Sensation and Perception

1. Sensation and Perception Lecturer: Doneisha Burke, MS.c

2. Sensation The study of sensation is concerned with the initial contact between organisms and their physical environment. Focus is on describing the relationship between various forms of sensory stimulation ( sound waves, pressure) and how these inputs are registered by our sense organs Sensory Receptors are cells of the body specialized for the task of transduction.

3. Sensation �How are the many forms of physical energy impacting our sensory systems converted into signals our nervous system can understand? Sensory receptors Cells of the body specialized for converting physical energy into neural impulses that are then transmitted to our brain (eye, ears, tongue, nose)

4. Sensation: How much Stimulation is Enough? Sensory Deprivation When deprived of all sensory input our bodies produce hallucinations to fill the void. Our detection level for sensory input is impressively low for most aspects of sensation Although our receptors are highly efficient they do not register all information in the environment at any given moment.

5. Sensation : How much Stimulation is Enough? In investigating the sensory capabilities of the various sense organs psychologists have sought to establish the r-ship between physical properties of stimuli (e.g brightness and loudness) and people�s psychological experience of them. Our sensitivity to stimuli changes from moment to moment as the body�s need to maintain homeostasis changes

6. Sensation : How much Stimulation is Enough? In response to these changes the term absolute threshold �the smallest amount of a stimulus that we can detect 50% of the time-has been coined to denote our sensory threshold.

7. Sensation : How much Stimulation is Enough? In order to measure the sensitivity of our sensory organs Psychophysical Procedures are used they include: The Method of Limits Employs the use of a series of ascending and descending trials. Both trials are rptd several times to provide a reliable estimate of the threshold.

8. Sensation: How much Stimulation is Enough? The Staircase Method Experimenter begins with a descending series until the person reports not hearing a sound then switches to an ascending series until the person indicates hearing the sound. The Method of Constant Stimuli The range of sound intensities to be tested are selected in advance and each tone is presented many times in an irregular order i.e some sounds are at, above or below the threshold. Participants respond yes/no.

9. Sensation: How much Stimulation is Enough? Sensory thresholds are not really fixed, i.e it changes with lapses in attention, fatigue etc. It has also been suggested that motivational factors play a role. Signal Detection Theory supports this claim � Theory suggesting that are no absolute thresholds for sensations. Rather, detection of stimuli depends on their physical energy and on internal and motivational factors associated with detecting their presence.

10. Sensation : How much Stimulation is Enough? How much change in a stimulus is needed before a shift can be noticed? Difference Threshold The amount by which 2 stimuli must differ in order to be just noticeably different and the smaller the change we can detect then the greater our sensitivity.

11. Sensation : How much Stimulation is Enough? Stimuli below the Threshold/Subliminal Perception The presumed ability to perceive a stimulus that is below the threshold for conscious experience. This speaks to the use of subliminal messages. Research indicates no evidence to support that subliminal messages are a powerful means of persuasion

12. Sensation : How much Stimulation is Enough? Sensory Adaptation is the reduced sensitivity to unchanging stimuli over time. It helps us to adapt and focus on important changes in the world around us key to survival�blinking, swallowing, the feel of our tongue in our mouth Danger! It can lessen sensitivity

13. Vision: The Eye Light energy is converted into signals our brain can understand as a result of the eye. It is here that light energy is converted into neural codes which our nervous system can understand. Cornea->Pupil->Iris->Lens->Retina->Cones (Fovea) & Rods->Bipolar cells->Ganglion Cells->Optic nerve which carries visual information to the brain. (pg 93)

14. Vision: The Process Light rays first pass through the cornea and enter the eye through the pupil whose size varies with lighting conditions. The iris is responsible for regulating the contracting and expanding of the pupil to let in varying amounts of light. From here light rays pass through the lens which allows us to focus on objects of varying distance. Light rays which leave the lens are then projected onto the retina at the back of the eyeball.

15. Vision: The Eye

16. Vision: The Eye Cornea- transparent structure through which light rays enter the eye. Pupil- An opening Located just behind the cornea through which light rays enter the eye. Iris- Coloured part of the eye which adjusts the amount of light entering the eye by dilating or constricting. Lens- Curved structure behind the pupil that bends light rays focusing them on the retina.

17. Vision: The Eye Retina- Surface on the back of the eye containing the rods and cones. Cones- Sensory receptors located in the Fovea that play a crucial role in seeing in bright light, colour recognition and our ability to notice fine detail (apprx. 5 mil) Rods- found outside the Fovea, they help us to see in a darkened room or at night (apprx 120 mil) Fovea- Area in the centre of the Retina in which Cones are highly concentrated.

18. Vision: The Eye Optic Nerve- A bundle of nerve fibres that exit the back of the eye and carry visual information to the brain. Blind Spot- The point in the back of the Retina through which the optic nerve exist the eye. This exit point contains no rods or cones and therefore insensitive to light.

