Sensation and Perception Flashcards
Pupil
The hole in the iris, which contracts in bright light and expands in dim light, and through which light enters.
Lens
The part of the eye located right behind the iris, and which helps control the curvature of the incoming light and can focus near or distant objects on the retina.
Max Wertheimer
(1880 – 1943) Co-founded Gestalt psychology, beginning with visual illusion known as the phi phenomenon. Concluded that the experience of this visual illusion has a “wholeness” that is different from the sum of its parts. Like other Gestalt psychologists, believed that an analysis of experience into parts is not a valid way of studying our conscious experience.
The Gate Theory of Pain
Created by Ronald Melzack and Patrick Wall. Proposes a special “gating” mechanism that can turn pain signals on or off, thus affecting whether or not pain is perceived. The gating mechanism is located in the spinal chord, and is able to block sensory input from large, thick sensory fibers before the brain is able to receive the pain signals.
Vestibular Sense
Has to do with our sense of balance and of our bodily position relative to gravity. The receptors for balance, the semicircular canals, are in the inner ear, above and behind the cochlea.
Kinesthesis
The sense that provides information through receptors in the muscles, tendons, and joints, enabling humans and other animals to control and coordinate their movements, including walking, talking, facial expressions, gestures, and posture. Also called kinesthesia; kinesthetic sense; movement sense.
Afterimages
Visual sensations that appear after prolonged or intense exposure to a stimulus. Afterimages have been used to support Hering’s theory of color vision, since the color of the afterimage will be the “opposite” of the original color.
2 Types of Processing
(relevant for all senses, not just vision)
- Bottom-up processing (data-driven processing): Responds directly to components of incoming stimulis on the basis of fixed rules and then sums up components to arrive at the whole pattern
- Top-down processing (conceptually driven processing): Guided by conceptual processes such as memories and expectations which allow the brain to recognize whole objects and then the components
4 Visual Constancies
- Size constancy: Tendency for the perceived size of an object to remain constant despite variations in the size of its retinal image
- Shape constancy: Tendency for the perceived shape of an object to remain constant despite variations in the shape of its retinal image
- Brightness constancy: Tendency for the perceived brightness of an object to remain constant despite changes in illumination
- Color constancy: Tendency for the perceived color of an object to remain constant despite changes in the wavelength of the light we see (e.g., colored glasses)
Proximal Stimuli
vs.
Distal Stimuli
The distal stimulus is the actual object or event out there in the world. The proximal stimulus is the information our sensory receptors receive about the object. In the case of vision, the proximal stimulus is the image on the retina.
Frequency Theory of Pitch Perception
The basilar membrane vibrates in synchrony with a sound, causing auditory nerve axons to produce action potentials at the same frequency. The downfall of this theory, in its simplest form, is that the refractory period of a neuron is typically about 1/1000 second, so the maximum firing rate of a neuron is about 1000 Hz, far short of the highest frequencies we hear.
Light Adaptation
When you walk out of a dark movie theater into a bright, sunny day, the visual process that takes place is called light adaptation. Less is known about the physiological basis for this.
Objective Dimensions of Sound
- Frequency: number of cycles per second, measured in Hertz (Hz); one Hz is one cycle per second; frequency is inversely related to wavelength; human sensitivity ranges from 20 Hz to ~ 200,000 Hz, with maximum sensitivity at about 1,000 – 3,000 Hz
- Intensity: amplitude or height of sound wave, measured in bels, or more commonly, decibels (one bel = ten decibels); sounds > 140 decibels tend to be painful to the human ear
Brightness and Illumination
Brightness is related to illumintaion, but it is not the same thing as illumination. Illumination is a physical, objective measurement that is simply the amount of light falling on a surface. Brightness is the subjective impression of the intensity of a light stimulus.
