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PSYC 100 Final Exam Notes pt.2.docx

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PSYC 100
Elaine Power

ND PSYCH 2 HALF Chapter 4: Biology of Behaviour October-27-11 12:15 PM Nervous system - 2 parts • Central nervous system o Brain and spinal cord o Made up of neurons and glia • Glia = supporting cells - serve supportive and protective functions helping the neurons to do their work • Peripheral nervous system o Includes cranial nerves and spinal nerves o Transmits sensory info from the rest of your body to the CNS o Transmits motor and other commands from CNS to other parts of the body o Can be subdivided • Skeletal - controls muscles • Autonomic - automatic control in the involuntary muscles and organs • Important terms o Neuron = individual nerve cell o Nerve = bundle of fibers o Tracts = nerves entirely within brain and spinal cord The Neuron • Specialized cells capable of transmitting info • Selectively communicate with other neurons to form circuits or networks • Neuron o Cell body - contains structures that maintain health and metabolism o Nucleus - contains genes, where protein is made o Dendrites - responsible for receiving info o Axon - transmits info o Axon terminals - conveys info to next neuron • Dendrites receive signal, cell body analyses it, axon transmits it • Gap between sending and receiving neuron = synapse • Myelin sheath allows electrical signal to travel faster down axon 3 neuron types 1. Sensory neurons - detect info from physical world and relay that info to brain (afferent neurons) 2. Motor neurons - send info from the brain to the body (efferent neurons) 3. Interneurons - integrate and communicate info between sensory and motor neurons Spinal reflex •Controlled at the level of the spinal cord (brain not directly involved) •Many types o When doctor hits your knee o When you touch fire and draw back • Brain is bypassed to increase speed of reaction, brain becomes aware of pain after Membrane and potentials •Inside of neuron is negatively charged (relative to outside) •Difference is -70mV •How does membrane maintain its charge o Neuron membrane is semipermeable o Cell membranes have ion channels o For a neuron at rest • Most of potassium (K+) channels are open - can pass back and forth across membrane • Most of sodium (Na+) channels are closed - mechanism pumps Na+ that leaks into cell back out  Result = lots of Na+ outside of neuron  K+ is pushed into neuron by repulsion via Na+ outside cell (also there are negatively charged proteins within the cell that are too large to pass through membrane) The action potential •Neuron maintains a negative charge •When neuron becomes excited the ion channel gates change their state •Changing ion concentrations on both sides very briefly causes electric potential to change from -70mV to +40mV o This reversal of change = action potential •Action potential travels down axon like a wave o Effect of multiple successive brief depolarization's along cell membrane • When neuron is stimulated o Sodium channels start opening o Closes potassium channels (holds on to K+ inside cell) o Na+ enters cell --> axon becomes more positive o Na+ channels are voltage gated • Voltage when channel opens up = threshold of activation • If enough stimulation, the neuron become sufficiently charged and moves form -70 to -55mV and achieves the threshold of activation • What happens: o neuron depolarizes (hits -55mV) o Sodium gates open o Sodium rushes in o Rush of sodium causes charge of inside the neuron to become relatively positive • Goes all way up to +40mV - change in potential = action potential o After 1/2 millisecond, K+ starts to move out of the cell and the Na+ gates close • Potential starts going back toward resting level (repolarizes) o Active pumps (ion transporters) pump Na+ out and K+ back in o Refractory period - neuron becomes slighly more negative than resting potential (-80mV) • Less sensitive to stimulation • Axonal propagation o Action potential only occurs on a small part of neuron membrane o When AP occurs at first point, change in membrane potential causes Na+ channels in the neighbouring region to open up • Generates action potential in this region as well o AP flows down neuron like wave o Refractory period keeps the action potential from going back in the direction it came The Nature of Action Potentials • "all or none" event - action potentially is either fully generated (if depolarization reaches threshold of activation) or