19. Vision: The Eye Acuity, the visual ability to see fine detail, is an important aspect of vision. Persons who are near/far sighted suffer from visual deficits in the shape of their eye or cornea and wear glasses to correct this. Dark Adaptation, the increase in sensitivity which occurs when we move from bright light to a dim environment.

20. Vision: The Eye Point of Information- Nearly 8 % of men and 0.4 % of women are less sensitive than the rest of us either to red and green or to yellow and blue. Colour Blindness in which the world is experienced in only varying shades of black and gray.

21. Vision: The Eye Visual Disorders Blindsight- damage to visual cortex in which persons report being blind yet respond to certain visual stimuli. Prosopagnosia- rare condition in which brain damage impairs a person�s ability to recognize faces.

22. Hearing: The Ear Inside the ear is an intricate system of membranes, small bones and receptor cells that transform sound waves into neural information for the brain.

23. Hearing: The Ear Pinna- The visible part of our hearing organ. Eardrum- A thin piece tissue just inside the ear , which moves ever so slightly to sound waves striking it. Cochlea- Fluid filled spiral shaped structure of the inner ear containing the sensory receptors for sound.

24. Hearing: The Ear But how exactly do we hear? Sound waves enter through the external auditory canal and produce slight movements which cause the middle ear bones to vibrate. The fluid within the COCHLEA then moves resulting in tiny HAIR CELLS (the sensory receptors for sound) located in the BASILAR MEMBRANE shifting their position thereby generating nerve impulses which we perceive as sound. These nerve impulses are transmitted to the brain via the auditory nerve.

25. Hearing: The Ear

26. Hearing: The Ear Physical & Psychological Qualities of Sound: Loudness Refers to amplitudes of sound waves, so as amplitude increase the sound appears louder. Pitch It is determined by the frequency of the sound waves that pass a given point/ secs. Timbre The quality of the sound we perceive which helps us to distinguish a flute from a trumpet.

27. Hearing: The Ear Detecting differences in Pitch Place Theory (Traveling Wave Theory) Theory suggesting that sounds of different frequencies cause different places along the basilar membrane to vibrate. Frequency Theory Theory suggesting that sounds of different pitch cause different rates of neural firing i.e high pitch sounds produce high rates of activity in the auditory nerve and vice versa.

28. Hearing: The Ear Sound Localization- How do I know where to turn my head? LOCALIZATION is the ability of the auditory system to locate the direction of a sound source. Sound from the side vs. the front or back.

29. Hearing: The Ear Hearing Loss is a result of damage to the sensory receptors for hearing i.e the tiny hair cells that line the floor of the basilar membrane. To measure hearing loss psychologists measure hearing thresholds at various sound freq. before and after exposure to sounds of certain intensity.

30. Hearing: The Ear Decibels in Everyday Life Whisper- 30dB Ringing phone-80dB Normal Convo- 60dB Prolonged exposure to Decibel Levels above 90 can produce permanent hearing loss Gunshot 165dB Ambulance Siren 120dB Headset on high 112dB Deploying Airbag 170dB

31. Smell & Taste Why study them together? Both respond to substances in solution (chemical sense) i.e substances that have been dissolved in fluid or gas. In everyday life both are interrelated. The stimulus for smell consist of molecules of various substances located in the air.

33. Smell Odorants enter the nasal passage and dissolve in the moist nasal tissues. This brings them into contact with receptor cells found in the olfactory epithelium. You and I have about 50 mil vs. cats and dogs with >200 mil

34. Smell Our sense of smell is restricted in terms of the range of stimuli to which they are sensitive, Why? Answer- In order for our olfactory sense to detect odours there has to be molecular weight (btw 15-300), that is why we can smell vodka (46) in a mixed drink and not the table sugar (342).

35. Taste The sensory receptors for taste are located in the small bumps on the tongue i.e PAPILLAE. Each PAPILLAE contains a cluster of taste buds possessing several receptor cells. Humans: 10,000 Chickens: 24 Catfish: >175,000 over the surface of their body. How many tastes are humans able to distinguish and what are they?

36. Taste Sweet Salty Sour Bitter Why then does it seem like we identify more?

38. Taste Not only are we aware of taste, but smell, texture, temperature, the pressure exerted on our tongue and mouth and many more other sensations. If these are however removed all we have are the 4- sweet, salty, sour and bitter.

39. Did you know? Tip of the nose phenomenon. Anosmia. Our memory of odours are impressive. Aromatherapy: lavender, cedar, peppermint and lemon.

40. Kinesthesia & Vestibular Sense 2 critical and often times ignored aspects of our sensory system. Kinesthesia-the sense that gives us information about location of our body parts with respect to one another and allows us to perform movement. E.g. touching your nose with your fingertip to driving a car. Kinesthetic information comes from receptors in our joints, ligaments & muscle fibres. Also vision and touch.

41. Kinesthesia & Vestibular Sense Vestibular Sense- refers to our sense of balance, It gives us information about body position, movement and acceleration (critical to S.o.B.) Sensory Receptors are located in the inner ear. i.e the 2 fluid filled Vestibular Sacs. They provide information about the body�s position in relation to the earth by tracking changes in linear movement.

