Visual Perception: Some Aspects

Perception is a complex process. For humans, who have a higher intelligent process than animals, it is even more complex. Perception begins with the initial process of receiving stimuli from the immediate environment. In a baby genetic processes initiate it in a very rudimentary manner. The baby receives stimuli from its immediate environment and from within itself and reacts to them, often with neural processes that are entirely instinctive. That is why the baby's reactions are so innately atavistic. It still does not have in place mnemonic processes that will allow it to react in a manner that will distinguish it as a human from other life forms on Earth. For example, when it feels hungry it cries, just as a kitten or puppy will. When it feels too hot or cold, the response is the same - irritated verbal protests. This is so because, firstly, it is too helpless to respond competently to the discomfort and alleviate itself of it. Instead, it is genetically geared to send distress signals to others around it so that these others become aware of its discomfort and initiate the responses that will bring back comfort. Within this complicated genetically initiated survival process of sending out distress signals and receiving positive alleviating responses from others in its immediate environment the baby gradually builds up mnemonic processes in its own neural network that store the knowledge of the positive responses that will allow it to survive successfully. This is the very initial process of human learning and development - using skilful perception to thrive.
In adults, perception is not as rudimentary as in babies but it can still be broken down into its componential processes in a rather loose manner. Adults receive stimuli from their environment and from within their own bodies and use either mnemonic processes or their intellect or both to respond to such stimuli. It may be that the baby's environment is confined to its immediate surroundings and its own body while, in an adult, it may be that the environment is much larger, even the entire universe. It may also be that the adult often responds to imaginative stimuli - stimuli that are not in the world altogether but are constructed of the adult's mnemonic processes in an intelligent manner. It is notable that the baby is initially incapable of constructing imaginative stimuli as it has very little experience in the world to be able to use its small mnemonic store to develop these altogether abstract notions. Also, while the baby's initial intelligent responses to stimuli are entirely developed of its small mnemonic store of such responses inducted from others the adult is capable of using his/her intellect to construct custom responses that are entirely generated from abstraction. These are imaginative responses that will allow the adult to deal with either totally unfamiliar stimuli or stimuli that he/she has not previously responded to successfully historically. Of these there are no experience that he/she has so that he/she cannot respond successfully to these from his/her mnemonic store. The baby, like most animals, even adult ones, is not capable of constructing either imaginative stimuli or responses because of its limited experience in the world. The baby cannot because of its inexperience though it has the potential intellect to do so later as it survives successfully in the world and builds up a sufficiently large mnemonic store. Animals, on the other hand, are limited in this aspect by their very limited intelligent capabilities. It is not that both babies and animals are entirely incapable of constructing imaginative stimuli or responses. It is only that these are very limited in them compared to an average adult human.

Visual perception is a componential process within the larger process of overall perception. It is entirely associated with the sensory stimuli that the eyes gather from the environment - immediate or, if possible, otherwise. Like the overall process of perception, visual perception also uses mnemonic stores within the neural network to generate responses to the stimuli received through the eyes. Adults have more complex responses while babies generate simple ones with the small stock of mnemonic data they have assimilated within their short experiential periods.

Vision

Human vision through the eyes uses two major componential techniques - color recognition and assessment of depth and motion. The primary structure within the eyes that senses the light is the screen-like retina that is well-supplied with the photoreceptor cells that actually receive the light coming from outside as stimuli. These photoreceptor cells convert the light energy into neural signals that are finally carried to the brain for interpretation and appropriate response preparation. There are two types of photoreceptors - the rods and the cones. The cone receptors sense color and intensity of light while the rod receptors are used primarily to sense in dim light (light of low intensity). It is not unusual that there are almost twenty times as many rod cells in the retina than cone cells. This is so because rod cell sensitivity has to be very high in comparison to cone cells as these cells have to sense light of very low intensity. While there is only one known type of rod cells there are three known types of cone cells. This is to assist in color vision that is one of the primary functions of the cone cells. Biologically, it is observed that all possible colors in their varying shades can be constructed out of three primary colors - blue, green and red. Thus, the three types of cone cells - S type (capable of receiving blue light of short (S) wavelengths), M type (capable of receiving green light of medium (M) wavelengths) and L type (capable of receiving red light of long (L) wavelengths) - suffice to interpret light of all colors. Color vision is a very complex process. Most light reflected off objects in the environment is a mixture of light of varying wavelengths and intensities. The cone receptors actually break up such light into their primary biologically significant components - the blue, green and red - that the S, M and L types of receptors become sensitive to. These receptors encode the varying wavelengths and intensities of their relevant color components for preparation of sending signals to the brain by neural pathways. The brain, in turn, assimilates these encoded signals and converts them back to color sensation that is compared to mnemonic data that is already there for proper color recognition.
Depth and motion assessment is the work of the stereoscopic vision enabled by two eyes.
Recent research (Chen et al, 2005) has pointed to genetic mechanisms wherewith expression of certain genes downgrades rod receptor action and upgrades cone receptor action for vision in bright light and, conversely, upgrades rod receptor action and downgrades cone receptor action in dim light.
The ratio of occurrence of rods to cones is usually determined by the habits - nocturnal or diurnal - of the organism whose eyes are being assessed. Thus, nocturnal creatures like the owl and the mole (that usually spends are large part of its life underground) have eyes amply supplied with rod receptors for ease of vision in dim light while humans and eagles, who are by habit diurnal, have a relatively large number of cone receptors for ease of vision in bright light.

