Textbook Notes (363,074)
Canada (158,173)
Psychology (4,731)
Psychology 1000 (1,558)
Chapter 5

Psychology Chapter 5 Notes.docx

29 Pages
Unlock Document

Western University
Psychology 1000
Mark Holden

Chapter 5: Sensation and Perception • Sensation: o Stimulation of the sensory receptors o Stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain o i.e. light  eye, sound waves  ear • Perception: o Organizing sensory input and giving it ‘meaning’ o i.e. recognizing a friend’s face or a melody, light of certain wavelength stimulates receptors in the eyes (sensation)  ‘red’ (perception) • Synesthesia: o The mixing of senses o May experience sounds as colours or tastes as touch sensations o Research found that all are born synaesthetic  neural pathways of infants are undifferentiated and lead to cross modal perceptions o Activity in one part of brain evokes responses in another part of the brain dedicated to another sensory modality • Transduction: o Process of ‘translating’ the physical, environmental stimulus into electrical signals (nerve impulses) o Visual receptors light in, electricity out; auditory receptors  sound waves in, electricity out; olfactory receptors: scent molecules in, electricity out • Process: o First translate stimulus to nerve impulses (transduction) o Specialized neurons called feature detectors break down and analyze the specific features of the stimuli o Then, these ‘pieces’ are reconstructed into a neural representation that is compared with previously stored information, such as what something looks, smells, or feels like o This matching of stimulus with internal storehouse of knowledge allows us to give it meaning, and experience a perception General Principles in Perception Research • Psychophysics: o Studies how physical stimuli are translated into psychological experiences o Studies relations between physical characteristics of stimuli and sensory capabilities o Includes:  Absolute Threshold  Difference Threshold  Magnitude Estimation Stimulus Detection: The Absolute Threshold • Idea: we can’t detect everything, so what is the weakest/lowest level we can detect? • Absolute Threshold o Lowest intensity necessary for a stimulus to be detected 50% of the time o Lower threshold means we are more sensitive Stimulus Detection Theory • Signal Detection Theory: o Concerted with factors that influence sensory judgments o Decision Criterion: a standard of how certain they must be that a stimulus is present before they will say they detect it. This can change from time to time depending on factors such as fatigue, expectation, potential significance of stimulus o Experiment of perceptible tone outcomes: Yes (hit), No (miss), Yes (False Alarm), No (correct rejection) o At low stimulus intensities, both participants and situation’s characteristics influence decision criterion. Bold participants have more his but also more false alarms, etc. o People can be more bold based on rewards and costs of correct/incorrect answers o Ex. Navy radar operator may be more likely to notice a faint blip on her screen during a war mission when a miss might have a disastrous consequence The Difference Threshold (Just Noticeable Difference JND) • Difference Threshold: o The smallest difference between two stimuli that people can detect 50% of the time o Ex. Difference between weight, difference between tones (musicians) • Weber’s Law: o The size of the JND is proportional to the magnitude of the first stimulus o Every stimulus has a different fraction/proportion o i.e. Weber’s fraction for lifting weights is 1/30 (textbook says 1/50 but is more around 1/30)  therefore you can notice difference between 300g and 310g but not 900g and 910g o As stimuli get more ‘intense’, difference must be increased to be perceived o Humans greater sensitivity in visual sense, animals may depend more on smell, humans also more sensitive to differences of pitch than loudness Psychophysical Scaling: • If we have a room with a 60 watt light, and turn on another do we perceive it as twice as bright? o ‘Does perception match sensation’? o If this level of light is a 10, what level is a 20? Or a 5? • Constant increases in stimulus intensity produce smaller and smaller (or larger and larger) increases in the perception of intensity o Different types of stimuli act very differently  i.e. line length, vs. brightness, vs. electric shock Perception Outside Awareness • Patient DF ‘blightsight’ o Perception can happen without conscious awareness • Subliminal perception: o Registering sensory input without conscious awareness  Limen = threshold  Extensively studied in advertising • i.e. Lipton Ice experiment o