CHAPTER 3 SENSATION AND PERCEPTION
Sensation - The process by which our sense receptors and nervous system receive and represent stimulus energies from our environment.
- The process of stimulating receptors
Perception - The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.
- Interpretation & selection of sensory input
Absolute Threshold - The minimum stimulation needed to detect a particular stimulus.
- The point where you can tell the stimulus is there vs. not there 50% of the time
Difference Threshold - The minimum difference in stimulation that a subject can detect 50% of the time. We experience the difference threshold as a just noticeable difference (jnd).
- The smallest change in the stimulus that is just detectable 50% of the time
- Ranges from gamma rays to radio waves
- Humans sense the band between about 400 and 750 nanometers
Electromagnetic Spectrum (Wavelength)
- The distance from the peak of one light or sound wave to the peak of the next. Electromagnetic wavelengths vary from the long pulses of radio transmission to the short blips of cosmic rays.
- Ranges from ~400nm to ~700nm
- Hue -- The dimension of color that is determined by the wavelength of light; what we know as the color names (blue, green, and so forth).
- Intensity -- The amount of energy in a light or sound wave, which we perceive as brightness or loudness, as determined by the wave's amplitude.
Major Eye Structures (Show Overhead S&P 2)
- The Retina - The light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information.
- Made of about 107 million transducers (100 million rods and 7 million cones)
- Rods - Retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when the cones don't respond.
- Mostly in the periphery
- More light sensitive
- Detect light and dark
- Insensitive to red
- Take 20-30 minutes to fully adapt to darkness
- Cones - Receptor cells concentrated near the center of the retina that function in daylight or in well-lit conditions. The cones detect fine detail and give rise to color sensation.
- Mostly in the fovea
- Less light sensitive
- Detect colors
- Have best detail vision
- Adapt fully to darkness in 2-3 minutes
- Fovea -- The central focal point in the retina, around which the eye's cones cluster.
- Iris - A ring of muscle tissue that forms the colored portion around the pupil and controls the size of the pupil opening.
- Pupil -- The adjustable opening in the center of the eye through which light enters.
- Lens -- The transparent structure behind the pupil that changes shape to focus images on the retina.
- Accommodation -- The process by which the eye's lens changes shape to focus the image of near objects on the retina.
- Optic Nerve: The nerve that carries neural impulses from the eye to the brain.
- "Blind Spot" - The point at which the optic nerve leaves the eye, creating a "blind" spot because no receptor cells are located there.
The Young-Helmholtz Trichromatic Theory
- The theory that the retina contains three different color receptors - one most sensitive to red, one to green, one to blue - which combined can produce any color.
- Three types of cones
- S-Cones (sensitive to blue)
- M-Cones (sensitive to green)
- L-Cones (sensitive to red)
- Color Vision - The "color" we see is dependent on the wavelength
- Blue (S-Cones): ~ 450 nm
- Green (M-Cones): ~ 520nm
- Red (L-Cones): ~ 650nm
The Opponent Process Theory
- The theory that opposing retinal processes (red-green, yellow-blue, white-black) enable color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green.
- Cells are connected so as to place sensations of
- Red in opposition to green
- Blue in opposition to yellow
- Black in opposition to white
Signal Detection Theory
- A theory stipulating that there is no single absolute threshold
- Involves the task of judging the presence of a faint stimulus ("signal").
- Signal detection researchers assume there is no single absolute threshold
- The detection of a weak signal depends partly on a person's experience, expectation, motivation, and level of fatigue.
- The trichromatic theory explains perception at the receptor level
- The opponent process theory explains it at higher brain levels
- Color Constancy - Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object.
- Cells in the retina are connected laterally by amacrine cells
- Works to enhance contrasts
Depth Perception - The ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance.
- Cues can be monocular or binocular
- Some appear to be innate, whereas others appear to be learned
Binocular Cues - Depth cues, such as retinal disparity and convergence, that depend on the use of two eyes.
- Retinal (Binocular) Disparity -- A binocular cue for perceiving depth, based on the fact that each eye gets a slightly different picture of the world; the greater the disparity (difference) between the two images the retina receives of an object, the closer the object is to us.
- Convergence -- the lenses of your eyes move closer together when things are close, farther apart when things are farther away
Monocular Cues - Distance cues, such as aerial and linear perspective and overlap, available to either eye alone.
- Relative Motion -- When we move, objects at different distances change their relative positions in our visual image, with those closest moving most.
- Relative Brightness -- Dimmer objects seem more distant.
- Relative Height - We perceive higher objects as farther away.
- Linear Perspective - Parallel lines converge into the distance
- Aerial Perspective -- Hazier objects appear more distant than nearby objects.
- Relative Size -- Bigger things appear to be closer
- Texture Gradient - Textures become finer as things become more distant.
