Visual sensation and visual perception are the processes by which we see and understand our surroundings. The difference between these processes and the dividing line where sensation ends and perception begins is debatable, however some distinctions can be made. .

             Sensation is a physiological function, and begins with reception, when the cornea and lens of the eye focus light on the photoreceptors (rods and cones) in the retina of the eye. After this, transduction occurs, transforming stimulus energy into nerve impulses. The next step is transmission, which is the movement of the data in the form of nerve impulses from the receptors to the brain. As sensation is physiological, all people obtain the same sensation from a given stimulus.

             Perception involves psychological processes, and the first automatic response is selection, which assists perceptual organisation and helps the brain sort the sensory elements into a whole picture. The next step is organisation, where elements are grouped into forms or shapes, followed by interpretation. Interpretation gives the stimulus meaning, and involves psychological characteristics such as attitude or prior experience and means that in some cases, our interpretation may vary from other people's. For example, two people sense a round, flat, shiny object, one from a poor country, another from a rich country. The rich person might understand the object to be a music compact disc because he has had prior experience with them, but the poor person may not know what it was as he has never seen one before. .

             The visual perceptual principles are processes which are applied to incoming visual stimuli to help explain any inconsistencies that may occur when the perception process takes place. There are three main types, the Gestalt principles, depth cues and perceptual constancies.

             The Gestalt principles are based on the concept that we perceive objects in the simplest possible manner (Grivas et al 1996 page108), and describes how the brain organises, groups and simplifies visual stimuli.