Sensation and Perception
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Transcript of Sensation and Perception
Sensation and PerceptionChapter Four
Sensation vs. Perception Sensation: the process of detecting a stimulus
such as light waves (vision) sound waves (hearing) chemical molecules (smell and taste) heat or pressure (touch) orientation or balance (kinesthetic senses)
Perception: the process of integrating, organizing and interpreting sensations
From a sensory point of view – mass of red, white and blue colors and horizontal and vertical lines
Perception allows you to interpret the splotches of color and array of lines as the American flag
Bottom-up processing – sensory analysis that starts at entry levels Used when we have no prior knowledge
Top-down processing – construction of perception based on experiences and expectations Used when we do have prior knowledge
Transduction – process by which sensory receptors convert the incoming physical energy of stimuli (like light waves) into neural impulses the brain can understand Sensations such as “red” and “cold” occur
only when the neural impulse reaches the brain
Selective attention – focusing conscious awareness on a particular stimulus Attention to one thing causes inattention to
something else Cocktail party effect – ability to attend to only one
voice among many Inattentional blindness – failing to see visible objects
when our attention is directed elsewhere Change blindness – failing to notice changes in the
environment
Thresholds Absolute threshold –
minimum amount of a stimulus that an observer can reliably detect at least 50% of the time
Thresholds -cont- Difference threshold – minimal difference needed to
notice a stimulus change; called “just noticeable difference” Noticing when the TV volume is turned down just one notch
Weber’s law – just noticeable difference will vary depending on its relation to the original stimulus Size of JND is proportional to the strength of the original
stimulus Noticing the addition of a 5-pound weight when bench
pressing 50 pounds but not when bench pressing 500 pounds
Thresholds -cont- Signal detection theory – tries to explain and
predict different perceptual mistakes we make False positive – we think we perceive a stimulus
that isn’t there Mistaking a stranger for someone you know on a
crowded street False negative – not perceiving a stimulus that is
present Not noticing directions on a test that tell you to write
in complete sentences
Sensory adaptation – when a constant stimulus is presented for a length of time, receptors fire less frequently and the sensation often fades or disappears Getting used to new running shoes or the
temperature of the water Does not affect vision
Vision
Vision: From the cornea to the retina Cornea – light waves first enter the eye here
Clear membrane covering the visible part of the eye Protects the eye and helps gather and direct incoming light
waves Pupil –opening in the middle of the iris
Changes size to let in different amounts of light Iris – colored part of the eye
Ring of muscle tissue that contracts or expands to control the size of the pupil
Muscles respond to light and inner emotions – constrict in parasympathetic calm and dilate in sympathetic arousal
Vision: From the cornea to the retina Lens – transparent structure located behind the pupil
that actually focuses and bends light as it enters the eye Accommodation – change in the curvature of the lens that
enables the eye to focus on objects at various distances Nearsightedness – results when the cornea and lens focus
on an image in front of the retina, making distant objects appear blurry
Farsightedness – results when the cornea and lens focus on an image behind the retina, making objects near the eye appear blurry
Vision: The retina Retina – light-sensitive membrane at the back of
the eye where the transduction of light waves into neural messages occurs Contains millions of sensory receptors for vision Rods – allow you to see in poorly light environments
Located primarily in the retina’s periphery Cones- sensitive to colors and bright light
Concentrated in the fovea – a small region in the center of the retina
Vision: The retina Bipolar cells – specialized neurons that connect
the rods and cones with ganglion cells Ganglion cells – specialized neurons that
connect to the bipolar cells Bundled axons of ganglion cells form the optic
nerve Blind spot – point where the optic nerve leaves
the eye and where there are no rods or cones, creating a blind spot in our vision
Feature detectors – nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle or movement
Theories of Color Vision Trichromatic or three-color theory – theorizes