- Shading -- Shadowing distinguishes bulges from indentations; Largely a learned cue
- Motion Parallax - Objects closer than our fixation point move opposite to our direction of motion; Objects farther away move in the same direction as us.
- Overlap or Interposition - Closer objects overlap objects that are farther away
- Our perception of objects can be easily fooled due, in part, to an array of predispositions we have:
- Closure -- The perceptual tendency to fill in gaps, thus enabling one to perceive disconnected parts as a whole object.
- Connectedness -- The perceptual tendency to perceive features, such as dots, as a single unit when uniform and linked.
- Proximity - A perceptual tendency to group together visual and auditory events that are near each other.
- Grouping -- The tendency to organize stimuli into coherent groups.
- Perceptual Set - A mental predisposition to perceive one thing and not another.
- Perceptual Constancy -- Perceiving objects as unchanging (having consistent brightness, color, shape, and size) even as illumination and retinal images change.
- Perceptual Adaptation -- In vision, the ability to adjust to an artificially displaced or even inverted visual field.
- Reveal information about the visual system
- Sometimes derive from perspective cues.
- Müller-Lyer Illusions
- The Poggendorf Illusion
- The Crossed Lines Illusion
- The Bending Lines Illusion
- Have 2 interpretations, can be switched at will
- Demonstrate the existence of top-down processing
- The Necker Cube
- The Schroeder Staircase
- Changing perspective gradually in a large picture can create impossible figures (as in some Escher prints).
- If the figure is large enough, you cannot perceive it all at once, so the change in perspective is not readily apparent.
- Contrast the relative ambiguity of the large and small figures on the 2 Tongs/ 3 Tongs slide.
- The whole is greater than the sum of its parts.
- A group of sensory elements forms something new that is greater than itself
- Figure-Ground - We organize the world so some parts of a stimulus appear to stand out (figure) in front of other parts (ground)
- Similarity - We group things that are similar in color, shape, etc. into single units and see them as belonging together
- Proximity - We perceive as a unit things that are closer together relative to other things
- Continuation - We group things together if they appear to form a continuous pattern
- Closure - We tend to complete figures with gaps in them, by ignoring the gaps and mentally filling in what we believe should be there
- Simplicity - We tend to impose the simplest, best-fitting interpretation on any stimulus.
Visual Capture -- The tendency for vision to dominate the other senses; we perceive filmed voices as coming from the screen we see rather than from the projector behind us.
- Sensing molecular movements in a medium
- A vacuum will not carry sound waves
- Frequency -- The number of complete wavelengths that pass a point in a given time (for example, per second).
- A tone's highness or lowness; depends on frequency.
- Loudness: determined by amplitude
- Timbre: Complexity of the sound (number of component waves involved in it)
- Pinna - The external ear. Amplifies sound. Funnels energy to the middle ear.
- Typanic Membrane (eardrum) - Moves in response to sound waves. Converts sound energy to mechanical energy
- Middle Ear - The chamber between the eardrum and cochlea containing the ossicles (three tiny bones) that concentrate the vibrations of the eardrum on the cochlea's oval
- The hammer (maleus)
- The anvil (incus)
- The stirrup (stapes).
- Transmits & amplifies motion of eardrum
- Inner Ear - The innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.
- Cochlea -- The coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses.
- Hair cells are attached to the basilar membrane.
- Converts mechanical energy to neural impulses.
- Bone Conduction: Sound is also transmitted to the cochlea through contact with skull bones. This is why your voice sounds odd in recordings
Responding to Sound
- Frequency Theory - In hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch.
- Different frequencies resonate on different parts of the basilar membrane.
- Doesn't explain perception of low frequencies.
- Firing rates of hair cells create pitch sensation
- Explains frequencies below 4000 Hz, but not above
- Hearing Loss
- Usually caused by continuous exposure to excessive noise. The louder the noise, the less exposure needed
- Nerve Deafness -- Hearing loss caused by damage to the cochlea's receptor cells or to the auditory nerves.
- Conduction Deafness -- Hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea.
- Consist of smell & taste
- Evoke memories, emotions
- Humans vary greatly in chemical sensitivity
- Senses vaporized molecules
- Consists of 10 million rods embedded in the olfactory epithelium
- Olfactory Bulbs: Matchstick-sized; Integrate signals from the olfactory rods, send them on to the brain
- Turbinate Bones: Filter out dust and warm incoming air. Protect the olfactory epithelium.