Difference Thresholds
How different two stimuli (in magnitude) must be before they are perceived to be different 50% of the time. Obtained by comparing a “standard stimulus” with a “comparison stimulus.” The comparison stimulus is adjusted until, at some point, the subject thinks that the comparison stimulus is equal to the standard stimulus, even though it isn’t. After repeated trials, the differences between the standard stimulus and the comparison stimulus are averaged. The important thing is not the difference itself, but the ratio of the difference threshold to the “standard stimulus.” This ratio is the basis of Weber’s Law.
4 Broad Categories of Touch
- Pressure
- Pain
- Warmth
- Cold
Cochlear Nerve, also called Auditory Nerve
The cochlear nerve or auditory nerve is a bundle of nerve fibers that carries hearing information from the cochlea of the inner ear directly to the brain.
Physiological Zero
A temperature that is felt by the skin as neither warm nor cold and that under ordinary conditions usually falls at about 85° to 90°F.
Signal Detection Theory
(in the context of psychophysics)
Suggests that other, nonsensory factors influence what the subject says she senses. These nonsensory factors include experiences, motives, and expectations. Response bias refers to the tendency of subjects to respond in a particular way due to nonsensory factors. Unlike the earlier psychophysics, signal detection theory gives us a way to measure both how well the subject can sense the stimulus (sensitivity) and response bias.
Signal Detection Theory
Signal detection theory is a means to measure the ability to differentiate between information-bearing patterns and random patterns that distract from the information.
Fovea
The middle section of the retina, containing only cones. As you move outward, the number of rods increases while the number of cones decreases. Therefore, visual acuity is best here, and this is the part of the eye that is most sensitive in daylight. At the periphery of the retina, there are only rods.
Duplicity (or Duplexity) Theory of Vision
The retina contains two kinds of photoreceptors: cones and rods. Cones produce photopic or color vision, whereas rods produce scotopic or corlorless night vision. Cones also give us the ability to see fine detail (rods do not).
The Steps of Sensory Information Processing
(common to all sensory systems)
- Reception: Each sensory system has receptors that react to physical external energy.
- Transduction: the translation of physical energy into neural impulses or action potentials.
- Once transduction occurs, the electrochemical energy is sent to various projection areas in the brain along various neural pathways and can be processed by the nervous sytem.
Sir Francis Galton
(1822 – 1911) One of the first researchers interested in individual differences. For six years, maintained an anthropometric lab in which he measured the sensory abilities of nearly 10,000 people.
Absolute Threshold
The minimum of stimulus energy needed to activate a sensory system.
Dichotic Listening
Technique used in the lab to study selective attention and lateralization of brain function within the auditory system. The two ears are simultaneously presented with two different messages. Generally, listeners are asked to shadow; that is, to repeat one of the messages as it is presented. Using this method, it has been demonstrated that listeners can indeed attend to one message and dampen out the other one.
Yerkes-Dodson Law
Performance is worst at extremely low or extremely high levels of arousal, and optimal at some intermediate level.
Wolfhang Köhler
(1887 – 1967) Gestalt psychologist who developed the theory of isomorphism.
Psychophysics
The branch of psychology that deals with the relationships between physical stimuli and mental phenomena.
Ames Room
Erroneous depth information confuses our notion of size in certain situations. In an Ames Room, the back left corner of the room is almost twice as far away as the back right corner, and there are distortions of floor-to-ceiling height. However, if you view the room through the peephole provided, the trapezoidal shape of both the back wall and the windows at the rear of the room make the room look like a normal rectangular room, with a back wall apparently perpendicular to the line of sight. Thus, someone standing by the larger left rear window appears equally as far away as someone standing at the closer right rear window, even though the visual angles subtended by the two people are quite different. The person on the left appears much smaller than the equally sized person on the right because you have been fooled into believing that the difference in visual angles is not due to a difference in distance.
The Significance of
Visual Angle
The visual angle determines the size of the image on the retina. The 2 things that determine the visual angle (and thus the retinal size of the object) are the size of the object and the distance between the object and the eye.
Eleanor Gibson and Richard Walk
Developed the visual cliff apparatus, which is used to sudy the development of depth perception.
