[baudrunner]

The process by which the transmission of visual information occurs from its reception on the retina right to the processing of the visual cortex is similar throughout and involves the transfer of information from neuron to neuron. The largest neuron in your body is found in the spinal cord and comes to/from the midbrain. It is a single cell about three feet long in the adult. The information transfer between adjacent nerve cells is through the biochemical stimulation between axon and dendrite in the healthy nervous system. I say healthy because in people with neuron diseases such as Altzheimers disease a backup system then employs the use of neurotransmitters such as acetylcholine which act as messengers between the cells when some of the cells in the information path are destroyed. This is why Altzheimers patients are given actylcholinesterase inhibitors, because the enzyme acetylcholinesterase is designed to break down acetylcholine since it wouldn't do for random acetylcholine molecules to be swimming around in the brain because the neurons would constantly be receiving false information, so it is broken down once its task is complete. In any event, signal transmission is, as I've said, biochemical in nature and involves a temporal component - ie. it takes time to produce the chemical reactions across the synapse, or between the cells.

An interesting experiment was once conducted in which cats were born and kept for their entire lives in controlled conditions. One group of cats lived in an environment where all the rooms were painted with horizontal black and white stripes on the walls. Another group was kept in an environment where all the walls were painted with vertical black and white stripes. The visual cortex of the cats revealed on autopsy that there was a direct correllation between the arrangement of the development of the neuron structures over the entire visual cortex with the orientation of the painted black and white stripes. The neuron bodies had developed complexity in alternating horizontal or vertical bands, depending on which group was being analysed.

The persistence of vision and the effects that are observed are directly related to the customization of the pattern of neural processing of the image information. This only happens when there is no continued stimulation of the retinal receptors as when the eyes are opened and in the retina continued residual excitation of adjacent cones and rods is temporarily observed and this is what we see. Our interpretation of light and dark areas when we have our eyes closed is entirely subjective, it is better to say that there are contrasting areas which appear as residual degrading image data. The apparent reversal of contrasting areas is probably related to the fact that the rods are quicker at information degradation than are the more complex cones, so the persistence of the cones lasts longer. In other words, the luminance information is lost before the color information is lost so the effect is that the contrasting areas seem to trade bright for dark.

The retina does not receive photons shooting through the lens of the eye. The characteristic modulations of information pertaining to the surface atoms of the objects that we perceive in our environment are effectively transferred atom by atom until they stimulate the retinal receptors and this occurs at the rate of atomic interaction, which occurs over a distance of 3x10^10 cm/sec at one G and one atmosphere of pressure. Visual information is received most effectively in the direct line of sight and deteriorates in quality of precision peripherally, and on the retina the modulations are converted to biochemical ion-based information transfer. Calcium and chlorine ions mediate the transfer process within the neuron and molecular activity in the synapse between axon and dendrite involving molecular transmitters and receptors pass the information between neurons. In order for us to perceive light, there must be a source of energy exciting the atoms in the medium, such as the sun or the light bulb or both, and a process of information exchange between atoms in the medium and biochemical activity beginning in the eye and continuing to the visual cortex is ongoing until the source of energy producing the excitations is removed.

[zeroca]

Visual cortex is the term applied to both the primary visual cortex (also known as striate cortex or "V1") and upstream visual cortical areas also known as extra-striate cortical areas (V2, V3, V4, V5). The primary visual cortex is anatomically equivalent to Brodmann area 17, or BA17. Brodmann areas are based on a histological map of the human brain created by Korbinian Brodmann.

I’ll analyze it in following posts, but let’s see how the animation from previous posts was constructed:

Then the second identical animation is taken (miving to opposite direction) and overlapped on the first. As you see, the perception of successive “run” of flashing light by visual system only after overlapping is detected.

The speed in previous (upper) two animations is 2 frames/sec.,
But in the animation below the speed of overlapped two animations was increased and equals to 12 frames/sec, i.e. difference is only in speed. The final animation is six times faster.

So, you see clearly that “running light” doesn’t exist actually, but it’s perceived by visual system, and even is perceived as motions in two different (opposite) directions, changing in turn within perceived picture.

[mkirkpatrick]

Originally Posted by zeroca

I’ll analyze it in following posts, but let’s see how the animation from previous posts was constructed:

Then the second identical animation is taken (miving to opposite direction) and overlapped on the first. As you see, the perception of successive “run” of flashing light by visual system only after overlapping is detected.