- Olfactory Rods: There are more than 100 different types. Each responds to different chemicals
- Smell Sensitivity
- Sense of smell varies among animals
- Dogs have 200 million olfactory rods, spread out in a much bigger nose
- Humans differ greatly in ability to detect smells
- The most sensitive people are 20 times more sensitive than the least
- Involves only 4 sensations: Sweet, sour, salty, bitter
- Most of what we consider taste is actually smell
- Texture is very important in enjoyment of food
- People love fats for the smooth feeling they give food (most are tasteless)
- The least numerous sensory receptors (humans have only about 10,000)
- There are no taste buds in the center of the tongue
- Taste buds constantly replaced (like olfactory rods)
- Taste sensitivity changes very little with age
- Enjoyment of food among the aged is reduced by loss of sense of smell
- The largest sensory apparatus, involves heat, cold, pressure, pain
- Sensitivity varies throughout the body, reflected in the amount of brain devoted to each section of skin
- The hands (especially tips of fingers) & face (especially lips) predominate
- Important for survival
- Motivates us to protect the body, tend injuries, rest, seek medical help.
- Gate Theory -- Melzak and Wall's theory that the spinal cord contains a neurological "gate" that blocks or allows pain signals to pass on to the brain.
- The "gate" is opened by the activity of pain signals traveling up small nerve fibers and closed by activity in larger fibers or by information coming from the brain.
- Suggests an area in the spinal cord where fast-conducting nerve fibers can block the messages of small, slow conducting fibers.
- Suggests humans can block pain even when severely injured
- Explains why the badly injured may not even notice an injury
- Slow firing of pain neurons
- Accupuncture & placebos work through endorphin release
- "Runner's high" involves endorphin production
- Can be blocked by endorphin-blocking drugs
- Kinesthetic Sense - The system for sensing the position and movement of individual body parts.
- Knowledge of the position and motion of body parts.
- Driven by receptors in muscles, joints, and ligaments
- Vestibular Sense
- Involves the semicircular canals & the vestibular sacs
- Senses acceleration, not uniform motion
- Equilibrium -- The sense of body movement and position, including the sense of balance.
- Motion sickness arises when vision and the vestibular sense give rise to different messages
- Influence by messages that are below your level of awareness (ex: taped messages that are below auditory level)
- Double-blind studies have found little support for the efficacy of subliminal persuasion tapes.
- Telepathy: Detecting others' thoughts
- Clairvoyance: Knowing things that can't be sensed
- Precognition: Predicting the future
- Psychology is concerned with evidence
- Evidence of psychic ability under controlled conditions is lacking
Okay, now here's a kinda put all together sort of thing ...
SENSATION To study sensation is to study an ageless question: How does the world "out there" get represented inside our heads? Put another way, how are the external stimuli that strike our bodies transformed into messages that our brains comprehend? Some Basic Principles Each species comes equipped with sensitivities that enable it to survive and thrive. We sense only a portion of the sea of energy that surrounds us, but to this portion we are exquisitely sensitive. Our absolute threshold for any stimulus is the minimum stimulation necessary for us to detect it. Signal detection researchers report that our individual absolute thresholds vary with our psychological state. Can we react to stimuli that are not only subthreshold (subliminal), but so weak that we could never consciously perceive them? Recent experiments reveal that we can process some information from stimuli too weak to recognize. But the restricted conditions under which this occurs would not enable unscrupulous opportunists to exploit us with subliminal messages. Nor is there any evidence or plausible theory that we can effortlessly "reprogram" our minds with subliminal tapes. To survive and thrive, an organism must also have difference thresholds low enough to detect minute changes in important stimuli. In humans, difference thresholds (also called just noticeable differences, or jnd's) increase in proportion to the size of the stimulus - a principle known as Weber's Law. The phenomenon of sensory adaption focuses our attention on changing stimulation by diminishing our sensitivity to constant or routine odors, sounds, and touches. Vision The task of our visual sense, as of each of our senses, is to receive stimulation, transduce it into neural signals, and send these neural messages to the brain. The energies we experience as visible light are a thin slice from the broad spectrum of electromagnetic radiation. After entering the eye through a cameralike lens, light waves strike the retina. the retina's rods and cones convert the light energy into neural impulses, which are coded by the retina before traveling up the optic nerve to the brain. Visual Information Processing In the cortex, individual neurons respond to specific features of a physical stimulus, and their information is pooled by higher-level brain cells for interpretation. Subdimensions of vision (color, movement, depth, and form) are processed separately and simultaneously, illustrating our brain's capacity for parallel processing. Color Vision Research on how we see color supports two nineteenth-century theorists. First, as the Young-Helmholtz three-color theory suggests, the retina contains three types of cones. Each is most sensitive to the wavelengths of the three primary colors (red, green, and blue). Second, as opponent-process theory maintains, the nervous system codes the color-related information from the cones into pairs of opponent colors, as demonstrated by the phenomenon of after-images and as confirmed by measuring opponent processes within the visual neurons of the thalamus. As illustrated by the phenomenon of color constancy under varying illumination, our brains construct our experience of color. Hearing The pressure waves we experience as sound vary in frequency and amplitude, and correspondingly in perceived pitch and loudness. Through a mechanical chain of events, sound waves traveling through the auditory canal cause minuscule vibrations in the eardrum. Transmitted via the bones of the middle ear to the fluid-filled cochlea, these vibrations create movement in tiny hair cells, triggering neural messages to the brain.