not at all (if it doesn't reach threshold) • Relatively slow process in contrast with telephone wires - body needs to make and process signals •AP sped up by myelin - myelin is fatty covering made up of Schwann cells (type of glial cell). Allows charge to jump from node to node (nodes of Ranvier) rather than having to travel the whole axon - called saltatory conduction •MS is an autoimmune disorder where myelin is destroyed which causes a degradation of neural transition The synapse •Space between axon terminal and dendrites of next neuron •Neurotransmitters held in vesicles •When AP reaches end of axon it causes the vesicles to move to the membrane of the axon terminal, fuse with it and release the neurotransmitter into the synaptic cleft •Neurotransmitter travels across cleft to dendrites of next neuron o Attaches itself to neurotransmitter receptor (the binding site of the receptor) o Receptors are chemical gated channels, open when stimulated by the right neurotransmitter (can also need a certain number of them to attach before it opens - threshold amount) Getting rid of neurotransmitters •Need to remove neurotransmitter so that the message stops •Done in 2 ways o Synaptic reuptake - taken back into axon terminal o Enzymatic breakdown - disabled by enzymes and converted into chemical that has no effect on binding site Neurotransmitters and action potentials •Neurotransmitters can be inhibitory or excitatory o Excitatory - excites postsynaptic cell (by opening sodium channels) o Inhibitory -inhibit postsynaptic cell (by opening chloride and potassium channels) • This hyperpolarizes the postsynaptic cleft (makes it more negative than it usually would be •Likelihood of AP depends on sum of excitatory and inhibitory potentials on the neuron at a given time Neurotransmitters and Behaviour •Neurotransmitters can be classified into 3 families (based on chemical structure) o Amines • Dopamine  Communicates which activities are rewarding  Activated by stress - used to guide behavior towards things that will lead to reward  Parkinson disease is caused by too little dopamine  Schizophrenia is caused by too much dopamine • Epinephrine and norepinephrine (aka adrenaline)  Causes burst of energy in body • Serotonin  Low serotonin = sad and anxious moods  Antidepressant drugs increase serotonin • Acetylcholine  Responsible for motor control at the junction between nerves and muscles  Involved in learning, memory, sleep and dreaming  Alzheimer's is associated with diminished acetylcholine functioning o Amino acids • Glutamate  Primary excitatory neurotransmitter in the brain • GABA  Primary inhibitory neurotransmitter in the brain  Without GABA synaptic excitation may get out of control and spread through brain  Epileptic seizures caused by lack of GABA o Peptides (large family - modulate emotions, perception of pain and response to stress) • Opioids  Bind to same postsynaptic cleft as opium  Analgesic- drug that diminish the perception of pain Neurotransmitters and drugs •Drugs that affect behaviour changes the nature of the neurotransmitter activity at the synapse •Drugs can block or enhance... o neurotransmitter synthesis in pre-synaptic neuron o neurotransmitter release from pre-synaptic neuron o binding at the post-synaptic neuron •Antagonists - drugs that diminish the effects of neurotransmitters •Agonists - drugs that enhance the effects of neurotransmitters •Examples o L-dopa - dopamine agonist, increases synthesis of dopamine, used to treat parkinson's o Amphetamine - domaine agonist - increases release of dopamine and blocks reuptake of dopamine o Naloxone - opioid antagonist, blocks opioid receptor sites without activating them, treats addiction to opiates o Nicotine - acetylcholine agonsit, mimics acetylcholine by attaching to binding site Hormones •Hormones act like neurotransmitters but travel over greater distances •Hormones released into blood system and transported to target cells The Brain Evidence for localization of function •Aphasia - language disorder resulting from brain damage o Language is more reliant on the left side of the brain o Understanding of language and language production differentiates depending on different areas on the left side of brain •Brain is symmetrical o Left hemisphere and right hemisphere connected by nerve fibers Structure of the brain •Can be divided into 7 major componets o Brainstem - middle of brain, only 1 o Cerebellum - middle of brain, only 1 o Hypothalamus (subcortical), middle of brain, only 1 o Thalamus (subcortical), 1 on each hemisphere o Basal ganglia (subcortical), 1 on each hemisphere o Limbic system (subcortical), 1 on each hemisphere o Cerebral cortex (surface that covers subcortical structures) 1. Brainstem •Lowermost part of brain, extension of spinal cord •Involved in control of automatic behaviours •Relays sensory info to brain areas •Oldest part of brain (evolutionarily) 1. Cerebellum (means 'middle brain') • Connected to the back of brain stem •Balance, coordination, precision 1. Hypothalamus •Regulate physiological functions through homeostasis •Controls pituitary gland (master gland of endocrine system) 1. Thalamus •Gateway to the cerebral cortex •Relays sensory info to cortex •Shuts the gate on incoming sensations during sleep 1. Basal ganglia •Important for initiation of planned movement •Learning and memory, automatizing of motor skills (riding bike, driving) 1. Limbic system •Structures that surround brainstem •Emotional behaviour •Amygdala - very important for emotional learning •Hippocampus - certain types of memory 1. Cerebral Cortex •Most recently evolved • Divided into 4 lobes •Controls complex mental functions •Folded surface o Surface itself = grey matter (cell bodies) o Axons of cell bodies = white matter Cortex •Largest part of brain •Folded surface o Folds = gyri o Valleys = sulci •4 lobes o Occipital o Parietal o Frontal o Temporal Methods to identify localization of cortical functions •Brain lesion (damage) studies o Take out part of the brain and observe effect o Ablation - localized brain lesions o Brain surgery is succesful for removing tumors • Focus - site causing seizures •Brain stimulation studies o Directly electrically stimulate the brain (with electrodes) o See how stimulation affects patient (brain has no pain receptors) o Stimulation caused… • Occipital - seeing lights • Temporal- auditory sensation (bells ringing) • Temporal cortex - evoke memories • Parietal lobe - sensation of touch • Frontal lobe - twitching in parts of body • Human brain stimulation and imaging techniques o Recent technology allows us to measure brain activity in different ways to map brain at work • Transcranial magnetic stimulation (TMS) - stimulates local areas of brain directly • Electroencephalography (EEG)- electrodes placed on head that pick up electromagnetic fields that are generated when neurons are active. Cant really determine where signal is coming from but can tell when it happens  Event-related potential - EEG signal driven by external stimulatino  MEG - records magnetic aspects of the brain's electromagnetic fields) • Hemodynamic imaging techniques  Sensitive to movement of blood around brain • Functional magnetic resonance (fMRI) and Position emission tomography(PET)- describe movement of blood flow to parts of the brain during stimulation. Can map both cortical and subcortical structures Functions of the cerebral cortex Localization of function lobe by lobe • Frontal lobe o Planning and movement o Back portion - primary motor cortex (part of brain that generates the motor commands that result in voluntary movement) o Prefrontal cortex (rest of lobe) - rational, goal directed activity, directing, maintaining attention, making and acting on plans • Temporal lobe o Contains primary auditory cortex - first cortical relay for hearing o Contains hippocampus and amygdala - parts of limbic system • Parietal lobe o Front part is primary somatosensory cortex - first cortical relay for touch info o Help perceive and move through spatial layout of environment o Lessions lead to hemispatial neglect - lack of awareness of one side of space • Occipital lobe o Visual perception o Primary visual cortex - located on banks of the calcarine sulcus Sensations November-01-11 1:51 PM Sensation vs perception • Related but different concepts • Sensation - process by which our sensory systems gather info about the environment o Closely related to brain processes - major topic in neuroscience • Perception - selection, organization and interpretation of sensations o Closely related to cognitive processes of though, language, attention and memory • Ex: the sensation of a light pressure on skin might be perceived as a gentle, loving touch History • Von Helmholtz o His approach led to acceptance of physiological explanations for mental phenomena o His work laid foundation for our understanding of the senses today • Weber and Fechner o Contemporaries of von Helmholtz o Developed methods for measuring the magnitude of human sensation o Led to field