showing the word ‘Lipton Ice’ and a nonsense word to people o Thirsty people drank Lipton ice 85% of the time o Not thirsty people still drank Lipton Ice 55% of the time Sensory Adaptation • a.k.a. ‘habituation’ • Sensory Adaptation: o Gradual decline in sensitivity to a stimulus over a prolonged stimulation o Sensory neurons are engineered to respond to a constant stimulus by decreasing their activity  i.e. wearing a watch, entering a swimming pool o Occurs at a neuronal level  Happens in all senses  Visual saccades prevent adaptation o Helps us concentrate on what is important o i.e. vision doesn’t totally disappear because of tiny involuntary eye movements that keep images moving about the retina The Sensory Systems Vision • stimulus for vision is electromagnetic energy (light waves) which are measured in nanometres • electromagnetic spectrum includes x-rays, TV and radio signals, infrared and ultraviolet rays • Human visual system sensitive to wavelengths extending from about 700 nanometres (red) down to 400 nanometres (blue-violet) Human Eye • Cornea: o The ‘bump’ at the front of the eye o Light waves first enter the eye through the cornea • Pupil o Adjustable opening that can dilate or constrict to control the amount of light that enters the eye o Basically a hole that allows a certain amount of light into the eye o Dilation is controlled by the coloured iris that surrounds the pupil o Low levels of light  pupil dilates and more light enter, high-levels of light  pupil constricting • Lens o Behind the pupil, an elastic (crystalline) structure that focuses light onto the retina o Accommodation: lens turns thicker to focus on near objects and thinner to focus on distant objects o Projects a 2D image onto the back of the eye  Image is actually upside-down and backwards  brain must ‘flip’ it back • Retina o Multilayered tissue at the rear of the fluid filled eyeball that is essentially an extension of the brain  Sends visual signals to the brain  Layers are different types of cells o Contains two types of light-sensitive receptor cells  rods and cones o Rods  120 million rods per eyeball  Extremely sensitive to light  vision in the dark  Many rods in one ganglion cell  500 times more light sensitive, but poor acuity  Don’t see colour  primarily black and white receptors  i.e. owls contain only rods, so they have great vision in dim light but no colour vision during the day o Cones  6 million cones per eyeball  Much less sensitive to light  work best in bright environment (day)  i.e. chipmunks and pigeons only have cones so they see world in living colour but have poor (no) night vision  the place with only cones is the fovea centralis o Cells of the Retina 1. Receptor cells  synapse with bipolar cells BACK OF THE EYE 2. Horizontal cells  allow sideways integration of retinal activity 3. Bipolar cells  synapse with about 1 million ganglion cells 4. Amacrine cells  allow sideways integration of retinal activity 5. Ganglion cells  axons collected in bundle to form optic nerve FRONT OF EYE • Input of more than 126 million rods and cones eventually turn into 1 million traffic lanes leading toward higher visual center • Rods and cones form the rear layer of the retina, but the light sensitive ends actually point away from the direction of the entering light so that they only receive a fraction of the light energy that enters the eye • Many rods and cones connected to bipolar cell • The image on the retina position that has the most rods would combine and connect to the few bipolar cells and their additive effects will make signals detectable • Same with cones (if retina image on fovea)  visual acuity • Visual acuity: ability to see fine detail is greatest when image projected directly to fovea • Animals like eagles and hawks have great visual acuity because they have 2 foveas o Fovea Centralis  Small area(<1mm ) in the center of the retina that is used for vast majority of vision  This is the portion of the eye that is involved in direct looking  Has the greatest density of receptors (ONLY cones) which connects to 1 ganglion cell  Great visual acuity in this area o Blind Spot  Ganglion cells are closer to the inside of the eye than the receptors  These ganglion cells travel to brain through the blind spot  Blind spot is the hole in the retina where there are no receptors  We are unaware of this blind spot because our brain fills in the missing part of the visual field • Myopia o Ability to see clearly depends on the lens’s ability to focus the image directly onto the retina o Eyeball is too long o Lens focuses the light in front of the retina, resulting in a blurred image for faraway objects • Hyperopia o Eyeball is too short o Lens focuses the light behind of the retina o ‘Farsighted’  Occurs frequently as part of aging Transduction • Transduction: o Process of ‘translating’ the physical stimuli into electric signals (nerve impulses) o Rods and cones have different ‘photo-pigments’  Photo-pigments are protein molecules that change shape when they absorb light  Change shapesodium channels to open action potential  releases neurotransmitter  Over time, photo-pigments change back to their original shape o The absorption of light by these photo-pigments produces a chemical reaction that changes the rate of neurotransmitter release at the receptor’s synapse with the bipolar cells o The greater the change in transmitter release, the stronger the signal passed to the bipolar cell and to the rest of the cycle o Takes time for photo-pigments to return to ‘ready’  there are always some ‘ready’ and some not  Can only detect light when ready  Constant turnover o Blinding flash of light will cause all the ‘ready’ photo-pigments to get used up o Not blinded for long because other pigments were getting close but were still ‘not ready’ • Dark Adaptation o Progressive increase in sensitivity to light (i.e. eyes adjusting to a dark theatre) o After absorbing light, a fair number of photo-pigments are ‘used up’ at any given time (likelihood of a photon hitting a ‘ready’ pigment is not 100%) o After a while in the dark, more and more photo-pigments have regenerated (photon hitting a ready photo pigment is much closer to 100%) o Done by focusing flashes of varying wavelength on fovea (cones) or periphery of the retina (rods) o Not a smooth increase in sensitivity over time because of differences between rods and cones o Rods  more sensitive to light, take longer to regenerate o Cones  less sensitive but take less time to regenerate • Light Adaptation o Progressive decrease in sensitivity to light (i.e. eyes adjusting as you exit the movie) o After a while in the dark, photo-pigments have regenerated (without immediate firing again) o When you walk into the lighted hallway, a large number of receptors will fire  blinded by light o Over time, the cells become staggered again and you adapt to the light • Rods, Cones, and Colour o Rods and the 3 different types of cones are sensitive to a certain range of light waves  Rods are most sensitive to bluish light, not sensitive at all to red light  World seems blue when we get up at the middle of the night  WWII pilots wear red sunglasses so they adapt to the dark and can see better when they go fight at night Colour Vision (3 Theories) • Colours of light add differently than colours of paint o Primary colours of light: blue, green, and red o Some combination of these can produce any colour in the visible spectrum  additive colour mixture  This is how colour TV works • Young-Helmholtz Trichromatic Theory: o We have 3 different types of cones, each are maximally stimulated by either blue, green, or red light o Each must send signals to the brain, depending on how much it is activated by a given wavelength o The visual system must then ‘add up’ the inputs and figure out the original ‘colour’ of the light o If all 3 cones are activated equally, then a pure white colour is perceived o Problems with Trichromatic Theory:  According to theory, yellow is based on red and green input • However, some people with red-green blindness can still see yellow  Colour after images: an image of different colour appears after a colour stimulus has been viewed steadily and then withdrawn • Opponent Process Theory o Thought that each cone responded to 2 opposite colours  Red/green, blue/yellow, black/white  Opposite colours were assumed to result in 2 different types of chemical reactions  Explanation of colour after-images: • Sensory adaptation for one colour • Then, when looking at white (all colours), only the ‘red’ half of that type of cone was able to respond (black rebounded with white, green rebounded with red) • Dual Process Theory o Currently the best understanding of colour vision o Turns out, both trichromatic and opponent process theories are partially correct  Cones are sensitive to blue, green, red  Opponent process theory also partially correct, but do not occur at the level of the cones • Happens more in ganglion cells, and in visual cortex • Colour Blindness o Most people have 3 cones  normal colour vision (trichromats) o Some people have 2 cones  colour blind  Referred to as dichromats • Not truly blind to colour, but can only see some • Missing red cone  red/green colour blind • Missing green cone  red green colour blind • Missing blue cone (rare)  