Sensation and Perception

Sensation

  • the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment
  • Bottom-Up Processing: analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information

Perception

  • the process of selecting, organizing, and interpreting sensory information, enabling us to recognize meaningful objects and events
  • Top-Down Processing: information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations

Psychophysics

  • the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them

Thresholds

  • Absolute Threshold: minimum stimulation needed to detect a particular stimulus (light, sound, pressure, taste, or odor) 50% of the time
    • Vision: a candle flame at 30 miles on a dark, clear night
    • Hearing: a ticking watch at 20 feet under quiet conditions
    • Smell: one drop of perfume diffused throughout 3 rooms
    • Taste: a teaspoon of sugar in 2 gallons of water
    • Touch: the wing of a fly falling on your cheek from 1cm away
  • Sublimal Threshold: when stimuli are below one’s absolute threshold for conscious awareness; sublimal perception is the ability to ^^detect information below the level of awareness^^
  • Difference Threshold: the minimum difference between 2 stimuli required for detection 50% of the time; we experience the difference threshold as a just noticeable differences
    • Weber’s Law: according to Ernst Weber, two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different

Sensory Adaptation

  • a decrease in sensory response to an unchanging stimulus; diminished sensitivity as a consequence of constant stimulation
  • LESSON: we perceive the world not exactly as it is, but as it is useful for us to perceive it

Selection

  • the senses act as ^^data reduction systems^^ -- only the most important selected in order to code and send to the brain

Biological Transducers

  • devices that convert one kind of energy into another
    • The eye transduces electromagnetic radiation. But the human eye can only transduce a tiny fraction of the ^^visible spectrum^^ (entire range of electromagnetic energies). In comparison, the eyes of honey bees can transduce electromagnetic spectrum invisible to humans.
    • The ear transduces sound waves. bats can transduce and hear sound waves humans cannot. Their echolocation ability allows them fly in darkness.

Analysis

  • what we experience is also influenced by ^^sensory analysis^^ (the process of separating sensory information into important elements)
  • as the senses process information, they divide the world into important ^^perceptual features^^ (basic elements of a stimulus, such as lines, shapes, edges or colors)

Trivia

  • A male silkworm moth has receptors so sensitive to the female sex-attractant odor that a single female need release only a billionth of an ounce per second to attract every male silkworm moth within a mile.
  • Frog eyes are highly sensitive to small, dark, moving spots, but the insect (spot) must be moving, or the frog’s “bug detectors” won’t work. A frog could starve to death surrounded by dead flies.

Sensory Coding

  • As the senses select and analyze information, sensory systems code it. ^^Sensory coding^^ refers to converting important features of the world into neural messages understood by the brain.
  • “Seeing” or “hearing” ^^take place in your brain^^, not in your eyes or ears. ^^Sensory localization^^ means that the type of sensation you experience depends on which brain area activated.

Sensation: Vision

  • the sense that people prize the most
  • Vision Spectrum: entire spread of electromagnetic energies to which the eyes respond; what strikes our eyes are not colors but pulses of electromagnetic energy
  • Wavelength: the distance from one wave peak to the next
    • Wavelengths determine
    • Hue (Color Sensations): the basic color categories of red, orange, yellow, green, blue, indigo, and violet; various hues correspond to the wavelength of the light that reaches our eyes
    • Intensity: the amount of energy in light waves determined by the waves amplitude or height; waves of greater amplitude (“taller”) carry more energy, causing the colors we see to appear brighter or more intense

Trivia

  • bees cannot see red but can see ultraviolet (beyond violet) light

Parts of the Eye

  • Cornea: transparent tissue which protects the eye and bends light to provide focus
  • Iris: colored muscle that expands and contracts to change the size of the opening (pupil) for light; the iris dilates or constricts in response to light intensity and even emotions; each iris is so unique that an iris-scanning machines could confirm your identity
  • Lens: focuses the light rays on the retina; the lens focuses the rays by changing its curvature in a process called ^^accommodation^^
  • Retina: the light-sensitive layer of cells (photoreceptors) at the back of the eye; easily damaged from excessive exposure to light like staring at an eclipse

