Chapter 5 Sensation Reading Map Friday, Nov 18193-199 Monday, Nov 21199-204 Tuesday, Nov 22Quiz chapter 4/study guide and cards due Wednesday, Nov 23essay.

Chapter 5 SensationReading Map

• Friday, Nov 18 193-199

• Monday, Nov 21 199-204

• Tuesday, Nov 22 Quiz chapter 4/study guide and cards due

• Wednesday, Nov 23 essay in class

• Thursday, Nov 24 204-212

• Friday, Nov 25 212-219

• Monday, Nov 28 219-229 – take home Chapter 5 quiz

• Tuesday, Nov 29 231-238 – hand in Chapter 5 quiz/study guide/cards

Sensation - Introduction (193)

• To represent the world in our head, we must detect physical energy from the environment and encode it as neural signals. This process is called sensation.

• When we select, organize and interpret our sensations, this is called perception.

The Forest Has Eyes (193)

Bottom-Up and Top-Down Processing (193)

• Bottom-Up sensory analysis starts at the sense receptors and works up to the brain - ex. We start by seeing colour and lines and eventually our brain “sees” the faces in the forest.

• Top-Down is guided by higher-level mental processes. We build perceptions drawing on our experience and perceptions - ex. We know the title of the painting and “see” the faces in the forest.

• TG p.4 - likelihood principle

Prosopagnosia (193)

• Failures of perception may occur anywhere between sensory detection and perceptual interpretation.

• Ex - temporal lobe area damage can lead to prosopagnosia where you have complete sensation but you cannot top-down process the information to recognize faces.

• On-line prosopagnosia test http://www.faceblind.org/facetests/index.php

Sensing the World (194)

• What stimuli cross our threshold for conscious awareness?

• Could we unknowingly be influenced by subliminal stimuli too weak to be perceived?

• Why are we unaware of unchanging stimuli, such as the watch pressing against our wrist?

Psychophysics (194)

• The study of how physical energy relates to our psychological experience.

• What stimuli can we detect? At what intensity?

• How sensitive are we to changing stimulation?

Absolute Thresholds (194)

• The minimum stimulation needed to detect a particular stimulus 50% of the time

• Ex. Sound of a mosquito?

Signal Detection Theory (194)

• Whether we detect a signal depends on the strength of he signal and our psychological states of experience, motivation, expectation and alertness

• This theory predicts when we will detect weak signals.

• People have different thresholds in different circumstances - ex. What do you hear outside your tent!

• People’s detection diminishes after about 30 minutes of judging when a faint signal appears.

Subliminal Stimulation (195)

• Subliminal means below one’s absolute threshold for conscious awareness

• Krosnick (1992) flashed kittens or dead body just before pictures of people. Subjects gave higher ratings to people paired with the kittens

Subliminal Stimulation (195)

• Can it prime our later memory? Bar & Biederman (1998) - flash a hammer then other images then the hammer again. Your chances of naming hammer are now 1 in 3 rather than 1 in 7 if hammer was flashed once.

Subliminal Stimulation (196)

• Bornstein & Pittman (1992) - flash the imperceptible word “bread” and subjects later detect a related word like “butter” faster than an unrelated word like “bottle”

The Bottom Line

• We can process subliminal information. It may have a subtle, fleeting effect on our thinking but it does not have a lasting effect

• Remember chapter 1 (p. 40) - in the tape experiment we saw the placebo effect. If I think I get the self-esteem tape, my self-esteem goes up regardless that my subliminal tape was on memory.

Difference Thresholds (197)

• Aka just noticeable difference - is the minimum difference a person can detect between an 2 stimuli half of the time.

• (Do envelop test)

Weber’s Law (197)

• The difference threshold increases with the magnitude of the stimulus - you will notice a 10 gram increase to a 100 gram weight but not to a 1000 gram weight because the difference threshold has increased.

