We use our sense of vision to see and interact with our environment. Oftentimes, the things we want to interact with are moving (for example when we try to catch a ball) or we ourselves are moving (when walking or driving). It is essential to have accurate information about where things are to interact successfully with them. Despite our nervous system working with relatively slow “hardware”, we excel at these tasks like no artificial system. It is not entirely understood how our brains achieve this.
A number of fascinating visual illusions demonstrate that the brain tries to compensate for delays in the input it receives from the eyes (and from other senses). For example in the flash-lag effect, a moving object that is perfectly aligned with a flash appears to be ahead in space. Here, the brain can predict the position of the moving object, but not that of the flash, and therefore we perceive mismatched positions. Several of our earlier papers showed that moving objects are indeed perceived in predicted positions (Maus & Nijhawan 2006, 2008, 2009)
In the flash-drag effect a stationary flash appears as “dragged” by nearby motion; physically aligned flashes are perceived as misaligned, when they are surrounded by motion in opposite directions. In this case, the flash is interpreted as part of the background motion, and its perceived location is biased by predictive localization.
In a recent paper (Maus et al., Neuron, 2013), we showed that the position representations in cortical motion area MT+ already reflect these predictions. Objects in this area are not represented where they were presented in the retina, but in predictive positions that might be a basis for perceptual prediction.
The eyes do not record perfect images of the whole visual field. Over time, regions on the retina can become damaged. In fact, even the healthy eye has a large “blind spot”: There are no photoreceptors at the optic disk, where the optic nerve leaves the eye ball. This blind spot can be easily observed when you close the other eye. Close your left eye, and look directly at the + in the picture below. At the appropriate viewing distance, the dot on the right side will disappear.
Although the brain does not receive information from the eyes about the visual region around the dot, it does not perceive a “hole” in this region. Instead the background is filled in with information from the surrounding region.
In some ongoing investigations in our lab, we showed that the brain does not only fill in static information from the surrounding region of the blind spot, but also uses visual motion information for filling-in (Maus & Nijhawan, 2008; Maus & Whitney, 2016).