Friday, December 30, 2011

Intertwining of vision and movement

Bodily movement plays the crucial role in our visual perception, as is shown in the Held and Hein's experiment. If there is no movement, there might be just a 'blur', a chaotic mixture of visual sensations.

Related to this point, I'd like to quote Merleau-Ponty's text.

Everything I see is in principle within my reach, at least within reach of my sight, and is marked upon the map of the "I can". Each of the two maps is complete. The visible world and the world of my motor projects are each total parts of the same Being.
[Merleau-Ponty, M. (1964). The Primacy of Perception. Northwestern Univ. Press. p.162]

It is by lending his body to the world that the artist changes the world into paintings. To understand these transubstantiations we must go back to the working, actual body--not the body as a chunk of space or a bundle of functions but that body which is an intertwining of vision and movement.

There is not a perception followed by a movement, for both form a system which varies as a whole.
[Merleau-Ponty, M. (1962). Phenomenology of Perception. Routledge. p.111]

The vision and the movement are deeply intertwined. As the self-actuated movement of the kitten developed the depth in vision, our movements of the eyes, the head, or the whole body transform the chaos of visual sensations into the adjusted visual perception with depth, forms, colors, and movements. It is not the mind's interpretation but bodily skills that give rise to changes in stimulation.

Vision is a kind of embodied skill. Maybe the painters are those who consciously practice this skill.

Saturday, December 17, 2011

Classic experiment by Held and Hein

The well-known experiment on vision performed by Held and Hein: They harnessed a pair of kittens to a carousel (see the figure). One of the kittens was harnessed but stood on the ground and was able to rotate around by itself, while the other, being placed in the gondola, was only moved passively. As the one kitten walked, both moved in the circle.

[Held, R. and Hein A. (1963). Movement-produced stimulation in the development of visually guided behavior. Jouranal of Comparative and Physiological Psychology
56(5): 872-876.]

None of them have received light before the experiment, as they both were reared in darkness from birth. The point of this experiment is that both kittens were made to learn to see the world, receiving the same visual stimulation. The difference was that the one could move actively, the other was moved passively.

According to Held and Hein, only the self-moving kitten developed the normal visual perception. The other one, which was deprived of self-actuated movement, could not develop the depth perception. For example, it doesn't blink to an approaching object. In its visual field, I think, something looks 'bigger' when approaching, but never looks 'nearer'. The change of patterns in the visual field does not have the spatial meaning for the kitten.

The self-actuated movement is necessary in order to develop the normal visual perception with depth. Our movement in the world, the movement from here to there or there to here, gives the dimension of depth to mere visual sensations. Movement is the key to understanding the vision.

Sunday, December 11, 2011

What is vision?

What is vision?

We tend to think, in general, that the vision (visual perception) is a passive process; visible light comes into our eyes and makes images on the retina. These are then transmitted via optic nerves and represented in the visual areas of the cerebral cortex. Once you open your eyes, a precise impression of the surrounding world is given to you. The visual system (eyes, optic nerves, visual areas) functions like a photograph or a mirror. It is believed to reflect the present world as it is.

But it does not seem the way things are. Oliver Sacks, a neurologist, describes the case of his patient Virgil, who restored the vision by surgery after 45 years of blindness:

Virgil told me later that in this first moment he had no idea what he was seeing. There was light, there was movement, there was color, all mixed up, all meaningless, a blur. Then out of the blur came a voice that said, "Well?" Then, and only then, he said, did he finally realize that this chaos of light and shadow was a face --- and , indeed, the face of his surgeon.
[Sacks, O. (1995). An Anthropologist on Mars. p.114]

There is no problem with patient's eyes, retina, or optical nerves. He is not blind anymore after the surgery, but his visual world is totally chaotic. To put it accurately, he is seeing but he is not able to get the meaning of what he sees. There is light, movement and colors but they are all mixed up as 'a blur'. He is receiving the visible light perfectly but his visual world is perfectly meaningless.

How should we think about this case?