• BUT, Weber’s Law says that regardless of the magnitude, 2 stimuli must differ by a constant proportion for their difference to be perceptible

• Light must differ by 8%, weight by 2% and tone by 0.3% for differences to be noticeable.

Sensory Adaptation (198)

• Our diminishing sensitivity to unchanging stimulus

• After constant exposure to stimulus, our nerve cells fire less frequently

• Enables us to focus on informative changes in our environment without being distracted by the constant stimulation of our normal surroundings

Vision (199)

• Transduction - converting stimulus energy into neural messages or impulses.

• Our eyes receive light energy and tranduce it into neural messages that the brain then processes into what you consciously see.

Stimulus Input: Light energy (200)

• Wavelengths visible to the human are the short waves of blue-violet light to longer waves of red light

• Other organisms see other portions of the spectrum

• What we “see” as colour are pulses of electromagnetic energy

Wavelength and Amplitude (200)

• Wavelength - determines hue -- short are blue and long are red

• Amplitude - big is bright and small is dull

The Eye (201)

• Pupil - adjustable opening in centre of eye through which light enters

• Iris - coloured muscle surrounding pupil. Responds to light intensity. Iris scanners detect uniqueness of our irises.

The Eye

• Cornea - protects eye• Lens - transparent

structure behind pupil. Accommodation of the lens is change to its curvature and thickness to focus near or far images on the retina

The Eye

• Retina - surface on which light rays focus

• Contains the receptor rods and cones

• Image is inverted on the retina. We see right-side-up because the retina doesn’t read the image as a whole. Instead, its receptor cells convert light energy into neural impulses (transduction) that are sent to the brain and constructed there into a perceived, up-right image.

Acuity (201)

• Acuity is our sharpness of vision.

• It can be affected by small distortions in the shape of the eye.

• With normal acuity, the image is focused by the cornea and lens on the retina.

Nearsightedness (201)

• Nearsighted - misshapen eyeball focuses light rays from distant objects in front of retina so when the image reaches the retina the rays are spreading out, blurring the image

• Nearsighted people see nearer objects more clearly than far objects.

Farsightedness (201)

• Farsighted - light rays from nearby objects reach the retina before they focus behind the retina.

Quinn Study (1999) (200)

• A study of 479 children found that 10% of children who slept in the dark before age 2 later became nearsighted, as did 34% of those who slept with a night light and as did 55% of those who slept in the light

• TURN OFF THE LIGHTS!!!

20/20 Vision

You see at 20 feet what someone with normal vision sees at 20 feet

The Retina (202)

• Contains receptor rods and cones

• Light energy striking rods and cones produces chemical changes that generate neural signals which activate the bipolar cells which activate the ganglion cells. The axons from the ganglion cells converge like a rope to form an optic nerve that carries information to the brain. Where the optic nerve leaves the eye there are no receptor cells - creating a blind spot

Rods and Cones (202)

• Rods - 120 million - more sensitive to light - detect black, white, grey

• Cones - 6 million - more sensitive to colour and detail - clustered in the fovea (the retina’s area of central focus) - work better in good light

Adapting to Dark (203)

• In a dark room our pupil’s dilate to let more light to reach the rods in the retina’s periphery. It takes about 20 minutes before our eyes adapt. 20 minutes parallels the average natural twilight transition between the sun’s setting and darkness.

Visual Information Processing (203)

• During fetal development a piece of brain migrates to the retina.

• Information travels --- retina --- bipolar cells --- ganglion cells --- optic nerve --- thalamus --- occipital lobe

Feature Detection (204)

• Hubel & Wiesel (1979) discovered feature detectors in the brain. Certain neurons respond to certain features. Perception arises from the interaction of many neurons, each performing a simple task. The visual cortex passes the information to areas in the temporal and parietal cortex.

• Hubel & Wiesel clip (1 minute) http://www.youtube.com/watch?v=IOHayh06LJ4

Different Brain Areas (205)

• Different areas of our brain respond to different objects and events

• Perrett identified nerve cells that specialize in responding to a specific gaze, head angle, posture or body movement.

