Sensation & Perception Psychology 201 Sensation & Perception Sensation is the detection and encoding of the changes in physical energy (e.g., light waves,

Sensation & Perception

Psychology 201


Sensation is the detection and encoding of the changes in physical energy (e.g., light waves, sound waves, pressure, kinetic energy, etc.) caused by environmental or internal events.


Our sense receptors, located in the sense organs (eyes, ears, tongue, nose, and skin) convert the physical energy into brain energy (i.e., electrochemical energy) in a process called transduction.


But sensations alone do not tell us much about the world until we perceive them. Sensations are just meaningless energy (e.g. light waves and sound waves) until we organize them into meaningful information (sights and sounds).




If a tree falls in the forest and no one is around, does it make a sound?

Why?

Senses

How many senses are there?

What are they?


1. sight2. sound3. taste4. smell5. touch

More senses6. heat7. cold8. pressure9. pain (Would any of you like to live a life without any pain?)10. itching11. balance12. nausea13. proprioception14. pheromones15. thirst16. hunger17. chemical pain (red hot peppers)18. infrared (snakes)19. electrical (sharks and platypuses)20. sonar (bats)21. magnetic north (birds and moles)

Reality

What is reality? What is real? Do we accurately perceive our world?

Demonstration #1Demonstration #2

Reality

Do we accurately perceive the world?

Our brains alter incoming signals

Our senses are amazingly sensitive.

It is commonly cited that a normal individual can:

1. see a candle, on a clear, and dark night from a distance of 30 miles

2. hear a watch ticking in a perfectly quiet room from 20 feet (if they don’t have tinnitus)

3. taste a teaspoon of sugar diluted in two gallons of water

4. smell a single drop of perfume diffused throughout a three bedroom apartment

5. fell the wing of a bee fall on their skin from a height of 1 centimeter

Light is Color

Objects absorb and reflect light

How many colors can we perceive?

We can discriminate among 200 steps in the visible spectrum.

We can distinguish among 500 levels of brightness.

We can discriminate among 20 levels of saturation (i.e., how little white light is reflected)

200 X 500 X 20 = 2 million colors!

Color is determined by the property of the object

Maple leaf before (a) and after (b) it changes color in the fall

Why do things look different in artificial light?

Light energy is transduced into neuronal energy

Transduction takes place in the retina.

120 Million Rods and 5 Million Cones per Eye

A Comparison of Rods and Cones

Rods

Achromatic Low Light

Less Acuity High Convergence Peripheral Vision

Longer Dark Adaptation 120 Million per Retina

Shaped like a Rod

Cones Chromatic More Light

More Acuity Less Convergence

Central Vision Quicker Dark Adaptation

5 Million per Retina Shaped like a Cone

Nocturnal vision is, in part, achieved by higher concentrations of rods.

Light is color and light affects the brain and mind.

Light causes melatonin secretion to stop and thereby regulates our circadian rhythms.

Newly discovered photosensitive ganglion cell affects melatonin secretion.

Newly discovered intrinsically photosensitive ganglion cell

http://www.brown.edu/Administration/News_Bureau/2001-02/01-080.html

Light is color and light affects the brain and mind.

Light affects mood (e.g., seasonal affective disorder).

Disruptions of light cause jet-lag and have been associated with cognitive impairment.

The characteristics of light and the architecture of our brain cause us to perceive color.

Neural Processing

Colorful illusions in your mind

You will see a green, black, and yellow flag. Stare at the circle in the middle for 30 seconds. Then, when the screen changes, blink once or twice and enjoy your color illusion.

Theories of Color Vision

Opponent-Process Theory suggests that color perception depends on receptors that make antagonistic responses to three pairs of colors. After-images

Theories of Color Vision Trichromatic Theory suggests that humans have three types

of receptors with differing sensitivities to different wavelengths. You can make any color by mixing red, green, and blue light

Theories of Color Vision Trichromatic Theory suggests that humans have three types

of receptors with differing sensitivities to different wavelengths. We appear to have three types of cones

Theories of Color Vision Opponent Process Theory

Trichromatic Theory

Which theory is correct?

Genetics affect color perception and color deficiency (not color blindness)

Color deficiency affects either blue/yellow or red/green perception.

Color deficiency is much more common in men, especially men with European ancestry (8%) (men with Asian ancestry 5%, men with African ancestry 3%).

