Introduction Chapter 4
Sensation and Perception
Sensation- detection of environmental stimuli- sounds, object, odors.
Perception- the process of integrating, organizing, and interpreting sensory
information so as to be meaningful
Principles of Sensation- sensation involves stimulation of sensory receptors
Sensory receptors- specialized cells that register various forms of
energy
Transduction- process by which a form of energy is converted into a
neural signal to be processes by the nervous system.
Sensory Thresholds- a threshold is the point at which a stimulus is
strong enough to be detected by a sensory receptor cell.
Absolute threshold- smallest possible strength of a stimulus
that can be detected half the time
Difference Threshold – smallest possible difference between
two stimuli that can be detected half the time.– also called just noticeable
difference
Weber’s law- the size of the just noticeable difference for each
sense- it is a constant proportion of the size of the initial stimulus.
Sensory adaptation- the decline in sensitivity to a constant stimulussensation is relevant to length of exposure to a stimulus.
Vision
Wavelength- the distance from one wave peak to another. Humans
only detect a small part of the electromagnetic spectrum.
Visual system- vision requires light waves being reflected from an
object to enter the eye, passing through the cornea, pupil and lens.
Cornea-clear membrane covering the front of the eye.
Pupil- black opening in the middle of the eye
Iris- colored structure- eye color- a ring of muscles that
controls the size of the pupil
Lens- transparent structure located behind the pupil that
focuses, bends light entering the eye.
Accommodation – process of the lens changing shape to
focus light onto the retina
Nearsightedness (myopia)-light is focuses in
front of the retina
Farsightedness- light is focused behind the retina
Presbyopia- aging causes the lens to become
inflexible, so light is focused behind the retina
Astigmatism- abnormal curve on the eyeball that
cases blurry vision in one direction.
Retina- membrane at the back of the eye that holds the sensory
receptors- rods & cones.
Rods- better at adapting to low light & peripheral vision
Cones- better in bright light, color vision, details
Fovea- holds mostly cones for sharp focus
Optic disk (blind spot)- point on the retina where the
optic nerve leaves the back of the eye, so there are no light receptors.
Bipolar cells- collect information from rods & cones,
then send that to:
Ganglion cells- analyze and encode visual information
and send it to the brain.
Optic nerve- carries sensory information from retina to brain
Optic chiasm- place in the back of eyes that both optic nerves
converge. Then they extend into thalamus.
Thalamus- sends the signals to the visual cortex at the back of
the brain.
Visual cortex- decodes the neural signals and interprets them
Feature detectors- specialized neurons in the visual
cortex that detect specific features of complex visual stimuli. They
recognized edges, angles, light and dark contrasts.
Color vision
Color perception involves 3 properties of the light wave:
Hue- also known as color of the wave length
Saturation (purity) has to do with clarity of color
Brightness- amplitude of the light wave- tall or short
Trichromatic theory of color vision-sensing color is duie to cones in
the retina that are sensitive to red light (long lengths), green light (medium
wavelengths), or blue light (short wave lengths). This theory explains color
blindness- red-green or yellow-blue- where a person can’t distinguish certain
colors.
Opponent-process theory- an afterimage is a visual experience that
happens after the source of stimulation is gone. This theory says the 4 basic
colors are divided into 2 pairs of color-sensitive neurons: red-green and
blue-yellow. When one member of a pair is stimulated, the other is inhibited.
Hearing (audition)
The Nature of Sound
Sound waves are physical stimuli that produce the sense of
sound.
Loudness- intensity (amplitude) of a sound wave, as seen in
the geight of the wave. Decibel is the measurement for loudness.
Pitch is the highness or lowness of a sound, determined by the
frequency of a sound wave- the rate of vibration or number of waves per
second. Hertz is the measurement of frequency- wave peaks per second.
Timbre is the quality of sound- the complexity of the sound
wave.
