Most diurnal animals are endowed with a visual system that senses and interacts with the complex and dynamic natural environment. Studying visual perception will not only help reveal its underlying mechanisms but also shed light on the constructive nature of the entire neural system.
Here, we focused on motion perception, one of the most ubiquitous visual functions shared across species. We explored how animals sense visual motion using two candidate stimuli, illusory and physical motions, and by applying both psychophysical and physiological methods.
Motion illusion represents the mismatch between perception and reality. Studying the neuronal response to illusions facilitates our understanding of the visual system through another window. In the experiment, we first proved that macaques, like humans, can perceive illusory motions. Later, we recorded single-neuronal responses in macaque MT and MST cortices. We found that neurons in both areas respond to illusions, while MT represents local and MST represents global illusory motions. Most importantly, illusory motion needs an extra time window for signal integration compared to physical motion (Luo et al., 2019 J Neurosci.).
In another project, we explored how the speeds of physical motion are encoded through the hierarchically structured dorsal visual pathway. We recorded V1, MT, and MST neuronal responses to stimuli of various speeds. We found that the tuning function changes dramatically along speed conditions in primary areas (V1) while remaining consistent in higher hierarchical areas (MST). These results demonstrate a reliable representation of moving objects across different speeds in the brain and indicate a nonlinear signal integration through the visual hierarchy.
Additionally, I will make a brief introduction about ongoing projects studying bistable perception occurring in symbolic numerals (Luo et al., in press J Vis.) and optic flow speed mechanisms in humans. Finally, I will provide some future expectations of exploring the interactions between dorsal and ventral visual pathways.