Wavelengths of light visible to the human eye
~ 400 – 800 nanometers
Simultaneous Brightness Contrast
A target area of a particular luminance appears brighter when surrounded by a darker stimulus than when surrounded by a lighter stimulus. An explanation for this phenomenon is lateral inhibition: if a retinal cell is excited, neighboring cells will be inhibited. Because the surrounding cells are inhibited, they do not fire as often, and the corresponding area appears not as bright. Lateral inhibition sharpens and highlights borders between light and dark areas.
Crossings of Visual Information
The image of the stimulus on the right side of each eye’s visual field forms the left half of each eye’s retina, and vice versa. At the optic chiasm in the brain, fibers from the nasal half of the retina cross paths. The nasal fibers from the left eye go to the right side of the brain, and vice versa. However, the fibers from the temporal halves of the retina do not cross paths. Thus, all the information from the left visual field of both eyes is processed in the right cerebral hemisphere, and vice versa.
Chromatic vs. Achromatic Color
Chromatic colors are any color in which one particular wavelength or hue predominates. For example, blue and green are chromatic colors, while white, gray, and black are achromatic colors, as they have no dominant hue (all wavelengths are present in equal amounts within those colors).
Rods vs. Cones
The two kinds of photoreceptors in the human retina are rods and cones. Cones are used for color vision and for perceiving fine detail. Cones are most effective in bright light, and allow us to see chromatic and achromatic colors. In reduced illumination, rods function better than cones but allow perception only of achromatic colors. Rods have low sensitivity to detail and are not involved in color vision. There are many more rods than cones in the human eye.
Limen
Another word for “threshold.” For instance, “subliminal perception” refers to perception of stimuli below a threshold––in this case, below the threshold of conscious awareness.
Psychophysics
(expanded definition)
Field concerned with measuring the relationship between physical stimuli and psychological responses to stimuli. One of the most important concepts in sensory perception is the concept of a threshold. There are two main types of threshold: absolute threshold and difference threshold.
Georg von Békésy
(1899 – 1972) Békésy’s Traveling Wave Theory: A sound impulse sends a wave sweeping along the basilar membrane. As the wave moves along the membrane, its amplitude increases until it reaches a maximum, then falls off sharply until the wave dies out.
Using strobe photography and silver flakes as a marker, found that the movement of the basilar membrane is maximal at a different place along the basilar membrane for each different frequency (although the whole basilar membrane vibrates for any given stimulus). High frequencies maximally vibrate the stiff base of the basilar membrane, near the oval window; low frequencies maximally vibrate the floppy apex, or tip, of the basilar membrane. This is sometimes called Békésy’s Traveling Wave Theory. (However, Békésy also found that low frequency tones, less than 400 Hz, maximally displace a very broad part of the basilar membrane.) Békésy’s Traveling Wave Theory partially supports Helmholtz’s Place-Resonance Theory.
Subjective Dimensions of Sound
There are at least 8, but should be familiar with 3: loudness, pitch, and timbre. Loudness is related to intensity, but cannot be measured in decibels. Pitch is related to frequency, but cannot be measured in Hertz. Timbre refers to the quality of the sound, and is related to the complexity of the sound wave, i.e. the mixture of frequencies.
Retina
The back of the eye; like a screen filled with neural elements and blood vessels. This is the image-detecting part of the eye. The duplexity or duplicity theory of vision states that the retina contains two kinds of photoreceptors (cones and rods). The organization of the retinal cells makes light pass through intermediate cell layers (including the retinal pigment epithelium, or RPE) before reaching, and stimulating, the photoreceptors. There is a blind spot (with no photoreceptors) where the optic nerve leaves the eye.
Proprioception
The general term for our sense of bodily position, including aspects of both vestibular and kinesthetic sense.
Robert Yerkes and John Dodson
Developed Yerkes-Dodson Law, which states that performance is best at intermediate levels of arousal.
Visual Cliff
Apparatus designed in the early 1960s, by Eleanor Gibson and Richard Walk, to assess infant depth perception. Even at 6 months, infants won’t cross; thus, even very young infants can perceive depth.