that the retina has three different color receptors – cones that detect the different colors red (long wavelengths), blue (short wavelengths) or green (medium wavelengths) – which when stimulated in combination can produce the perception of any color Does not explain afterimages and color blindness
Theories of Color Vision Opponent-process theory – theorizes that ganglion cells
process color in opposing pairs of red or green, black or white, and blue or yellow colors The visual cortex also encodes color in terms of these
three opponent pairs Explains afterimages – visual experiences that occurs after
the original source of stimulation is no longer present When you look at the color red for a long time, you fatigue
the sensors for red; when you switch your gaze and look at a blank page, the opponent part of the pair for red will fire and you will see a green afterimage
Theories of Color Vision Color blindness
Typically caused by deficiency in cones Most common is related to deficiencies in red-
green system
Hearing
Sound Waves Ear transforms vibrating air into nerve impulses,
which our brain decodes as sounds The amplitude (strength) of sound waves determines
their loudness Waves vary in frequency – number of complete
wavelengths that pass a point in a given time Frequency determines the pitch (highness or
lowness) that we experience Long waves have low frequency, short waves have high
frequency
The Outer Ear Collects sound waves The pinna
Flap of skin and cartilage attached to each side of our head Catches sound waves and channels them into the auditory canal
The auditory canal Sound waves travel down the auditory canal and bounce into the
ear drum The eardrum or tympanic membrane
Tightly stretched membrane located at the end of the auditory canal Eardrum vibrates when hit by sound waves; vibrations match the
intensity
The Middle Ear Amplifies sound waves Hammer, anvil and stirrup (collectively called ossicles)
Three tiny bones in the middle ear Joint action doubles the amplification of sound
Oval window Small membrane separating the middle ear from the
inner ear Stirrup transmits amplified vibrations to the oval window
and oval window relays vibrations to the cochlea
The Inner Ear Transduces sound waves into neural messages Cochlea
Spiral-shaped, fluid-filled structure that contains the basilar membrane and hair cells
Basilar membrane Runs the length of the cochlea Holds the hair receptors for hearing
Hair cells Sensory receptors embedded in the basilar membrane Hair cells transduce the physical vibration of the sound waves
into neural impulses
Distinguishing Pitch Pitch – relative highness or lowness of a sound Frequency theory – theory differences in pitch are due to the rate
of neural impulses traveling up the auditory nerve We sense pitch because the hair cells fire at different rates
(frequencies) in the cochlea Explains how low-frequency tones are transmitted to the brain
Place theory – theory that differences in pitch result from stimulation of different areas of the basilar membrane Higher-frequency sounds cause maximum vibrations near the
stirrup end of the basilar membrane; lower frequency sounds cause maximum vibrations at the opposite end
Explains how high-frequency tones are transmitted to the brain
Loss of Hearing Conduction deafness
Caused when the bones in the middle ear are damaged and can’t transmit sound waves to the inner ear
Causes can include tumors, objects in ear canal, infections or otosclerosis (genetic degeneration of the middle ear bones)
Nerve deafness Caused by damage to the cochlea, hair cells or auditory nerve Treated with hearing aids or cochlear implants Causes include infections, genetic defects, exposure to loud
noises, trauma, high blood pressure, diabetes and MS
Touch and the Sensory Cortex
Touch Touch receptors aren’t evenly distributed among the
different areas of our bodies More densely concentrated in the face, hands and lips
than on the legs or back Gate-control theory of pain – the brain regulates
pain by sending signals down the spinal cord that either open or close sensory pathways or “gates” Brain signals gates to open = pain is experienced or
intensified Brain signals gates to close = pain is reduced
Vestibular sense – provides a sense of balance and equilibrium Inner ear contains receptors that are especially
important for maintaining balance Semicircular canals are filled with fluid and lined
with hair like receptor cells that shift in response to motion, providing the brain with important information about the body’s posture and head position
Kinesthetic sense – gives us feedback about the position and orientation of specific body parts
Chemical Senses Taste (or gustation)
Chemicals from food are absorbed by taste buds on our tongue
Taste buds are located on papillae – bumps you can see on your tongue Are located all over the tongue and some parts of the
