Download Ch 4 Sensation and Perception

Chapter 4
Sensation and Perception
Sensation and Perception: The
Distinction
• Sensation : stimulation of sensory
receptors and produces neural impulses
• Perception: selection, organization, and
interpretation of sensory input
• Psychophysics = the study of how
physical stimuli are translated into
psychological experience
Psychophysics: Basic Concepts
• Sensation begins with a detectable
stimulus
– Psychological versus physical
• Fechner: the concept of the threshold
– Absolute threshold: detected 50% of the
time.
– Just noticeable difference (JND): smallest
difference detectable
• Weber’s law: size of JND proportional to size of
initial stimulus
Examples of Absolute Thresholds
• Vision: a candle flame at 30 miles on a dark,
clear night
• Hearing: the tick of a watch under quiet
conditions at 20 feet.
• Taste: one teaspoon of sugar in 2 gallons of
water
• Smell: one drop of perfume diffused into the
entire volume of a six room apartment
• Touch: the wing of a fly falling on your cheek from
a distance of 1 centimeter
Psychophysics: Concepts and Issues
• Signal-Detection Theory: Sensory processes +
decision processes = detection
– applications
• Sensory Adaptation: Decline in sensitivity
• Transduction: Where (in vision, it is in the
retina) does the energy (in vision it is
electromagnetic energy) of the stimulus become
converted to electrical/chemical energy and the
signal is sent to the brain.
Subliminal Perception
• Subliminal Perception: registration of input
without conscious awareness.
– 1957 study in a movie “Eat Popcorn”
– Objective evaluation – studies have not confirmed
the influence of subliminal messages:
– Subliminal Perception: What our unconscious
perceives (4 min)
Vision: The Stimulus
• Light = electromagnetic radiation
– Amplitude: perception of brightness
– Wavelength: perception of color
– purity: mix of wavelengths
• perception of saturation, or richness of colors.
The Eye: Converting Light into
Neural Impulses
• The eye: housing and channeling
• Components:
– Cornea: where light enters the eye
– Lens: focuses the light rays on the retina – Iris: colored ring of muscle, constricts or
dilates via amount of light
– Pupil: regulates amount of light
The Retina: An Extension of the
CNS
• Retina: absorbs light, processes
images, and sends information to the
brain
• Optic disk: where the optic nerve
leaves the eye (The blind spot)
• Receptor cells:
– Rods: black and white/ low light vision
– Cones: color and daylight vision
• Adaptation: becoming more or less sensitive to
light as needed – F 4.10
Optic Nerve, Blind Spot & Fovea
Optic nerve: Carries neural impulses from the eye to the brain.
Blind Spot: Point where optic nerve leaves the eye, because there
are no receptor cells located here, it creates a blind spot. Fovea:
Central point in the retina, around which the eye’s cones cluster.
http://www.bergen.org
10
The Retina and the Brain: Visual
Information Processing
• Light -> rods and cones -> neural signals > bipolar cells -> ganglion cells -> optic
nerve -> optic chiasm ->thalamus>
opposite half brain -> primary visual
cortex.
Figure 4.15 The what and where pathways from the primary visual cortex
Shape Detection
Specific combinations of temporal lobe activity occur
as people look at shoes, faces, chairs and houses.
14
Feature Detectors in the Visual Cortex
Principles of Perception
• Gestalt principles of form perception:
– figure-ground, proximity, similarity, continuity, closure,
and simplicity
– Point of view effects
• Recent research:
– Distal (stimuli outside the body) vs. proximal
(stimulus energies impinging on sensory receptors)
stimuli.
– Perceptual hypotheses
• Context
– Object recognition – object background consistency –
Perceptual Learning
• Change in the brain that alters how we process sensory
information
• Perceptual Habits: Ingrained patterns of organization and
attention
– Other-Race Effect: Tendency to be better at recognizing faces
from one’s own racial group than faces from other racial or ethnic
groups
– Active Movement: Self-generated action; accelerates perceptual
adaptation
– Context: Information surrounding a stimulus; affects perception
– Frames of Reference: Internal standards for judging stimuli
Hearing: The Auditory System
• Stimulus = sound waves (vibrations of
molecules traveling in air)
– Amplitude (loudness)
– Wavelength (pitch)
– Purity (timbre)
• Wavelength described in terms of frequency:
measured in cycles per second (Hz)
– Frequency increase = pitch increase
• Sound pressure (SPL) – decibels
Loudness
ratings and
potential
hearing
damage.