Monochromatism or true colorblindness occurs in 1 out every 100,000 people.

Ishihara Test

Ishihara Test

“Color blindness…”

Why is the term color blindness a poor term?

Color Perception varies among Animals

Insects and ultraviolet Snakes and infrared Nocturnal animals have more rods

Color Perception varies among Species Bees can detect three colors: ultraviolet, blue, and

yellow, but not red. The ability to see red is rare for insects. The butterfly is an exception; they can perceive the

widest range of visual wavelengths (310 nm to 700 nm)

From: http://landsat.gsfc.nasa.gov/education/compositor/http://www.robijns.nl/prod-info/julbo_zonnebrillen.php

Color Perception Varies among Humans

Newborns do not possess cones and therefore can’t perceive color or detail.

The lack of cones also affects visual acuity

Color Perception Disorders

Color deficiency (retinal) Color blindness (cortical) Synesthesia Brain Damage

Cortical Color Blindness or Cerebral Achromatopsia

Mr. I was in an automobile accident and experienced brain damage. He wrote Dr. Oliver Sacks and said “My brown dog is dark gray. Tomato soup is black. Color TV is a hodge-podge…”

Mr. I had been a successful painter.

Cerebral Achromatopsia




More Brain Damage

Visual Motion Blindness or Akinetopsia

From: http://www.undergrad.ahs.uwaterloo.ca/~tbolton/Dorsal%20Disorders.htm

Questions

What color is the sound of a fog-horn?

What color is the sound an old-fashioned bicycle horn makes?

What color is a siren?

Synesthesia

Some people see sounds, feel sights, taste words, or see emotions.

Synesthesia is experienced when stimulating one sensory modality leads to a perceptual experience in another.

Color-word synesthesia may be most common and vowel sounds may be most common triggering stimuli (e.g., a = blue or red; e = yellow or white; o = yellow, red, white, or black; u = blue or black).

http://web.mit.edu/synesthesia/www/karen.html

SynesthesiaPitch (Hz) Loudness (dB) Visual Experience 30 100 a strip 12-15 cm. in length and the color of old,

tarnished silver

50 100 a brown strip against a dark background with red-tongue-like edges

100 86 a strip with a reddish-orange hue in the center and it gradually faded towards the edges until it ended in

pink 250(alto sax =196) 64 a velvet cord with fiber jutting out on all sides

500 (violin=440) 100 a streak of lighting splitting the heavens in two

500 74 dense orange color that which made him feel as though a needle had been thrust into his spin

2000 113 "It looks something like fireworks tinged with a pink- red hue. The strip of color feels rough and

unpleasant and has an ugly taste- -rather like a briny pickle…you could hurt your hand on this

one”

Does color exist in the external world or only in our minds? What makes a tomato red? Why do long wavelengths (usually) look red? Support for color existing in our minds:

Animals’ color perception Color deficiency or blindness Cortical color blindness Synesthesia Illusions

Page 104 (26)

Some major subdivisions of the Human cerebral cortex

Copyright © 2002 Wadsworth Group. Wadsworth is an

imprint of the Wadsworth Group, a division of

Thomson Learning

Monocular versus binocular depth cues

How do we know how far away an object is by simply looking at it?

Overview of Questions

How can we see far into the distance based on the flat image of the retina?

Why do we see depth better with two eyes than with one eye?

Why don’t people appear to shrink in size when they walk away?

Binocular Depth Cues

Oculomotor - cues based on sensing the position of the eyes and muscle tension Convergence - inward movement of the eyes

when we focus on nearby objects Accommodation - change in the shape of the

lens when we focus on objects at different distances

Figure 8.2 (a) Convergence of the eyes occurs when a person looks at something that is very close. (b) The eyes look straight ahead when the person observes something that is far away.

Monocular Depth Cues

Monocular - cues that come from one eye Pictorial cues - sources of depth information

that come from 2-D images, such as pictures

Interposition - when one object partially covers another

Relative height - objects that are higher in the field of vision are more distant


Relative size - when objects are equal size, the closer one will take up more of your visual field

Perspective convergence - parallel lines appear to come together in the distance

Familiar size - distance information based on our knowledge of object size

Figure 8.3 A scene in Tucson, Arizona containing a number of depth cues: occlusion (the cactus occludes the hill, which occludes the mountain); perspective convergence (the sides of the road converge in the distance); relative size (the far motorcycle is smaller than the near one); and relative height (the far motorcycle is higher in the field of view; the far cloud is lower).