Multistable Perception,
or the “reversible figure” illusion
Stimulus pattern in which two alternative, equally compelling perceptual organizations spontaneously oscillate. One example is the Necker Cube (familiar “3D” drawing of a cube). Another example is the vase/face figure/ground oscillation.
Cocktail Party Phenomenon
You are having a conversation with one person, when all of a sudden, your ears perk up because someone half a room away mentions your name.
Moon Illusion
The moon on the horizon appears to be larger than the moon at its zenith. One explanation is distance cues like buildings.
George Berkeley
(1685 – 1753) Developed a list of depth cues that help us to perceive depth.
The visual system of newborns
At birth, infants are unable to discern fine details but are able to follow an object or light with their eyes when it is placed in the center of their visual field. Furthermore, newborns can perceive color, simple figures, and sharp contrast, and can even see in dim light. Ability to see fine detail improves rapidly.
Cornea
The clear, domelike window in front of the eye that gathers and focuses incoming light.
ROC Curve
(Receiver Operating Characteristic)
Used to graphically summarize a subject’s responses in a signal detection experiment. John A. Swets refined the use of ROC curves. More generally, an ROC curve is a graphical plot that illustrates the diagnostic ability of a binary classifier system as its discrimination threshold is varied. The ROC curve is created by plotting the true positive rate (TPR) against the false positive rate (FPR) at various threshold settings.
John A. Swets
Refined the use of ROC curves in signal detection theory.
Ronald Melzack and Patrick Wall
Proposed gate theory of pain.
James J. Gibson
Studied depth cues (especially texture gradients) that help us to perceive depth. Husband of Eleanor Gibson, who studied visual cliff (also concerning depth perception) with Richard Walk.
Subtractive vs. Additive
Color Mixture
Subtractive color mixture occurs when we mix pigments. Additive color mixing has to do with lights.
Two-Point Threshold
The minimum distance necessary between two points of stimulation on the skin such that the points will be felt as two distinct stimuli. The size of the two-point threshold depends on the density of nerves in particular areas of the skin.
Animal Experiments on Visual Development
Used to separate out the contribution of nature vs. nurture. Most find that experience plays an important role in the development of the visual system, and that there are sensitive periods during which experience is maximally effective. However, these animal studies do not necessarily generalize to humans.
Just Noticeable Difference
(JND)
Measures the same thing as the difference threshold, but in different units. If a given difference threshold is 2 ounces, then 2 ounces would equal 1 JND, 4 ounces would equal 2 JNDs, etc.
Gustav Fechner
Psychophysics researcher who in the mid-19th century discovered a relationship between physical stimuli and psychological responses to stimuli. He formulated what he called Weber’s Law, which states that the minimum increase of stimulus which will produce a perceptible increase of sensation is proportional to the pre-existent stimulus. Fechner also formulated Fechner’s Law, which is a modification of Weber’s Law. Specifically, Fechner’s Law states that the intensity of our sensation increases as the logarithm of an increase in energy rather than as rapidly as the increase.
Fechner’s Law
and
Stevens’ Power Law
(both are mathematical, but must know the general ideas)
Fechner’s Law is an equation relating intensity of sensation to intensity of stimulus. Fechner’s Law is a modification of Weber’s Law and states that sensation increases along with intensity, but with diminishing returns. Around the middle of the 20th century, Stanley Smith Stevens performed some experiments whose results suggested that Fechner’s Law might be incorrect. He found that his results were best fit by another equation, which has come to be known as Stevens’ Power Law. Like Fechner’s Law, Stevens’ Power Law relates intensity of stimulus to intensity of sensation.
Weber’s Law
See physical flashcard.
Hermann von Helmholtz
(1821 – 1894) Developed Young-Helmholtz trichromatic theory of color vision; also developed place-resonance theory of pitch perception. Was a German physician (like Ernst Weber) and also a physicist.
Also was first to measure the speed of a nerve impulse (in terms of reaction), and is often credited with the transition of psychology into the field of the natural sciences.
