ABSTRACT
Everyone has, at one time or other, experienced a sensory deception. Some better known deceptions of the senses include visual or optical illusions that are commonplace experiences in everyday life. Examples include visual after-effects and illusions such as the Müller-Lyer illusion (see Figure 13.1 ). Sensory deceptions such as illusions are the product of a normally functioning brain that has evolved to process sensory information about the world in certain ways. There is no clear demarcation between real perceptions, misperceptions and hallucinations. Rather, there is a gradation, a continuum, of experiences which depends on the relative contribution of sensory input, internal processes, and other biological, psychological and social determinants. All of the sensory modalities can be deceived (visual, auditory, olfactory, gustatory and somatic).
