Optical and Auditory Illusions

The human brain is not merely a receptor of qualia, like a microphone or camera. The brain processes raw data received from the environment, and converts this data into perception. Sensory data gets converted into meaning via areas in the posterior cortex of the brain called the association zones. Perception is a function of consciousness, and how we perceive a sensory stimulus is learned. The learning process involves memory function (Solms and Turnbull, 2002).

The split brain experiments of Gazzaniga gives us clues to which side of the cortex is responsible for creating illusions. The work of the right hemisphere is more apt at turning shapes into forms and melody from notes because it has the tendency to create wholes from parts. This is the basis of our optical and auditory illusions.

Artists and psychologists throughout history have been fascinated with the use of illusions.  The latter, in fact, use illusions often instinctively in order to render 3 dimensional objects onto 2 dimensional spaces. One notable artist and painter is Josef Albers (1888-1976). Albers famous series, Homage to the Square, is a beautiful study of color interactions. He presented color theory as a way to offer illusion of depth, space and temperature. Commonly found on buildings are also trompe l’oeil paintings that have 3D effects, accomplished with the clever painting of drop shadows as illustrated in figure 1.  With the simple grey shades, we perceive the shape as sticking out of the paper.


Figure 1 (Picture by Nicole Helbig)

Notable researchers of optical illusions have studied various forms of optical illusions. Some of these illusions, like the figure-ground puzzles allow the eyes to see two different motives on the same picture, but at different instances, depending on where one’s focus of the picture lies. A famous example is Rubin’s vase, developed around 1915.  Rubin discovered the first phenomenological laws of figure/background articulation (Albertazzi, 1999). The figure is seen to become differentiated from the background in an alternating manner because of the chromatic contrast between the shapes. The lines in which the figure and ground are clearly separate and provide the contrast.

Gestalt psychology was developed during the time of the First World War.  The major contributors at that time were Kurt Koffka, Max Wertheimer and Wolfgang Köhler.  Their premise is that objects are perceived within an environment in their context. In other words, we perceive parts and pieces and perceive these as whole “gestalts”. Similar objects are also seen as groups, rather than discreet pieces.


Kanizsa triangle

The Kanizsa triangle is an example of a figure that forces our minds to create phantom shapes that were not illustrated on the diagram because our minds perceive the missing shapes nevertheless. Figure 2 is my attempt at recreating such an optical illusion.

Figure 2

Müller-Lyer created a simple, but clever illusion consisting of a stylized arrow. Lengths of the line that make the central part of the arrow can be seen as longer or shorter than the other, depending on whether the ends of the arrow have sharp points pointing outwards or inwards, even though the lengths of both arrow lines are similar.  This kind of optical illusion, unlike the figure ground puzzles, cannot be willfully “unseen”.  Researchers like Berry (1968), however have found evidence that optical illusions like the Müller-Lyer illusion do not get seen by peoples of cultures who have not the exposure to certain rectilinear.  What we infer from this phenomenon is that perception, like culture, is learned.

Auditory illusions are interesting because we may often be exposed to them unawares. I had some difficulty distinguishing from the sample of African music played in class which notes were really played and which were auditory illusion created by “a fast running sequence of sounds in disjunct intervals” (Kubik, 2010). It is hard to imagine that one is hearing that which is not really there, and that the sounds are the product of our perception. Most incredible about this piece is that the instruments are traditional instruments played by hand.

Other popular audible illusions have been created with electronic instruments. Audible illusions, like optical illusions, come in various forms.  Some examples are Binural beats, where by two pure tones are played in each ear leading the listener to perceive an illusionary third tone.  Risset’s rhythmic effect is used often in modern day disco-techs. Named after Jean Claude Risset (b. 1938), the beats give the impression of being in perpetual acceleration.



Albertazzi, L. (1999). Shapes of Forms: From Gestalt psychology and phenomenology to ontology and mathematics 275. NY: Springer Science & Business Media.

Berry, J. W. (1968). Ecology, perceptual development and the Müller-Lyer illusion, British Journal of Psychology 59 (3): 205–210,

Kubik, G. (2010). Theory of African music (Vol. 2). University of Chicago Press. p.107

Mundy-Castle, A. C. (1966). Pictorial depth perception in Ghanaian children. International Journal of Psychology, 1(4), 289-300.

Solms, M., & Turnbull, O. (2002). The brain and the inner world: An introduction to the neuroscience of subjective experience. Karnac Books.


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