Visual Problems

  • Hyperopia: difficulty focusing nearby objects (far-sightedness) because the eye is too short
  • Myopia: difficulty focusing distant objects (near-sightedness) because the eye is too long
  • Astigmatism: defects in the cornea, lens, or eye that cause some areas of vision to be out of focus
  • Presbyopia: far-sightedness caused by aging

Optic Nerve, Blind Spot, and Fovea

  • Optic Nerve: carries neural impulses from the eye to the brain
  • Blind Spot: point where the optic nerve leaves the eye because there are no receptor cells located there
  • Fovea: central point in the retina around which the eye’s cones cluster
  • Peripheral Vision: vision at edges of visual field (side vision), many superstar athletes have excellent peripheral vision

Light Control

  • Cones: visual receptors for ^^colors and bright light (daylight)^^ have 6.5 million; color and detail sensitive
  • Rods: visual receptors for ^^dim light^^; only produce ^^black and white^^; have 120 million; non-sensitive to color and detail

Anatomy of the Retina

  • Note that the light does not fall directly on the rods and cones. It must first pass through the cornea, the lens, the vitreous humor (a jelly-like substance that fills the eyeball), and the outer layers of the retina. Only about half of the light at the front of the eye reaches the rods and cones -- testimony to the retina’s amazing sensitivity

Visual Acuity

  • the sharpness of visual perception; normal acuity is designated 20/20 vision (at 20ft in distance, you can distinguish what the average person can see at 20ft)
  • Tests
    • sharpness is indicated by the smallest grating still seen as individual lines
    • Snellen Chart: requires that you read rows of letters of diminishing size until you can no longer distinguish them
    • Landolt Rings: require no familiarity with letters; all that is required is a report of which side has a break in it

Visual Information Processing

  • Processing of several aspects of the stimulus simultaneously is called ^^parallel processing^^. The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc.

From Sensation to Recognition

Scene → Retinal Processing → Feature Detection → Parallel Processing → Recognition

  • Retinal Processing: receptor rods and cones → bipolar cells → ganglion cells
  • Feature Detection: brain’s detector cells respond to specific feature -- edges, lines, and angles
  • Parallel Processing: brain cell teams process combined information about color, movement, form, and depth
  • Recognition: brain interprets the constructed image based on information from stored images

Color Vision

  • Trichromatic Theory: color vision theory which suggests that the eye must contain 3 receptors that are sensitive to ^^red, green, blue^^
    • other colors produced by a combination of these
    • black and white produced by rods
  • Opposite Process Theory: color vision theory based on 3 “^^systems^^”: red/green, blue/yellow, black/white
    • exciting one color in a pair (red) blocks the excitation in the other member of the pair (green)
    • Afterimage: visual sensation that remains after stimulus is removed (seeing flashbulb after the picture has been taken)

Color Blindness

  • Genetic disorder in which a person is unable to perceive colors. The color blind person either locks cores or has cones that do not function normally. Total color blindness is rare, but some people can have inability to distinguish some colors (color weakness). Red-green color blind people see both colors as the same, usually a yellowish brown. Yellow-blue color blindness is quite rare.

Trivia

  • Dogs lack receptors for the wavelength of red, giving them only limited dichromatic color vision.

Dark Adaptation

  • The dramatic increase in retinal sensitivity to light that occurs after a person enters the dark; similar to going from daylight into a dark movie theater. It takes 30-35 minutes of complete darkness to reach maximal sensitivity to light. At which point, your eye will be 100,000 times more sensitive to light.

