Sensation and Perception (187-256)

1. Sensation and Perception (187-256) How many senses do humans have? Vision, Hearing, Taste, Smell and Touch… Is that it? There are different levels for each – i.e. Touch includes pressure, warmth, cold and pain Sensation – Process of receiving information from the environment Perception – Process of organizing sensory data and making it meaningful

2. Sensation • Absolute Threshold – The weakest amount of a stimulus needed in order to be sensed – the minimum intensity of a given stimulus that is detectable 50% of the time • Ex. Hearing Test – No sound, then a faint beep – 1st beep = Absolute Threshold • Although they vary from person to person, values have been determined for each of the five major senses.

3. Absolute Threshold Values • Vision – A candle flame viewed from a distance of about 30 miles away on a dark night • Hearing – Ticking of a watch from about 20 feet away in a quiet room • Smell – One drop of perfume diffused throughout a small house • Taste – One teaspoon of sugar dissolved in a gallon of water • Touch – Wing of a fly falling on a cheek from a distance of about 0.4 inch • http://www.bbc.co.uk/science/humanbody/body/interactives/senseschallenge/

4. Subliminal Messages • Stimuli that are below the absolute threshold

5. Difference Threshold • The Difference Threshold or Just Noticeable Difference (JND) is the smallest amount of a change needed in a stimulus before we detect a change • Ex. Toothpick on the skin • Ex. Books piled in your hands

6. Weber’s Law • The amount of change needed to produce a JND is a constant proportion of the original stimulus intensity • Ex. Adding weights to the bench press

7. Signal Detection Theory • SDT provides a method for studying sensory processes while accounting for elements such as the setting, your physical state, attitude and moods • City noises versus suburban noises • A soldier in wartime vs. peacetime • Sensory Adaptation

8. Transduction • Receptor cells work to transduce environmental energy into neural impulses • Ex. Electromagnetic energy is transduced into electrochemical impulses

9. Vision • Vision is the most dominant of the human senses – we tend to believe what we see first, and only secondarily do we accept information from taste, smell, hearing or touch • Ex. Colored Ketchup and Bagels on St. Patty’s Day

10. Light – Electromagnetic Energy • Not all light is visible to humans • Although other organisms can see different portions of the electromagnetic spectrum, ROY G BIV is the only portion visible to humans • ROY G BIV is listed, in order, from the longest to the shortest wavelength

11. Physical Characteristics of Light • Wavelength – The distance from one peak to the next – wavelength determines the Hue, or color that we experience • Intensity – The amount of energy in light waves determined by the height or amplitude of the wave. Determines the brightness that we experience

12. The Eye • When you take a picture with a camera, light enters through an opening and is focused on a sensitive surface – “the film” • Chemicals on the film are changed by the light and create a lasting impression of the image that entered the camera • http://www.youtube.com/watch?v=JadaWSDxBYk&safety_mode=true&persist_safety_mode=1

13. Parts of the Eye • Cornea – A clear outer covering, behind which is a fluid. • Iris – Colored, circular muscle that opens and closes into larger or smaller circles in order to control the amount of light getting into the eye • Lens – Similar to the lens on a camera – Helps you to focus the objects that you see onto the back of the eye to the photoreceptors

14. Parts of the Eye • Pupil – The opening that changes size as the iris adjusts to cover or uncover the lens. Also affected by psychological factors, but not foolproof • Retina – The back of the eye which contains millions of photoreceptors – like the film of a camera • Optic Nerve – The bundle of nerves that carry neural impulses from the eye to the brain

15. Parts of the Eye • Blind Spot – The point at which the optic nerve exits the eye – It is “blind” because there are no photoreceptors in this location • Blind spot demo – Draw two dots • Fovea – The central focal point in the retina around which the cones cluster

16. Photoreceptors on the Retina • Rods – Very sensitive to the violet range of wavelengths – we only see black and white with them because they contain no color chemicals. Used for night vision because they respond very well to low levels of light – rods turn on when it gets dark • Cones – Used for daylight vision and respond best to red wavelengths – shut off at night • Mnemonic Devices – A-Rod-Yanks uniforms, Ice Cream Cone and Road Cones • http://www.nei.nih.gov/health/eyediagram/

