Why are we susceptible to visual illusions? Describe 3 different types of illusion and discuss what they tell us about vision.

The sense of vision is arguably our most powerful perceptual tool for gathering information from the surrounding environment. However, the near real-time image perceived from light entering our eyes is far from a perfect representation of reality and perhaps better described as a mentally constructed rendition. The information is received in fragmented format as it is divided between two eyes which in turn individually further divide left and right information streams. This fragmented information is reconstituted by the brain to provide a best-fit version of reality. It is highly limited by the neurological apparatus from which it arises, as the fragmented stream of visual information is subjected to a significant degree of manipulation by the brain to produce a complete image of reality (Borst, G. & Kosslyn, S.M. 2008).

Approximately 30% of the brain is allocated to vision. The amount of information which is received via our sense organs is far greater than what can be interpreted by the brain, which routinely filters out much of this information to reduce energy expenditure and free up biological and cognitive resources (Peck, E. M et al. 2013). Vision is particularly labour and energy intensive so it’s not surprising that the brain makes short-cuts to render our visual reality so that other concurrent streams of information are not neglected.

The blind spot is a classic example of an illusion created by the brain to fill in the gap of missing information. We all possess a small area on the retina known as the blind spot, which does not contain photoreceptive cells and is located at the site where the optic nerve breaches the retinal wall. This area corresponds to an invisible patch in our field of view as no information is received from it. So instead this invisible patch gets filled in by our brain based on adjacent information from the visual field and information from the other eye. These neurological adaptations, combined with the fact that the blind spots in each eye do not overlap in our field of view creates the illusion of seamless vision. The blind spot also demonstrates the fragmented nature of information received by the brain which reconstructs the various fragments into a complete image.

Below is an image I took whilst hiking in the Swiss alps. It demonstrates the illusion of depth perception. Here it is not our neurological makeup which causes the illusion as is the case with the blind spot, but our predisposition for framing objects relative to their surroundings. The image appears to show a man with his hand placed on a rock which he is looking down at. This generates the illusion of him being bigger than the rock, his hand upon it and it being beside him. However the rock is in fact a mountain peak a few hundred metres away. The familiarity of human – object interaction, a product of conditioning, has fooled our brains into falsely interpreting this illusion.

Another example which falls into this category is the perceived size of the moon. When the moon is high in the sky it appears relatively small, however when it is by the horizon and particularly when its visual form interacts with objects at the horizon level it appears significantly larger despite the distance between observer and moon remaining consistent. This signifies the role of perceptual distortions in visual processing (Kaufman, L. & Kaufman J.H., 1999).

Another example of how our cognitive biases create illusory visual features is demonstrated with the revolving mask as explained in Richard Dawkins ‘God Delusion’. We are first presented with a view of the upright front of the mask, which appears as the face of Charlie Chaplin and as the mask rotates on its vertical axis, the hollowed rear of the mask when viewed front on also appears as a face with features projecting towards the viewer. So even though the concaved rear of the mask has little resemblance to the facial form, the illusion is created as we are inherently predisposed to view faces and anything even closely resembling a face may create the illusion of one. This is further shown in a three dot triangular formation within a circle which might crudely represent two eyes and a mouth in a ‘proto-face’. Showing evidence for our social orienting bias (Shah, P. et al. 2013).

The evidence base demonstrated by visual illusions clearly shows the fragmentary nature and interpretation bias of our visual processing. Each case described has an evolutionary rational which may enhance survival or limit energy expenditure.

 

Borst, G. & Kosslyn, S.M. (2008). Visual mental imagery and visual perception: Structural equivalence revealed by scanning processes. Memory & Cognition 2008, 36 (4), 849-862.

Lee, K.S., Huang, X., and Fitzpatrick, D. (2016). Topology of ON and OFF inputs in visual cortex enables an invariant columnar architecture. Nature, Published online, April 27, 2016.

B y Denise Grady|Tuesday, June 01, 1993. The Vision Thing: Mainly in the Brain. http://discovermagazine.com/1993/jun/thevisionthingma227

 

Karnath HO, Rüter J, Mandler A, Himmelbach M. (2009). The anatomy of object recognition–visual form agnosia caused by medial occipitotemporal stroke. J Neurosci. 6: 585462. doi: 10.1523/JNEUROSCI.5192-08.2009.

Rensink RA, O’Regan JK, and Clark JJ (1997). To See or Not to See: The Need for Attention to Perceive Changes in Scenes. Psychological Science, 8:368-373 doi: 10.1111/j.1467-9280.1997.tb00427.

Peck, E. M., Afergan, D., Jacobs, R.J.K. (2013).Investigation of fNIRS Brain Sensing as Input to Information Filtering Systems. Proceedings of the 4th Augmented Human International Conference. Stuttgart, Germany — March 07 – 08, 2013

Punit Shah, P., Gaule, A., Bird, G., Cook, R. (2013). Robust orienting to protofacial stimuli in autism. Volume 23, Issue 24, pR1087–R1088, 16 December 2013

Kaufman, L. & Kaufman J.H., (1999). Explaining the moon illusion. Proceedings of the National Academy of Sciences of the United States of America, October 25, 1999