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AP Psychology

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  1. AP Psychology 2.3 Sensation and Perception

  2. Sensation • Process by which our sensory receptors respond to light, sound, odor, textures, and taste • Our eyes, ears, nose, tongue, and skin comprise an elaborate sensory system that receives and processes information from the environment

  3. Sensation • Each sense organ contains specialized cells called receptors which detect and then convert… • light waves - vision • sound waves - hearing • chemical molecules – taste, smell • pressure – touch … into neural impulses that are transmitted to the brain. • adults totally deprived of sensory input for long periods of time • experience hallucinations • impaired efficiency in all areas of intellectual functioning

  4. Perception • Process by which the brain actively selects, organizes and assigns meaning to incoming neural messages sent from sensory receptors • Example… • Sensory point of view – the American flag is a mass of red, white, and blue colors and horizontal and vertical lines • Perception – you interpret these splotches of color and array of lines as the American flag

  5. Basic Principles of Sensation • Transduction • Process by which sensory receptors convert the incoming physical energy of stimuli (ie. Light waves) into neural impulses the brain can understand • Philip Zimbardo – “process seems so immediate and direct that it fools us into assuming the sensation of redness is characteristic of a tomato or the sensation of cold is a characteristic of ice cream” • In reality…sensations such as “red” or “cold” occur only when neural impulses reach the brain

  6. Transduction

  7. Basic Principles of Sensation • Absolute Threshold • min. amount of a stimulus that an observer can reliably detect at least 50% of the time • Anything less goes unnoticed Examples… • Vision – candle flame 30 miles (clear, dark night) • Hearing – watch ticking 20 feet away • Smell – one drop of perfume in a 3-room apartment • Taste – 1 tsp. of sugar in 2 gallons of water • Touch – a bee wing dropped on your back from a cm

  8. Basic Principles of Sensation • Difference Threshold • Minimal difference needed to notice a stimulus change • aka – JND / “Just Noticeable Difference” • Example – TV volume at 50, take it down a notch until you notice the difference

  9. Basic Principles of Sensation • Weber’s Law • German Psychologist – Ersnt Weber (1795-1878) • Observed the JND will vary dependent on its relation to the original stimulus • The size of the JND is proportional to the strength of the original stimulus • Example • Weight lifter bench pressing 50 lbs would notice an additional 5 pounds • Weight lifter bench pressing 500 lbs would not notice an additional 5 pounds

  10. Weber’s Law

  11. Basic Principles of Sensation • Signal Detection Theory • Problem with traditional thresholds • Assumed if signal exceeded one’s AT, it would be sensed / if below one’s AT, it would not • Did not account for characteristics of the perceiver • Example – notice change in volume because that is the focus • A new theory • No single absolute threshold • Detection is based on a combination of stimulus intensity, background noise, and a person’s physical condition, biases, and level of motivation • EX – a soldier in wartime would detect fainter stimuli than one in peacetime

  12. Basic Principles of Sensation • Signal Detection Theory cont. • When using in experiments, psychologists sort the trials into one of four categories… • Signal is present – the person can decide that it present or absent (called hits or misses) • Signal is absent – the person can still decide that the signal is either present or absent (called false alarms or correct rejections)

  13. Basic Principles of Sensation • Sensory Adaptation • Occurs when a constant stimulus is presented for a length of time. When this happens receptors fire less frequently and the sensation often fades or disappears. • Examples… • Jogger puts on a new pair of shoes, he or she immediately notices the different feel. However, after going for a jog, he or she does not notice the difference • Swimmer dives into a pool, you notice the water is chilly. However, after swimming for a while, you do not notice the water temperature

  14. The Human Visual System • Our most important and complex sense! • Transduces light waves into neural messages that the brain processes into what we consciously see.

  15. The Human Visual System • From the Cornea to the Retina… • Cornea • Light waves from the outside world first enter through • Clear membrane / protects eye / helps gather and direct incoming light waves • Pupil • Small opening in middle of iris • Changes size to let in different amounts of light

  16. The Human Visual System • From the Cornea to the Retina… • Iris • Colored part of the eye • Ring of muscle tissue that contracts or expands to control the size of the pupil (respond to light and emotions) • Sympathetic (dilate) Parasympathetic (constrict)

  17. The Human Visual System • From the Cornea to the Retina… • Lens • Transparent structure behind the pupil that focuses and bends light as it enters the eye • Accommodation – change in the curvature of the lens that enables the eye to focus on objects at various distances (eye adjusts itself)

  18. The Human Visual System • Nearsightedness (Myopia) • Visual acuity problem that results when the cornea and lens focus an image in the front of the retina • As a result, distant objects appear blurry • 25% of US population

  19. The Human Visual System • Farsightedness (Hyperopia) • Visual acuity problem that results when the cornea and lens focus an image behind the retina • As a result, objects near the eye appear blurry • 25% of the US population

