Sensation and Perception Flashcards
Perception
A process that makes sensory patterns meaningful. It is perception that makes these words meaningful, rather than just a string of visual patterns. To make this happen, perception draws heavily on memory, motivation, emotion, and other psychological processes.
Sensation
The process by which stimulation of a sensory receptor produces neural impulses that the brain interprets as a sound, a visual image, an odor, a taste, a pain, or other sensory image. Sensation represents the first steps in processing of incoming information.
How does stimulation become sensation?
The brain senses the world indirectly because the sense organs convert stimulation into the language of the nervous system: neural messages.
Transduction
Transformation of one form of energy into another- especially the transformation of stimulus information into nerve signals by the sense organs. Without transduction, ripe tomatoes would not appear red.
Sensory adaptation
Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while, as when a swimmer becomes adapted to the temperature of the water.
Sensory habituation (perceptual adaptation)
Perception of sensations is partially due to how focused we are on them
Cocktail-party phenomenon
The involuntary switch of attention when someone says your name
Absolute threshold
The amount of stimulation necessary for a stimulus to be detected. In practice, this means that the presence or absence of a stimulus is detected correctly half the time over many trials.
Subliminal messages
Stimuli below the absolute threshold
Some claim it can change behavior
Difference threshold
The smallest amount by which a stimulus can be changed and the difference be detected half the time.
Just noticeable difference (JND)
Same as the difference threshold
Weber’s Law
This concept says that the size of a JND is proportional to the intensity of the stimulus; the JND is large when the stimulus intensity is high and is small when the stimulus intensity is low.
Fechner’s Law
The magnitude of a stimulus can be estimated by the formula S=klogR, where S=sensation, R=stimulus, and k=a constant that differs for each sensory modality (sight, touch, temperature, etc.)
Steven’s power law
A law of magnitude estimation that is more accurate than Fechner’s law and covers a wider variety of stimuli. It is represented by the formula S=kI^a, where S=sensation, k=a constant, I=stimulus intensity, and a=a power exponent that depends on the sense being measured.
Signal detection theory
Explains how we detect “signals”, consisting of stimulation affecting our eyes, ears, nose, skin, and other sense organs. Signal detection theory says that sensation is a judgement the sensory system makes about incoming stimulation. Often, it occurs outside of consciousness. In contrast to older theories from psychophysics, signal detection theory takes observer characteristics into account.
Response criteria (receiver operating characteristics)
Factors influencing signal detection (how motivated we are to detect certain stimuli, what we expect to perceive)
False positive
When we think we perceive a stimulus that is not there
False alarm
False negative
Not perceiving a stimulus that is present
Miss
Hit
Correctly detecting a stimulus that is there
Correct rejection
not perceiving a stimulus that is not there
How are the senses alike? And how are they different?
The senses all operate in much the same way, but each extracts different information and sends it to its own specialized processing region in the brain.
Energy senses
Vision, hearing, and touch
Gather light, sound waves, pressure
Chemical senses
Taste and smell
Gather chemicals
Vision
The dominant sense in human beings
Involves gathering light with the eyes
Cornea
Protective covering of the eye that helps focus the light
Pupil
Light goes through this
Controlled by the iris
Opens to let more light in
Smaller to let less light in
Lens
During accommodation, focuses the light that enters the pupil
Curved and flexible to focus the light
Photoreceptors
Light-sensitive cells (neurons) in the retina that convert light energy to neural impulses. The photoreceptors are as far as light gets into the visual system.
Feature detectors
Groups of neurons in the visual cortex that respond to different types of visual images
Some for lines, curves, motion, and many other features
Pathway of light in eye
Cornea –> aqueous humor –> pupil (manipulated by iris) –> lens focuses –> vitreous humor –> retina (fovea for clear sight) –> optic nerve
Retina
The thin, light-sensitive layer at the back of the eyeball. The retina contains millions of photoreceptors and other nerve cells.
Transduction of light in the retina
Incoming light –> photoreceptors –> bipolar cells synthesize –> ganglion cells –> optic nerve –> cortex
Rods
Photoreceptors in the retina that are especially sensitive to dim, black-and-white light but not to colors.
Cones
Photoreceptors in the retina that are especially sensitive to colors but not to dim light.
Fovea
The tiny area of sharpest vision in the retina.
An indentation at the very center of the retina that contains the highest concentration of cones.
