Coates, D. R. | Search bioRxiv

bioRxiv2024

Characteristics of spatial summation in the magnocellular, parvocellular, and koniocellular pathways

In this study, we characterize the spatial summation properties of targeted magnocellular, parvocellular, and koniocellular pathways within the central 20{degrees} of visual field using chromatic transformations in DKL color space. For the magnocellular and koniocellular conditions, critical areas of complete spatial summation were found for all eccentricities. For the parvocellular conditions, complete spatial summation was absent within the stimulus size ranges tested. We also describe an anatomically and physiologically motivated model of receptive field pooling using probability summation. Model simulations suggest that the critical area of summation can be explained by the dendritic field size of underlying retinal ganglion cells, corroborating our psychophysical data.

neuroscience↗

bioRxiv2024

Cortical Dynamics during Contour Integration

Integrating visual elements into contours is important for object recognition. Previous studies emphasized the role that the primary visual cortex (V1) plays in this process. However, recent evidence suggests that contour integration relies on the coordination of hierarchical substrates of cortical regions through recurrent connections. Many previous studies presented the contour at the same onset-time as the trial, which caused the subsequent neural imaging data to incorporate both visual evocation and contour integration activities, and thus confounding the two. In this study, we varied both the contour onset-time and contour fidelity and used EEG to examine the cortical activities under these conditions. Our results suggest that the temporal N300 represents the grouping and integration of visual elements into contours. Before this signature, we observed interhemispheric connections between lateral frontal and posterior parietal regions that were contingent on the contour location and peaked at around 150ms after contour appearance. Also, the magnitudes of connections between medial frontal and superior parietal regions were dependent on the timing of contour onset and peaked at around 250ms after contour onset. These activities appear to be related to the bottom-up and top-down attentional processing during contour integration, respectively, and shed light on how these processes cooperate dynamically during contour integration.

neuroscience↗