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Sensation & Perception
Chapter 3
Sensation & Perception
Sensation
Stimulation of the senses
How input is registered by our senses
Perception
How we organize & interpret sensations
An active, not passive process
Enables us to understand & make sense of the sensations we continually experience
Perception & sensation are dual processes; you need both!
Sequence of events that produce a sensation:
1. Need a form of energy, either external or internal.
2. Stimulates a receptor cell in a sense organ (energy must be sufficient enough for receptor to respond).
3. Receptor sends out a coded electrochemical signal.
4. As a signal passes along sensory nerves to CNS, it is further coded.
5. Signal reaches the brain. 6. You respond!
Sensation
Sensory receptors:
Highly specialized cells
Located in eyes, ears, nose, tongue, skin, & elsewhere
Accomplishes coded task
The Brain “Creates” Sensory Experiences:
The brain is isolated within the skull, listening to the “clicking” of coded neural signals coming over millions of nerve fibers.
The “clicks” of an optical nerve are not any more visual than the “clicks” of an auditory nerve, but the brain interprets the “clicks” on an optic nerve as visual nerve energy & they give rise to visual experience instead of sounds, tastes, or smells.
Sensation: The Process
Transduction
Process by which physical properties of stimuli are converted into neural signals & then transmitted to brain
Sensory deprivation
When deprived of sensations, we create it by means of hallucinations
What is the least amount of sensation we can detect?
TASTE
SMELL
TOUCH
AUDITORY
VISUAL
What stimuli we can detect seems to be designed to maximize our survival.
Thresholds
Difference Threshold
`You have heard a sound. How much stronger does the sound have to be before you notice that it has become louder?`
Aka: “just noticeable difference”
Will vary from person to person
The stronger the stimulation, the bigger the difference must be in order for you to detect it
Some sense are more sensitive than others to change
Stimuli below threshold
Subliminal perception
Q: Can we sense or be affected by subthreshold stimuli that remain outside our conscious awareness?
Sensory Adaptation
Our sensitivity to an unchanging stimulus tends to decrease over time
Practical advantages
Disadvantages
Vision
The Eye:1. Light enters the eye
through the cornea
2. Light passes through the pupil
3. Light passes through the lens
4. Light leaving the lens is projected on the retina, in the back of the eyeball
2 Types of light-sensitive receptors:1. Cones (named for their shape)
Located in the center of the retinaResponds to light & dark & colorsOperates chiefly in daylightConnected to bipolar neurons
2. Rods (named for their shape)Responds to only varying degrees of light & dark, not colorsChiefly responsible for “night vision”Connected to bipolar neurons
Vision
Bipolar neuronsNeurons with only one axon & one dendriteCarry info to ganglion cells optic nerve brain
LightElectromagnetic spectrumWavelength determines what we experience as colorAs wavelength increases from small to large our sensations shift from violet-blue (short) to orange (med.) to red (long)
Brightness
Functions of the Visual System:Acuity
– 2 Types:– Static visual acuity– Dynamic visual acuity
Abnormalities– Nearsightedness– farsightedness
Vision
Dark adaptation– Rods & cones become more sensitive
to light in response to lowered levels of illumination
Light adaptation– Reverse process
Eye Movements– Version Movements
• Involuntary• Saccadic• pursuit
Eye Movements– Vergence Movements
Color Vision2 Theories:Trichromatic Theory
– Helmholtz suggested certain cones were sensitive to green, while others were sensitive to red, or blue & by mixing the three you could experience all hues
Opponent Processing Theory– Hering proposed the existence of 3
pairs of color recptors
Processing Visual Information
Research: feature detectors
3 Types:Simple cells
Complex cells
Hypercomplex Cells
Do we process visual information hierarchically?
Hearing
Q: If a tree falls in the woods and there is no one there to hear it, does it make a sound? (How would psychologists answer this question)A:
The EarPinna
Middle Ear– Malleus– Incus– stapes
Oval Window
Cochlea
Basilar Membrane
Receptor Cells– Thousands of tiny hair cells– Fibers are pushed & pulled by
vibrations of basilar membrane
Sound
Properties of Sound:Sound waves
1. Amplitude2. Frequency3. Timbre
Pitch Perception (2 Views)1. Place Theory2. -sound is detected by
different places that are vibrating on the basilar membrane
2. Frequency Theory• - sounds of different pitch cause
different rates of neural firing
Touch
Skin – largest sensory organ
Skin Senses– Different receptors for different sense?
Pain– Some have a high tolerance for
pain– Beliefs about pain can affect our
perception of it– Research has found that pain is
not related to level of tissue damage
2 Types of pain– Quick & sharp– Dull & throbbing
Pain Perception– Gate-Control Theory: a
“neurological gate” in the spinal cord controls transmission of pain impulses to the brain
– Current emotional state affects pain perception
Smell
Sense of smell is @ 10,000 x’s more sensitive than tasteAppears to decrease with age
How we smell:Substance enters nasal passageDissolves in moist nasal tissueReceptor cells in olfactory epithelium
Why can we smell alcohol in drinks and not sugar in drinks?
Odor Sensitivity:
Related to gender & age
Can people distinguish many different odors?
Taste
4 Basic Tastes:
SweetSaltySourBitter
Why do we perceive more flavors?
Kinesthesia & Vestibular Sense
Kinesthesia
Gives information about the location of our body partsAllows us to perform movementsWhere does information come from?
Vestibular Sense
Monitors equilibrium and gives information regarding body position, movement, and acceleration
2 Kinds of Vestibular Sensation:
Body Rotation – arises from 3 semicircular canals in inner ear.
Gravitation & Movement – forward, backward, up, and down.
– Sense arises from vestibular sacs
Perception
The “way” in which we select & organize sensory inputHow we experience meaningful patterns in the jumble of sensory information
Selective AttentionCan we attend to all stimuli?Advantages = we don’t get overwhelmedDisadvantages = we “miss” stimuli that may be meaningful
Laws of Perceptual Grouping:(108)
1. Laws of Similarity2. Law of Good Continuation3. Law of Proximity4. Law of Closure5. Laws of Common Region6. Laws of Simplicity
Perceptual Constancies
Tendency to perceive aspects of the world as unchanging despite varied sensory input
Size Constancy – tendency to perceive a physical object as having a constant size.
Shape Constancy – to perceive a physical object as having a constant shape.
Brightness Constancy – to perceive objects as having a constant brightness even when they are viewed under different illumination.
Figure & Ground Relationship:
Figure – has a definite shape & location in space.
Ground – has no shape, seems to continue behind the figure & has no definite location.