17. Color Vision • A person with normal color vision can distinguish between almost 7 million different color shades • Roughly 1 out of every 50 people are colorblind (Color-deficient) • Color blind people are unable to see color either as the result of an absence of, or a malfunction of the cones – dichromatic instead of trichromatic • http://www.youtube.com/watch?v=CWyrp3hu4KE&safety_mode=true&persist_safety_mode=1

18. Theories of Color Vision • Young-Helmholtz Tri-chromatic Theory – Normal human vision depends on three different kinds of cones on the retina – all of the colors that we see are Red, blue, green, or a mixture of these

19. Theories of Color Vision • Hering’s Opponent-Process Theory – Normal human vision is the result of opposing retinal processes – Red/Green, Yellow/Blue and White/Black. • When incoming visual information is relayed to the thalamus, some neurons are “turned on”, while others are “turned off”. • Helps to explain afterimages

20. Afterimages • Afterimages occur when our neural response to a given color tires and, as a result, you see the opposing color when viewing a white surface

23. Result of Color Vision • Color-vision is a two-part process: • Red, green and blue cones of the retina respond to different color stimuli • The nervous system then processes the opponent cells as the information passes to the visual cortex

24. Hearing (Audition) • Humans hear a wide range of sounds, but respond best to frequencies that are in the range of the human voice • Humans are very sensitive to faint sounds – survival mechanism…however, not too sensitive – Ex. “Ants marching” • Tremendous ability to distinguish between a variety of sounds – Ex. Voices of people you know

25. How do we hear? • Sound waves (air molecules) collide with one another, much like the ripples in a pond after a splash • Our ears detect changes in air pressure and then transduce them into neural impulses which our brains decode as sounds that have meaning to us • http://www.youtube.com/watch?v=_ovMh2A3P5k&feature=related&safety_mode=true&persist_safety_mode=1

26. Physical Properties of Sound Waves • Wavelength – the shorter the wavelength, the higher the frequency, or number that can pass in a given period of time. The shorter the wavelength, the higher the pitch will be (how high or low a tone is) • Amplitude – the greater the amplitude or height of the wave, the louder the sound will be – vice versa

27. How is sound measured? • The loudness of a sound is measured in a unit called Decibels, abbreviated dB. • Zero decibels is considered the absolute threshold for hearing – the ticking of a watch 20 ft. away in a quiet room

28. Decibel ratings for familiar sounds: • 140 decibels – Shotgun blast • 120 decibels – Thunder • 90-100 decibels – Subway Train • 60 decibels – Normal conversation • 20 decibels – Whisper • 0 decibels – Absolute Threshold

29. The Ear – Outer, Middle and Inner • Outer Ear – The visible portion is known as the auricle or pinna • The pinna channels sound waves through the auditory canal to the eardrum – a tight membrane that vibrates with the sound waves

30. The Middle Ear • The vibrations of the eardrum are transmitted by the middle ear through three tiny bones – the Malleus (Hammer), the Incus (Anvil) and the Stapes (Stirrup) - to a snail-shaped tube in the inner ear called the Cochlea

31. The Inner Ear • The incoming vibrations cause the cochlea’s membrane to vibrate the fluid in the tube • This motion causes ripples in the basilar membrane, which is lined with hair cells • The hair cells bend, triggering impulses in adjacent nerve fibers. These hair cells send neural messages to the brain • Loudness is determined by the number of hair cells activated

32. How is pitch determined? • Place Theory – States that we hear different pitches because sound waves trigger activity at different places along the cochlea • Confirmed by cutting holes into cochleas of cadavers • Explains how we sense high pitches

33. How is pitch determined? • Frequency Theory – Suggests that the basilar membrane vibrates with incoming sound waves • This vibration triggers neural impulses to the brain at the same rate as the sound wave • The result is that the brain reads pitch from the frequency of the neural impulses • Explains how we sense low pitches • Hearing Test http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearing-test/

34. Hearing Loss • Conduction Deafness – Occurs when there is poor transfer of sounds from the eardrum to the inner ear –often overcome by a hearing aid • Sensorineural Deafness – Results from damage to the hair cells or auditory nerve – caused by age and prolonged exposure to loud noise or music – hearing aids are often of little help • Stimulation Deafness –Very loud sounds damage the hair cells in the cochlea • http://www.youtube.com/watch?v=yQ17csWENEo&feature=related&safety_mode=true&persist_safety_mode=1 • http://www.youtube.com/watch?v=FEH28KdxjAY&feature=related&safety_mode=true&persist_safety_mode=1