Ernst Weber
(1795 – 1878) German physician who is considered one of the founders of experimental psychology. In 1834, Weber published a book called De Tactu (About Touch in Latin), in which he introduced the notion of just noticeable difference (JND) in sensation. Weber’s Law was labeled as such by Gustav Fechner.
Stanley Smith Stevens
Developed Stevens’ Power Law as an alternative to Fechner’s Law.
Place-Resonance Theory of Pitch Perception
The basilar membrane resembles the strings of a piano, with each area along the membrane tuned to a specific frequency. Each frequency activates the hair cells at only one place along the basilar membrane, and the nervous system distinguishes among frequencies based on which neurons respond. The downfall of this theory is that the various parts of the basilar membrane are bound together too tightly for any part to resonate like a piano string. The place-resonance theory is usually attributed to Hermann von Helmholtz, though it was widely believed much earlier.
George Berkeley
In 1709, George Berkeley listed 3 depth cues:
- Interposition: If one object covers another, the partially hidden object is seen as farther away
- Relative size: Comparison of retinal size of object to actual size of object gives cue to depth
- Linear perspective: Parallel lines appear to converge as they recede into the distance
Hubel and Wiesel
Studied feature detection in visual cortex and discovered simple, complex, and hypercomplex cells.
Ewald Hering
(1834 – 1918) Developed opponent process theory of color vision
Emmert’s Law, or the
Size-Distance Invariance Principle
Emmert’s Law states that objects which generate retinal images of the same size will look different in physical size if they appear to be located at different distances. Specifically, the perceived linear size of an object increases as its perceived distance from the observer increases. In other words, size constancy depends on apparent distance. The farther away the object appears to be, the more the scaling device in the brain will compensate for its retinal size by enlarging our perception of the object. Erroneous depth information confuses our notion of size in certain situations, for instance, the Ames Room.
How the hair cells that compose the organ of Corti bend
Sound waves cause the eardrum / tympanic membrane to vibrate, in turn causing the bones in the middle ear (the ossicles) to vibrate. The movement of the last of the ossicles, the stirrup / stapes, causes the oval window to vibrate. This causes the cochlear fluid to vibrate at the same frequency. This vibration gives rise to a traveling wave in the basilar membrane, which in turn causes the hair cells (of the organ of corti) to bump into the relatively immovable tectorial membrane above and bend.
The Inner Ear
The inner ear contains the cochlea, which is filled with a saltwater-like fluid called cochlear fluid. There are a couple of membranes that run the length of the cochlea; the most important is the basilar membrane. The organ of Corti rests on the basilar membrane along its entire length. The organ of Corti is composed of thousands of hair cells. These hair cells are the receptors for hearing, analogous to the rods and cones in the eye. When these hair cells bend, the bending is transduced into electrical charges in some way not fully understood. These signals are then transmitted out of the cochlea along the cochlear nerve, also called the auditory nerve.
4 Illusions of Motion
- Apparent motion (stroboscopic movement, or the phi phenomenon): When two or more stationary lights flicker in succession.
- Induced motion: A stationary point of light appears to move when the background moves.
- Autokinetic effect: A stationary point of light when viewed in an otherwise totally dark room appears to move.
- Motion aftereffect: If a moving object is viewed for an extended period of time, it will appear to move in an opposite direction when the motion stops.
6 Gestalt Laws of Form Perception
- Similarity: The human eye tends to build a relationship between similar elements within a design
- Continuation: The human eye follows the paths, lines, and curves of a design, and prefers to see continuous flow rather than separated objects
- Closure (also called reification): The human eye prefers to see complete shapes. Perception will “fill in” missing information
- Proximity (also called emergence): Simple shapes arranged together can create a more complex image
- Figure / Ground: The human eye isolates shapes from backgrounds
- Prägnanz (encompasses the other laws): People will perceive and interpret ambiguous or complex images as the simplest form(s) possible
3 Depth Cues Not Included
in George Berkeley’s Work
- Texture gradients: As scene recedes from viewer, the surface texture of the object appears to change (from the work of James J. Gibson)
- Motion Parallax: When observer moves, objects in a stationary environment appear to move relative to distance from observer (kinetic depth effect is a special kind of motion parallax in which an object moves, rather than the perceiver)
- Binocular disparity (stereopsis): Each eye sees a slightly different scene; when the brain combines the scenes, we get perception of depth
Structures of the Ear
There are three main parts to the ear: the outer ear, the middle ear, and the inner ear. A sound wave first reaches the pinna, the fleshy part of the ear visible from the outside. The main function of the pinna is to channel sound waves into the auditory canal, also in the outer ear. The auditory canal channels the sound to the eardrum, also called the tympanic membrane or tympanum, which forms the boundary between the outer ear and the middle ear.
