can produce slower and more lasting forms of adaptation. Also, repeated sensory stimulation appears to temporarily decrease the gain of thalamocortical synaptic transmission. Adaptation of cortical responses was stronger and recovered more slowly. History In the late 1800s, Hermann Helmholtz, a German physician and physicist, extensively researched conscious sensations and different types of perception. He defined sensations as the "raw elements" of conscious experience that required no learning, and perceptions as the meaningful interpretations derived from the senses. He studied the physical properties of the eye and vision, as well as acoustic sensation. In one of his classic experiments regarding how space perception could be altered by experience, participants wore glasses that distorted the visual field by several degrees to the right. Participants were asked to look at an object, close their eyes, and try to reach out and touch it. At first, the subjects reached for the object too far to the left, but after a few trials were able to correct themselves. Helmholtz theorized that perceptual adaptation might result from a process he referred to as unconscious inference, where the mind unconsciously adopts certain rules in order to make sense of what is perceived of the world. An example of this phenomenon is when a ball appears to be getting smaller and smaller, the mind will then infer that the ball is moving away from them. In the 1890s, psychologist George M. Stratton conducted experiments in which he tested the theory of perceptual adaptation. In one experiment, he wore a reversing glasses for 21½ hours over three days. After removing the glasses, "normal vision was restored instantaneously and without any disturbance in the natural appearance or position of objects." On a later experiment, Stratton wore the glasses for eight whole days. By day four, the images seen through the instrument were still upside down. However, on day five, images appeared upright until he concentrated on them; then they became inverted again. By having to concentrate on his vision to turn it upside down again, especially when he knew images were hitting his retinas in the opposite orientation as normal, Stratton deduced his brain had adapted to the changes in vision. Stratton also conducted experiments where he wore glasses that altered his visual field by 45°. His brain was able to adapt to the change and perceive the world as normal. Also, the field can be altered making the