Bipolar cells
Combine impulses from receptor cells and transmit to ganglion cells
Ganglion cells
Integrate several bipolar cells into a single fire
Horizontal cells
Connect receptors to each other
Amacrine cells
Link bipolar cells to other bipolar cells and ganglion to other ganglion cells
Optic nerve
The bundle of neurons that carries visual information from the retina to the brain.
Made up of the axons of ganglion cells and sends impulses to the lateral geniculate nucleus in the thalamus.
Blind spot
The point where the optic nerve exits the eye and where there are no photoreceptors. Any stimulus that falls on this area cannot be seen.
Optic chiasma
Each optic nerve comes together and is subdivided into inner/outer vision bundles. Inner bundles cross over to the other hemisphere
The spot where the nerves cross each other
Optic tract
Bundles from both eyes travel to the primary visual cortex in the occipital lobe in the back of the brain
Brightness
A psychological sensation caused by the intensity of light waves.
Occipital lobe
Contains the visual cortex
Receives the impulses from the cells of the retina, which activate feature detectors
How visual stimulation goes from the eyes to the brain
Lens of eye reverses image on retina –> left side of each retina = right visual field, and vice versa –> optic nerve –> optic chasma (left side of retina crosses over to left hemisphere, right to left) –> optic tract –> lateral geniculate nucleus –> visual association cortex –> primary visual cortex
Wavelength influences
Color
Intensity (amplitude) influences
Brightness
Color
Also called hue. Color is not a property of things in the external world. Rather, it is a psychological sensation created in the brain from information obtained by the eyes from the wavelengths of visible light.
Electromagnetic spectrum
The entire range of electromagnetic energy, including radio waves, X rays, microwaves, and visible light.
Visible spectrum
The tiny part of the electromagnetic spectrum to which our eyes are sensitive. The visible spectrum of some creatures may be slightly different than our own.
Long wavelengths create
Red
Short wavelengths create
Blue
Trichromatic theory
The idea that colors are sensed by three different types of cones sensitive to light in the red, blue, and green wavelengths. The trichromatic theory explains the earliest stage of color sensation.
Opponent-process theory
The idea that cells in the visual system process colors in complementary pairs, such as red or green or as yellow or blue. The opponent-process theory explains color sensation from the bipolar cells onward in the visual system. If one sensor is stimulated, its pair is inhibited from firing.
Afterimages
Sensations that linger after the stimulus is removed. Most visual afterimages are negative afterimages, which appear in reversed colors.
Color blindness
Typically a genetic disorder (although sometimes the result of trauma) that prevents an individual from discriminating certain colors. The most common form is red-green color blindness.
Hearing
The energy sense that uses sound waves that are collected by the ears
Sound waves
Vibrations in the air that are collected by the ears
Amplitude
The physical strength of a wave. This is usually measured from peak (top) to valley (bottom) on a graph of the wave. In hearing, determines loudness (dB)
Frequency
The number of cycles completed by a wave in a given amount of time, usually a second. In hearing, determines pitch (MHz)
Tympanic membrane
The eardrum.
Cochlea
The primary organ of hearing; a coiled tube in the inner ear, where sound waves are transduced into nerve messages.
Basilar membrane
A thin strip of tissue sensitive to vibrations in the cochlea. The basilar membrane contains hair cells connected to neurons. When a sound wave causes the hair cells to vibrate, the associated neurons become excited. As a result, the sound waves are converted (transduced) into nerve activity.
Organ of Corti
Neurons activated by movement of the hair cells
Pitch
A sensory characteristic of sound produced by the frequency of the sound wave.
Pitch theories
Describe the processes involved in hearing pitch
Place theory and frequency theory
Place theory
Hair cells in the cochlea respond to different frequencies of sound based on where they are located in the cochlea
Higher pitches
Frequency theory
Hair cells fire at different rates in the cochlea
Lower tones
Loudness
A sensory characteristic of sound produced by the amplitude (intensity) of the sound wave.
Timbre
The quality of a sound wave that derives from the wave’s complexity (combination of pure tones). Timbre comes from the Greek word for “drum,” as does the term tympanic membrane, or eardrum.
Conduction deafness
An inability to hear resulting from damage to structures of the middle or inner ear.
Nerve deafness (sensorineural deafness)
An inability to hear, linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve or higher auditory processing centers.
