3 (Roggeman, Santens, Fias, & Verguts, 2011 ; Park, Dewind, Woldorff, & Brannon, 2016 ; Fornaciai, Brannon, Woldorff, & Park, 2017 ; Fornaciai & Park, 2018b ; Harvey & Dumoulin, 2017 ;), and likely interacting with multiple perceptual systems (Fornaciai & Park, 2017 ). In a previous work by our group (Fornaciai & Park, 2018 a), we reported a neural signature of attractive serial dependence emerging early in the visual stream, and even in an almost completely passive-viewing paradigm.…”