Components of the Middle Ear
3 tiny bones, called ossicles, which are the smallest bones in the human body:
- hammer / malleus
- anvil / incus
- stirrup / stapes
These transmit the vibrations of the tympanum (aka tympanic membrane or eardrum, which forms the boundary between the outer and middle ear) to the inner ear. The edge of the stirrup / stapes rests on the oval window, which is the entrance to the inner ear.
David Hubel and Torsten Wiesel
Found a neural basis for feature detection theory, which suggests that all complex stimuli can be broken down into individual parts (features), each of which is analyzed by a specific feature detector. They performed their research on the visual cortex of cats. They distinguished 3 different types of cells: simple, complex, and hypercomplex. Simple cells respond to information about orientation; complex cells respond to advanced information about orientation, such as movement; and hypercomplex cells respond to information about abstract concepts like object shape. Hubel and Wiesel measured cell responses using the latest research methodologies available to sensory psychologists at the time: single-cell recording, sometimes called recording from single nerve fibers.
From the optic chiasm, visual information goes where in the brain?
- The lateral geniculate nucleus of the thalamus
- The visual cortex in the occipital lobe
- The superior colliculus
5 types of receptors that receive
Tactile Information
- Pacinian corpuscles (deep pressure)
- Meissner corpuscles (touch)
- Merkel discs (gentle touch)
- Ruffini endings (warmth)
- Free nerve endings (pain, heat / cold, light touch; slow to adjust, so less sensitive to abrupt changes in stimulation)
Auditory Pathways in the Brain
The auditory nerve projects to the superior olivary complex in the brainstem, the inferior colliculus, the medial geniculate nucleus of the thalamus, and the auditory cortex of the temporal lobe.
Brain Structures Important in
Sensation and Perception
- Lateral geniculate nucleus of the thalamus (vision)
- Superior colliculus (vision)
- Visual cortex in occipital lobe (vision)
- Inferior colliculus (audition)
- Medial geniculate nucleus of the thalamus (audition)
- Auditory cortex in temporal lobe (audition)
- Superior olivary complex in the brainstem (audition)
- Somatosensory cortex (touch)
Taste and Smell
Taste and smell are chemical (not mechanical). The receptors for taste are groups of cells called taste buds found in little bumps on the tongue called papillae. The smell receptors are in the upper nasal passage, in the olfactory epithelium. Taste information travels to the taste center in the thalamus, while smell information travels to the olfactory bulb in the forebrain.
5 Visual Illusions
See physical flashcard.
Summation of the research on pitch perception,
according to Kaplan
Frequency theory is operative for tones up to about 500 Hz, place theory is operative for tones higher than about 4,000 Hz, and both mechanisms are operative between 500 Hz and 4,000 Hz. The volley principle comes into play for frequencies above 100 Hz.