The Necker Cube (205)

• As your perception of the Necker cube shifts every few seconds, so does neural activity in your visual cortex. Although the same image continues to strike the retina, the brain constructs varying perceptions.

Parallel Processing (206)

• Our brains parallel process - does several things at once.

• We construct our perceptions by integrating the work of different visual areas - colour, depth, movement, form - that work in parallel.

• The retina projects to many different visual cortex areas. Facial recognition uses about 30% of the cortex. Hearing only uses about 3%.

• Computers are faster but linear/humans are slower but parallel.

Blindsight (207)

• If you loose a portion of your brain’s visual cortex to surgery or stroke, you may experience blindness in part of your field of vision. However, you may still “know” what is in your blind field spot.

• Shown a series of sticks in the blind field, patient will report seeing nothing but they will know that all the sticks were vertical.

Colour Vision (208)

• Our difference threshold for colour is so low that we can detect 7 million colour variations

• 1 in 50 is colour deficient - usually this person is male because the defect is genetically sex-linked

Young-Helmhotz Trichromatic Theory (209)

• Retina contains 3 colour receptor cones sensitive to red, green or blue. When we stimulate combinations of these cones we see other colour. Ex. When red and green are stimulated, we see yellow.

Paint v. Light

• Mixing paint is subtractive --- red, blue and yellow makes black (no light is reflected).

• Mixing light is additive ---- green, blue and red makes white (all light is reflected)

Colour Deficient People (209)

• Most lack functioning red or green cones so their vision is dichromatic instead of trichromatic

• People with a red-green deficiency have trouble perceiving the number within this design.

Ewald Hering Afterimages (209)

• Hering explained how people blind to red and green could still see yellow.

• He discovered opponent colours. When you stare at the first colour and then look away, you will see the opponent colour - or the afterimage.

• Opponents are red/green, blue/yellow and black/white.

Afterimages

• Opponent process theory explains afterimages. We tire our green response by staring at green. When we then stare at white (which contains all colours, including red) only the red part of the green/red pairing will fire normally.

Colour Vision Summary

• Occurs in 2 stages• The retina’s red, green and blue cones respond in

varying degrees to different colour stimuli (YH theory)

• Their signals are then processed by the nervous system’s opponent-process cells, en route to the visual cortex.

• And now ----- add colour contancy as a concept

Colour Constancy (210)

• Perceiving familiar objects as having consistent colour, even if changing light alters the wavelengths reflected by the object.

• Our experience of colour comes not just from the object, but also from its context. If we vary the context, the colour appears to change even though it really doesn’t change.

Hearing (212)

Sound Wave (212)

• Compressed and expanded air

• Brief air pressure changes that our ear detects and then changes into neural impulses which our brain decodes as sound (transduction)

Loudness and Pitch (212)

• Sound waves vary in length (frequency) - a long wave is a low pitch and a short wave is a high pitch.

• Sound waves also vary in strength (amplitude) which determines loudness.

Decibels (212)

• Measure sound energy

• 0 decibels = absolute threshold for hearing

• Every 10 decibels = a 1- fold increase in sound

• Prolonged exposure to sounds over 85 decibels leads to hearing loss

The Ear (213)

• Outer ear channels sound waves through auditory canal to ear drum

• Ear drum vibrates• Middle ear’s hammer, anvil and

stirrup amplify and relay vibrations into the cochlea (inner ear) which is filled with fluid

• Fluid vibrations cause the basilar membrane (lined with hair cells) to ripple bending the hair cells

• Hair cell movements trigger neural impulses in the nerve fibers that converge to form the auditory nerve

• Temporal lobe’s auditory cortex decodes the neural impulses

Loudness (214)

• Loudness is interpreted by the number of hair cells activated.

