Christian Windischberger¹, David Linhardt¹, Siddharth Mittal¹, Michael Woletz¹; ¹High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna

Population receptive field (pRF) modelling quantifies the organizational properties of visual cortex areas by mapping locations in the visual field to corresponding regions in the cortex. While this method is powerful and reproducible (Linhardt et al, 2022), measurement parameters and analysis choices can significantly influence the results. One crucial factor is the choice of visual stimulus. Our laboratory has developed a fast pRF analysis framework that enables parallel simulation of thousands of artificial time courses (Mittal et al. 2024). Using this framework, we simulated the variability of two commonly used stimuli (moving bar and wedge/ring) and compared them to experimental results (Linhardt et al. 2021). We simulated ground-truth positions distributed across the visual field and generated noisy time-courses using Gaussian white noise. For each position, we obtained pRF parameters (x, y, sigma) and analyzed their distributions. To evaluate parameter estimation accuracy, we calculated root-mean-square errors across different locations in the visual field. Error distributions revealed systematic patterns across the visual field. Both stimulus variants showed lower errors near the fovea and increased errors toward stimulus boundaries, an effect attributable to reduced encoding power when pRFs extend beyond the stimulus edge. The bar stimulus produced higher eccentricity errors in peripheral regions compared to the wedge/ring, while the latter showed higher errors in central regions. Interestingly, pRF size parameter errors followed an opposite trend, with the wedge stimulus showing higher peripheral errors and the bar stimulus showing higher central errors. These patterns suggest that each stimulus type has distinct advantages for different regions of the visual field. These simulation results provide an objective method for comparing visual stimulation paradigms in pRF mapping by quantifying parameter variability across the visual field. This approach offers valuable insights for optimizing experimental design in visual neuroscience research and understanding the inherent limitations of different stimulus configurations.

Acknowledgements: This research was funded in whole or in part by the Austrian Science Fund (FWF) [https://www.doi.org/10.55776/P35583]