Category Archives: Perception

Depth Illusions As Street Art

The talented artist Edgar Mueller demonstrates the use of paint to transform a pavement into a cliff face. The time-lapse photography shows how passers-by know how they are supposed to relate to the image by avoiding walking in some areas and standing carefully in other areas.

An index of the site can be found here. The page contains links to all of the articles in the blog in chronological order. Twitter: You can follow ‘The Amazing World of Psychiatry’ Twitter by clicking on this link. Podcast: You can listen to this post on Odiogo by clicking on this link (there may be a small delay between publishing of the blog article and the availability of the podcast). It is available for a limited period. TAWOP Channel: You can follow the TAWOP Channel on YouTube by clicking on this link. Responses: If you have any comments, you can leave them below or alternatively e-mail justinmarley17@yahoo.co.uk. Disclaimer: The comments made here represent the opinions of the author and do not represent the profession or any body/organisation. The comments made here are not meant as a source of medical advice and those seeking medical advice are advised to consult with their own doctor. The author is not responsible for the contents of any external sites that are linked to in this blog.

Depth Illusions

ContrastIllusionPerspectiveThis is a brief post about depth illusions. Previous posts have looked at other aspects of illusions and give us an insight into how the brain processes the visual world. Potentially this can help us to understand other phenomenon such as hallucinations. The videos below show some great examples of depth illusions – generating the appearance of a 3 dimensional world in a 2 dimensional scene. An artist guides us on how some of the techniques that help to realise the effect of depth.

Depth Illusion

Pencil Drawing Depth Illusion

Tutorial on Bringing Depth to Drawings

An index of the site can be found here. The page contains links to all of the articles in the blog in chronological order. Twitter: You can follow ‘The Amazing World of Psychiatry’ Twitter by clicking on this link. Podcast: You can listen to this post on Odiogo by clicking on this link (there may be a small delay between publishing of the blog article and the availability of the podcast). It is available for a limited period. TAWOP Channel: You can follow the TAWOP Channel on YouTube by clicking on this link. Responses: If you have any comments, you can leave them below or alternatively e-mail justinmarley17@yahoo.co.uk. Disclaimer: The comments made here represent the opinions of the author and do not represent the profession or any body/organisation. The comments made here are not meant as a source of medical advice and those seeking medical advice are advised to consult with their own doctor. The author is not responsible for the contents of any external sites that are linked to in this blog.

Animated Optical Illusions

The optical illusion above was created by using a filter moving across a composite image. The video below shows you how to create this type of illusion.

Illusions tell us something about how our visual systems process the world around us and can help us to understand conditions where vision doesn’t work properly (e.g perceiving moving objects when there are none). The illusions above are interesting in that the brain perceives a rotational movement as the filter moves sideways.

The illusion reminded me of the zoetrope. The movement in the illusion above occurs because the sheet moves across the stationary image whereas in the zoetrope the images are moving in space. However there are filters in both cases that order the images across time to create the illusion. Recent examples of zoetropes use stroboscopic lighting in place of the line filters.

How to Create a Zoetrope

The BRAVIA-drome – An Example of a Zoetrope

The zoetrope is similar to films. Films and moving images are now pervasive. Considering the illusions above reminds us that when we watch a film we are using a technology which works because of our biology. Developments in the field of psychophysics contribute to film and television. The above illusions give us an insight into the building blocks of our biological visual motion processing.

Earliest Film (1888)

An index of the site can be found here. The page contains links to all of the articles in the blog in chronological order. Twitter: You can follow ‘The Amazing World of Psychiatry’ Twitter by clicking on this link. Podcast: You can listen to this post on Odiogo by clicking on this link (there may be a small delay between publishing of the blog article and the availability of the podcast). It is available for a limited period. TAWOP Channel: You can follow the TAWOP Channel on YouTube by clicking on this link. Responses: If you have any comments, you can leave them below or alternatively e-mail justinmarley17@yahoo.co.uk. Disclaimer: The comments made here represent the opinions of the author and do not represent the profession or any body/organisation. The comments made here are not meant as a source of medical advice and those seeking medical advice are advised to consult with their own doctor. The author is not responsible for the contents of any external sites that are linked to in this blog.

The Meaning of Vision (And How Bumble Bees See Illusions)

Dr Beau Lotto gives a fascinating talk on how illusions tell us about the context of vision. Transforming the retinal signal into our perception of the world is a subtle process. Each part of this process might seem strange when reflected back to us through the carefully selected illusions shown here. These ‘mirrors’ into our own vision system give us profound insights that can also tell us something about our evolution.