Sensation: Hearing

Hearing

  • Audition: the sense or act of hearing
  • Sound Waves: the stimulus point for hearing, which are compressing and expanding air molecules
  • the ears transform the vibrating air into nerve impulses, which our brain decodes as sounds
    • Amplitude (Sound Intensity): The ^^physical “height” of sounds^^ tells us how much energy it contains; corresponds to sense ^^loudness^^
    • Frequency (Pitch): the ^^number of waves per second^^ correspond to the perceived pitch (higher or lower tone)
    • ^^long waves^^ have low frequency -- and low pitch
    • ^^short waves^^ have high frequency -- and high pitch

Parts of the Ear

  • Outer Ear (Pinna): ^^collects and sends^^ sounds to the eardrum
  • Middle Ear: chamber between tympanic membrane (eardrum) and cochlea containing the auditory ossicles -- the 3 bones that vibrate and concentrate the vibrations of the eardrum on the cochlea’s oval window
    • malleus (hammer)
    • incus (anvil)
    • stapes (stirrup)
  • Inner Ear: innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs
  • Cochlea: coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals
  • Organ of Corti: center part of the cochlea containing hair cells, canals, and membranes
  • Hair Cells: receptor cells within cochlea that transduce vibrations into nerve impulses; once dead they are never replaced

Deafness

  • Conduction Deafness: occurs when the transfer of vibrations from the outer ear to the inner ear is weak (e.g., damaged eardrums or ossicles); compensate with amplifier (hearing aid)
  • Sensorineural Hearing Loss: caused by damage to inner ear hair cells or auditory nerve
    • hearing aids useless in these cases, since auditory messages cannot reach the brain
    • Cochlear Implant: electronic device that stimulates auditory nerves; still not very successful

Localization of Sounds

  • because we have 2 ears, sounds that reach one ear faster than the other ear cause us to localize the sound

Preventable Hearing Problem

  • Stimulation Deafness: damage caused by exposing hair cells to excessively loud sounds; typical at rock concerts

Perception

  • the subjective experience of sensory information after having been subjected to cognitive processing

Templates

  • stored representations of objects enabling object recognition
  • Size Constancy: perceived size of an object remains the same, despite changes in its retinal image
  • Native Perception: a perceptual experience based on innate processes (e.g., ability to see line in a paper)
  • Empirical Perception: a perception based on prior experience (e.g., car seen from a distance as a toy, but still interpreted as a car)
  • Shape Constancy: the perceive shape of an object unaffected by changes in its retinal image
  • Brightness Constancy: apparent brightness of an object stays the same under changing lighting conditions

Perceptual Grouping

  • Figure-Ground Organization: probably in-born, part of a stimuli appears to stand out as an object (figure) against a less prominent background (ground)
  • Reversible Figure: figure and ground that can be reversed

Gestalt Principles of Organization

  • Nearness: stimuli that are near each other tend to be grouped together
  • Similarity: stimuli that are similar in size, shape, color, or form tend to be grouped together
  • Closure: tendency to complete a figure so that it has a consistent overall form
  • Contiguity: nearness in time and space; perception that one thing has caused another
  • Common Region: stimuli that are found within a common area tend to be seen as a group

Depth Perception

  • Definition: ability to see 30 space and to accurately judge distances
  • Visual Cliff: apparatus that looks like the edge of an elevated platform or cliff
  • Depth Cues: features of environment, and messages, that supply information about distance and space
  • Monocular Depth Cue: depth cue that can be sense with 1 eye
  • Binocular Depth Cue: depth cue that can be sensed with 2 eyes
Binocular Depth Cues
  • Retinal Disparity: a source of binocular depth cue that happens because of the discrepancy in the images that reach the right and left eyes based on the fact that the eyes are about 2.5in apart
  • When the two images are fused into one overall image, stereoscopic vision (3D perception of space and depth due to the fact that the eyes receive different images)
  • Convergence: when you look at something soft closer, your eyes must turn in (converge) to focus the object
Monocular Depth Cues
  • Accommodation: bending of the lens of the eye to focus on nearby objects; changes in the sensations from muscles attached to each lens flow back to the brain which helps us to judge distances within about 4ft of the eyes
  • the illusion of depth is created on a 2D with ^^pictorial depth cues^^ (features found in paintings, drawings, and photographs that impart information about space, depth, and distance)
Pictorial Cues for Depth
  • Linear Perspective: based on apparent convergence of parallel lines in environment
  • Overlap (Interposition): when one object partially blocks another
  • Texture Gradients: texture changes can contribute to depth perception; coarse textile implies closeness, fine texture implies distance
  • Relative Motion (Motion Parallax): nearby objects move a lot as your head moves; distant objects move slightly

