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C126 Perception Spring 2021
Lecture notes for perception SP 2021
Terms in this set (44)
Why would we want to take this course?
The first is that a huge proportion of our brain is devoted to vision.
The second reason is that we can understand the brain by studying vision.
Another reason we study vision is that it's an enormously complicated problem, but it seems effortless. When you open your eyes, you see the world immediately, seemingly instantaneously.
A fourth reason that we want to use visual perception as an example, as a, as a primary focus in this semesters because science division is really accessible.
A large part of your brain is devoted to vision
- you know about your pupil. That's where light goes in.
- The sclera is the white of your eye
- the iris is the colored bar code like structure that's unique to each individual.
Occipital lobe here in the ____, the parietal lobe, which is on the _____, the frontal lobe, and the temporal lobe --> what is the acronym from front to back?
Occipital lobe here in the back, the parietal lobe, which is on the top, the frontal lobe, and the temporal lobe.
In fact, half or more than ____ of your brain is really devoted to visual processing. The brain is largely geared towards visual processing.
A second reason we want to study visual perception in particular, I really focus on it just because we can understand the brain more broadly by studying ________.
You can recognize different identities and you can, you can attribute emotion, emotions to these, to these spaces. You can even recognize faces down here that are incomplete, black and white. The one on the bottom right here is called a _____________________
It's a region of the brain on the underside over here, off the cortex at the back of the brain.
the fusiform face area.
This FFA region in the fusiform face area is a smallish area back here that has cells that are almost entirely devoted to face processing. This area of the brain is particularly important for face recognition among a few other specific regions. And it highlights a principle of our brain processing, which is called localization of function. It's a kind of organization that the brain uses for processing information and specialized so-called modules. When this area of the brain is damaged, we have something called
what is face blindness? AKA ______________
Prosopagnosia. It's the inability to recognize the identity of a particular face. And so when you encounter faces are a crowd of phases. What you see are a bunch of people, but you don't know who those people are. It's an amazingly debilitating disorder.
Now, what does the FFA tell us or damage to the FFA?
What it tells us is that there's an organization principle, a general principle that the brain has modules or specific regions that are devoted to specific perceptual tasks like face perception, but also other things, not just face perception.
How is light is converted from one source to another source.
Light, for example, is transduced by the visual system, by the retina. From electromagnetic radiation into electrical and chemical signals that the brain can use. Light transduction is a, is a conversion of light into another sort of information.
unique point of view illusion
There are many artists out there that do this. What he's done is create chalk pictures on flat cement surfaces that depict or appear to depict three-dimensional structure. So this looks like a pit and this looks like a bath on the right. And yet it's flat cement. There is no three-dimensionality to this. There's no jumping into this pool of water. It's entirely an illusion.
Artist is creating queues!!!!
depth is only in our
create a two-dimensional interpretation from a three-dimensional scene --> Alexa oil painting on wall
How do we study visual perception and perception more generally?
We use psychology, and in particular, we use phenomenology in psychophysics.
simply studying how things look, how things appear, and scrutinizing why they appear, the way they appear.
an objective science. The goal is to relate a physical stimulus with a psychological state. So that's the combination of psycho, psychological and physics. The state of things. By relating a physical stimulus with a psychological state, we can come up with a kind of transfer function. It's a kind of a way of describing. A mathematical relationship between what's out in the world of physical state and once in our brain. In other words, what we perceive.
when we're trying to understand images, or we're trying to build a computer system or an algorithm that can understand images. What we're doing is modeling the visual system to
try to understand that artificial visual systems are out there in some form, but universally they are very rudimentary at best. Some of them are very good at very specific tasks, but it's a very, very specific and narrow range of tasks that he had. Artificial visual systems are good at. For example, we might have a computer vision system for recognizing tumors or for recognizing faces. And yet those, those algorithms only work under a very narrow range of circumstances. They're not general, broad purpose. Visual processing systems like your brain, it, you can understand faces under all kinds of different contexts, like the black and white images that I showed you before. And yet, an artificial visual system can't do that only under very specific circumstances. Doesn't artificial visual system work very well?
It is a flat surface and yet your interpretation of the world is ________
three-dimensional. You experience the world as having depth, as having three-dimensional structure for that three-dimensional structures not available on your retina. So you have a 3D world, 2D retinal image, but your perception is three-dimensional again. So how does the brain do that? How does the brain into? Or construct a 3D interpretation from a 2D retinal image. It's a difficult problem and it's something we're going to talk about later in the semester.
A fourth reason that we study vision in particular is because it's really ___________
the feeling of self-motion when something nearby is moving.
feeling of self motion driven by the visual motion on your retina.
A heuristic is
kind of a rule of thumb or a trick or a shortcut.
So there are some recurring concepts in this course that we're going to encounter frequently.