42. Kinesthesia & Vestibular Sense When we move our bodies e.g.. Tilting the head from side to side hair cells bend in proportion to the rate of change in our motion. It is this movement that causes attached nerve fibres to fire neural signals which are then sent to the brain.

43. Kinesthesia & Vestibular Sense When do we become aware of our vestibular sense? After activities which make us dizzy. Vestibular information also comes from other senses esp. vision. When the two are in conflict it can lead to motion sickness.

44. The Somatosenses (Pain, Touch & Temperature) Did you know that the skin is our largest sensory organ? There are several skin senses Touch/pressure Warmth Cold Pain Why are certain areas of your body more sensitive than others?

45. The Somatosenses (Pain, Touch & Temperature Answer: receptors in our skin are not evenly distributed Face and fingers are more sensitive than legs because receptors are much more densely packed. Psychologists distinguish between 2 types of touch Passive vs. Active Object comes in contact with the skin & vice versa.

46. Pain Perception Pain sensation has no specific stimulus, however the sensation of pain originates in free nerve endings located throughout the body in the skin, around muscles and in internal organs. 2 types of pain exist Quick and sharp- what we feel from a cut. Dull and throbbing- what we feel from a sore muscle/back injury.

47. Pain Perception Gate Control Theory- a theory suggesting that the spinal cord contains mechanisms that can block transmission of pain to the brain Pain messages carried by the large fibres cause the gate to close whereas messages carried by the small fibres do not. This can help to explain why sharp pain is relatively brief and dull pain the opposite.

48. Pain Perception This theory also helps to explain why vigorous stimulation of an area succeeds in reducing pain. So using an ice pack, rubbing the skin near the injury or even acupuncture can have a soothing effect as it stimulates activities in the large nerve fibres which close the �gate� and reduces pain. This is known as a counter measure.

49. Pain perception Other factors which affect our perception of pain include: Current emotional states Culture (physical difference in pain threshold vs. social learning) Cognitive processes Pain causes a shift in thought and behaviour thereby redirecting our attention to the pain.

50. Pain Perception: the role of cognitive processes The extent to which we experience pain results from an interplay btw 2 factors. Characteristics related to pain The context in which the pain emerges Cognition/thought appears to play a critical mediator role which determines the extent to which we focus on pain relative to these factors. Procedures that redirect attention are therefore effective countermeasures

51. Pain Perception: the role of cognitive processes Hypnosis Cognitive behavioural procedures Based on the notion that our thoughts, feelings and beliefs can dramatically influence our perceptions of pain. Positive vs. negative thought Beliefs (page 106)

52. Perception: Putting it all together Transmission of sensory information from sensory receptors to the brain is only part of the picture. Of equal importance is PERCEPTION- the way in which we select, organize and interpret sensory input to achieve a grasp of our surroundings.

53. Perception & Attention When you are engrossed in a good book, a movie or even a phone conversation, what do you notice happens? By shifting attention what then happens? The reason you were not aware before is that we cannot absorb all of the available sensory information in our environment. That is why we SELECTIVELY ATTEND- paying attention to certain aspects of our environment while putting less important aspects in the background.

54. Perception & Attention Selective Attention has advantages and disadvantages such as� Can you shut out everything? The cocktail party phenomenon Certain characteristics of stimuli can cause attention to shift suddenly e.g. novelty, colour, sudden change. This ability is critical to survival as it alerts us to immediate dangers in our environment.

55. The Plasticity of Perception This refers to the extent to which perception is innate or learned. Innate 2 lines of research support this side. Persons born without sight/ loose it shortly after birth and then have it restored can in fact make at least partial sense out of the visual world soon after regaining sight. For e.g. they can follow moving objects.

56. The Plasticity of Perception Research with young babies a few hours old suggest that numerous perceptual abilities (auditory & visual) are present at birth. Learned Kittens raised in darkness except for being exposed to vertical and horizontal stripes. Recent research shows that organisms are able to compensate for deficits through enhanced abilities in their other senses.

57. Extra Sensory perception Can we gain information about the external world without use of our 5 basic senses? ESP- perception without a basis in sensory input Does it really exist? Bem and Honorton have recast this question in terms of a hypothetical process known a Psi.

58. Extra Sensory perception Psi- Unusual processes of information or energy transfer that are currently unexplained in terms of known physical or biological mechanisms. Parapsychologists suggest that there are actually several distinct forms of psi: Precognition Clairvoyance Telepathy Psychokinesis

59. Extra Sensory perception Precognition- the ability to foretell future events Clairvoyance- the ability to perceive objects or events that do not directly stimulate your sensory organs. Telepathy- the direct transmission of thought from one person to the next. Psychokinesis- the ability to affect the physical world purely through thought.

60. Extra Sensory perception Does it really exist? Failure to replicate instances of psi All aspects of our behaviour must ultimately stem from biochemical events of which none appears to account for psi. Evidence for support comes from persons deeply convinced of its existence.