Prevalence of multiple subtypes of binocularly-modulated visual neurons in the mouse superior colliculus

A central role of the visual system is to integrate inputs from both eyes to form one coherent visual perception. The superior colliculus (SC) plays a central role in visual processing, gaze orientation and vergence eye movements necessary for binocular vision. Indeed, the SC receives direct inputs from both the contralateral and ipsilateral eye and binocularly-modulated neurons have been identified in the SC of multiple species. However, evidence for binocular processing in rodents, particularly mice, has not been functionally confirmed. In this study we recorded visually-evoked activity in the mouse SC while presenting visual stimuli to each eye individually or both together and reveal a surprising diversity of binocularly-modulated responses. Strikingly, we found that ~2/3 of all identified neurons in the anteromedial SC were binocularly-modulated. Furthermore, we identified four binocular subtypes based on their differential responses under varying ocularities of stimulus presentation. Interestingly, we found both orientation- and direction- selective (OS and DS, respectively) neurons in all four binocular subtypes. And, tuning properties of binocular neurons were distinct from neighboring monocular neurons, exhibiting more linear spatial summation. Together, these data suggest that binocular neurons are prevalent in the anteromedial SC of the mouse. Additionally, the distinct tuning properties of binocular neurons suggest a previously unappreciated complexity of visual processing in the SC, which may contribute to binocular perception.

Perception of 3D Symmetrical and Nearly Symmetrical Shapes

The human visual system uses priors to convert an ill-posed inverse problem of 3D shape recovery into a well-posed one. In previous studies, we have demonstrated the use of priors like symmetry, compactness and minimal surface in the perception of 3D symmetric shapes. We also showed that binocular perception of symmetric shapes can be well modeled by the above-mentioned priors and binocular depth order information. In this study, which used a shape-matching task, we show that these priors can also be used to model perception of near-symmetrical shapes. Our near-symmetrical shapes are asymmetrical shapes obtained from affine distortions of symmetrical shapes. We found that the perception of symmetrical shapes is closer to veridical than the perception of asymmetrical shapes is. We introduce a metric to measure asymmetry of abstract polyhedral shapes, and a similar metric to measure shape dissimilarity between two polyhedral shapes. We report some key observations obtained by analyzing the data from the experiment. A website was developed with all the shapes used in the experiment, along with the shapes recovered by the subject and the shapes recovered by the model. This website provides a qualitative analysis of the effectiveness of the model and also helps demonstrate the goodness of the shape metric.