The tunnel effect is a perceptual phenomenon where the brain will assume that an object is persistent when it disappears beyond an occlusion and then reappears. For example, if a person sees a horse trot behind a barn and a horse come out on the other side, she will assume it is the same horse, as long as the trajectory of the animal makes sense. While this might seem obvious, it actually involves some complicated cognitive maneuvering and plays an important role in the visual processing of moving objects.
Researchers who study the tunnel effect note that if a subject sees a moving object and it becomes occluded by an obstacle, the subject will predict where and when the object will reappear. The brain relies on the trajectory and speed of the object before it vanishes to calculate this information, although it tends to underestimate travel time through the “tunnel,” the time when it is invisible because of the occlusion.
Through the tunnel effect, the brain will perceive a persistent object moving through the same space and time, even if it disappears and reappears. Without this perceptual phenomenon, if something disappeared behind another object and reappeared, the brain might think it was a different object. Cognitively, the brain could be puzzled about what happened to the first object, and also unsure about the origins of the “new” object. A version of this can be seen in playing peek-a-boo with very young infants, who are still developing cognition and perception and may not at first understand what happens when a parent manipulates an object in and out of view.
The tunnel effect can also involve a moving occlusion and a stationary object. A person standing on a street corner, for example, might notice a news stand on the opposite corner. When a car goes by and occludes the news stand, the brain assumes it will reappear after the car passes, and that it will be the same news stand. Interestingly, in studies on how the tunnel effect works, researchers have shown that tricks like changing the color or size of the object do not fool the brain, and it still reads the object as persistent, rather than thinking it is new.
Human perception is complex. Some perceptual phenomena are hardwired and start to manifest at a very young age, while others develop during the infancy stage and start to mature. Providing children with a rich environment is critical for the facilitation of cognitive development. Without stimuli, children will miss out on chances to develop important wiring in their brains, and they may never catch up.