inside of the cheeks and roof of the mouth More densely packed taste buds = more intense taste
Humans sense five different types of taste: sweet, salty, sour, bitter and umami (savory or meaty taste)
Chemical Senses Smell (or olfaction)
Mucous membrane at the top of each nostril contains receptor cells that absorb airborne chemical molecules
Receptor cells communicate neural messages to the olfactory bulb
Impulses from the olfactory bulb don’t go to the thalamus Nerve fibers connect to the brain at the amygdala and
then to the hippocampus
Sense and Associated Receptors
Energy
Senses
Vision Rods, Cones (in Retina)
Hearing Hair cells connected to the organ of Corti (in cochlea)
TouchTemperature, pressure, pain nerve endings (in the skin)
Chemical
Senses
Taste (gustation)
Sweet, sour, salty, bitter, umami taste buds (in papillae on the tongue)
Smell (olfaction)
Smell receptors connected to the olfactory bulb (in the top of the nose)
Body Positio
n Senses
Vestibular sense
Hair like receptors in three semicircular canals (in the inner ear)
Kinesthetic sense
Receptors in muscles and joints
Perceptual Organization
Gestalt Principles of Organization Founded by Max Wertheimer in early 1900s Maintains that we actively process our
sensations according to consistent perceptual rules Rules create whole perceptions (gestalts) that are
meaningful, symmetrical and as simple as conditions allow
Figure-ground relationship – organization of the visual field into objects (figures) that stand out from their surroundings (ground) Your brain organizes black
markings in a book as letters and groups them into words and sentences Letters = figure White page = ground
Perceptual Grouping Law of similarity – tendency to perceive objects of a similar
size, shape or color as a unit or figure Organizing a crowd at a football game into home fans, visiting
fans, band members and cheerleaders Law of proximity – tendency to perceive objects that are
physically close to one another as a single unit Grouping visiting fans into a single, homogenous group
Law of closure – tendency to fill in the gaps in an incomplete image Scoreboard reads “HO E and VISI ORS” and your brain fills in
missing M and T to complete the words
Constancy Size constancy – objects closer to our eyes will produce
bigger images on our retinas, but we take distance into account in our estimations of size Knowing an object doesn’t grow or shrink in size as it moves
closer or farther away Shape constancy – objects viewed from different angles
will produce different shapes on our retinas, but we know the shape of an object remains constant
Brightness constancy – we perceive objects as being a constant color even as the light reflecting off the object changes
Shape constancy
Perceived Motion Stroboscopic effect – images in a series of still
pictures presented at a certain speed will appear to be moving
Phi phenomenon – series of light bulbs turned on and off at a particular rate will appear to be one moving light
Autokinetic effect – if people are asked to stare at a spot of light projected steadily onto the same place on a wall of an otherwise dark room, they will report seeing it move
Depth perception Ability to perceive three-
dimensional space and to accurately judge distance
Visual cliff experiment Supports conclusion that
perception in humans is innate and emerges during infancy
Monocular depth cues Require the use of only one eye to process
distance or depth cues
Monocular depth cues Linear perspective -
parallel lines appear to converge toward a vanishing point as they recede into the distance
Carlo Crivelli’s The Annunciation
Monocular depth cues Aerial perspective –
distant objects often appear hazy and blurred compared to close objects
Pieter Bruegel the Elder’s The Harvester
Monocular depth cues Relative size - if two or
more objects are assumed to be similar in size, the object that appears larger is perceived as being closer
George Seurat’s Sunday Afternoon on the Island of La Crande Jatte
Monocular depth cues Motion parallax - as you move, you use the
speed of passing objects to estimate the distance of the objects
On the interstate, nearby telephone poles, fences and roadside signs seem to zip by faster than distant hills
Binocular depth cues Require the use of both eyes to process distance or
depth cues Convergence – binocular depth cue in which the closer
the object, the more the eyes converge, or turn inward Retinal disparity – binocular depth cue in which
separation of the eyes causes different images to fall on each retina when two retinal images are very different, we interpret
the object as being close by; when they are more nearly identical, the object is perceived as being farther away