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Sensation and Perception

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Presentation on theme: "Sensation and Perception"— Presentation transcript:

1 Sensation and Perception
Chapter 3

2 Sensation vs. Perception
The experience of sensory stimulation Perception The process of creating meaningful patterns from raw sensory information

3 The Nature of Sensation

4 The Basic Process Receptor cells Doctrine of specific nerve energies
Specialized cells that respond to a particular type of energy Doctrine of specific nerve energies One-to-one relationship between stimulation of a specific nerve and the resulting sensory experience For example, applying pressure with your finger to your eye results in a visual experience transparent protective coating over the front of the eye

5 Sensory Thresholds Absolute threshold
The minimum amount of energy that can be detected 50% of the time

6 Absolute Thresholds Taste: 1 gram (.0356 ounce) of table salt in 500 liters (529 quarts) of water Smell: 1 drop of perfume diffused throughout a three-room apartment Touch: the wing of a bee falling on your cheek from a height of 1cm (.39 inch) Hearing: the tick of a watch from 6 meters (20 feet) in very quiet conditions Vision: a candle flame seen from 50km (30 miles) on a clear, dark night

7 Sensory Thresholds Sensory adaptation Difference threshold
An adjustment of the senses to the level of stimulation they are receiving Difference threshold The smallest change in stimulation that can be detected 50% of the time Also called the just noticeable difference

8 Sensory Thresholds Weber’s Law
States that the difference threshold is a constant proportion of the specific stimulus Senses vary in their sensitivity to changes in stimulation

9 Subliminal Perception
The notion that we may respond to stimuli that are below our level of awareness Research shows that the effect only occurs in controlled laboratory studies Research outside the laboratory shows no significant effect of subliminal information

10 Extrasensory Perception
Refers to extraordinary perception such as Clairvoyance – awareness of an unknown object or event Telepathy – knowledge of someone else’s thoughts or feelings Precognition – foreknowledge of future events Research has been unable to conclusively demonstrate the existence of ESP

11 Vision

12 The Visual System Cornea Pupil Iris
Transparent protective coating over the front of the eye Pupil Small opening in the iris through which light enters the eye Iris Colored part of the eye

13 The Visual System Lens Retina Fovea Focuses light onto the retina
Lining of the eye containing receptor cells that are sensitive to light Fovea Center of the visual field

14 Receptor Cells Cells in the retina that are sensitive to light
Visual receptors are called rods and cones

15 Receptor Cells Rods Cones About 120 million rods
Respond to light and dark Very sensitive to light Provide our night vision Cones About 8 million cones Respond to color as well as light and dark Work best in bright light Found mainly in the fovea

16 Receptor Cells Bipolar cells Ganglion cells Blind spot
Receive input from receptor cells Ganglion cells Receive input from bipolar cells Blind spot Area where axons of ganglion cells leave the eye

17 Adaptation Dark adaptation Light adaptation Afterimage
Increased sensitivity of rods and cones in darkness Light adaptation Decreased sensitivity of rods and cones in bright light Afterimage Sense experience that occurs after a visual stimulus has been removed

18 From Eye to Brain Optic nerve Optic chiasm
Made up of axons of ganglion cells carries neural messages from each eye to brain Optic chiasm Point where part of each optic nerve crosses to the other side of the brain

19 Color Vision Properties of color
Hue – refers to colors such as red and green Saturation – refers to the vividness of a hue Brightness – the nearness of a color to white

20 Theories of Color Vision
Additive color mixing Mixing of lights of different hues Lights, T.V., computer monitors (RGB) Subtractive color mixing Mixing pigments, e.g., paints

21 Theories of Color Vision
Trichromatic theory Three different types of cones Red Green Blue-violet Experience of color is the result of mixing of the signals from these receptors Can account for some types of colorblindness

22 Forms of Colorblindness
Approximately 10% of men and 1% of women have some form of colorblindness Dichromats People who are blind to either red-green or blue-yellow Monochromats People who see no color at all, only shades of light and dark

23 Theories of Color Vision
Trichromatic theory cannot explain all aspects of color vision People with normal vision cannot see “reddish-green” or “yellowish-blue” Color afterimages

24 Have students stare at this slide for about 30 seconds, then move to next slide which is a blank screen. They should see the red, white, and blue flag.