1. One is auto calibration.
2. A second is called neural democracy rules.
3. A third is called measure than model.
4. A fourth is replace ambiguity with certainty.
5. And a fifth is betting on the familiar or the non accidental.
Auto calibration means
that the visual system has to maintain a kind of equilibrium.
But your visual system adjusts that adjustment, that adaptation, that is auto calibration. It's your visual system adjusting to the prevalent conditions that are present for you.
Another example is outer auto calibration in motion.
So sometimes you're moving, you might be running through the world or something like that and you might be encounter a lot of motion. Your visual system adapts to this.
Take a look at this blue cross right at the center of this display. We keep looking at that Blue Cross, Blue x right at the middle and stare right at it. Don't move your eyes to keep staring at that Blue Cross. Quickly. Notice that there is something called a
motion after effects
Contractionary motion is _____
the motion of those rings that contracts toward the center, toward what you're looking at, toward the blue x. Because of all that contractionary motion, your visual system says, well, this is the new normal. And the new normal is what we have to get used to. And so the visual system tries to get used to that. The problem is when the statue appears, that's different than the new normal. The way it's different is that it's relatively speaking, it's growing. Now. It's physically stationary. But compared to what you had been looking at before, it's sure seems like it's getting bigger.
And that's how the visual system is doing. It's trying to
maintain a kind of equilibrium. It's trying to adapt to the prevailing condition.
The visual system is trying to maintain a kind of equilibrium and that's called
The 4th concept we'll see often is
neural democracy rules.
What we mean by neural democracy is
a population of neurons, a population of units in your brain. You've got something called neurons that we'll talk about in the next lecture. The cells, these neurons come in, in high quantity, are millions and millions of them. What the brain does is take a, essentially a vote of that population of neurons.
So then three more concepts that we're going to encounter in this course. Repeatedly.
- Measurement model
- replace ambiguity with certainty and
- bet on the familiar or non accidental.
What do these mean?
- What your brain is doing is measuring things.
- It take some information from the outside world. in the case of vision that takes some retinal information, information out of the world comes into your eye, hits the back of your eye, the back of your eyes called the retina. And it measures that information, so it measures a bunch of light. Now imagine you hear your retina does this, your eye measures a bunch of light spots. Here's some light spots right over here, and write a bunch of flashlights, for example. Now the visual system measures that information, but it needs to come up with an idea of what is causing that. So it needs to model that information, need to come up with a hypothesis about what is causing that pattern of lights, a pattern of flashlights. So first your visual system measure something, measures a bunch of light spots, and then it models it. It comes up with an idea and a hypothesis about what might be causing it. Now, in this case, it's highly ambiguous. These are a bunch of flashlights arranged in an arrow like fashions pointing upward. So you might infer that it's an, it's an arrow or maybe it's a bird or something like that. It could be an infinite number of things. But as soon as it starts moving, it becomes immediately obvious what it is. It's a person walking.
Instead, your visual system makes a
model, creates an hypothesis about what causes that.
So there are multiple possible interpretations, but your blank, but your brain replaces the ambiguity with certainty. --> continue statement / process
- It measures some light.
- It models an idea which is based on your familiarity with the, with familiarity and previous experience.
- And then it comes up with a, with a, with a model and replaces the ambit, ambiguous interpretation, a certain interpretation.
You might have to think it through to realize that what your brain has access to is only
the retinal image.
So the most common non accidental model means the visual system selects the most
likely, and it's usually on one or two interpretations that are possible. Or most likely could have been an infinite number. But really it almost always boils down to one or two.
Most people perceive this corner as being closer to you. That's a convexity preference or convexity prior or convexity dominating interpretation.
And that's because we have a general convexity prior, general convexity preference. And that's because things in the world most often are actually convex, not concave. Convex means popping out at you.
popping out at you.
pictures rotating / brain interprets as changing expression. Why?
The possible, one of the possible interpretations, one of the possible models, one of the possible hypotheses for this retinal image is that the faces are folded like an accordion.
Faces are solid convex structures.
An alternative hypothesis is simply that the faces are changing expression
Faces changing expression are commonly encountered according, faces are never encountered and so you perceive these phases as changing expression.
Even though what's actually happening is they're just folded.
Okay, in this course, we're going to encounter a lot of recurring concepts and we're going to study a lot of low level, mid-level perception that we've already mentioned already, like face perception, colour perception in motion perception.
But we're also going to study high level perception like visual memory, attention, and consciousness.
One of the questions that we have to talk about is whether and what we see when we open our eyes.
So when we're seeing things one, we think we're seeing things, how much detail do we actually get access to?
What it highlights is that we have relatively limited access to the information that's in the scene.
If you had full access, complete access than detecting a change would be easy. You would automatically detected, detected very quickly. But you don't detect things very quickly when I change. And that's because you have limited capacity to, to attend to and store information in each individual seen that experience.
Retina is where
back of eye
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