The Prevailing Theory of Pitch Perception
The prevailing theory of pitch perception is a combination of place resonance theory and frequency theory. For low-frequency sounds (up to about 100 Hz), the basilar membrane vibrates in synchrony with the sound waves, in accordance with frequency theory, and auditory nerve axons generate one action potential per wave. Soft sounds activate fewer neurons, while stronger sounds activate more neurons. As sounds exceed 100 Hz, it becomes harder for any single neuron to continue firing in synchrony with the sound waves. At higher frequencies (up to ~ 4000 Hz), multiple auditory neurons coordinate their firing according to the volley principle. Beyond ~ 4000 Hz, even staggered volleys can’t keep pace. For frequencies > 4000 Hz, we use a mechanism similar to place-resonance theory. The basilar membrane varies from stiff at its base, where stirrup meets cochlea, to floppy at the other end of the cochlea, the apex. The highest frequency sounds maximally vibrate hair cells near the base, etc.––Békésy’s Traveling Wave Theory
Iris
The colored part of the eye, made up of involuntary muscles and autonomic nerve fibers, which controls the size of the pupil and therefore the amount of light entering the eye.
Connection between visual receptors (rods and cones)
and the optic nerve
The connection is not direct. Several layers of interneurons in between: horizontal cells, bipolar cells, amacrine cells, and ganglion cells. Rods and cones connect with horizontal cells, which connect with bipolar cells, which connect with amacrine cells (amacrine cells interpose 30% of the time), which connect with ganglion cells. The ganglion cells group together to form the optic nerve. Many more receptors than ganglion cells, so each ganglion cell has to represent the combined activity of many rods and cones, resulting in loss of detail. On average, the number of cones converging onto individual ganglion cells is smaller than the number of rods converging onto individual ganglion cells.
Cochlea (plural is Cochleae)
The cochlea is a spiralled, hollow, conical chamber of bone in the inner ear.
The 2 acellular (not composed of cells) membranes
in the cochlea of the inner ear
- The basilar membrane (upon which the organ of Corti rests)
- The tectorial membrane (“tectorial” in anatomy means forming a cover); the tectorial membrane covers the organ of Corti; the hair cells of the organ of Corti bend because they bump into the tectorial membrane, which is relatively immoveable
Dark Adaptation
Caused by the regeneration of rhodopsin, the photopigment in the rods. Rhodopsin is made up of a vitamin A derivative, called retinal, and a protein, called opsin. When a molecule of rhodopsin absorbs a photon of light, the pigment begins to decompose, or split, into retinal and opsin. This is called bleaching. After bleaching, it takes time for the pigments to regenerate. (Another name for retinal is retinene1)
A photopigment is a pigment whose chemical state depends on its degree of illumination.
A pigment is the natural coloring matter of animal or plant tissue.
2 Basic Theories of Color Vision
The Young-Helmholtz (Trichromatic) Theory holds that there are 3 types of color receptors (cones): red, blue, and green. The Hering (Opponent-Process) Theory states that there are 3 opposing pairs: red-green, blue-yellow, and black-white. Modern research supports the Young-Helmholtz (Trichromatic) Theory, but shows that the Hering (Opponent-Process) Theory applies to other cells in the visual system, such as the cells in the lateral geniculate nucleus of the thalamus.
Donald Broadbent
Proposed Filter Theory of Attention: If a stimulus is attended to, it will be passed through the filter and analyzed further. If it is not, it will be lost. According to Filter Theory, selective attention is an all-or-nothing process. More recent evidence indicates that this is not the case.
Wolfgang Köhler
One of the founders of Gestalt psychology. Responsible for the theory of isomorphism, which suggests that there exists a one-to-one correspondence between the object in the perceptual field and the pattern of stimulation in the brain. Isomorphism hasn’t fared well empirically.
Ernest Wever and Charles Bray
In 1930, proposed volley theory of pitch perception in response to a criticism of the frequency theory of pitch perception. The volley theory states that groups of neurons of the auditory system respond to a sound by firing action potentials slightly out of phase with one another so that when combined, a greater frequency of sound can be encoded and sent to the brain to be analyzed.
2 Major Research Methods for
Studying Visual Perception in Infants
- Preferential looking: two different stimuli are presented side by side; if infant looks longer at one of them, it is inferred that the infant can perceive the difference between the stimuli
- Habituation: a stimulus is presented to infant, infant eventually stops attendint to it; a different stimulus is presented––if the infant attends to it, it is inferred that the infant can perceive the difference between the old and new stimuli