35. Touch • The sense of “Touch” is actually a mix of at least four, distinct skin touches – Pressure, warmth, cold and pain • Pain is the body’s way of telling us that something has gone wrong and that we need to change our behavior • Some people are born without the ability to feel pain while others experience chronic pain – Ex. “Fire alarm” • http://www.youtube.com/watch?v=1vLsZ_dXFAg&safety_mode=true&persist_safety_mode=1

36. Gate-Control Theory • The spinal cord contains a neurological “gate” that either blocks pain signals or allows them to pass through • Spinal cord contains both small and large nerve fibers – the small fibers “open” the gate while the large ones “close” it • Pain can be lessened by stimulating “gate-closing” activity – Ex. Massage, acupuncture • http://www.youtube.com/watch?v=F656dufb3EQ&safety_mode=true&persist_safety_mode=1

37. Pain and the Brain • “Pain is increased by attending to it” – Darwin • Pain is a property of both the senses and the brain • Phantom Limb Pain – The brain believes that it will be getting an incoming sensory message, so the body prepares for it despite the fact that there may be no limb present • http://www.youtube.com/watch?v=hlQZmNlPdHQ&safety_mode=true&persist_safety_mode=1 • http://www.youtube.com/watch?v=YL_6OMPywnQ&safety_mode=true&persist_safety_mode=1 • Distracting your brain from a painful stimulus can help to lessen the sensation – Ex. Dental Spa

38. Taste • Our sense of taste involves four basic sensations – Sweet, Sour, Bitter and Salty – All other tastes are mixtures • Taste is a chemical sense – The little bumps on the top and sides of the tongue are called papillae • Inside the papillae are more than 200 taste buds, each containing a pore that “catches” food chemicals • These molecules are then sensed by roughly 50 taste receptor cells that project hairs onto the pores • http://www.youtube.com/watch?v=N42c52lCQNc&safety_mode=true&persist_safety_mode=1

39. Different tastes are picked up by different parts of the tongue: • Sweet – Front tip • Sour – Middle sides • Bitter – Middle rear • Salty – Front sides and back sides • Taste buds are essential to taste, but smell also plays an important role

40. Smell (Olfaction) • Smell is a chemical sense • Airborne molecules travel up the nostrils to receptors located at the top of the nose • Receptor cells then send messages to the olfactory bulb of the brain • Messages then travel to the temporal lobe and the limbic system

41. Olfaction “Tidbits” • Nursing infants and mothers have a heightened sensitivity to scents • Cologne and perfume instantly remind us of people • Ex. Febreeze • Emotional responses to smells are “hard-wired” • Ex. Response of an adult and baby to a lemon

42. Perception • Perception is defined as the process of understanding and interpreting sensations • Our primary means of recognizing objects is through the perception of its form • Gestalt – German for “form” – Stressed that the whole is different from the sum of the parts • Basketball perception demo • http://www.sharpbrains.com/blog/2006/09/28/attention-and-working-memory/

43. Gestalt Laws of Perception • Figure-Ground – Figure – any object perceived as being highlighted against, or in contrast to, some kind of “unhighlighted” ground or surroundings • Ex. http://www.youtube.com/watch?v=4LbNKJpodEk&safety_mode=true&persist_safety_mode=1

44. Closure – If a figure has gaps, we complete it by “filling them in” to form an object

45. Connectedness/Continuity – we perceive smooth, continuous patterns rather than discontinuous ones

46. Proximity – Elements that are close to one another are grouped together

47. Similarity – If figures are similar to each other, then we group them together.Ex. Marching band vid

48. Depth Perception • Seeing images in 3-D allows us to estimate their distance from us even though the images produced on the retina are only two-dimensional • Ex. Julian Beever http://www.youtube.com/watch?v=XOS-a7vjeEU&feature=related&safety_mode=true&persist_safety_mode=1 • Depth perception appears to be inborn • Ex. Visual Cliffs • http://www.youtube.com/watch?v=eyxMq11xWzM&feature=related&safety_mode=true&persist_safety_mode=1

49. Binocular Cues • Our eyes are about 2 ½ inches apart – our retinas receive slightly different images of the world

50. Retinal Disparity • The difference between the two images perceived by our eyes – the greater the disparity, the closer the object – vice versa