sensation and perception. our sensational senses what is the difference between sensation and...
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Sensation and Perception
Our Sensational Senses
What is the difference between sensation and perception?
What is psychophysics? How do we measure the senses? What is sensory adaptation? When do you experience sensory
overload?
Defining Sensation and Perception Sensation
The detection of physical energy emitted or reflected by physical objects.
It occurs when energy in the external environment or the body stimulates receptors in the sense organs.
The study of sensation is the study of energy.
Perception The process by which the brain
organizes and interprets sensory information.
Ambiguous Figure
Colored surface can be either the outside front surface or the inside back surface Cannot
simultaneously be both
Brain can interpret the ambiguous cues two different ways
Separate Sensations Sense receptors
Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain.
Transduction: the process where physical energy is converted to electrochemical.
Sensation & Perception Processes
Why do have different senses?
Different sensorys exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain.
Synthesia A condition in which stimulation of
one sense also evokes another.
What is Psychophysics? Discipline within psychology that
quantitatively investigates the relationship between physical stimulus and the sensations and perceptions they affect.
1860-Gustav Fechner is founding father Do you remember what Wilhelm Wundt did?
He built on Fechner’s work and started his own psychological research lab!
We can measure senses by…
Absolute threshold Difference threshold Signal-detection theory
Absolute Threshold The smallest quantity of physical energy that
can be reliably detected by an observer (50% of the time in general population)
Absolute Sensory Thresholds
Vision: A single candle flame from 30 miles on a dark, clear
night Hearing:
The tick of a watch from 20 feet in total quiet Smell:
1 drop of perfume in a 6-room apartment Touch:
The wing of a bee on your cheek, dropped from 1 cm Taste:
1 tsp. Sugar in 2 gal. water
Difference Threshold The smallest difference in stimulation that
can be reliably detected by an observer when two stimuli are compared;
Also called Just Noticeable Difference (JND). Weber’s Law: JND is proportional to stimulus
intensity Greater the magnitutude of the stimulus, the
larger the difference must be to be noticed
Signal-Detection Theory A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision
process. Bias plays a role in detecting stimulus. It can be psychological or physical. (mom and her new baby)
Four Possible Outcomes on each trial in detection of stimulus Hit: signal present participant sensed it Miss: Signal present but participant did not sense it False Alarm: Signal absent but participant reported sensing it Correct Rejection: Signal absent and participant did not report it
Sensory Adaptation and Deprivation
Adaptation (Habituation) The reduction or disappearance of
sensory responsiveness when stimulation is unchanging or repetitious.
Prevents us from having to continuously respond to unimportant information (our clothes).
Deprivation The absence of normal levels of sensory
stimulation.
Sensory Overload
Overstimulation of the senses. Can use selective attention to
reduce sensory overload. Selective attention
The focusing of attention on selected aspects of the environment and the blocking out of others.
Go to Perception
Vision: What do we see? Eye, see? What makes up the eye? Why is the visual system is not a
camera? How do we see colors? How do we construct the visual world?
Vision
Most important sense (evolution) Photoreceptors gather light, send it
to neuron, occipital lobe for decoding
What We See Hue
Visual experience specified by color names and related to the wavelength of light.
Brightness Lightness and luminance; the visual
experience related to the amount of light emitted from or reflected by an object.
Saturation Vividness or purity of color; the visual
experience related to the complexity of light waves.
What We See
Hue Brightness Saturation
An Eye on the World Cornea
Protects eye and bends light toward lens.
Lens Focuses on objects
by changing shape. Iris
Controls amount of light that gets into eye.
Pupil Widens or dilates
to let in more light.
An Eye on the World Retina
Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision.
This is where transduction takes place (rods and cones) Rods
Visual receptors that respond to dim light. Light and dark but no color.
