Visual Stimuli

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From the course by Duke University

Visual Perception and the Brain

129 оценки

Duke University

Visual Perception and the Brain

129 оценки

Learners will be introduced to the problems that vision faces, using perception as a guide. The course will consider how what we see is generated by the visual system, what the central problem for vision is, and what visual perception indicates about how the brain works. The evidence will be drawn from neuroscience, psychology, the history of vision science and what philosophy has contributed. Although the discussions will be informed by visual system anatomy and physiology, the focus is on perception. We see the physical world in a strange way, and goal is to understand why.

From the lesson

Background

Visual Stimuli4:01

Making an Image5:58

Summary of Topic Two1:32

Meet the Instructors

Dale Purves
M.D.
Duke Institute for Brain Sciences

This second topic is about visual stimuli,

we talked before about images and well, those are stimuli.

But now we need to talk more specifically about what stimuli are,

how they're formed, and what kind of limitations there are.

On what we can see, as we basically create visual

stimuli that end up leading us to perception.

So let's begin in this first lesson by talking a little

bit about light and electromagnetic radiation.

So here's the electromagnetic spectrum, and I guess most of you know.

But maybe some of you haven't thought about this and

don't, that this is the range of

radiation that exists in the physical world.

And it extends from very, very short wavelength,

cosmic rays at one end to much longer radio waves at the other end.

And these being in terms of kilometers, this being in terms

of tiny femtometer wavelengths, and of course we don't see all that.

We see only a tiny portion of this electromagnetic spectrum which extends

over many orders of magnitude.

And it's this that defines light, so light is kind of

often a loosely used term, but it actually means that

part of the spectrum that we human beings evolve to see.

These other things that are out here, shorter wavelengths, longer wavelengths

than what we see than light are of course there physically, but we don't see them.

And they are measured with various instruments that you can imagine,

x-ray detectors, radar and so on.

So light is really defined by human evolution and

it can only be used rather loosely to talk and

incorrectly to talk about these other aspects of radiation.

Let's blow up the little piece of the spectrum that we see,

of the electromagnetic spectrum that we see, and look at it in more detail.

So the wavelengths that we see, range from

about 400 nanometers to 700 nanometers.

And that's really a tiny range, but this is the range that normally we can see.

Other animals can see more into the ultraviolet,

more into the infrared,

for the purposes of the niches in which they exist.

But in our niche, this is the range that we have evolve to see and

in fact, all animals with visual systems don't go very far away from

the kinds of spectral light that we're capable of seeing.

Because the energy out here, begins to damage cells and

the energy here, is really heat.

And detected better as, for example some snakes do with heat detectors than with

vision and light detectors.

So that's the range that we see and

its colored because as we'll come back and talk about in a later module.

Of course we see colors and how we see colors,

I've already introduced you to the anomalous way that we see them.

And we're going to talk much more about that, but

all of these things are again critically important.

For how we think about vision, what its demands are and

how we're solving those demands.

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