In babies visual perception, as other component perceptive processes such as auditory and olfactory ones, is simple as the average baby lacks enough sophisticated mnemonic stores to enable relative complexity of visual recognition of objects as per their color, depth and motion. When the baby sees colors, bright ones attract it more than light ones simply because bright colors generate a more intense sensation. It is notable that while babies may be subjected to bright colors periodically to stimulate their visual capabilities it is advisable not to do so very often as their tender eyes require light colors for proper restfulness, a state more conducive to a baby's well-being than any other. Babies gradually build up a proper mnemonic store of colors, depths and motive association as they grow up until they can distinguish colors, depths and motions even in unfamiliar objects, as adults can. This, of course, is the case for human babies. The very young of other animals may perceive color, depth and motion in varying degrees as the survival requirements of such animals demand.

Color Vision: Colorblindness

People with normal visions are called trichromats. This signifies that all their cone types - the S, M and L types - are normally functional and their perception of colors is standard as per human biology (Visual Expert, 2006). The three cone types signify that humans are liable to three types of abnormalities in color vision. These are 1) anomalous trichomacy; 2) monochromacy and 3) dichromacy.
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Anomalous Trichromacy:

Anomalous trichromacy is a colorblindness condition that is relatively mild. The patient has all three cone types functional but there are varying degrees of impairment in assessing the intensities of some or all components of the stimulating light. This signifies that the patient is technically capable of perceiving all colors but has difficulties in perceiving all possible hues and nuances because there is defect in assessing the intensities. Anomalous trichromacy is a complex cone receptor disorder and there are too many possible variations for this paper to put all of them down. It may be that the functional impairments may affect all or one or two of the cone receptor types. Also, such impairments may be various as these may concern assessment of either wavelengths or intensities of some or all components of the stimulating light.

Monochromacy:

Monochromats are truly colorblind because they have normal functionality in only one of the three types of cone receptors. Since proper perception of only primary color cannot aid in distinction of any composite color at all unless the stimulating light comprises only of the color type of the normally functioning cone receptor type. Thus, monochromacy with normal S cone receptors can mean that the patient will only perceive blue light properly while all other colored light will be perceived as varying degrees of brightness according to the intensities (Visual Expert, 2006). There is no color distinction unless the stimulating light is purely blue. This is likewise for the other cone types. They would perceive an Ishihara plate (Diagram available in reference websites) as a monochromatic disk with varying levels of brightness without any color distinction.

Dichromacy:

Dichromats are people with deficiency in one cone type. They match light with only two primaries. Protanopes and deuteranopes are red-green (longer wavelengths) colorblind and see only yellows and blues. These are fairly common while the third type of dichromat, being uncommon, is tritanopic with blue-yellow (shorter wavelengths) color blindness (Visual Expert, 2006). While a visually normal person would perceive the Ishihara plate numbers (Diagram available in reference websites) as - A=8, B=5, C=29 and D=74 - dichromats may perceive them as - A=3, B=2, C=70 and D=21 (Dichromats, Undated). Ishihara plates are part of some unique devices, visually relevant structures usually, that are used to determine normalcy or abnormalcy in human vision. Some of the sites referenced with this paper have other such devices that the reader can safely use to test color vision but it is nevertheless recommended that expert medical advice at first hand be used to do this.

Motion and Depth

Two separate neural pathways lead away from the retinal ganglia cells to the brain. These ganglia cells are the starting points from where the transducted signals, the light energy trapped by the three photopigments in the cones converted into neural signals, are carried away by the nervous system to the brain. These latter, the two neural pathways, are the parvocellular pathway, responsible for perceiving color and fine details, and the magnocellular pathway, responsible for perceiving motion and depth (Rheingans, P., Undated). Processing along the magncellular pathway is independent of wavelength and depends only on the intensity (Rheingans, P., Undated). It is not extraordinary that the same pathway processes both motion and depth as intensities of the stimulating light determine these. Since this pathway is responsible for determining the location and boundaries of objects (the orientation of the object), factors that determine depth, it is also responsible for determining motion, which depends on the same factors in spatial translation. Location and boundary signifies an apparently spatial relationship when the object is static but, when the object is moving and in spatiotemporal duality, location and boundary, perceived by the same brain locations, signifies another manifest spatiotemporal relationship - that of motion.