Cones Visual receptors involved in color vision. Most
humans have 3 types of cones. Best in bright light, can sharply focus 5 million different shades but we only have 150 in our
language
Blind Spot
Blind Spot
At the point where the optic nerve exits the back of the eye there are no rods and cones so no receptors for vision
Head and eye movements work avoid “blind spots” in our vision
The Structures of the Retina
Why is the Visual System not a Camera?
Much visual processing is done in the brain. Some cortical cells respond to lines in
specific orientations (e.g. horizontal). Other cells in the cortex respond to other
shapes (e.g., bulls-eyes, spirals, faces). Feature-detectors
Cells in the visual cortex that are sensitive to specific features of the environment.
Hubel & Wiesel’s Experiment
How We See Colors
Trichromatic theory Opponent process theory
Trichromatic Theory
Young (1802) & von Helmholtz (1852) both proposed that the eye detects 3 primary colors:
red, blue, & green All other colors can
be derived by combining these three.
Opponent-Process Theory A competing theory of color vision, which
assumes that the visual system treats pairs of colors as opposing or antagonistic
States there are two types of cones One responds to red and green, the other to
blue and yellow, while the rods receive black and white input
As one color in each pair is excited, the other is inhibited
Afterimages
Stare at the white, what do you see?
Stare at the light bulb for 30 seconds….
Why does this happen? When you focus on the black light bulb, light
sensitive photoreceptors in your retina respond to incoming light. The longer you stare at the black light bulb, your photorecpeptors become desentitized or fatigued.
Photopigment is “bleached” by constant stimulation. The desensitization is strongest for cells viewing the brightest area and weaker for darker images.
When screen becomes white, the least depleted cells respond more strongly producing the brightest part of the after image: the glowing light bulb.
This is a negative after image. (dark areas turn light)
Test of Color Deficiency
Hearing
Do you hear what I hear? How does the ear hear? How do we construct the auditory
world?
Hearing
Sounds created by vibrations push air molecules back and forth changing air pressure.
Changes in air pressure=sine wave Frequency Theory:
Fast waves=frequency (high or low) High waves=amplitude (loud or
soft)
What We Hear Loudness
The dimension of auditory experience related to the intensity of a pressure wave.
Pitch The dimension of auditory experience related
to the frequency of a pressure wave. Place Theory: Suggests we identify pitch of
sounds according to the location of vibrations on the basilar membrane
Timbre (pronounced “TAM-bur”) The distinguishing quality of sound; the
dimension of auditory experience related to the complexity of the pressure wave.
Listen to the Hearing Test
Ultimate Hearing Test When do you stop hearing the sound? http://www.youtube.com/watch?v=igGroIcga3g
Hertz: Unit of measure for the frequency of sound
An Ear on the World
Auditory Localization
Sounds from different directions are not identical as they arrive at left and right ears
Loudness Timing Phase
The brain calculates a sound’s location by using these differences.
Virtual Barber Shop: http://www.youtube.com/watch?v=IUDTlvagjJA
Hearing is possible… When ear and brain convert sine
waves from sound Sound travels into ear, bone in the
middle ear transfers into inner ear where the sound makes fluid waves
Vibration of fluid waves stimulate tiny hairs to generate nerve impulse
Brain then analyzes sound.
Other Senses
Taste: savory sensations Smell: The sense of scents Senses of the skin The mystery of pain The environment within
Taste: Savory Sensations
Transduction: chemical molecules and saliva dissolve Papillae
Knoblike elevations on the tongue, containing the taste buds (Singular: papilla).
Taste buds Nests of taste-receptor cells.
Taste Buds
Photograph of tongue surface (top), magnified 75 times.
10,000 taste buds line the tongue and mouth.
Taste receptors are down inside the “bud”
Children have more taste buds than adults.
Four Tastes
Four basic tastes Salty, sour, bitter and sweet.
Different people have different tastes based on: Genetics Culture Learning Food attractiveness
Smell: The Sense of Scents
Very primitive! But very useful. Close connection to memory Airborne chemical molecules enter the nose and circulate
through the nasal cavity. Vapors can also enter through the mouth and pass into
nasal cavity. Receptors on the roof of the nasal cavity detect these
molecules.