• If a hair cell loses sensitivity to soft sounds, it may still respond to loud sounds.

A Noisy Noise Annoys (214)

• Brief, extremely intense sound or prolonged, intense sound both damage receptor cells and auditory nerves

• A noise is harmful if you can’t talk over it

• Ringing ears is an alert to potential damage

• Unpredictable, uncontrollable, loud noise causes more frustration and error.

Bone-Conducted Sound (TG)

• TG 5-14 - hanger

• Beethoven (who was deaf) could hear his piano by putting his walking stick in his mouth and resting it on the piano

Pitch - Place Theory (214)

Herman Helmhotz’s Place Theory - sound waves trigger different places along the

cochlear basilar membrane- High pitches at the beginning and low pitches at

the end o the membrane- This theory is good for high pitches but it doesn’t

explain low pitches because the neural impulses they generate are not so neatly organized on the basilar membrane

Pitch - Frequency Theory (215)

• Says that the whole basilar membrane vibrates and sends neural impulses = to the frequency. So a sound wave of 100 waves/second sends a matching wave in neural impulses to the brain.

• This theory is good for low pitches BUT neurons can’t fire faster than 1000 times per second yet many pitches (upper 1/3 of piano) have faster frequencies.

• SO, we need a third theory!

Pitch - Volley Theory (215)

• Neurons alternate firing so that a group of neurons can achieve frequencies above 1000/second.

• This theory is best for middle pitches

• Think of a firing squad

How do we locate sound? (215)

• Our ear placement allows us to hear stereophonic hearing (3 dimensional)

• Sound travels at 750 miles/hour and our ears are 6 inches apart.

• Sound waves will strike one ear sooner and more intensely. Our auditory system can detect a just noticeable difference of .000027 second.

• Brain parallel processes timing and intensity then merges the information to pinpoint the sound’s location.

• Finger snap demo

Hearing Loss (216)

2 types of of hearing loss

1. Conduction Hearing Loss

2. Sensorineural Hearing Loss

Conduction Hearing Loss (216)

• Damage to the mechanical system that conducts sound waves to the cochlea

• Ie. Eardrum puncture• Damage to hammer, anvil

stirrup• Digital hearing aids help

by amplifying vibrations and compressing sound

Sensorineural Hearing Loss (216)

• Damage to cochlea’s receptor (hair) cells or to the auditory nerves (AKA nerve deafness)

• Caused by disease, aging, prolonged exposure to loud noise

• Once dead, the cells stay dead

Cochlear Implants (216)

• Electronic device that translates sounds into electric signals that, wired into the cochlea’s nerves, convey information to the brain.

• They don’t work for people whose young brains never learned to process sound

Sensorineural Hearing Loss (216)

• Forge (1993) discovered ways to chemically stimulate hair cell regeneration in guinea pigs and rat pup.

• Some day, we may be able to trick the human cochlea into regenerating hair cells

• Until then, we are limited to use of the cochlear implants.

Ethics of Hearing (217)

• The deaf say it is not a disability and they object to using cochlear implants on young children who haven’t learned to speak

• Signing is considered a unique and valid language

• Should deaf children learn both sign and English?

• A deaf person’s auditory cortex is more sensitive to touch and visual stimuli.

Touch (219)

• Sense of touch is a combination of 4 skin senses: pressure, warmth, cold and pain

• But, there is no simple relationship between what we feel at a given spot and the type of specialized nerve ending found there. The relationship between warmth, cold and pain and the receptors that respond to them is a mystery.

