version 0.10 (c) 2007 celest visi n star light, star bright, let’s explore light how you perceive...

Version 0.10 (c) 2007 CELEST

VISINStar Light, Star Bright, Let’s Explore Light

How You Perceive Light

How many black dots can you count?


HOW DO WE SEE?


DO WE SEE LIKE A CAMERA?

Unlike a camera, human vision is a perceptual process involving many parts of the brain.

or digital sensor


What do we need in order to see?

A source of light

A source of reflected light

an eye to receive light

an eye to receive light


When light falls on a surface, some of it is absorbed and some of it is reflected.

HOW DO WE SEE OBJECTS THAT DO NOT PRODUCE LIGHT?

reflected

absorbed

Our eyes can detect the reflected light.


DARK AND LIGHT SURFACES

absorb most of the lightthat falls on them, andreflect little.

reflected

absorbed

reflected

absorbed

Dark surfaces Light surfacesabsorb little of the light that falls on them, andreflect most.


HOW DO WE SEE THINGS IN THE DARK?

You can’t see in total darkness, because you need light to see.

However, you can see if there is a little light.But how?


EDGE DETECTORS!

Vision is sensitive to the difference or contrast between two surfaces.

In terms of vision, contrast is the comparison between the reflected light of one surface and another.

A comparison is computed as a ratio of two measures.

How does contrast affect which owl you see in each picture?


HOW DO WE KNOW WHAT IS GOING ON AROUND US?

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Vision, one of the five senses, controlled by specific types of cells, that send messages to a specific part of the brain.

Name the other four senses.

All of the senses are controlled by different types of cells that send messages to different parts of the brain.


OUR FIVE SENSES LET US PERCEIVE THE WORLD

http://nanonline.org/nandistance/mtbi/ClinNeuro/agnosia.html

Smell and Taste

Vision Touch

Hearing

Back of head Front of head


WHAT IS “PERCEPTION”?

Some perceptions are illusory.

Perception is the process of acquiring, “interpreting,” selecting, and organizing sensory information.

Do you always see what is “really” there?


WHITE’S ILLUSION

How many shades of gray are in the picture?


WHITE’S ILLUSION

Only one!


Are squares A and B the same shade of gray?

ADELSON’S CHECKERED SHADOW ILLUSION


Yes!

ADELSON’S CHECKERED SHADOW ILLUSION


How does the human brain and eye

accomplish the task of perceiving?


THE HUMAN EYE

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The eye is actually an organ in the shape of a ball. From the outside you can see the pupil and the iris. The pupil is what lets light inside the eye.

Pupil

Iris

The human eye is very complex


Inside the Eye…

The lens directs the light to the retina at back of the

eye where the photoreceptors receive the light and

send information to the brain via the optic nerve.

THE HUMAN EYE

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Lens

Retina

Optic Nerve

Pupil

Iris


VISION AND THE BRAIN

Light stimulates photoreceptors sending messages to the visual cortex.


THE VISUAL PATHWAY

Adapted from Frisby 1979


BASIC DEFINITIONSh

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REFLECTED LIGHT

Illuminant

Illuminance Luminance

Photoreceptors on the retina

Based on the diagram, define illuminant, illuminance, luminance,

and photoreceptor.


BASIC DEFINITIONSh

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BrightnessPerception

Define reflectance and brightness perception.

Reflectance

version 0.10 (c) 2007 celest visi n star light, star bright, let’s explore light how you perceive...

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