Sensation and Perception

Chapter 6

Our Sensational Senses Defining sensation and perception The riddle of separate senses Measuring the senses Sensory adaptation Sensory overload

Defining Sensation and Perception Sensation

The detection of physical energy emitted or reflected by physical objects.

It occurs when energy in the external environment or the body stimulates receptors in the sense organs.

Perception The process by which the brain organizes and

interprets sensory information.

Ambiguous Figure

Colored surface can be either the outside front surface or the inside back surface Cannot

simultaneously be both

Brain can interpret the ambiguous cues two different ways

The Riddle of Separate Sensations Sense receptors

Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain.

Sensation & Perception Processes

Doctrine of Specific Nerve Energies

Different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain.

Synthesia A condition in which stimulation of one sense

also evokes another.

Measuring Senses Absolute threshold Difference threshold Signal-detection theory

Absolute Threshold The smallest quantity of physical energy that can

be reliably detected by an observer.

Absolute Sensory Thresholds Vision:

A single candle flame from 30 miles on a dark, clear night Hearing:

The tick of a watch from 20 feet in total quiet Smell:

1 drop of perfume in a 6-room apartment Touch:

The wing of a bee on your cheek, dropped from 1 cm Taste:

1 tsp. Sugar in 2 gal. water

Difference Threshold The smallest difference in stimulation that

can be reliably detected by an observer when two stimuli are compared;

Also called Just Noticeable Difference (JND).

Signal-Detection Theory A psychophysical theory that divides the detection of

a sensory signal into a sensory process and a decision process.

Stimulus is

Present

Stimulus is

Absent

Response: “Present”

Hit False Alarm

Response: “Absent”

Miss Correct Rejection

Sensory Adaptation and Deprivation Adaptation

The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious.

Prevents us from having to continuously respond to unimportant information.

Deprivation The absence of normal levels of sensory

stimulation.

Sensory Overload Overstimulation of the senses. Can use selective attention to reduce

sensory overload. Selective attention

The focusing of attention on selected aspects of the environment and the blocking out of others.

Vision What we see An eye on the world Why the visual system is not a camera How we see colours Constructing the visual world

What We See Hue

Visual experience specified by colour names and related to the wavelength of light.

Brightness Lightness and luminance; the visual experience

related to the amount of light emitted from or reflected by an object.

Saturation Vividness or purity of colour; the visual experience

related to the complexity of light waves.

What We See

Hue Brightness Saturation

An Eye on the World Cornea

Protects eye and bends light toward lens.

Lens Focuses on objects by

changing shape. Iris

Controls amount of light that gets into eye.

Pupil Widens or dilates to let

in more light.

An Eye on the World Retina

Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision.

Rods Visual receptors that respond to dim light.

Cones Visual receptors involved in colour vision. Most

humans have 3 types of cones.

The Structures of the Retina

Why the Visual System is not a Camera

Much visual processing is done in the brain. Some cortical cells respond to lines in

specific orientations (e.g. horizontal). Other cells in the cortex respond to other

shapes (e.g., bulls-eyes, spirals, faces). Feature-detectors

Cells in the visual cortex that are sensitive to specific features of the environment.

Hubel & Wiesel’s Experiment

How We See Colours Trichromatic theory Opponent process theory

Trichromatic Theory Young (1802) & von

Helmholtz (1852) both proposed that the eye detects 3 primary colours: red, blue, & green

All other colours can be derived by combining these three.

Opponent-Process Theory A competing theory of

colour vision, which assumes that the visual system treats pairs of colours as opposing or antagonistic.

Opponent-Process cells are inhibited by a colour, and have a burst of activity when it is removed.

Afterimages

Test of Colour Deficiency

Constructing the Visual World Form perception Depth and distance perception Visual constancies: When seeing is

believing Visual illusions: When seeing is misleading

Form Perception Gestalt principles describe the brain’s

organization of sensory building blocks into meaningful units and patterns.

Figure and Ground Proximity

Seeing 3 pair of lines in A.

Similarity Seeing columns of

orange and red dots in B.

Continuity Seeing lines that connect

1 to 2 and 3 to 4 in C. Closure

Seeing a horse in D.

Depth and Distance Perception Binocular Cues:

Visual cues to depth or distance that require the use of both eyes.

Convergence: Turning inward of the eyes, which occurs when they focus on a nearby object.

Retinal Disparity: The slight difference in lateral separation between two objects as seen by the left eye and the right eye.

Depth and Distance Perception

Monocular Cues: Visual cues to depth or distance that can be

used by one eye alone.

The Ames Room A specially-built room

that makes people seem to change size as they move around in it

The room is not a rectangle, as viewers assume it is

A single peephole prevents using binocular depth cues

Visual Constancies The accurate perception of objects as stable

or unchanged despite changes in the sensory patterns they produce. Shape constancy Location constancy Size constancy Brightness constancy Colour constancy

Shape Constancy Even though these images cast shadows of

different shapes, we still see the quarter as round

Visual Illusions

Illusions are valuable in understanding perception because they are systematic errors. Illusions provide hints about perceptual strategies.

