Two Mechanisms of Vision: Ambient Vision and Focal Vision (4 Viewers)

[HenRun]

This conversation, while fascinating, has reached the point where (for me) it may as well be written in Akkadian, on small clay tablets.

I think the language used is Saccadean. That is what my eyes tell my brain, at least.
My reply to you is as a matter of fact written on a tablet. Hope it is legible to you, my hieroglyphics are often misinterpreted.

The Crow I usually enlist for writing my clay tablets in cunaeform has the weekend off. Also, I have not fired up the kiln so claybaking is not taking place today.

All kidding aside, this is a lot to digest but very interesting.

 

[tenex]

A remarkable discovery by Triesman and her colleagues is that the sub-conscious and parallel processing of certain elementary attributes is automatically reported to our conscious awareness only when a salient feature is present in a particular location and not present elsewhere.

One can ask whether this is a "remarkable discovery" or a careful scientific elaboration of something quite obvious, that must go back very far indeed on the evolutionary timeline, long before humans or human consciousness. (It is after all why camouflage also evolved.) And even whether the result is "reported to our conscious awareness", since our gaze tends to be directed there before we know why.

 

[Maljunulo]

It is my understanding that, although it is intuitively obvious, and has been widely accepted for millennia, there is no scientific “proof” that the optimum shape for a wheel is round. (circular)

However, I may have missed it somewhere.

 

[Omid]

Helen: A blind monkey that could "see" everything

A rhesus monkey, named Helen, was part of a study into the neuropsychology of vision, led by Lawrence Weiskrantz in the psychology laboratory at the University of Cambridge. In 1965, Prof. Weiskrantz had surgically removed the primary visual cortex at the back of Helen’s brain. Following the operation, Helen appeared to be quite blind.

But, as we have discussed in this thread, in mammals there are two main pathways from the eye to the brain: an evolutionarily ancient one – the descendant of the visual system used by fish, frogs and reptiles – that goes to the optic tectum in the mid-brain, and a newer one that goes up to the cortex. We have called the evolutionary ancient one "Ambient Visual System" and the newer one the "Focal Visual System" (See Post #1). In Helen, the older visual system was still intact. If a frog can see using the optic tectum, why not Helen?

In 1966 while Prof. Weiskrantz was away at a conference, his PhD student Nicholas Humphrey took the chance to investigate further. He sat with Helen and played with her, offering her treats for any attempt to engage with me by sight. To his delight, she began to respond. Within a few hours, Humphery had Helen reaching out to take pieces of apple from is hand; within a week, she was reaching out to touch a small flashing light… Seven years later (as shown in the video below), she was running round a complex arena, deftly avoiding obstacles, picking up peanuts from the floor.

I have attached Dr. Humphery's paper about Helen's visual capabilities published in the New Scientist magazine more than 50 years ago. It is a fascinating proof of the existence of an independent Ambient Visual System which operates silently beneath conscious awareness.

 

[Holger Merlitz]

These experiments are scary, but certainly fascinating. Nowadays probably hard to justify ethically. But I guess there must be reports about humans, too, who had accidents or strokes and thereby parts of their visual cortex disabled.

Cheers,
Holger

 

[tenex]

The term "blindsight" has been applied to the perceptions of humans with damage to the visual cortex, who seem the ideal research subjects not least for their ability of speech. But they turn out not to be conscious of these and can't describe them. The deficits in ability seem similar to those described in this fifty-year-old(!) paper.

But of course animal experimentation continues for various purposes, notably toxicity testing, on the presumption that ethics don't apply. Groups like Ärzte gegen Tierversuche campaign against it with little success. "Helen" was probably a macaque, some species of which are now threatened in the wild largely due to this.

 

[Omid]

Object-centered vs Ego-centered reference frames

In Post #1 I mentioned that the Ambient Visual system uses the "Ego Center", a hypothetical point that most visual scientist think is located between the eyes and somewhat behind them, as the reference point from which objects distance and directions are determined. In other words, the Ambient Visual System uses a polar coordinate which is anchored on the observer's "body" not on a point on the surface of the "retina". Depth in this mode of vision is mainly perceived using parallax: Binocular parallax gives very accurate depth information within the Peripersonal space which is the immediate space around our bodies, typically within reach, where we actively interact with objects and the environment. Motion parallax produced by head and body movement together with the height of our eyes above ground give accurate distance information within our Extrapersonal action space (upto about 30m).

In contrast, the Focal Visual System has a reference frame which is centered on the fovea region of the retina. Therefore, when looking directly at an object, it can "lock onto the object" and see features of the object in relation to each other and in relation to its surrounding neighborhood (without registering the relation between the observed object(s) and the Ego). This object-centered reference frame allows the Focal Visual system to be able to "see" and interpret visual information about relative position of objects independent of one's own position in space. Linear perspective seems to be a key factor in creating an impression of "depth" in this mode of vision.

In normal visual experience, these two modes of vision are so seamlessly integrated that we barely notice the distinction. But in some unusual situations, such as looking at pictures or paintings and also when looking through binoculars, these two visual mechanisms become dissociated. This dissociation allows as to see and enjoy paintings even when we are not positioned at the correct center of perspective of the image.

When looking at a painting, the Ambient Visual System, does not recognize the illusion of depth created by perspective and "sees" a flat 2D patch of colors located at a short distance in front of the Ego center. Only our Focal Vision can read and understand the language of linear perspective in paintings, photographs and images we see through our binoculars

Andrea Mantegna (1431-1506), The Martyrdom of Saint Christopher