More significantly, motion itself assists human vision with changing perceptions that, in turn, assists in assessing relative depths - 3D structures and relative positioning or orientation (Rheingans, P., Undated). People with visual motion perception deficiencies, sometimes because of difficulties in perceiving varying brightnesses or intensities, have great difficulty, among other things, in perceiving depth and spatiotemporal orientation of objects around them. Motion perception is particularly assisted by binocular vision or stereopsis where both eyes, in conjunctive function, can distinguish varying intensities emanating out of varying orientations in apposition. This is so as one eye perceives the object in one orientation with varying intensities while the other eye perceives the same object from a slightly variant orientation. This variance in orientation, though very slight, also varies intensities and a comparative analysis of the slightly varying intensities emanating from the same object plane but variant for both eyes allows the brain to assess depth and, consequently, motion. It is notable here that not only the light reflected off the object is assessed but also the light or its absence from the object surroundings is also assessed in terms of varying intensities and wavelengths. This is the essential derivation of orientation from which object depth derives.

Object Recognition

The earlier part has demonstrated that there are many components to vision such as color, depth and motion. Depth is derived from orientation since no object becomes distinct unless it is posited against something, even its own background. This distinction of the object from its surroundings is known as object recognition and the eyes achieve this primary visual function by assimilating the following object qualities - color, depth and motion, if any. All these object qualities are determined from the qualities of the light emanating both from the object and its surroundings. The brain can then recognize the object against its background by contrasting the qualities of the light emanating from the object against those of the light emanating from its background or surroundings. Thus, object recognition during vision can only be perfect when all functional components of the eyes - the rods, cones, neural components, etc. - are without defect. Any defect such as colorblindness or defects in assessing depth can cause defects in object recognition. This is so because all the qualities of the object - color, depth and motion - are necessary in recognizing it. Thus, object recognition may be taken as the most reliable indicator of the efficiency of all the other functionalities of vision and prefect vision. It has been proved that neural cells that initiate object recognition (OR) need more complex activation criteria than cells that initiate the other functionalities of vision (Tanaka, K., 1997). Since OR is partly mnemonic and not entirely dependent upon sensual modalities (Pietrini, P., et al, 2004) it is logical to conclude that only when the other vision structures processing the other vision functionalities are working efficiently OR is efficient itself. This makes it historically dependent upon sensual modalities and it may be said that a person with vision impairments in any other vision component will not be efficient or normal in Orause, historically, his/her mnemonic store is flawed as per assessment of any or all of the three primary object qualities - color, depth and motion. The flaw in the mnemonic store depends, of course, on the particular type of visual defect the person is afflicted with.
Typically, a small baby will have difficulties in recognizing objects since its mnemonic data store is meager and it cannot use experience to determine object qualities, as an adult may. Only those objects that are very familiar, such as the mother or nurse or its favorite rattle, may become immediately apparent to the baby.

It is believed that so much will suffice for a short paper such as this.

Thank you,

Sumanta Sanyal.

Reference

Chen, Jichao, et al, The Rod Photoreceptor-Specific Nuclear Receptor Nr2e3 Represses Transcription of Multiple Cone-Specific Genes, The Journal of Neuroscience, January 5, 2005, 25(1); 118-129.

Color Blindness, Visual Expert, 2006. Extracted on 11th December, 2006, from: http://www.visualexpert.com/FAQ/Part4/cfaqPart4.html

Dichromats, Undated. Extracted on 11th December, 2006, from: http://cvision.ucsd.edu/dimono.htm

Pietrini, Pietro, et al, Beyond sensory images: Object-based representation in the human ventral pathway, PNAS, April 13, 2004, Vol. 101, No. 15. Extracted on 11th December, 2006, from: http://www.pnas.org/cgi/content/full/101/15/5658#top

Rheingans, Penny, Motion and Interaction, Undated. Extracted on 11th December, 2006, from: http://www.cs.umbc.edu/~rheingan/SIGGRAPH/motion.intro.pdf

Tanaka, Keiji, Mechanisms of visual object recognition: monkey and human studies, Current Opinion in Neurobiology, 1997, 7: 523-529. Extracted on 11th December, 2006, from: http://www.vision.caltech.edu/CNS179/papers/tanaka97.pdf

Bibliography

Goldstein, E Bruce, Sensation and Perception, ISBN: 0534362508 (Paperback), June 1999 Edition, Breton Publishing Co.