The Path of sound- sound waves are collected in the outer ear,
amplified in the middle ear, and transduced or transformed into neural
messages in the inner ear.
Outer ear-part of the ear that collects sound waves.
Pinna- the odd flap of skin attached to each side of your
head which catches sound waves and funnels them into the ear canal.
Eardrum – separates the outer ear from the inner ear- a
membrane at the end of the ear canal that vibrates when sound waves hit it.
Middle ear- part of the ear that amplifies sound waves and
consists of the hammer, anvil, & stirrup.
Oval window is stimulated by the stirrup. If these inner
bones are brittle or damaged, then conduction deafness occurs.
Inner ear- is where sound is transduced into neural impulses.
Cochlea- fluid-filled tube coiled in a spiral. Fluid ripples
in response to vibrations from the oval window.
Basilar membrane- membrane within cochlea that holds
the cilia or hair cells.
Hair cells (cilia) pick up the vibrations of waves. If
damaged, there is nerve deafness, which a hearing aid can’t help. There are
cochlear implants that can help, however. Transduction occurs when the
physical vibration of a sound wave is converted into neural impulses.
Theories of audition
Frequency theory- idea that the basilar membrane vibrates at
the same frequency as the sound waves. Useful in understanding how low
frequency sounds are sent to the brain.
Place theory- idea that different frequencies cause larger
vibrations at different locations along he basilar membrane. Useful to
understand how high frequency sounds are sent to the brain.
Chemical senses: Smell & Taste- The sensory receptors for taste and smell
are specialized to respond to different types of chemical substances.
Smell (olfaction)
Molecules- sensory stimuli for smell are molecules in the air.
They hit:
Olfactory receptor cells in the nasal cavity on hairs, cilia
connected to olfactory neurons.
Olfactory nerve is made up of axons of olfactory neurons.
Olfactory bulb is the place in the brain that receives olfactory
information- the only neurons that directly link the brain and the outside
world. This place is called the olfactory cortex. People widely vary in
sensitivity to smells.
Taste (gustation)- occurs from stimulation of special receptors in the
mouth
Taste buds are specialized receptors inside the cheeks and on
the tongue, roof of the mouth, & throat.
Neural pathways takes the sensory message to the thalamus in
the brain, which sends it to regions of the cortex. There are 4 major taste
qualities- sweet, salty, sour, and bitter- and they combine to form all other
tastes. Different taste buds respond to one of the 4 sensations.
Skin senses give us information about our physical status and interaction
with the environment. Body senses inform us about our orientation in space
Touch and temperature- the skin is the largest sense organ- 20 sq.
ft. and six pounds.
Pacinian corpuscle is an important receptor in touch
perception.
Sensory receptors are unevenly distributed among parts of the
body. Some parts are densely packed- lips, mouth, hands, face and highly
sensitive to subtle varieties of pressure, touch, temperature. Hot- is caused
by warm and cold spots on the body being stimulated at the same time.
Pain is a sensation of discomfort or suffering that can occur in
varying intensity.
Gate-control theory says that pain is a product of
physiological and psychological factors that cause spinal “gates” to open and
relax patterns of intense stimulation to the brain which experiences them as
pain.
Free nerve endings are small-diameter sensory fibers in
the skink muscles or internal organs. These nerve endings carry their
messages to the spinal cord, and release Substance P, a neurotransmitter.
Open spinal gates – substance P sends its message
through open spinal gates to the thalamus. The brain may regulate pain by
sending signals down the spinal cord to open or close the gates. Open gatesone experiences pain. Closed gates- pain is reduced.
Endorphins- are neurotransmitters that moderate pain
and are produced in many parts of the brain and body. One’s emotional state
can influence endorphin production, blood flow, muscle tension,
physiological arousal, and heart rate. All these things moderate pain.
Movement, position, & balance
Kinesthetic sense- perceiving the location and position of body parts
in relation to one another.
