There is likelihood that people who see daggers in the air, as well as people who spot faces in the fire, question the validity of their visual perception. The justification behind this bears the same mark as the reason why people classify magicians as “illusionists” and not “saints”. The world of knowledge and experiences that is stored in a healthy brain enable us to distinguish between a genuine phenomena and an illusion – essentially, the former may be inferred from information we know about the world, and the latter somehow contradicts or does not follow the rules we have acquired.

This subconscious top-down processing that our brain employs when we come into contact with stimuli around us does at times distort our perception of things, as is shown obviously by the Hermann grid in figure 1 with the squares and dots. How many grey dots are there? If I am not mistaken, there are none at all. However, that is reason speaking, and my eyes tell me otherwise. Why is this so? The eye is often paralleled to a camera, but is this allusion valid? Firstly, we know from research that the eyes do not see the complete picture of the world.One snapshot taken from the eye-camera would produce a picture like figure 2. The other shocking fact is that the objects in the external world do not really have colour at all.

All coloured objects around us are so only because the eyes are highly sensitive to differences in wavelengths of light in the visible spectrum (of the electromagnetic spectrum). The third fact that we know about is that our brain does not interpret the world in photographic templates. Technically speaking, there is no “picture in the brain” that we can talk about.As Richard Gregory points out in “Eye and Brain”, speaking of a picture in the brain would suggest an internal eye to visualise it, which will result in an infinite regression of eyes and brains. What actually occurs is that the rods and cons in the retina convert light energy into neural impulses, which are then earned to the visual cortex in the brain via the optic nerve.

Therefore, what the brain receives is “chains of electrical impulses, which by their code and patterns of brain activity, represent objects”.So essentially we understand, from the fact that illusions exist, that there is a disparity between what we perceive and what exists in external reality, since the world really is a manifestation of the “glass” that look through, wherein the “glass” is in conjunction with our personal experiences, as well as information gained from our environment. When the map in our mind does not coincide with the picture that we perceive, there is often a distortion, or illusion which occurs. Typically, illusions become likely when the stimulus is unclear, when information is missing, when elements are combined in unusual ways, of when familiar patterns are not apparent”. The famous artist and mathematician M.

C. Escher was a person who explored the notion of ambiguous stimuli. In his one of his famous works, Ascending and Descending, attached as figure 3, the people at the top of the building are observed to be moving upwards or downwards all the time, when they do not really proceed either higher or lower in the end. What could be a possible rationale behind this visual fluke?Points A and B (as labelled) is actually of similar height, while path C remains ambiguous, as to whether there is an ascent at all. By manipulating these few conditions, he is able to create a stairway that is essentially progressing upwards or downwards all the time.

What is important about painters like Escher and Dali not so much the impressionistic ability that they possess, but’ rather, the subjectivity and relativity (the name of another piece of work by Escher, attached as of the world that they attempt to depict. Does it mean then that our world as we see it, is not “real”, but just an interpretation of our senses?It is not possible to refute that, and it is also highly possible that there is a “noumenal” world we are unaware of. It does not mean, however, that we avoid finding out as much as we can about the sensory world that we are able to perceive, or to understand the nature of illusions and ambiguous stimuli. Reverting back to the Hermann grid, it is possible to postulate the reason why we see alternating and non-fixed black dots through an understanding of the way our eyes work.

I he receptor cells in the eyes are the culprits this phenomenon, When certain cells in the retina fire, it inhibits the firing of adjacent cells.This causes us to visualise the dark dots that are outside our area of focus. Another interesting example similar to the Hermann grid is shown in figure 5. In this case, the pink boxes that are surrounded by adjacent green boxes seem to be much darker that the other pink boxes (which are surrounded by white boxes) in the diagram.

They only seem to be so because our eyes perceive two simultaneous dark colours, which result in the intervention of the receptor cells, as in the case of the Hermarin grid.This is not different to the way our eyes interpret information in our environment. A woman who dons on a black dress would seem much slimmer than a woman in a white dress, just as a house with red walls would seem smaller than a house with pale yellow walls. The presence and absence of light, and our perception of brightness, plays a key role in these cases. Whether it may be a face in the fire, or a face on Mars (figure 6), there is no avoiding illusion in our every day life.Just as some clouds may look like a dragon and a tree may look starkly humanoid, we seldom believe that these shapes actually are the entities they “embody”.

It makes a difference whether you think your curtains have a life of their own or if David Blame can really fly, and this ability to differentiate, which is not inherent in our cognitive abilities, is only possible through our interaction and experiences in life, and the contributions and continued research that Science has provided us with. There is essentially no dagger in the air- the only one which exists, is in our minds.