blue/yellow colour blind  Monochromats (only sensitive to black/white)  truly colour blind o Protanope  red weakness, able to see blue and short wavelengths o Deuteranope  similar to protanope, weak to green o Tritanope  blue-yellow weak, weak to blue Visual Pathway to Brain • Optic Nerve  thalamus (relay station)  primary visual cortex • The primary visual cortex has specific regions that correspond to specific areas of your retina. There is a point to point correspondence between tiny regions of the retina and groups of neurons in visual cortex o Similar to a ‘map’ of the visual scene  At least 10 duplicate mappings o Maps are distorted o The fovea (synapses of cones with bipolar and has high visual acuity) is represented by a large area of the visual cortex • Deeper into the visual cortex, groups of neurons are combined to receive and integrate sensory nerve impulses originating in specific regions in the retina o These cells are known as feature detectors o Feature detectors  fire selectively in response to stimuli  Some cells that respond only to lines of a specific orientation (characteristics)  Based on patterns of firing  i.e. A would be constructed by lines / \ and –  other feature detectors combine colour inputs (dual process model), depth, or movement  Still retains a ‘map like’ positioning (each feature-detection system may start with its own map, hence the 10 maps) o Different streams for different features are processed in parallel (simultaneously analyze colours, shape, distance, movement) and constructs a unified image of its properties o Brief, high frequency ‘bursts’ of firing in sensory neurons may function as feature detectors • Final step in constructing visual representation occurs when analyzed and recombined information by the visual cortex goes deeper and is routed to other cortical regions. This is known as visual association cortex o Object perception (naming) o More complex features of the visual are combined and interpreted o The process that began with nerve impulses from rods and cones (sensing) now ends with us ‘recognizing’ for what the object ‘is’ o Action  object • Scientists have discovered that some neurons in brain respond not only to basic stimulus characteristics, but also to complex stimuli that we obtain special meaning from experience o i.e. amygdala only respond to 3/50 scenes, all of Bill Clinton o neuron was probably created within the brain to register this celebrity • In Sum: 1. Receptors detect light (patterns of receptor firing brings to next stage) 2. Basic Features (patterns of basic features brings to next stage) 3. Complex features/object recognition/interaction Audition • Stimulus of hearing is sound waves (form of mechanical energy) o Sound is essentially longitudinal waves o Vibrations cause compression and expansion of (air) molecules o Sound waves have two characteristics: frequency and amplitude o Frequency:  How many ‘pulses’ or cycles (sound waves) per second  Use hertz (Hz) to measure cycles per second (1 Hz equals one cycle per second)  Perceived as pitch  Higher frequency (hertz), the higher the perceived pitch  Humans are capable of detecting sound frequencies of 20-20,000 Hz (12,000 in elderly)  Most common sounds are in the lower frequencies (piano from 27.5 to 2186, soprano’s voice from 250-1100 hertz) o Amplitude:  Vertical size of the sound waves  Amount (strength) of compression and expansion of the molecules in the medium  Perceived as loudness  Differences in amplitude are expressed as decibels (db), a measure of the physical pressures that occur at the eardrum  Lowest is 0 db, human pain at around 120db (absolute threshold is 0 db) Auditory Transduction: From Pressure Waves to Nerve Impulses • Transduction system is made up of tiny bones, membranes, and liquid-filled tubes designed to translate pressure waves into nerve impulses • At speed of about 1200 km/h, sound waves travel into auditory canal leading to the eardrum, a membrane that vibrates in response to the sound waves • Beyond the eardrum is the middle ear (cavity that holds 3 tiny bones, size of a grain of rice) • These bones  the hammer (malleus), anvil (incus), and stirrup (stapes) amplify the sound waves more than 30 times • The hammer is attached firmly to the eardrum, stirrup is attached to another membrane, and the oval window forms the boundary between middle and inner ear • The inner ear contains the cochlea • In sum, steps in hearing: 1. Vibration in air molecules 2. Vibration of ear drum 3. Vibration of tiny bones (malleus, incus, stapes)  amplify vibrations more than 30x 4. Vibration in the oval window 5. Cochlea • Cochlea: • Spiral shaped