Chapter 4:

Sensation & Perception

​

“All knowledge has its origins in our perceptions.” – Leonardo Da Vinci

​

Vision

Hearing

Smell

Taste

Touch

​

Definitions

• Sensation
• process of detecting, converting, and transmitting raw sensory information into neural impulses (transduction)
• Perception
• process of selecting, organizing and interpreting sensory information
• enables us to recognize meaningful objects and events

Sense organs: �eyes, ears, nose, tongue, skin, & internal body organs

Happens in the brain!

Processing

• Bottom-Up (parts to whole)
• Top-Down (whole to parts)
• Expectations drive perception

Ex: you have ingredients and must put them together to make something edible

Ex: you have ingredients and a recipe & picture of a completed cake and you must recreate the cake

Top-Down Processing example

• Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

​

Top down/ bottom up

Guitar player or old people

Fruit or face

Sensation- Thresholds

• Absolute Threshold
• minimum stimulation needed to detect a particular stimulus 50%

​

• Difference Threshold
• minimum difference between two stimuli that a subject can detect 50% of the time
• just noticeable difference (JND)
• increases with magnitude

Ex: listen to headphones and indicate the earliest you hear a tone

Ex: listen to headphones and indicate when you hear a change in volume of sound

Easier to tell the difference between 100 & 101Hz than 1000 & 1001Hz

Sensation- Thresholds

• When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”.

Sensation- Thresholds

• Weber’s Law- the difference threshold is proportional (stronger stim, more change needed)
• light intensity- 8%
• weight- 2%
• tone frequency- 0.3%
• Sensory Adaptation: diminished sensitivity with constant stimulation

- receptors higher up in sensory system get tired and fire less frequently

Apply it! Come up with 3 examples

Vision: Stare at center

Sensation- Thresholds

• Signal Detection Theory
• predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise)
• assumes that there is no single absolute threshold
• High expectations- false positives
• Low expectations- false negatives
• detection depends partly on person’s

-experience -motivation

-expectations -level of fatigue

Vision: Stabilized Images on the Retina

Vision: Physical Properties of Waves

Perception of light and sound

• Transduction: conversion of one form of energy to another
• Wavelength: Hue (color) and pitch
• Amplitude: brightness and loudness
• Purity of wavelength: saturation of color and timbre for sound

Vision: Spectrum of Electromagnetic Energy

Vision: Parts of the Eye

• Cornea: transparent covering on the front of the eye
• Fovea: central point of focus on the back of the eye
• Pupil: adjustable opening in the center of the eye
• Iris: a ring of muscle the forms the colored portion of the eye around the pupil and controls the size of the pupil opening
• Lens: transparent structure behind pupil that changes shape to focus images on the retina

Accommodation: change in shape of lens focus near objects

• Retina
• Layers of neurons on inner surface of eye
• light sensitive
• contains rods and cones
• beginning of visual information processing

Blind Spot: area of retina where optic nerve leaves back of eye

Vision: Parts of the Eye

Retina’s Reaction to Light Receptors

Cones

• near center of retina (fovea)
• fine detail and color vision
• daylight or well-lit conditions

​

Rods

• Located in periphery of retina
• detect black, white and gray
• twilight or low light

Pathways from the Eyes to the Visual Cortex

Vision

• Acuity: the sharpness of vision
• Nearsightedness
• nearby objects seen more clearly
• lens focuses image of distant objects in front of retina
• Farsightedness
• faraway objects seen more clearly
• lens focuses near objects behind retina

​

Farsighted Nearsighted Normal Vision Vision Vision

Color-Deficient Vision

• People who suffer red-green blindness have trouble perceiving the number within the design

Visual Information Processing

• Trichromatic (three color) Theory
• Young and Helmholtz
• The eye contains three different types of cones capable of responding to various wavelengths of light
• red
• green
• blue