The speed in previous (upper) two animations is 2 frames/sec.,
But in the animation below the speed of overlapped two animations was increased and equals to 12 frames/sec, i.e. difference is only in speed. The final animation is six times faster.

So, you see clearly that “running light” doesn’t exist actually, but it’s perceived by visual system, and even is perceived as motions in two different (opposite) directions, changing in turn within perceived picture.

Zeroca,I could only look at it for a moment,made me feel dizzy!Great work.
regards michael.

[zeroca]

unnecessary post

[zeroca]

Until considering upstream visual cortical areas, also known as extra-striate cortical areas (V2, V3, V4, V5), I’d like to analyze visual perceptions in case of physiological and several pathological processes from retina up to primary visual cortex – Brodman area 17 (occipital area). First I will place image of mentioned path, then – image of physiological scotoma, i.e. confined, bordered defect in the field of vision. As we mentioned above (post #6 of this thread), in normal field of vision always exists scotoma, named as blind spot. This scotoma corresponds to projection of disc of optic nerve: blind spot is situated on temporal side of field of vision, approximately at the angle of 15 degrees from the point of fixation, and is situated so because disc of optic nerve is on nasal side of retina from yellow spot (image – post# 20 of this thread). I’ll explain it further.



Physiological scotoma:


scheme for fields of vision for both eyes:

[baudrunner]

I think that your mind is rather more preoccupied with impression than it is with understanding. You don't appear easily impressed yourself so you are not innocent. You find yourself actually talking back to yourself in this thread. That is odd.

[zeroca]

Thank you for kind comments. You are good observer and your opinions are always useful.
Anyway I’ll proceed with my explanations:
Scotoma - confined, bordered defect in the field of vision can be positive and negative, absolute and relative:
1. Absolute scotoma is when in this part of field of vision white and colored objects aren’t perceived.
2. Relative scotoma – when white colored objects are perceived less distincty (as gray), but colors of colored objects – less saturated than in normal parts of field of vision.
3. Positive scotoma – defect in the field of vision, which patient sees in form of black (or sometimes colored) spot, which covers the part of viewed object.
4. Negative scotoma – isn’t perceived by patient, but can be detected with examination of patients, and negative scotomas are observed mainly in cases of affection of visual tract (visual passes), i.e. by examining of localization of scotoma (localization of them is just interesting for us) we can unmistakably detect, which part of visual pass is affected, i.e. what physiological function particular part of visual pass is responsible for.
The good example of absolute negative scotoma is physiological scotoma, or blind spot (considered by us above - test for eye, post #6 of this thread).

[zeroca]

By disposition scotomas are central and peripheral. If the part of retina – corresponding zone to yellow spot is affected, the central vision suffers heavily. The causes of central and peripheral scotomas are various, but mainly the retina is affected.



Here are schemes of some different forms of scotomas (yellow field on the diagram – field of vision; excuse me, but who doesn't know, I'll clarify for them - yellow field is just what patient sees, i.e. black spots below within field of vision are scotomas):
Each diagram is for right eye.
1. Central scotoma;
2. Para-central and peripheral scotomas;



3. Annular scotoma;
4. Sector-shaped scotoma.

[zeroca]

Diseases, affecting the higher parts of visual path – chiasma, optical tract, sub-cortical ganglions, corresponding areas of occipital convolution, are accompanied with typical changes within field of vision – the half-parts (half-vision) of field of vision are lost, or constriction of field in the form of quadrants are observed.
Cancers of hypophysis, or inflammatory processes of basis cranii affect internal parts of chiasma, i.e. crossed internal fibers (coming out from nasal parts of retinas of both eyes- see red point below), so appears bitemporal heteronymous [crossed] hemianopsia– loss of temporal halfs of fields of vision of both eyes:



Red point - pathological process. Scheme is for both eyes.

[zeroca]

Binasal hemianopsia is when affection of chiasma concerns uncrossed fibers, and this type of hemianopsia is extremely rare, as in this case two opposite (symmetric) parts of chiasma must be involved (see images below), for instance calcification of both internal carotid artery at ephippium (Turkish saddle):

Small black temporal-side spots within field of vision, as you guessed, are physiological scotomas - blind spots:


I’d like to emphasize, that when uncrossed fibers are affected (they are colored in violet on the animation), that means that corresponding zones of retinas of both eyes (colored in violet) aren’t affected and receive image of outer object, but this image isn’t conducted to higher perceptive centers for final perception (as damage is within visual path), and unaffected retinas’ corresponding zones within field of vision are lost.