The Ear: Three Divisions
• External ear (pinna): collects sound.
• Middle ear: the ossicles (hammer, anvil,
stirrup)
• Inner ear: the cochlea
– a fluid-filled, coiled tunnel
– contains the hair cells, the auditory receptors
– lined up on the basilar membrane
Figure 4.49 The human ear
Figure 4.50 The basilar membrane
The Auditory Pathway
•
•
•
•
Sound waves vibrate bones of the middle ear
Stirrup hits against the oval window of cochlea
Sets the fluid inside in motion
Hair cells are stimulated with the movement of
the basilar membrane
• Physical stimulation converted into neural
impulses
• Sent through the thalamus to the auditory cortex
(temporal lobes)
Theories of Hearing: Place or
Frequency?
• Hermann von Helmholtz (1863)
– Place theory: different portions (or places) along
the basilar membrane are activated by a specific
frequency
• Other researchers (Rutherford, 1886)
– Frequency theory: suggests that the entire basilar
membrane is activated to differing degrees by
different frequencies
• Georg von Bekesy (1947)
– Traveling wave theory suggests that a
combination of both the Place and Frequency
theories explain hearing.
Auditory Localization: Where Did that Sound Come From?
• Two cues critical:
• Intensity (loudness)
• Timing of sounds arriving at each ear – F
4.51
– Head as “shadow” or partial sound barrier
• Timing differences as small as 1/100,000
of a second
Hearing Deficits
Older people tend to hear low frequencies well but suffer
hearing loss for high frequencies.
27
The Chemical Senses: Taste
• Taste (gustation)
• Physical stimulus: soluble chemical substances
– Receptor cells found in taste buds
– 25% of people have a very large number of taste buds.
They are “supertasters”.
• Pathway: taste buds -> neural impulse ->
thalamus -> cortex
– Four primary tastes: sweet, sour, bitter, and salty (maybe
a 5th “umami”, a savory taste)
– Taste: learned and social processes
• Culture and taste –
– May explain why some people enjoy hot peppers
The Chemical Senses: Smell
• Smell (Olfaction)
– Studies show women’s smell sensitivity is better
than men’s.
• Physical stimuli: substances carried in the air
– dissolved in fluid, the mucus in the nose
– Olfactory receptors = olfactory cilia
• Pathway: Olfactory cilia -> neural impulse > olfactory nerve -> olfactory bulb (brain)
– The only sensory information that does not go
through thalamus
© Richard Costano, Discover Magazine, 1993
Fig. 5.25 Receptors for the sense of smell (olfaction). Olfactory nerve fibers respond to gaseous
molecules. Receptor cells are shown in cross section at the left of part (a). (c) On the right, an
extreme close-up of an olfactory receptor cell shows the fibers that project into the airflow inside the
nose. Receptor proteins on the surface of the fibers are sensitive to different airborne molecules.
Smell and Memories
Brain region (red) for
smell is closely connected
with brain regions (limbic
system) involved with
memory, that is why strong
memories are made
through the sense of smell.
Skin Senses: Touch
• Physical stimuli = mechanical, thermal, and
chemical energy impinging on the skin. receptors/detector –
• Pathway: Sensory receptors -> the spinal
column -> brainstem -> cross to opposite side
of brain -> thalamus -> somatosensory
(parietal lobe)
• Temperature: free nerve endings in the skin
• Pain receptors: also free nerve endings
– Two pain pathways: fast vs. slow
Gate Control Theory of Pain
• Gate Control Theory: Pain messages from
different nerve fibers pass through the
same “neural” gate in the spinal cord.
– If gate is closed by one pain message, other
messages may not be able to pass through
Other Senses: Kinesthetic and Vestibular
• Kinesthesis - knowing the position of the
various parts of the body
– Receptors in joints/muscles
• Vestibular - equilibrium/balance
– Semicircular canals
Fig. 5.30 The vestibular system.
Vestibular System and Motion
Sickness
• Motion sickness is directly related to vestibular
system
• Sensory Conflict Theory: Motion sickness
occurs because vestibular system sensations
do not match sensations from the eyes and
body
– After spinning and stopping, fluid in semicircular
canals is still spinning, but head is not
– Mismatch leads to sickness
• Medications, relaxation, and lying down might
help