Numerosity tuning in human association cortices and local image contrast representations in early visual cortex

• Published in: Nature communications Vol. 13; no. 1; pp. 1340 - 15
• Main Authors: Paul, Jacob M., van Ackooij, Martijn, ten Cate, Tuomas C., Harvey, Ben M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 15.03.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 59/36; 631/378/2613/2614; 631/378/2649; Brain Mapping - methods; Cognition; Cognitive ability; Frequency analysis; Frequency dependence; Frequency domain analysis; Functional magnetic resonance imaging; Humanities and Social Sciences; Humans; Image contrast; Information processing; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; multidisciplinary; Neural networks; Occipital Lobe; Photic Stimulation; Representations; Retina; Science; Science (multidisciplinary); Spatial analysis; Spatial distribution; Visual cortex; Visual Cortex - diagnostic imaging; Visual Cortex - physiology; Visual Perception - physiology; Visual stimuli
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-29030-z

Human early visual cortex response amplitudes monotonically increase with numerosity (object number), regardless of object size and spacing. However, numerosity is typically considered a high-level visual or cognitive feature, while early visual responses follow image contrast in the spatial frequency domain. We find that, at fixed contrast, aggregate Fourier power (at all orientations and spatial frequencies) follows numerosity closely but nonlinearly with little effect of object size, spacing or shape. This would allow straightforward numerosity estimation from spatial frequency domain image representations. Using 7T fMRI, we show monotonic responses originate in primary visual cortex (V1) at the stimulus’s retinotopic location. Responses here and in neural network models follow aggregate Fourier power more closely than numerosity. Truly numerosity tuned responses emerge after lateral occipital cortex and are independent of retinotopic location. We propose numerosity’s straightforward perception and neural responses may result from the pervasive spatial frequency analyses of early visual processing. The authors show that spatial frequency domain Fourier power closely but nonlinearly follows numerosity, simplifying computing numerosity from early visual responses. Monotonic early visual cortex and neural network responses follow Fourier power, while later tuned responses follow numerosity.