coil that is filled with fluid • Contains the basilar membrane (sheet of tissue) and organ of corti that rests on the membrane  The basilar membrane layers on the base of the cochlea  The organ of corti contains 16,000 auditory hair cells (receptor cells)  Tips of the haircells are attached to the tectorial membrane that overhangs the basilar membrane along the whole length of the cochlea  Hair cells synapse with the neurons of the auditory nerve which, in turn, sends the impulses via the auditory relay station in the thalamus to the auditory cortex in the temporal lobe • Stimulating Auditory Hair Cells: • Vibrations reach the cochlea  pressure created at the oval window sets the fluid inside the cochlea into motion (next step) • ‘Waves’ in the cochlear fluid • Bend the auditory hair cells  triggers a release of a neurotransmitter substance into the synaptic space between the hair cells and the neurons of the auditory nerve, resulting in nerve impulses that go to the auditory cortex • Auditory Cortex (brain) Hearing Loss • In Canada alone, almost 3 million people (10% of pop.) suffer from some form of hearing loss • Conduction Deafness: o Any type of deafness caused by damage to the mechanical system (up to the hair cells) o Problems with transmitting sound waves to the cochlea (up to the hair cells) o i.e. punctured eardrum, damage to ossicles, damage to cochlea o can be often treated with hearing aids so sounds are amplified • Nerve Deafness: o Caused by any type of damage involving neurons (including the hair cells) o Caused by damaged receptors within the inner ear or damage to the auditory nerve itself o Aging, disease, exposure (leading cause) can cause nerve deafness o Constant exposure to loud sounds (machine in factory) eventually cause workers to lose hair cells at a point on the basilar membrane, and causing hearing loss for that frequency o Cannot be treated o i.e. 1986 The Who concert, guinea pig with loud rock music. Reached 120 db within 50 M, guitarist suffered hearing loss o don’t exposure yourself to hazardous levels of noise Coding of Pitch and Loudness • auditory system transforms the sensory qualities of loudness and pitch into the language of nerve impulses • Coding Loudness: o Louder, higher amplitude sound saves cause hair cells to bend more  Releases more neurotransmitter substance at the point where they synapse with auditory nerve cells, resulting in a higher rate of firing within the auditory nerve  Certain neurons have higher thresholds than others, so they will only fire if the hair cell is heavily bent from an intense sound  Loudness is coded both by firing rate and which specific cells are sending signals • Coding Pitch: o Frequency Theory  Nerve impulses sent to the brain match the frequency of the sound wave  Sound waves have a certain frequency… maybe the nerve hair cells fire at that same frequency  i.e. therefore, 30 hertz sound wave from piano should send 30 volleys of nerve impulses per second to the brain  However, because neurons are limited in their rate of firing, individual impulses fired by groups of neurons produce maximum frequencies of firing of about 1000/second  How do we perceive frequencies such as a 4,000 hertz note from same piano?  Remember refractory period! o Place Theory  Waves in the cochlear fluid peak at different points, depending on the frequency of the sound  Specific point where the fluid wave peaks and most strongly bends the hair cells serves as a frequency coding cue  High frequency sounds peak early, low frequency sounds peak later  Similar to the manner in which the retina mapped onto the visual cortex, auditory cortex has a tonal frequency ‘map’ that corresponds to specific areas of the cochlea o Turns out, BOTH theories are partially correct  Frequency theory applies to sounds with low frequencies  Place theory applies to sounds with higher frequencies  Pitch is coded BOTH by firing rate and which specific cells are sending signals Sound Localization • How do we tell where a sound is coming from? o Nervous system uses information concerning the time and intensity differences of sounds arriving at the two ears to locate the source of sounds in space o Differences in timing between the ears  A sound from your right takes a little more time to reach your left ear than your right ear o Differences in loudness between the ears  Sounds are harder to hear the farther away you are  A sound from your right is a little louder at your right ear o i.e. when a sound is in front of you, both ears hear it at the same intensit
More Less

Related notes for Psychology 1000

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.