Stimulus for vision
Light waves
Sense organ for vision
Eye
Receptor for vision
Rods and cones of retina
Vision sensations
Colors, brightness, patterns, motion, texture
Stimulus for hearing
Sound waves
Sense organ for hearing
Ear
Receptor for hearing
Hair cells of the basilar membrane
Hearing sensations
Pitch, loudness, timbre
Stimulus for skin senses
External contact
Sense organ for skin senses
Skin
Receptor for skin senses
Nerve endings in skin
Skin sensations
Touch, warmth, cold
Stimulus for smell
Volatile substances
Sense organ for smell
Nose
Receptor for smell
Hair cells of olfactory epithelium
Smell sensations
Odor (musky, flowery, burnt, minty, etc.)
Stimulus for taste
Soluble substances
Sense organ for taste
Tongue
Receptor for taste
Taste buds of tongue
Taste sensations
Flavors (sweet, sour, salty, bitter)
Stimulus for pain
Many intense or extreme stimuli: temperature, chemicals, mechanical stimuli, etc.
Sense organ for pain
Net of pain fibers all over the body
Receptor for pain
Specialized pain receptors, overactive or abnormal neurons
Pain sensations
Acute pain, chronic pain
Stimulus for kinesthetic and vestibular senses
Body position, movement, and balance
Sense organ for kinesthetic and vestibular senses
Semicircular canals, skeletal muscles, joints, tendons
Receptor for kinesthetic and vestibular senses
Hair cells in semicircular canals; neurons connected to skeletal muscles, joints, and tendons
Kinesthetic and vestibular sensations
Position of body parts in space
Vestibular sense
The sense of body orientation with respect to gravity. The vestibular sense is closely associated with the inner ear and, in fact, is carried to the brain on a branch of the auditory nerve
Kinesthetic sense
The sense of body position and movement of body parts relative to each other (also called kinesthesis)
Olfaction
The sense of smell
Pheromones
Chemical signals released by organisms to communicate with other members of their species. Pheromones are often used by animals as sexual attractants. It is unclear whether or not humans employ pheromones.
Gustation
The sense of taste- from the same word root as “gusto”- also called the gustatory sense
Skin senses
Sensory systems for processing touch, warmth, cold, texture, and pain
Touch
Activated when skin is indented, pierced, or experiences a change in temperature
Gate-control theory
An explanation for pain control that proposes we have a neural “gate” that can, under some circumstances, block incoming pain signals
Some messages have higher priority than others
Fast twitch fibers vs slow twitch fibers
Fast: stimulate by shaking
Block slow fibers
Release endorphins
Slow: pain!
Ways to control pain
- Gate control theory (shaking, stimulating fast fibers)
- Attention
- Hypnosis
- Placebo
Placebo effect
A response to a placebo (a fake drug), caused by subjects’ belief that they are taking real drugs.
What is the relationship between sensation and perception?
Perception brings meaning to sensation, so perception produces an interpretation of the world, not a perfect representation of it.
Percept
The meaningful product of perception- often an image that has wen associated with concepts, memories of events, emotions, and motives
Feature detectors
Cells in the cortex that specialize in extracting certain features of a stimulus
Binding problem
Refers to the process used by the brain to combine (or “bind”) the results of many sensory operations into a single percept. This occurs, for example, when sensations of color, shape, boundary, and texture are combined to produce the percept of a person’s face. No one knows exactly how the brain does this. Thus the binding problem is one of the major involved mysteries in psychology.
Bottom-up processing
Perceptual analysis that emphasizes characteristics of the stimulus, rather than our concepts and expectations. “Bottom” refers to the stimulus, which occurs at step one of perceptual processing.
Top-down processing
Perceptual analysis that emphasizes the perceiver’s expectations, concept memories, and other cognitive factors, rather than being driven by the characteristics of the stimulus. “Top” refers to a mental set in the brain- which stands at the “top” of the perceptual processing system
Proximal stimuli
Retinal images
Distal stimuli
Physical objects in the world
Perceptual constancy
The ability to recognize the same object as remaining “constant” under different conditions, such as changes in size, shape, orientation, and color
Size constancy
We keep a constant size in mind for object and know that it does not grow or shrink as it moves close or farther away
Shape constancy
We know the shape of an object is constant despite being viewed from different angles
Brightness constancy
We perceive objects as being a constant color even as the light reflecting off the object changes
Stroboscopic effect
Images in a series of still pictures presents at a certain speed will appear to be moving
Used in movies or flip books
Phi phenomenon
Series of lightbulbs turned on and off at a particular rate will appear to be one moving light
Autokinetic effect
If a spot of light is projected steadily onto the same place on a wall of an otherwise dark room and people are asked to stare at it, they will report seeing it move
Illusion
You have experienced an illusion when you have a demonstrably incorrect perception of a stimulus pattern, especially one that also fools others who are observing the same stimulus. (If no one else sees it the way you do, you could be having a delusion or a hallucination).