The Moon Illusion

  • Moon Illusion: apparent changes in size that occurs as the moon moves from the horizon (large moon) to overhead (small moon)
  • Apparent-Distance Hypothesis: an explanation of the moon illusion stating that the horizon seems more distant that the night sky

Perceptual Expectancies (Set)

  • Perceptual Constructions: mental models of external events
    • we don’t just believe what we see, we also see what we believe
  • Perceptual Expectancy (or Set): a readiness to perceive in a particular manner, induced by strong expectations; may be created by past experience, motives, context, or suggestions that we are ready to apply to a stimulus even though applying it is inappropriate

Perceptual Learning

  • Perceptual Learning: changes in perception that can be attributed to prior experience; a result of changes in how the brain processes sensory information
  • Perceptual Habits: created by learning, these are ingrained patterns of organization and attention that affect our daily life
  • Illusion: a misleading or distorted perception of an existing stimuli where length, position, motion, curvature, or direction is consistently misjudged
  • Reality-Testing: obtaining additional information to check on the accuracy of perceptions

Extrasensory Perception (ESP): Fact or Fallacy

  • Parapsychology: study of paranormal phenomena, including ESP and psychokinesis, and other Psi phenomena (events that seem to defy accepted scientific laws). ESP is the claim that perception can occur apart from sensory input
    • Clairvoyance: purported ability to perceive events or gain information in ways that appear unaffected by distance or normal physical barriers
    • Telepathy: purported ability to communicate directly with another person’s mind
    • Precognition: purported ability to accurately predict future events
    • Psychokinesis (Mind-over-Matter): purported ability to exert influence over inanimate objects by willpower
ESP Issues
  • Difficulty of Excluding Coincidence
    • If a hunch turns out to be correct, it is interpreted as precognition or clairvoyance. If it is not confirmed, it is simply forgotten. But coincidences occur quite often
  • Run of Luck
    • statistically unusual outcome could occur by chance alone (e.g., getting 5 heads in a row, 2 jackpots with 6 pulls of a slot machine)
  • Inconclusive Research
    • many spectacular findings cannot be replicated (reproduced or replicated)
  • Stage ESP and Fraud
    • simulating of ESP for entertainment purposes based on sleight of hand, deception, and patented gadgets
  • Conclusion
    • existence of ESP has not been scientifically demonstrated; positive results are usually inconclusive and easily criticized

Eyewitness Testimony

I saw it with my own eyes.

Factors Affecting the Accuracy of Eyewitness Perceptions
  • Wording of Questions
    • an eyewitness testimony about an event can be affected by how the questions put to that witness are worded
  • Post Event Information
    • eyewitness about an event often reflects not only what was actually seen but also information obtained later
  • attitudes, expectations, an eyewitness’ perception and memory for an event may be affected by his or her attitudes and expectations
  • Alcohol Intoxication
    • impairs later ability recall events
  • Cross-Racial Perceptions
    • eyewitnesses are better at identifying members of their own race than they are at identifying people of other races
  • Weapon Focus
    • the presence of a weapon impairs an eyewitness’ ability to accurately identify the culprit’s face
  • Exposure Time
    • the less time an eyewitness has to observe an event, the less well she or he will perceive and remember it
  • Unconscious Transference
    • eyewitnesses sometimes identify as a culprit someone they have seen in another situation or context
  • Color Perception
    • judgments of color made under monochromatic light (such as orange street light) are highly unreliable
  • Stress
    • very high levels of stress impair the accuracy of eyewitness perceptions

Perceptual Awareness

  • Habituation: a type of learning that happens when we cease paying attention to familiar stimuli
  • Dishabituation: a reversal of habituation; creative people actively attend to stimuli, even those that are repeated