Abstract
The ventral visual pathway is crucially involved in integrating low-level visual features into complex representations for objects and scenes. At an intermediate stage of the ventral visual pathway, V4 plays a crucial role in supporting this transformation. Many V4 neurons are selective for shape segments like curves and corners; however, it remains unclear whether these neurons are organized into clustered functional domains, a structural motif common across other visual cortices. Using two-photon calcium imaging in awake macaques, we confirmed and localized cortical domains selective for curves or corners in V4. Single-cell resolution imaging confirmed that curve- or corner-selective neurons were spatially clustered into such domains. When tested with hexagonal-segment stimuli, we find that stimulus smoothness is the cardinal difference between curve and corner selectivity in V4. Combining cortical population responses with single-neuron analysis, our results reveal that curves and corners are encoded by neurons clustered into functional domains in V4. This functionally specific population architecture bridges the gap between the early and late cortices of the ventral pathway and may serve to facilitate complex object recognition.
Highlights
The visual system faces the daunting task of combining highly ambiguous local patterns of contrast into robust, coherent and spatially extensive complex object representations (Connor et al, 2007; Haxby et al, 1991; Mishkin et al, 1983)
We found neurons with high curve selectivity index (CVSI) or corner selectivity index (CNSI) were spatially clustered (Figure 2A-D), and these neurons were selective to the orientation of the integral curves or corners (Figure 2E-H; 91.6% of the neurons are significantly tuned to the orientation of curves or corners; one-way ANOVA, p < 0.05)
Using two-photon Calcium imaging, we identified cortical patches in macaque V4d selective for curves or corners (Figure 1E-F), with individual curve and corner selective neurons consistently clustered spatially (Figure 3A)
Summary
The visual system faces the daunting task of combining highly ambiguous local patterns of contrast into robust, coherent and spatially extensive complex object representations (Connor et al, 2007; Haxby et al, 1991; Mishkin et al, 1983). Such information is predominantly processed along the ventral visual pathway (areas V1, V2, V4, and Inferotemporal cortex [IT]). Positioned in-between the local orientation architecture of V1 and the global object architecture of IT lies cortical area V4, exhibiting visual selectivity that demonstrates integration of simple-towards-complex information (Pasupathy et al, 2019; Roe et al, 2012; Yue et al, 2014), and extensive anatomical connectivity across the visual hierarchy (Gattass et al, 1990; Ungerleider et al, 2008)
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