Sensation and Perception

Chapter 4

The Basics

• Sensation – Involves the stimulation of sensory receptors and the transmission of sensory information to the central nervous system

» i.e. spinal cord and brain

• Things that tip off sensory receptors:• Light, sound, smells, etc.

The Basics

• Perception – How we interpret sensory stimulation

• Football field example

– Perception reflects learning, expectations and attitudes

Absolute Threshold

• The weakest amount of a stimulus that can be tested

• Dogs v. Humans

– Thresholds are different amongst people– More sensitive than others

Some established absolute thresholds are:vision: a candle flame 30 miles away on a clear night.

hearing: a watch ticking 20 feet away taste: 1 teaspoon of sugar dissoved in 2 gallons of water

smell: a single drop of perfume in a three-room house touch: a bee's wing falling a distance of 1 centimeter onto the cheek.

Difference Threshold

• The minimum amount of difference detected between two stimuli

• Tone• Hue• Piles of sand

Signal-Detection Theory

• Distinguishing sensory stimuli that takes into account all factors of self and environment

• We focus on what we consider important

Sensory Adaptation

• Process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli– Eyes adapting to darkness– Waves on a beach– Traffic

Section 2 - Vision

• Color spectrum – Roy G. Biv

The Eye

• Similar to a camera

• Light enters the eyes, and then is projected onto a surface– The amount of light that enters is determined

by the opening in the colored part of the eye » The pupil

The Eye

• Once light enters, it meets the lens– The lens adjusts to distances of objects by

changing its thickness» Finger test – near / far

The Eye

• The changes in thickness and light project a clear image onto the retina – The retina acts like the film of a camera– Neurons in your retina that are sensitive to

light are called photoreceptors– Once the photoreceptors are activated a

nerve carries the information to the brain – occipital lobe

The Blind Spot

• We need the blind spot to see

• A point left empty of photoreceptors – room for information to travel

– Circle test

Rods and Cones

• 2 kinds of photoreceptors– Rods – sensitive only to the brightness of light– Cones – provide color

Dark and Light Adaptation

• Your ability to see in low light improves for 45 minutes

• Sundown

• Adaptation to light happens much more quickly

Visual Acuity

• Vision tests for sharpness– 20/20

• As you age your lenses become brittle, and you may become farsighted

• Holding reading material further away

Color Vision

• Human beings can see up to 1 million different hues

• Animals are more sensitive to certain colors

• The color circle

• Afterimages

• Color blind – distinguishing colors from each other

• Total color blindness is extremely rare

Section 3

• Hearing – a series of vibrations in the form of sound waves in its own unique pitch or loudness– Hearing experiment

Pitch

• The more cycles (sound waves) per second, the higher the pitch (high or low)– Women’s voices are at a higher pitch than

men’s because their vocal cords tend to be shorter

– Humans – 20 to 20,000 per second– Dogs / Dolphins / other animals in excess of

20,000

Loudness

• Measured in dB (decibels)– Loudness is determined by the height /

amplitude of sound waves» 0 decibels is the threshold (a watch heard ticking at

20 feet away)

Locating Sound

• Perception of sound• Infinite possibilities

– How your body / senses react to sound

Deafness

• Inherited / Disease / Injury / Old Age

• Conductive Deafness – – Damage to middle ear, sound is not amplified

• Helped with hearing aides

• Sensorineural Deafness– Damage or elimination of neurons, damage to

auditory nerve• Cannot be helped if nerve itself is damaged• Cochlear implants can help neuron loss

Section 4

• Other Senses –– Smell – incredibly important, apples and

onions would be relatively the same otherwise– Taste – Spheres of the tongue

• Smell and taste work together when eating

Skin Senses

• Touch• Infants grow quickly and stay healthier if

touched– Older people do better if they have pets

(cats / dogs)

• Body is covered in hairs, many too small to see– Sensory receptors lie at the base of the hair

• Do we actually “touch”?

Temperature

• Differences are all relative– Fevers– Outside heat (Summer)– Swimming pools– A/C

Pain

• The more pain receptors are located in a certain body, they more we will feel

• Point of contact > Spine > Thalamus > Brain (processing)– Prostaglandins help transmit messages

» Ibuprofen and aspirin help slow prostaglandins

Pain

• Why does rubbing or scratching painful areas help?

• Mixed signals

• Phantom limb pain

Body Senses

• Vestibular Sense– Sensory organs in your ears monitor your

motion and relation to gravity– Balance, standing, changing speeds, etc.

• Kinesthesis– Position and motion of your body– Copying body motions

Section 5

• Perception – the way our body makes sense of our sensory impressions

• Gestalt psychology – “The whole is more than the sum of its parts”

Rules of Perceptual Organization

• Closure – filling in the gaps to get a complete picture– Fig 4.11 (p. 93)

» Filling in the blanks because dogs are familiar to you

Rules of Perceptual Organization

• Figure-Ground Perception– What do we perceive as the figure and what

do we perceive as the background» Fig 4.12 (Vases or Faces)

Rules of Perceptual Organization

• Other Rules -– Laws of:

• Proximity• Similarity• Continuity• Common Fate

Rules of Perceptual Organization

• Perception of Movement– To sense movement we need a change of

position– Your senses need clues to tell you that you

are moving– Trees, road bumps, etc.

Rules of Perceptual Organization

• Stroboscopic Motion– The illusion of movement

• Flipbooks• Movies on reels

– Subliminal messages

– Perception smoothes out the gaps– Humans prefer smooth images

Rules of Perceptual Organization

• Depth Perception– The “distance away”– Monocular clues – the appearance of 3-D on

2-D surfaces – i.e. paintings

» Clearness, shadow, texture, overlapping, perspective

– This is done through stimulation of retina

Monocular Cues

• Clearness – faraway objects seem less detailed• Perspective – parallel lines coming together or moving

apart• Overlapping – placing of one object in front of another• Shadows and highlights – give a 3-D feel• Texture Gradient – closer objects have more texture

(gradient – progressive change)• Motion parallax – the tendency of objects to seemingly

move forward or backward depending on distance away• Moon, stars v. trees and rocks while driving

Binocular Cues

• Need both eyes v. one eye for monocular– 2 cues in binocular:

• Retinal Disparity • Convergence

Binocular Cues

• Retinal Disparity – only works on objects that are very close– Difference of angles of an object as seen by

both retinas

• Convergence – associated with a tightness of the eye muscles on things up close– Magic Eye puzzles

Perceptual Constancies

• Size Constancy – Comes through experience– Perceiving an object as one size no matter

the distance– Pygmy example p. 98

Perceptual Constancies

• Color Constancy– The tendency for objects to maintain color no

matter the light quality

• Brightness Constancy – Tendency to find an object equally bright even

when its surroundings change

Perceptual Constancies

• Shape Constancy – The knowledge an item has one shape

» i.e. top of a glass from different angles

Visual Illusions

• When the rules of constancies are violated