Our ability to process movement and perform tasks such as differentiating left from right is a fundamental skill necessary to life. Surprisingly, this ability is not innate. Instead, our ability to detect and respond to moving objects—known as direction selectivity—is a learned response shaped by our early visual experiences.

Through his research, Dr. Leonard White seeks to understand how we develop the ability to process movement and direction. At Duke, Dr. White serves as the Associate Director of the Duke Institute for Brain Sciences and holds faculty appointments as an Associate Professor in Neurobiology, Neuroscience, and Psychology. His work aims to answer a fundamental question: is experience permissive or instructive? This question explores whether experiences simply create opportunities for development or whether they actively inform or direct developmental processes.

Above: Dr. Leonard White. Image courtesy of Duke Bass Connections.

Direction selectivity refers to the phenomenon in which cortical neurons in the visual cortex that are responsible for processing visual information respond more strongly to motion in one direction versus another. This property of neurons helps us track moving objects and is critical for navigating our very active environments. 

The visual cortex is like a complex network of roads, where each road represents a neuron, and the traffic flowing on them symbolizes neural activity triggered by visual stimuli. Imagine that these roads are poorly constructed and very few traffic lights exist to direct vehicles quickly and efficiently. This scenario describes the state of the visual cortex in a visually naive animal—one that has little to no visual experience. At this early stage, it is difficult for the brain to process motion because neurons respond weakly and inconsistently. But as we build better roads and insert more efficient traffic lights (through increased visual experience), the flow of traffic (the brain’s ability to process motion) begins to improve.

Dr. White’s research explores this analogy by studying how exposure to visual movement shapes brain function in naive ferrets and assessment of brain function, using two advanced imaging techniques: intrinsic signal imaging and 2-photon calcium imaging. Intrinsic signal imaging observes changes in the optical properties of the brain as different regions become active. By measuring the balance of deoxygenated and oxygenated hemoglobin, this imaging technique assesses how much light is absorbed by a column of brain tissue when activated. 2-photon imaging involves injecting calcium dye into brain cells to observe the intensity of fluorescence. This fluorescence will indicate neural activity in the brain. Together, these techniques revealed that when ferrets were exposed to moving stimuli, their brains formed “direction” columns, clusters of neurons specialized for processing motion.

This research has implications for developing better modes of care for visual rehabilitation. For example, by understanding how “direction” columns develop, researchers can help improve orientation and mobility training for individuals with visual impairments.

Overall, the results suggest that early exposure to movement is essential for visual development. Limited exposure to movement during childhood—whether due to developmental issues or visual impairments—could impact one’s ability to develop normal motion-processing abilities. Dr. White’s research provides profound insights into the complex mechanisms of motion perception, paving the way for better care and rehabilitation strategies in the future.

Above: Visual circuitry in the brain. Image courtesy of Ophthalmology Training.