Research on how we hear pitch supports both the place theory, which best explains the sensation of high-pitched sounds, and frequency theory, which best explains the sensation of low-pitched sounds. We localize sound by detecting minute differences in the loudness and timing of the sounds received by each ear. Hearing Loss Hearing loss linked to conduction and nerve disorders can be caused by prolonged exposure to loud noise and by diseases and age-related disorders. Touch Our sense of touch is actually four senses: pressure, warmth, cold, and pain, that combine to produce other sensations, such as "hot." One theory of pain is that a "gate" in the spinal cord either opens to permit pain signals traveling up small nerve fibers to reach the brain or closes to prevent their passage. Because pain is both a psychological and physiological phenomenon, it often can be controlled through a combination of medical and psychological treatments. Taste Taste, a chemical sense, is likewise a composite of four basic sensations: sweet, salty, sour, and bitter, and of the aromas that interact with information from the taste buds. Smell Like taste, smell is a chemical sense, but there are no basic sensations for smell, as there are for touch and taste. Like other stimuli, odors can spontaneously evoke memories and feelings. Body Position & Movement (Kinethetics) Our effective functioning requires a kinesthetic sense, which notifies the brain of the position and movement of body parts, and a sense of equilibrium, which monitors the position and movement of the whole body. Sensory Restriction People temporarily or permanently deprived of one of their senses typically compensate by becoming more acutely aware of information from the other senses. Temporary experiences of sensory restriction often evoke a heightened awareness of all forms of sensation. Under supervision, sensory restriction may provoke a therapeutic boost for those seeking control over problems such as smoking. PERCEPTION From a top-down perspective, we see how, aided by knowledge and expectations, we transform sensory information into meaningful perceptions. Perceptual Illusions Visual and auditory illusions were fascinating scientists even as psychology emerged. Explaining illusions required an understanding of how we transform sensations into meaningful perceptions, so the study of perception became one of psychology's first concerns. Conflict between visual and other information is usually resolved with the mind accepting the visual data, a tendency known as visual capture. Perceptual Organization The early Gestalt psychologists were impressed with the seemingly innate way in which we organize fragmentary sensory data into whole perceptions. Our minds structure the information that comes to us in several demonstrable ways: Form Perception -- To reorganize an object, we must firrst perceive it (see it as a figure) as distinct from surrounding stimuli (the ground). We must also organize the figure into a meaningful form. Several Gestalt principles - proximity, continuity, closure, and connectedness - describe this process. Depth Perception -- Research on the visual cliff reveals that many species perceive the world in three dimensions at, or very soon after, birth. We transform two-dimensional retinal images into three-dimensional perception by using binocular cues, such as retinal disparity, and monocular cues, such as the relative sizes of objects. Perceptual Constancy - Having perceived an object as a coherent figure and located it in space, how do we recognize it - despite the varying images that may cast upon our retinas? Size, shape, and brightness constancies describe how objects appear to have unchanging characteristics regardless of their distance, shape, or motion. These constancies explain several of the well-known illusions. For example, familiarity with the size-distance relationships in a carpentered world of rectangular shapes makes people more susceptible to the Muller-Lyer illusion. Sensory Restriction and Restored Vision For many species, infancy is a critical period during which experience must activate the brain's innate visual mechanisms. If cataract removal restores eyesight to adults who were blind from birth, they remain unable to perceive the world normally. Generally, they can distinguish figure from ground and perceive colors, but they are unable to distinguish shapes and forms. In controlled experiments, infant kittens and monkeys have been reared with severely restricted visual input. When their visual exposure is returned to normal, they, too, suffer enduring visual handicaps. Perceptual Adaption Human vision is remarkably adaptable. Given glasses that shift the world slightly to the left or right, or even turn it upside down, people manage to adapt their movements and, with practice, to move about with ease. Perceptual Set Clear evidence that perception is influenced by our experience - our learned assumptions and beliefs - as well as by sensory input comes from the many demonstrations of perceptual set and context effects. The schemas we have learned help us to interpret otherwise ambiguous stimuli, a fact that helps explain why some of us "see" monsters, faces, and UFOs that others do not. Is There Perception Without Sensation? Many people believe in or claim to experience extrasensory perception. Parapsychologists have tried to document several forms of ESP - telepathy, clairvoyance, and precognition. But for several reasons, especially the lack of reproducible ESP effect, most research psychologists remain skeptical.