26 Theories of Color Vision
Opponent-process theory Three pairs of color receptors Yellow-blue Red-green Black-white Members of each pair work in opposition Can explain color afterimages Both theories of color vision are valid

27 Color Vision in Other Species
Other species see colors differently than humans Most other mammals are dichromats Rodents tend to be monochromats, as are owls who have only rods Bees can see ultraviolet light

28 Hearing

29 Sound Sound waves Frequency
Changes in pressure caused by molecules of air moving Frequency Number of cycles per second in a wave, measured in Hertz (Hz) Frequency determines pitch

30 Sound Amplitude Overtones Timbre Magnitude (height) of sound wave
Determines loudness, measured in decibels (dB) Overtones Multiples of the basic tone Timbre Quality of texture of sound

31 The Ear Eardrum Middle ear
Contains three small bones; the hammer, anvil, and stirrup These bones relay and amplify the incoming sound waves

32 The Ear Oval window Cochlea Membrane between middle ear and inner ear
Part of inner ear containing fluid that vibrates This causes the basilar membrane to vibrate

33 The Ear Basilar membrane Auditory nerve
Membrane in the cochlea which contains receptor cells, called hair cells Auditory nerve Connection from ear to brain Provides information to both sides of brain

34 Theories of Hearing Place theory Frequency theory Volley Principle
Pitch is determined by location of vibration along the basilar membrane Frequency theory Pitch is determined by frequency hair cells produce action potentials Volley Principle Pattern of sequential firing determines pitch

35 Hearing Disorders About 28 million people have some form of hearing damage in the U.S. Can be caused by Injury Infections Explosions Long-term exposure to loud noises

36 The Other Senses

37 Smell Detecting common odors
Odorant binding protein is released and attached to incoming molecules These molecules then activate receptors in the olfactory epithelium Axons from those receptors project directly to the olfactory bulb

38 Smell Women have a better sense of smell than men Anosmia
Complete loss of the ability to smell

39 Smell Pheromones Pheromones stimulate the vomeronasal organ (VNO)
Used by animals as a form of communication Provides information about identity Also provides information about sexual receptivity Pheromones stimulate the vomeronasal organ (VNO) Information from the VNO is sent to a special part of the olfactory bulb used for pheromonal communication

40 Taste Four basic tastes Recent discovery of fifth taste Sweet Salty
Sour Bitter Recent discovery of fifth taste Umami

41 Taste Receptor cells are located in taste buds
Taste buds are located in papillae on the tongue Chemicals dissolve in saliva and activate receptors

42 The Other Senses

43 Kinesthetic Senses Kinesthetic senses provide information about speed and direction of movement Stretch receptors sense muscle stretch and contraction Golgi tendon organs sense movement of tendons

44 Vestibular Senses Vestibular senses provide information about equilibrium and body position Fluid moves in two vestibular sacs Vestibular organs are also responsible for motion sickness Motion sickness may be caused by discrepancies between visual information and vestibular sensation

45 The Skin Senses Skin is the largest sense organ
There are receptors for pressure, temperature, and pain Touch appears to be important not just as a source of information, but as a way to bond with others

46 Pain Serves as a warning about injury or other problem
Large individual differences in pain perception Gate control theory Neurological “gate” in spinal cord which controls transmission of pain to brain

47 Pain Biopsychosocial theory Placebo effect
Holds that pain involves not just physical stimulus, but psychological and social factors as well Placebo effect Shows that when a person believes a medication reduces pain, their pain is often reduced even though no medication was given Pain relief is likely the result of endorphin release

48 Pain Alternative approaches Hypnosis Self-hypnosis Accupuncture

49 Perception This is a pointillized picture of the front half of an orange motorcycle. Included as a way to demonstrate that our minds can figure out an image even if the image is not very clear.

50 Perceptual Organization
Figure-ground We perceive a foreground object (figure) against a background (ground) Animals may look like the background they inhabit as a way of destroying figure-ground distinction

51 Perceptual Organization
Other principles of organization Proximity Similarity Closure Continuity

52 Perceptual Organization
Perceptual Constancy Our tendency to perceive objects as stable and unchanging despite changing sensory information Size constancy Shape constancy Brightness constancy Color constancy

53 Perception of Distance and Depth
Monocular cues – those that require only one eye Aerial perspective Texture gradient Linear perspective Motion parallax Superposition

54 Perception of Distance and Depth
Binocular cues – those that require both eyes Retinal disparity Convergence

55 Localizing Sounds We use both monaural and binaural cues Loudness
Louder sounds are perceived as being closer Time of arrival Sounds will arrive at one ear sooner than the other This helps determine direction of the sound

56 Perception of Movement
Apparent movement Illusion that still objects are moving Autokinetic illusion Perceived motion of a single object Stroboscopic motion Created by a rapid series of still pictures Phi phenomenon Apparent motion created by lights flashing in sequence

57 Visual Illusions Occur because of misleading cues in the stimulus
Gives rise to false perceptions

58 Individual Differences and Culture in Perception
Motivation Our desires or needs shape our current perceptions Values Expectations Cognitive Style Experience and Culture Personality

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