  20. The Human Visual System • Retina • Light-sensitive membrane at the back of the eye • Contains millions of sensory receptors for vision • Transduction of light waves into neural messages occurs

  21. The Human Visual System - Retina Rods Cones Photoreceptors in the retina Sensitive to colors and bright light Concentrated in the center of the retina (fovea) Images that do not fall on the fovea tend to be perceived as blurry or indistinct • Photoreceptors in the retina • Sensitive to dim light but not to color • Allow you to see in poorly lit environments • Cats have better night vision than humans because they have a higher portion of rods to cones than humans

  22. The Human Visual System • Retina… • Bipolar Cells – specialized neurons that connect rods and cones with the ganglion cells • Ganglion Cells – specialized neurons that connect to the bipolar cells (bundled axons form the optic nerve)

  23. The Human Visual System • Blind Spot • Point where the optic nerve leaves the eye there are no rods or cones • Because there are no rods or cones, we have a tiny hole or blind spot • Normally we are unaware because our eyes are always moving

  24. The Human Visual System • Visual Cortex • Optic nerve carries visual information to • Lies in the occipital lobe at the back of the brain

  25. The Human Visual System • Color Vision • Humans can identify about 7 million different color combinations • Two color vision theories • Trichromatic or three-color theory • Opponent-process theory

  26. The Human Visual System • Trichromatic Theory (three-color) • Three primary colors (red, green, blue) • Any color can be created by combining light waves of these three colors • Hermann von Helmholtz (1821-1894) proposed that the eye must have color receptors that correspond to these primary colors • Has been proven that the retina does have cones especially sensitive to the three primary colors

  27. The Human Visual System • Opponent-process theory • The Trichromatic theory explains how color processing works in cones, but not what happens in the ganglion cells and the rest of the visual system • The ganglion cells process color in opposing pairs • Red-green / black-white / blue-yellow • Visual cortex also encodes color in terms of these three pairs • Explains afterimages

  28. The Human Visual System • Afterimage • Visual experience that occurs after the original source of stimulation is no longer present • Example • green, black, yellow flag • red, white, blue flag

  29. The Human Visual System • Color Blindness • Genetic disorder (recessive – X) that prevents an individual from distinguishing between certain colors • Have a deficiency in their cones • Most common form is red-green deficiency (certain pigments) • Rare to see no color at all (only about 500 reported cases ever!!) • 1 in 10 men / very few women

  30. The Human Auditory System • Hearing plays a role in language development and social interactions. It also alerts us to dangerous situations • It transduces sound waves into neural messages that the brain then processes into what we consciously hear • aka – audition • Amplitude – loudness • Frqeuency - pitch

  31. The Human Auditory System • Outer Ear • Pinna • Flap of skin and cartilage • Catches sound waves and channels them to the auditory canal • Auditory Canal • Sound waves travel down and bounce into the ear drum • Eardrum (tympanic membrane) • Tightly stretched membrane located at the end of the auditory canal • Vibrates when hit by sound waves (match the intensity and frequency of sound waves)

  32. Outer Ear

  33. The Human Auditory System • Middle Ear • Amplifies sound waves • Hammer, anvil, and stirrup • Three tiny bones • Joint action doubles the amplification of sound • Oval Window • Stirrup transmits the amplified vibrations to oval window • Small membrane separating the middle ear from inner ear • Relays vibrations to the cochlea

  34. Middle Ear

  35. The Human Auditory System • Inner Ear • transduces sound waves into neural messages • Cochlea • Spiral-shaped, fluid filled structure that contains the basilar membrane and hair cells • Greek word for “snail” • Basilar membrane • Runs length of cochlea / holds hair cell receptors • Hair cells • Sensory receptors embedded in basilar membrane • Transduce the physical vibration of sound waves into neural impulses

  36. Inner Ear

  37. The Human Auditory System • Brain • As hair cells bend, they stimulate the cells of the auditory nerve • The auditory nerve carries the neural impulse to the thalamus and then to the temporal lobe’s auditory cortex

  38. Distinguishing Pitch (highness/lowness) • Frequency Theory • Basilar membrane vibrates the same frequency as sound waves • Explains how low frequency sounds are transmitted • Does not explain faster high frequency sounds (neurons cannot fire faster than 1000 times per second) • Place Theory • Different frequencies excite different hair cells at different locations along the basilar membrane • High-frequency sounds cause max vibrations near the stirrup • Lower-frequency sounds cause maximum vibrations at the opposite end

  39. Frequency Theory ^^^ • Place Theory >>>

  40. Loss of Hearing*most due to damage or old age Conductive Deafness Nerve (Sensorineural) Deafness Caused by damage to the cochlea, hair cells, or auditory nerve Exposure to noises such as headphones playing at full blast can damage cells and cause permanent hearing loss Hearing aids cannot help nerve deafness since damage to hair cells and auditory nerve is almost always irreversible • Caused when the tiny bones in the middle ear are damaged and cannot transmit sound waves • Hearing aides can amplify sound and help overcome