• Only pressure has identifiable receptors

Warm + Cold = Hot (220)

• If you grab hoses for ice cold water and warm water at the same time, you will perceive the combined sensation of burning hot

• See figure 5.24

Pain (220)

• Protects us from unchecked infections and further injury

• Is a property not only of the senses, but also of the brain

• - ex. Phantom pain in amputated limbs indicates that the brain can misinterpret spontaneous nervous system activity that occurs in the absence of normal sensory input

• Other senses can also be “phantom”

Vision v. Pain (221)

• Unlike vision, the pain system is not located in a simple neural cord running from a sensing device to a definable area in the brain

• There is no single type of stimulus that triggers pain (like light) and no special receptors for pain (like rods and cones)

Pain Gate-Control Theory (221)

• Theory by Melzack (psychologist) and Wall (biologist) (1965)

• The spinal cord contains a neurological gate that either blocks pain signals or allows them to pass on to the brain

• The spinal cord contains small nerve fibers that conduct most pain signals and large fibers that conduct most other sensory signals. When tissue is injured, he small fibers activate and open the neural gate and you feel pain. Large fiber activity closes the gate blocking the pain

Pain Gate-Control Theory

• So, a way to treat pain is to stimulate (electrically, massage, acupuncture) gate-closing activity in the large fibers - ie. Icing a bruise triggers gate-closing cold messages

• The pain gate can also be closed by the brain if we are distracted from pain and soothed by the release of endorphins.

Memory and Pain (222)

• We tend to remember pain’s peak and how much pain we felt at the end of a procedure.

• We tend to overlook a pain’s duration.

• So, doctors should lengthen painful procedures but taper their intensity (rather than doing it quickly but really painfully)

Pain Control (222)

• Pain is physical and psychological and is treated in both ways

• Drugs, surgery, acupuncture, electrical stimulation, massage, exercise, hypnosis, relaxation therapy, thought distraction

Pain Control (222)

• An example is the Lamaze method of childbirth that uses relaxation (deep breathing and muscle relaxation), counter-stimulation (massage) and distraction (focus on a photo)

Fire Walking (223)• Is this mind over

matter?• Or do the wood coals

poor conductors of heat?

• I don’t think I will insist on gather empirical data on this one!

Taste (224)

• Involves 4 basic sensation of sweet, sour, salty and bitter

• A 5th sense of taste for “umami” has been discovered (MSG flavour enhancer)

Taste (224)

• Inside each bump on your tongue are about 200 taste buds. Each taste bud contains a pore that catches food chemicals. Taste receptor cells project antenna-like hairs into the pore. The receptor cells respond to different taste stimuli.

Taste (224)

• Taste receptor cells reproduce themselves every week or so. As you age, the number of your buds decrease and so does your taste sensitivity. Smoking and alcohol speeds up the loss of taste buds.

Taste and Emotion (224)

• Emotional response to taste is inate.

• Newborns react to sweet and better as do adults.

• There is a sensory interaction (one sense may influence another) between taste and smell.

Smell (225)

• Called olfaction• Is a chemical sense like taste• Molecules of substance carried in the air reach a

tiny cluster of 5 million receptor cells at the top of each nasal cavity which respond selectively to certain smells

• Smell receptors recognize odors individually - odor is not separated into elemental odors like light is.

Smell (225)

• The receptor cells send messages to the brain’s olfactory bulb, and then to the temporal lobe’s primary smell cortex and to the parts of the limbic system involved in memory and emotion

Odor Molecules (225)

• Odor molecules have a unique shape and size but we don’t have 1 distinct receptor for each odor. Instead odors trigger a combination of receptors.

Smell (225)

• Smell peaks in adulthood then declines

• An odor’s attractiveness is learned

• Odors can evoke memories and feelings. A hotline runs between the brain area that gets information from the nose and the brain’s ancient limbic centers associated with memory and emotion.

The 6th Sense (227)

• Our sixth sense is our awareness of our body position and movement.

• Kinesthesis - the sense of our body’s position and movement (of individual body parts)

• Vestibular sense - our sense of the head (and thus our body’s) position and movement

Vestibular Sense (227)

• Our ear’s semicircular canals and vestibular sacs contain fluid that move when our head rotates or tilts. This stimulates the hair-like receptors to send signals to neurons and we sense our body position and maintain our balance.