Sensation and Perception
Unit 4
The Basics of Sensation
-
Sensation
- Behavior often begins with sensory input
- Process by which we receive, transform, and process stimuli presented
to sensory organs
- Sensory receptors – in sensory organs
- Detect stimuli from the outside world
- Very sensitive to certain types of stimuli
- Form of light, sound , odors
- Psychophysics – how we experience such stimuli
The Basics of Sensation
-
Absolute and Difference Thresholds
- Absolute threshold
- Smallest amount of stimulus reliably detected
- Variation in sensitivity among individuals
- Difference threshold: amount to determine difference of level of same
stimulus
-Just-noticeable difference (JND)
-Weber’s law
-Must change stimulus by a constant proportion for change to be
detected
What do You See?
The Eye
The Image
The Parts
-
The Eye: The Visionary Sensory Organ
- Contains the sensory receptors to
detect light
- Cornea – transparent covering on
the surface of the eye
- Iris – Muscle surrounding pupil;
adjust to permit entry of light –
adjustment is a reflex
- Pupil – size of opening is
controlled by iris
The Eye
The Image
The Parts
-
The Eye: The Visionary Sensory Organ
- Lens – changes shape to
adjust to distance of object
(accommodation)
- Retina – receives the image
created by light striking it;
contains photoreceptors –
rods and cones
The Eye
The Image
The Parts
Bipolar cells – interconnection cells
Ganglion cells – each projection axon is one
nerve fiber
Optic nerve
- Large bundle of ganglion nerve fibers
- Transmits visual information to the brain
- Creates blind spot
Fovea
- Contains only cones
- Site for sharpest vision
Vision Options
Color Vision: Sensing Color
-Color Receptors (cones) transmit
different messages to the brain
-Hermann von Helmholtz –
trichromatic theory
-Three types of color receptors
– red, green, and blue-violet
-Dichromatic: only see two of
the three color receptors
Vision Options
Color Vision: Sensing Color
-Monochromatic: only see in
shades of grey
The Ear
-
The
Ear
Sound: Sensing Waves of Vibrations
- Energy that travels in waves (vibrations)
- Must have a medium in order to exist
- Characteristics
- Amplitude (loudness) – the height of the wave
- Frequency – number of complete waves, or cycles per
second
- Travels much more slowly than light
- Measured in decibels (dB), and indication of perceived
loudness
The Ear
-
The Ear: A Sound machine
- Sound waves are captured and converted to neural form
- Ear components
- Eardrum – membrane that vibrates in response to sound waves
- Ossicles – three tiny bones in middle ear
- Hammer (malleus)
- Anvil (incus)
- Stirrup (stapes)
- Perception of pitch is related to wave frequency
The Ear
- Cochlea – fluid filled snail-shaped bony tube
- Basilar membrane – vibrates within the cochlea
- Organ of Corti – gelatinous structure lined with hairs cells
- Hair cells – auditory receptors
- Auditory nerve – transmits auditory messages to brain
- Perception of pitch is related to wave frequency
Theories & Principles
-Frequency theory
-Perceived frequency depends on how often the auditory nerve fires
-Volley principle
- If neurons work together and alternate their firing, they can exceed
the limitations of 1,000 firing per second
-Place Theory
-Idea the each frequency vibrates at a particular spot on the basilar
membrane
-Olfaction: What Your Nose Knows
-Chemicals in the air that the nose can respond to
-Lock-and-key fitting of molecules into odor receptors
-Olfactory nerve – transmits odor information to brain
-Olfactory bulb – brain destination; odor information does not
travel through thalamus
-Pheromones – chemical substances that play a role in behavior
-Taste: The Flavorful Sense
-Four basic tastes: sweet, sour, salty and bitter
-Flavors are a result of combinations of tastes
-Taste cell – taste receptors
-Taste buds – pores or opening on tongue
-Taste sensitivity partly genetic
The Sense of
Touch
• Sensed by the nerves just
below the skin
– Pressure
– Pain
– Temperature
The Sense of
Touch
-The Kinesthetic and Vestibular Senses: Of Grace and Balance
-Kinesthetic sense tells us bout body position and body movement
-Vestibular sense monitors body position in space
-Aids in keeping one’s balance
-Informs whether we are moving quickly or slowly
-In ear’s semicircular canals – movement of fluid relates body position
-Dizziness: semicircular canal fluid still moving though we have
stopped
-Perception: The Brain organizes and interprets sensations
-Attention: did you Notice that?
-Attention: the first step in perception
-Selective attention: limit attention to certain stimuli
-Habituation: results from exposure to a constant stimulus
Perception
-Perceptual Constancies
-Shape constancy – shape seen as the same across various perspectives
-Size constancy – size perceived as same regardless of distance from
perceiver
-Color constancy – color perceived the same despite changes in lighting
-Brightness constancy – brightness seen as the same though illumination
may change
-Cues to Depth Perception
-Binocular cues – need both eyes
-Retinal disparity – slightly differing image, what each eyes
What do You See?
Continuity
We tend to perceive figures or objects as belonging together
if they appear to form a continuous pattern
Closure (Connectedness)
We perceive figures with gaps in them to be complete
Similarity
We perceive figures which look alike as being grouped
together
Proximity
We perceive things close together as being in sets
What do You See?
Top-Down Vs. Bottom-UP
Top-Down processing looks first at the whole picture and then
breaks it apart into pieces (deductive reasoning)
Top-Down Vs. Bottom-UP
Bottom-Up looks first at the pieces and then creates the big picture
(inductive reasoning)
Pumpkin
Cranberries
Stuffing
Mashed Potatoes
Turkey
Green Beans
Corn