Synchronization of visual perception within the human fovea.

The human brain constructs a model of the world by processing sensory signals with distinct temporal characteristics that may differ in generation and transmission speed within a single sensory modality. To perceive simultaneous events as occurring at the same time, the brain must synchronize this sensory information, yet the mechanisms underlying such synchronization remain unclear. By combining human neural recordings, behavioral measurements and modeling, we show that in the human visual system, this process begins in the fovea centralis, the retinal region used for reading and recognizing faces. Reaction times to foveal single-cone photostimulation were similar across the central visual field, although visual information from neighboring foveal cones travels along axons of highly different lengths. From direct measurements of action potential propagation speeds, axon diameters and lengths in the human fovea centralis, we found that longer foveal axons have larger diameters and increased propagation speeds. We conclude that the human brain orchestrates axonal conduction speeds of unmyelinated axons in the retina to synchronize the arrival times of sensory signals. These results suggest a previously unknown mechanism by which the human brain synchronizes perception.