Olfactory System
Sensitivity to Touch
Gate-Control Theory of Pain Experience of pain
depends (in part) on whether the pain impulse gets past neurological “gate” in the spinal cord and thus reaches the brain.
Neuromatrix Theory of Pain
Theory that the matrix of neurons in the brain is capable of generating pain (and other sensations) in the absence of signals from sensory nerves.
The Environment Within Kinesthesis
The sense of body position and movement of body parts; also called kinesthesia.
Equilibrium The sense of balance.
Semicircular Canals Sense organs in the inner ear, which
contribute to equilibrium by responding to rotation of the head.
What do you see?
Perception
To what extent are our perceptions of the environment accurate? Perception is the process of selecting
information from the environment and interpreting that information.
Perception brings meaning to sensation.
It produces an intrepretation of the world not a perfect representation!
Stare at the image for 30 seconds….
Which line is longer?
What picture looks like a whole room?
Feature Detectors
Still a mystery to most psychologist.
These are a bundle of cells in the brain whose purpose is to detect certain features of stimuli (such as lines, shapes, angles, movements)
Discovered by David Hubel and Torsten Wiesel.
How do we perceive the world? Attention- a process in which
consciousness is focused on particular stimuli Selective Attention – ability to focus on one
stimulus while excluding other stimuli that are present
Divided Attention – ability to respond to more than one stimulus
Cocktail Party Effect: demonstrates that attention can be divided but you can hear things that are important to you (like hearing your name in a busy room)
What do you pay attention to?
The Amazing Color Changing Card Trick
http://www.youtube.com/watch?v=voAntzB7EwE
Awareness Test http://www.youtube.com/watch?v
=Ahg6qcgoay4
How do we process stimuli?
The ability to discriminate among shapes and figures. Bottom-up processing – information
processing that beings at the stimulus and continues to higher brain centers
Top-down processing – information processing that begins in higher brain centers (what we already know) and proceeds to receptors of stimulus
Is this Top Down or Bottom Up?
The Count Censored –
http://www.youtube.com/watch?v=B-Wd-Q3F8KM Top Down Processing Example
How do we construct the visual World?
Form perception Depth and distance perception Visual constancies: When seeing is
believing Visual illusions: When seeing is
misleading
Form Perception
Gestalt principles describe the brain’s organization of sensory information into meaningful units and patterns.
Refers to recognition and identification of faces, words, shapes, melodies, etc. Feature-analysis theory – theory of pattern
perception stating that we perceive basic elements of a structure and then mentally create a complete picture
Pragnanz Theory: We see the simpliest pattern possible.
Prototypes-matching theory – patterns are identified by being compared against a set of prototypical patterns stored in memory
Form Perception (cont.) Figure-ground perception – tendency to organize that
visual field into objects (figures) that stand apart from surroundings (ground)
Closure – Filling in missing information from the perceptual array by closing in gaps
Laws of Grouping Similarity – grouping things on the basis of how similar
they are to one another Proximity – grouping things on the basis of how near
they are to one another
Figure and Ground
MC Esher Relativity
Waterfall
Tree
Depth and Distance Perception
Binocular Cues: Visual cues to depth or distance that
require the use of both eyes. Convergence: Turning inward of the
eyes, which occurs when they focus on a nearby object.
Retinal Disparity: The slight difference in lateral separation between two objects as seen by the left eye and the right eye.
Depth and Distance Perception
Monocular Cues: Accommodation
Bulging and elongating of lens Effective only for objects within 25 feet
Motion parallax – phenomenon where near objects are seen as moving more rapidly that far objects when the viewer’s head is moving
Texture gradient – texture of a surface receding in the distance changes in clarity, blurring at further distances
Linear perspective – produced by apparent converging of parallel lines in the distance
The Ames Room A specially-built room
that makes people seem to change size as they move around in it
The room is not a rectangle, as viewers assume it is
A single peephole prevents using binocular depth cues
Research suggests that the visual system is upset by redundancy
of patterns (when there is nothing apparently there).