Index: There are indices for the TAWOP site here and here Twitter: You can follow ‘The Amazing World of Psychiatry’ Twitter by clicking on this link. Podcast: You can listen to this post on Odiogo by clicking on this link (there may be a small delay between publishing of the blog article and the availability of the podcast). It is available for a limited period. TAWOP Channel: You can follow the TAWOP Channel on YouTube by clicking on this link. Responses: If you have any comments, you can leave them below or alternatively e-mail justinmarley17@yahoo.co.uk. Disclaimer: The comments made here represent the opinions of the author and do not represent the profession or any body/organisation. The comments made here are not meant as a source of medical advice and those seeking medical advice are advised to consult with their own doctor. The author is not responsible for the contents of any external sites that are linked to in this blog.

Do Cats See Illusions Too?

The video above was uploaded on YouTube by Rasmusab. The cat is looking at the rotating snake illusion. This is a powerful visual illusion created by the talented Professor Akiyoshi Kitaoka. Professor Kitaoka has created many remarkable visual illusions combining an artistic talent with a deep understanding of human vision. Professor Kitaoka’s website contains many other effective illusions some of which are produced using simple shapes.

What Might the Cat Be Seeing?

Does the cat see the illusion? We can’t know for sure but the cat paws at one and then another of the circles. When we look at the circles we see what Professor Kitaoka describes as an anomalous motion effect. The cat moves quickly as if trying to catch escaping prey. This happens repeatedly. Unlike us the cat is not quietly admiring a visual illusion but appears to believe that it is real and that what is seen demands immediate action. Since we see anomalous motion it is not too much of a step to take to assume that the cat shares our perception. We can not say for certain if the cat is seeing the illusion but is it possible to find better indirect evidence that the cat sees this as we do? When the cat stops pawing at the images this is even more interesting. We might think of habituation as an explanation. However it is also possible that the cat has gained insight into what is happening.

Does this mean that Cats might hallucinate?

Illusions are not hallucinations. Hallucinations occur in the absence of a sensory stimulus. Actually it is a little more complicated. When our eyes are open, the retina is receiving light from across the visual field. Therefore when hallucinations are seen we would expect that part of the visual field to also be receiving sensory input if the eyes are open. Therefore it is more sensible to say that the hallucinatory image and the sensory input from that part of the visual field are distinct and can be clearly distinguished from each other.  In the above case we might think that the cat were hallucinating if it were pawing in the same way at a blank sheet of paper.

Does this tell us something about illusions in people?

The lineages of cats and humans diverged many millions of years ago. Both cats and humans are classified as placental mammals. A recent estimate suggests that humans and cats shared a common ancestor as recently as 65 million years ago. There are two ways that humans and cats might be able to see the same type of visual illusion. The first is where humans and cats have conserved features of our visual system after our divergence. The second possibility is that our visual systems developed very differently after our divergence. However at some point later on both species adapted to the environment and found the same ‘solution’ to an environmental problem but one which just happened to be caught out by the moving snakes illusion. This latter case is convergent evolution – where two species converge on the same adaptation to the environment. The first possibility is the most likely – visual adaptations that work would be conserved but would still remain susceptible to phenomenon such as the moving snakes illusion.

Professor Kitaoka has therefore produced an illusion that gives us insight into a feature of our visual system that has possibly been conserved for 65 million years. This may involve the Retina or parts of the Visual Cortex. This illusion also reminds us that we may share aspects of our conscious experience with cats and other animals.

Index: There are indices for the TAWOP site here and here Twitter: You can follow ‘The Amazing World of Psychiatry’ Twitter by clicking on this link. Podcast: You can listen to this post on Odiogo by clicking on this link (there may be a small delay between publishing of the blog article and the availability of the podcast). It is available for a limited period. TAWOP Channel: You can follow the TAWOP Channel on YouTube by clicking on this link. Responses: If you have any comments, you can leave them below or alternatively e-mail justinmarley17@yahoo.co.uk. Disclaimer: The comments made here represent the opinions of the author and do not represent the profession or any body/organisation. The comments made here are not meant as a source of medical advice and those seeking medical advice are advised to consult with their own doctor. The author is not responsible for the contents of any external sites that are linked to in this blog.