Visual Information Processing

Opponent-Process Theory: opposing retinal processes enable color vision

“ON” “OFF”

red green

green red

blue yellow

yellow blue

black white

white black

The 2 Theories

How the Brain Perceives

x

​

• Binocular Cues: clues about distance using two eyes
• Retinal Disparity: right and left eyes see slightly different views
• Convergence: the degree to which the two eyes must converge to focus
• Monocular Cues: clues about distance based on the image in either eye
• Linear Perspective: parallel lines converge in the distance
• Relative Size:
• Interposition:
• Texture Gradient:
• Light and shadow
• Height in plane

Pictorial depth cues

Perceptual Constancies: Size,Shape,Brightness, Color

Visual Perception: Constancies

• Perceptual Constancies: the ability to experience a constant perception even when what is reflected on the retina changes

​

• Color: an object will be perceived as the same color even if the color reflected on the retina changes �(ex: when an object is placed in the shade)

​

• Size: an object will be perceived as the same size even if the size reflected on the retina changes �(ex: dog running toward you is not seen as growing in size)

​

• Shape: an object will be perceived as the same shape even if the shape reflected on the retina changes �(ex: door opening toward you is still perceived as rectangular)

Illusions

Audition (Hearing)

• Audition
• the sense of hearing
• Frequency
• the number of complete wavelengths that pass a point in a given time
• Pitch
• a tone’s highness or lowness
• depends on frequency

The Stimulus

• Vibrations of sound waves
• Amplitude: loudness
• Wavelength: pitch
• Purity: timbre

The Intensity of Some Common Sounds

Audition: The Ear

• Outer Ear (pinna)
• Auditory Canal
• Eardrum
• Middle Ear
• hammer
• anvil
• stirrup
• Inner Ear
• oval window
• cochlea
• basilar membrane
• hair cells (cilia)

Audition: Pitch Perception

• Place Theory (high pitch)
• the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated
• Frequency Theory (low pitch)
• the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch

How We Locate Sounds

• Localization of Sound
• Sound is heard in the nearest ear first
• Sound is heard loudest in the nearest ear

Audition: Loss

• Conduction Hearing Loss
• hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea
• Nerve Hearing Loss
• hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve

Older people

tend to hear

low frequencies

well but suffer

hearing loss for

high frequencies

Visual Information Processing

• Feature Detectors
• neurons in the visual cortex respond to specific features
• shape
• angle
• movement

​

• Parallel Processing
• simultaneous processing of several dimensions through multiple pathways
• color
• motion
• form
• depth

​

​

Visual Perception: Gestalt- the whole is greater than the sum of its parts

• Gestalt Principles (gestalt = an organized whole. We tend to integrate pieces of info. into meaningful wholes)
• Proximity
• Simplicity (law of good form)
• Connectedness
• Closure
• Continuity
• Similarity
• Phi Phenom

What affects taste?

Taste

• Taste Sensations
• sweet
• sour
• salty
• Bitter
• Umami
• Sensory Interaction
• the principle that one sense may influence another
• as when the smell of food influences its taste

• The Stimuli: chemical substances that are soluble
• The Anatomy: taste buds on the papillae
• Perception of taste & flavor
• Numerous factors can impact the flavor of food (Ex: temperature of the food, texture, prior condition of the mouth, health state of the organism, smell)

The Tongue

Smell

Smell (Olfaction)

• The Stimuli: chemical substances that are soluble
• The Anatomy: receptors are olfactory cilia which lie on the roof of the nasal passage and sinus
• Sense DOES NOT get filtered by thalamus
• Taste and smell interact to produce flavor

Perceptual Illusions

Age, Sex and Sense of Smell

Touch

• Skin Sensations
• pressure
• only skin sensation with identifiable receptors
• warm
• cold
• pain

Touch

• Numerous types of receptors lie in varying depths in the skin
• Four Basic Skin Senses
• Hot
• Cold
• Pressure
• Pain

Pain

• Gate-Control Theory
• Theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain

​

• Substance P is related to pain

​

Body Position and Movement

• Kinesthesis
• the system for sensing the position and movement of individual body parts
• Vestibular Sense
• the sense of body movement and body’s position relative to gravity
• including the sense of balance
• Semicircular canals in ears

Parapsychology

• Paranormal- beyond normal
• telepathy, ESP, out of body experience…