Atmospheric perspective - distance objects are fuzzy and have a blue tint

Texture gradient - equally spaced elements are more closely packed as distance increases

Shadows - indicate where objects are located

Figure 8.5 A scene along the coast of California that illustrates atmospheric perspective.

Figure 8.6 A texture gradient in Death Valley, California.


Motion parallax - close objects in direction of movement glide rapidly past but objects in the distance appear to move slowly

Deletion and accretion - objects are covered or uncovered as we move relative to them Also called occlusion-in-motion

Binocular Depth Perception

Binocular (or retinal) disparity - difference in images between the two eyes Difference can be described by examining

corresponding points on the retina that connect to same places in the cortex

Figure 8.16 The two images of a stereoscopic photograph. The difference between the two images, such as the distances between the front cactus and the window in the two views, creates retinal disparity. This creates a perception of depth when (a) the left image is viewed by the left eye and (b) the right image is viewed by the right eye.

Binocular Depth Information - continued

Stereopsis - depth information provided by binocular disparity Stereoscope uses two pictures from slightly

different viewpoints 3-D movies use the same principle and

viewers wear glasses to see the effect Random-dot stereogram has two identical

patterns with one shifted to the right

Stereograms

http://www.eyetricks.com/3dstereo.htm

Figure 8.33 Two cylinders resting on a texture gradient. The fact that the bases of both cylinders cover the same number of units on the gradient indicates that the bases of the two cylinders are the same size.

Size Constancy

Perception of an object’s size remains relatively constant

This effect remains even if the size of the object on the retina changes

Demonstration

Look at the red circle on the next slide for 30 seconds.

Then look at a piece of paper and blink a few times. How many inches across do you perceive the circle after image to be?

Then look at the wall…

Figure 8.31 The principle behind the observation that the size of an afterimage increases as the afterimage is viewed against more distant surfaces.

Light directly on each coin. Each coin was the same distance from the observer. Which did they think was the farthest away?

I wondered why the baseball was getting bigger. Then, it hit me.

Visual Illusions

Nonveridical perception occurs during visual illusions

Müller-Lyer illusion: Straight lines with inward fins appear shorter

than straight lines with outward fins Lines are actually the same length

Which is larger?

Front Monster or back monster?

Figure 8.34 The Müller-Lyer illusion. Both lines are actually the same length.

Müller-Lyer Illusion

Why does this illusion occur? Misapplied size-constancy scaling:

Size constancy scaling that works in 3-D is misapplied for 2-D objects

Observers unconsciously perceive the fins as belonging to outside and inside corners

Outside corners would be closer and inside would be further away

Müller-Lyer Illusion - continued

Since the retinal images are the same, the lines must be different sizes

Problems with this explanation: The “dumbbell” version shows the same

perception even though there are no “corners” The illusion also occurs for some 3-D displays

Figure 8.35 According to Gregory (1973), the Müller-Lyer line on the left corresponds to an outside corner, and the line on the right to an inside corner. Note that the two vertical lines are the same length (measure them!).

Figure 8.39 The Ponzo (or railroad track) illusion. The two horizontal rectangles are the same length on the page (measure them), but the far one appears larger.

Fig. 8-40, p. 187

The Ames Room

Two people of equal size appear very different in size in this room

The room is constructed so that: Shape looks like normal room when viewed

with one eye Actual shape has left corner twice as far away

as right corner

Figure 8.41 The Ames room, showing its true shape. The woman on the left is actually almost twice as far away from the observer as the woman on the right; however, when the room is viewed through the peephole, this difference in distance is not seen. In order for the room to look normal when viewed through the peephole, it is necessary to enlarge the left side of the room.

Fig. 8-40, p. 187

The Ames Room - continued

Why does the illusion occur? One possible explanation:

Observer thinks the room is normal Women would be at same distance One has smaller visual angle (R) Due to the perceived distance (D) being the

same Her perceived size (S) is smaller

The Ames Room - continued

Another possible explanation: Perception of size depends on relative size One woman fills the distance between the top

and bottom of the room Other woman only fills part of the distance Thus, first woman appears taller

What is the difference between these two animals?

Documents

Sensation & Perception Psychology 201 Sensation & Perception Sensation is the detection and encoding of the changes in physical energy (e.g., light waves,