Ambiguous figures
Images that are capable of more than one interpretation. There is no “right” way to see an ambiguous figure.
Hallucination
A misperception experienced only by the individual
Explanation for Müller-Lyer illusion
Brain thinks it is seeing the inside and outside corners of a building in perspective – learned?
Gestalt psychology
From a German word that means “whole” or “form” or “configuration”. (A gestalt is also a percept.) The gestalt psychologists believed that much of perception is shaped by innate factors built into the brain.
Figure
The part of a pattern that commands attention. The figure stands out against the ground.
Ground
The part of a patter that does not command attention; the background.
Closure
The gestalt principle that identifies the tendency to fill in gaps in figures and to see incomplete figures as complete.
Like top-down processing
Laws of perceptual grouping
The gestalt principles of similarity, proximity, continuity, and common fate. These “laws” suggest how our brains prefer to group stimulus elements together to form a percept (gestalt).
Law of similarity
The gestalt principle that we tend to group similar objects together in our perceptions.
Gestalt rules
Principles that govern how we perceive groups of objects
Normally perceive objects as groups, not isolated elements
Law of proximity
The gestalt principle that we tend to group objects together when they are near each other. Proximity means nearness.
Law of continuity
The gestalt principle that we prefer perceptions of connected and continuous figures to disconnected and disjointed ones
Law of common fate
The gestalt principle that we tend to group similar objects together that share a common motion or destination
Law of Prägnanz
The most general gestalt principle, which states that the simplest organization, requiring the least cognitive effort, will emerge as the figure. Prägnanz shares a common root with pregnant, and so it carries the idea of a “fully developed figure”. That is, our perceptual system prefers to see a fully developed gestalt, such as a complete circle– as opposed to a broken circle.
Depth cues
Allow us to differentiate between what is near and what is far
Divided into monocular and binocular cues
Binocular cues
Information taken in by both eyes that aids in depth perception, including binocular convergence and retinal disparity.
Convergence
Binocular depth cue
Point at which one pencil becomes two pencils
The more the eyes converge, the closer the object must be
Binocular disparity
Binocular depth cue
Hole in hand
Far away object projects similar images into retina
The closer it is, the more disparity
Monocular cues
Information about depth that relies on the input of just one eye–includes relative size, light and shadow, interposition, relative motion, and atmospheric perspective.
Learning-based inference
The view that perception is primarily shaped by learning (or experience), rather than by innate factors.
Perceptual set
Readiness to detect a particular stimulus in a given context– as when a person who is afraid interprets an unfamiliar sound in the night as a threat.
Motion parallax
Monocular depth cue
Objects in the distance appear to move more slowly
Pictorial cues
Monocular depth cues
Interposition, linear perspective, relative size, texture gradient, atmospheric perspective, shadow
Interposition
Pictorial cue
Objects that block the view to other objects just be closer
Linear perspective
Pictorial cue
Objects in distance seem to converge
Relative size
Pictorial cue
Objects in distance look smaller
Texture gradient
Pictorial cue
Can see details in texture close to us but not far away
Atmospheric perspective
Pictorial cue
Smog
Shadow or shading
Pictorial cue
Shading implies where the light source is, showing depth and position of objects
Explanation for Ponzo illusion
Experience with structures featuring parallel lines that seem to converge in the distance – people in Guam, for instance, do not experience the illusion
Gustav Fechner
1801-1887
Contributed to Weber’s law on JND
David Hubel
1926-present
Discovered that groups of neurons in the visual cortex respond to different types of visual images
(Feature detectors)
Ernst Weber
Psychophysicist who created Weber’s law, which computes the JND
Also discovered that each sense varies according to a constant
(For hearing it is 5%, for vision 8%)
Torsten Wiesel
(1924-present)
Discovered that groups of neurons in the visual cortex respond to different types of visual images
(Feature detectors)
Eleanor Gibson
Visual cliff experiment to determine when human infants can perceive depth