Visual Constancies The accurate perception of objects
as stable or unchanged despite changes in the sensory patterns they produce. Shape constancy Location constancy Size constancy Brightness constancy Color constancy
Shape Constancy Even though these images cast
shadows of different shapes, we still see the quarter as round
Which line is longer?
Visual Illusions
Illusions are valuable in understanding perception because they are systematic errors.
Illusions provide hints about perceptual strategies. In the Muller-Lyer illusion (above) we tend to
perceive the line on the right as slightly longer than the one on the left.
The Ponzo Illusion Linear perspective
provides context Side lines seem to
converge Top line seems
farther away But the retinal
images of the red lines are equal!
Fooling the Eye
The cats in (a) are the same size The diagonal lines in (b) are parallel You can create a “floating fingertip frankfurter”
by holding hands as shown, 5-10” in front of face.
Perceptual Powers: Origins and Influences
Depth perception appears around 6 months of age Psychological and cultural influences on
perception We use prior experience and learning when we interpret
sensory information City dwellers vs. country dwellers will experience the
Ponzo Effect differently when around large buildings Two competing theories:
Learning Theory: Learned depth cues Innate Theory: Born with certain depth cues
Bottom Line: Perception is an interaction of nature vs. nurture
Glass surface, with checkerboard underneath at different heights
Visual illusion of a cliff Baby can’t fall
Mom stands across the gap Babies show increased
attention over deep side at age 2 months, but aren’t afraid until about the age they can crawl (Gibson & Walk, 1960)
The Visual Cliff-40 Studies
The Visual Cliff
Psychological and Cultural Influences on Perception
We are more likely to perceive something when we need it.
What we believe can affect what we perceive. Emotions, such as fear, can influence
perceptions of sensory information. Expectations based on our previous
experiences influence how we perceive the world.
Perceptual Set A habitual way of perceiving, based on expectations.
All are influenced by our culture.
Perceptual Set
What you see in the centre figures depends on the order in which you look at the figures: If you scan from the left, see an old woman If you scan from the right, see a woman’s figure
Context Effects Word Game The same physical
stimulus can be interpreted differently
We use other cues in the situation to resolve ambiguities
Is this the letter B or the number 13?
Subliminal Perception
Perceiving without awareness visual stimuli can affect your behavior
even when you are unaware that you saw it
nonconscious processing also occurs in memory, thinking, and decision making
these effects are often small, however, and difficult to demonstrate and work best with simple stimuli
Subliminal Perception
Perception versus Persuasion there is no empirical research to
support popular notions that subliminal persuasion has any effect on a person’s behavior
persuasion works best when messages, in the form of advertising or self-help tapes, are presented above-threshold, or at a supraliminal level
Extrasensory Perception
Extrasensory Perception (ESP): The ability to perceive something without
ordinary sensory information This has not been scientifically
demonstrated Three types of ESP:
Telepathy – Mind-to-mind communication Clairvoyance – Perception of remote events Precognition – Ability to see future events
Parapsychology
The study of purported psychic phenomena such as ESP and mental telepathy.
Persinger suggests that psychic phenomena are related to signs of temporal lobe epilepsy in otherwise neurologically normal individuals.
Most ESP studies produce negative findings and are not easily replicated.
Parapsychology
J. B. Rhine conducted many experiments on ESP using stimuli such as these.
Rhine believed that his evidence supported the existence of ESP, but his findings were flawed.
Quiz over Perception What is selective attention? According to feature analysis theory,
how do we identify objects that we percieve?
What is the figure ground relationship? Which Gestalt principle helps our
perception of WWWW XXX? Your mother claims she was able to
read your mind and knew you would try to sneak some food before dinner. What form of ESP might she claim?