MiniLD #45 – hosted by Sos Sosowski – September 2013

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Seeing And Perceiving

by timtipgames - Mini LD 45 Entry

Use WASD to move around.
Aim at boxes with the mouse and remove them by "shooting" at them with the left mouse button.

Turn different shaders on and off by pressing the keys:
X, C, and V.

I'll have to make a video with a longer explanation. The short version:
Everything in this "game" is inspired by and modeled after early processing stages of the humans eye.

Here's a lengthy explanation :) Currently no time for corrections so please excuse my non-native-english-mistakes :)


Key C - The Color Shader
Simulates color perception on the retina. There is a part of the retina that is called the fovea, which is very small and roughly located in the center of the retina. Its size is ~ 1-2 degrees of visual field. To give an impression of what that means: If you reach out with your arm and show one thumb up, the foveas size is ~the size of your thumb-nail.

Only the fovea is covered with cones, which are responsible for color perception. The rest of the retina is covered with rods which can only "see" black and white (and some blueish light frequencies).

The shader does not reflect, that peripheral parts of the retina are much more sensitive to light (and roughly the blue spectrum of light) than the foveal parts.

One can experience that phenomenon when looking at stars at night: When you look the sky there seem to be stars that you can only see when you are not trying to look at them directly and they seem to disappear as soon as you try to focus them. In fact they do not disappear (thank god) but they are only perceived by the rods in the periphery of your visual field and the light sensitivity of the cones on the retina is not sufficient.

Key X - The Spatial Resolution Shader

This shader shows another difference between the foveal part and the peripheral part of the retina. The fovea has a much higher density of receptors then the peripheral parts. That leads to the fact that one can only see "sharp" at the central part of the visual field.

The cones (and some rods) in the fovea have a 1:1 relationship of sensor to signal. In a pixel analogy you could say that the surface of one sensor correlates to 1 perceived pixel.

The rods in the periphery are not only arranged in a much lower density, but several sensors are aggregated to one signal. So in a simplified pixel analogy you could say that the surface of several sensors build the signal for 1 perceived pixel. This leads to a lower resolution of the percept the further you move away from the fovea. So lower density and difference in processing of signals lead to lower resolution.

Key V - The Saccadic Suppression And Tremor Shader

The signal that reaches our eye when we make eye-movements is theoretically not different to the signal that would be produced if the world moved around us. So why do we not have the feeling that the whole world is moving around us all the time?
One possible explanation is found in the concept of reafference, which states that the brain produces an expectation about what is going to happen during the eye movement and negates the movements effect based on that expectation (that's extremely simplified).
While that theory accounts for a lot of effects in the humans movement system there's an effect that is actually measurable in the brain by modern methods like FMRI, the so called "saccadic suppression". Shortly before a saccade (a fast eye movement) begins, the brain inhibits the visual perception and processing so barely anything is actually visible to the brain during the moving phases. You can easily observe that by looking into a mirror and trying to watch your own eye moving - you will only see the end of the movement, if at all.

The eye is constantly moving, even if we fixate a fixed point, there's a constant jitter on the eyeball. One possible explanation is, that the muscle tension that supports the rapid eye-movements also calls this "tremor". Another explanation is related to the behaviour of neurons. If a neuron is stimulated it may respond to that stimulus. If it is stimulated repeatedly within a short time inveral the response will actually decay. If our eye would be presented by exactly the same stimulus for a while, we actually wouldn't see that it is there any more because the neurons responsible for the percept wouldn't respond any more. By constantly moving the eye around through the constant jitter, it avoids that the neurons are stimulated in the same way and "get tired" of the stimulus.

To be continued ...

Downloads and Links


goerp says ...
Sep 25, 2013 @ 1:33pm

WOW. Beautiful.

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