In the Muller-Lyer illusion (above) we tend to perceive the line on the right as slightly longer than the one on the left.

The Ponzo Illusion Linear perspective

provides context Side lines seem to

converge Top line seems

farther away But the retinal

images of the red lines are equal!

Fooling the Eye

The cats in (a) are the same size The diagonal lines in (b) are parallel You can create a “floating fingertip frankfurter” by

holding hands as shown, 5-10” in front of face.

Hearing What we hear An ear on the world Constructing the auditory world

What We Hear Loudness

The dimension of auditory experience related to the intensity of a pressure wave.

Pitch The dimension of auditory experience related to

the frequency of a pressure wave. Timbre (pronounced “TAM-bur”)

The distinguishing quality of sound; the dimension of auditory experience related to the complexity of the pressure wave.

An Ear on the World

Auditory Localization Sounds from different

directions are not identical as they arrive at left and right ears Loudness Timing Phase

The brain calculates a sound’s location by using these differences.

Other Senses Taste: savoury sensations Smell: The sense of scents Senses of the skin The mystery of pain The environment within

Taste: Savoury Sensations Papillae

Knoblike elevations on the tongue, containing the taste buds (Singular: papilla).

Taste buds Nests of taste-receptor cells.

Taste Buds Photograph of tongue

surface (top), magnified 75 times.

10,000 taste buds line the tongue and mouth. Taste receptors are

down inside the “bud”

Children have more taste buds than adults.

Four Tastes Four basic tastes

Salty, sour, bitter and sweet. Different people have different tastes based

on: Genetics Culture Learning Food attractiveness

Smell: The Sense of Scents

Airborne chemical molecules enter the nose and circulate through the nasal cavity. Vapors can also enter through the mouth and pass into

nasal cavity. Receptors on the roof of the nasal cavity detect these

molecules.

Olfactory System

Sensitivity to Touch

Gate-Control Theory of Pain Experience of pain

depends (in part) on whether the pain impulse gets past neurological “gate” in the spinal cord and thus reaches the brain.

Neuromatrix Theory of Pain Theory that the

matrix of neurons in the brain is capable of generating pain (and other sensations) in the absence of signals from sensory nerves.

The Environment Within Kinesthesis

The sense of body position and movement of body parts; also called kinesthesia.

Equilibrium The sense of balance.

Semicircular Canals Sense organs in the inner ear, which

contribute to equilibrium by responding to rotation of the head.

Perceptual Powers: Origins and Influences

Inborn abilities Critical periods Psychological and cultural Influences on

perception

The Visual Cliff

Glass surface, with checkerboard underneath at different heights Visual illusion of a cliff Baby can’t fall

Mom stands across the gap Babies show increased

attention over deep side at age 2 months, but aren’t afraid until about the age they can crawl (Gibson & Walk, 1960)

The Visual Cliff

Critical Periods If infants miss out on

experiences during a crucial period of time, perception will be impaired.

When adults who have been blind since birth have vision restored, they may not see well

Other senses such has hearing may be influenced similarly.

Psychological and Cultural Influences on Perception

We are more likely to perceive something when we need it.

What we believe can affect what we perceive. Emotions, such as fear, can influence perceptions

of sensory information. Expectations based on our previous experiences

influence how we perceive the world. Perceptual Set

A habitual way of perceiving, based on expectations.

All are influenced by our culture.

Perceptual Set

What you see in the centre figures depends on the order in which you look at the figures: If you scan from the left, see an old woman If you scan from the right, see a woman’s figure

Context Effects The same physical

stimulus can be interpreted differently

We use other cues in the situation to resolve ambiguities

Is this the letter B or the number 13?

Puzzles of Perception Subliminal Perception Extrasensory Perception: Reality or

Illusion?

Subliminal Perception Perceiving without awareness

visual stimuli can affect your behaviour even when you are unaware that you saw it

nonconscious processing also occurs in memory, thinking, and decision making

these effects are often small, however, and difficult to demonstrate and work best with simple stimuli

Subliminal Perception Perception versus Persuasion

there is no empirical research to support popular notions that subliminal persuasion has any effect on a person’s behaviour

persuasion works best when messages, in the form of advertising or self-help tapes, are presented above-threshold, or at a supraliminal level

Extrasensory Perception Extrasensory Perception (ESP):

The ability to perceive something without ordinary sensory information

This has not been scientifically demonstrated Three types of ESP:

Telepathy – Mind-to-mind communication Clairvoyance – Perception of remote events Precognition – Ability to see future events

Parapsychology The study of purported psychic phenomena

such as ESP and mental telepathy. Persinger suggests that psychic phenomena

are related to signs of temporal lobe epilepsy in otherwise neurologically normal individuals.

Most ESP studies produce negative findings and are not easily replicated.

Parapsychology

J. B. Rhine conducted many experiments on ESP using stimuli such as these.

Rhine believed that his evidence supported the existence of ESP, but his findings were flawed.