Proprioceptors are sensory neurons in the muscles and joints
that communicate information to the brain about changes in body position
and muscle tension.
Vestibular sense- sense of balance or equilibrium by responding to
changes in gravity, motion, and body position.
Vestibular sensations come from the ear’s semicircular canals
and vestibular sacs. They are filled with fluid and lined with receptor cells
that shift in response to motion, gravity, or changes in body position.
Perception- we aren’t merely reading our world based on incoming data- we
are organizing incoming data, interpreting it, and relating it to past
information and context. This is why several people witnessing an event can
give very different reports of what they saw. Eye-witnesses are notoriously
inaccurate.
Bottom-up processing (data-driven processing) flow of
sensory data into the brain.
Top-down processing (conceptually driven processing)
perceptions are shaped by our personal experiences
Max Wertheimer founded Gestalt psychology in the early
1900’s. these psychologists emphasized that we perceive figures in wholesgestalts (unified whole), rather than bits or pieces of sensory information.
Shape is our primary cue to what an object is.
Principles of perceptual organization
Figure-ground relationship – refers to the fact that when we
view a scene, we separate elements of the scene into figure (main element of
scene) and ground (background of scene). There can be figure-ground
reversals, however, illustrating the power of psychology to determine what
is the most important aspect of the scene for us.
Perceptual grouping- the way we organize elements to
produce stable perceptions of whole objects:
Similarity
Closure
Good continuation
Proximity
Pragnanz (simplicity)- when multiple interpretations are
possible, the perceptual interpretation that comes to us is the one that
produces the best, simplest, and most stable shape.
Depth perception- how far away is it? The use of visual cues to
perceive the distance or 3-dimensional characteristics of objects.
Monocular cues- depth cues that can be processed by either
eye alone
Relative size- object that is larger is seen as closer
Overlap- when one object blocks the view of another,
the blocked object is seen as being farther away
Aerial perspective- faraway objects appear hazy
Texture gradient- objects farther away have less distinct
texture or sharpness
Linear perspective- parallel lines seem to meet in the
distance; the closer the lines appear, the farther away they seem
Motion parallax- when you are moving, closer objects
seem to move faster than distant objects.
Pictorial cues in art- when any of these cues are used in
art to create the perception of distance or depth
Accommodation of the lens shape- we use information
from the changes in the shape of the lens of the eye to estimate distance
Binocular cues- these cues require both eyes
Convergence- the degree to which muscles rotate our
eyes to focus on an object
Binocular disparity- our eyes are set a couple of inches
apart, causing a different image of an object to be cast on the retina of each
eye
Motion perception- where is it going? WE make certain assumptions
when we perceive movement- that the object moves while the background
remains stationary.
Induced motion- the illusion of motion that occurs because we
have a tendency to assume the background is stationary.
Stroboscopic motion- illusion of motion that occurs when a
light briefly flashes at one location, followed a tenth of a second later by
another light briefly flashing at a second location
Auditory- sounds help us judge distance and direction. And as
they pass us, the sound changes when coming or going- think of a siren
Perceptual constancy – the tendency to perceive objects as constant and
unchanging despite changes in sensory input.
Size constancy- the perception that an object remains the same size
despite its changing image on the retina.
Brightness constancy- perception that the brightness of an object
seems to stay the same even though the lighting conditions change
Perceptual illusions- a misperception of the true characteristics of an object
Muller-Lyer illusion- misperception of the identical length of 2 lines,
based on arrows pointed inward or outward at each end
Moon illusion- misperception that the moon is larger when it is on the
horizon than when it is directly overhead. The retinal size of the moon is the
same in all positions, but it does appear to shrink as it moves into the sky.
Impossible figures- visual riddles that capitalize on our urge to
organize visual elements into a meaningful whole. What we see is not
merrely a reflection of the world, but our subjective interpretation of it.
Perceptual set – the influence of prior assumptions and expectancies on
perceptual interpretations.