of psychophysics • Muller o Doctrine of specific nerve energies o Our brain has no access to physical stimulus itself o Info is collected through neurons, receptors and nerves activated by stimulus o Every sensory domain has an adequate stimulus • Type of physical energy to which is it more-or-less uniquely sensitive o Although sensations feel direct and immediate they are not Sensory Systems • Different species detect different stimulus • Senses act like gates, let some info in and keeps other out • Sensory systems have receptor cells o Detect energy and convey signals to brain about environment through neural firing o Can convey different types of information (ex: seeing different colours) • How? Not sure but we know that neurons can use different codes Neuron codes • Place (or labeled-line) code o Neurons in different places in the body signal different qualitative features o Ex: where the light hits on the retina - cells that are hit in retina tell organism where the stimulus is out there • Population (or pattern) code o Info is conveyed through a whole group of cells o Analogy: lite-brite - image depends on a pattern of activity across the whole array o This is how olfactory system in your nose works • Temporal code o Neurons can fire at different speeds o The frequency of a sound (perceived as pitch) can be coded in the firing rate of a group of neurons o Loudness and brightness also coded in firing rate Sensory adaptation • Term for what happens to sensation when you fatigue sensory neurons • Defined as change in sensitivity that happens when a sensory system is repeatedly stimulated in the same way • System will become less responsive • Allows organism to ignore stimuli that remain unchanged and to react to sudden change in stimulation (ex: react to a predator) • Adaptation also reduces the amount of info needed to be processed by brain Sensory Systems • 5 senses o Seeing (Vision) o Hearing (Audition) o Taste (Gustation) o Smell (Olfaction) • Taste and smell often grouped together (chemical senses) o Touch (Somatosenses) - include... • Skin senses of touch, temperature and pain • Internal senses (how you know position of your limbs • Vestibular senses (sense of balance and acceleration) • Most perception is multisensory - senses work together! • Each sense has a complex transduction process by which electrical potentials in receptor cells develop in response to physical stimuli • Each receptors varies its response to stimuli o Differ quantitatively (energy level of stimulation - sound intensity) o Differ qualitatively (type of stimulus energy - light colour) • Using codes each sensory system passes info along to cortex of brain where further processing occurs (so that sensations are organized and interpreted as perceptions) • For many senses info travels along cranial nerves to brain • 12 cranial nerves pass through holes in skull and deliver info to brain Vision Light • Stimulus for vision is light • Light is electromagnetic radius • Light is made up of particles called photons • Photons travel in waves • Light has 3 characteristics o Wavelength - corresponds to colour (visible 400nm - 700nm) o Amplitude (or intensity) - corresponds to brightness (higher amplitude = brighter light) o Purity - corresponds to psychological dimension of saturation and colour (hue) • Very waves are seen as pure (usually mix of different light waves) • Ex: 650nm appears red but adding other wavelengths will make it appear washed out or pinkish or purplish colour (less saturated) - if enough of another colour is added, colour will change • The eye • Sensory receptor of vision • 2 functions o Focus light on retina (back of eye) o Transduce (convert) light energy into neural impulses • Cornea, pupil and lens focus light onto retina o Cornea - transparent covering of the eye • Brings light into eye • Acts as fixed focus lens to give general focus to light o Pupil - opening in the iris (black dot) • Changes its size to increase or decrease amount of light entering eye o Lens - transparent structure behind pupil • Changes shape through action of muscles (to focus on objects) • accommodation  Short and fat for close items  Long and skinny for far items • Stiffens with age so cant become short and fat - need glasses! •The retina - inner surface of the back of the eye o Where photoreceptors are located o 2 classes of photoreceptors: rods and cones (more rods than cones) o Rods and cones transduce light energy into neural impulses o Retina consists of 3 layers • Rods and cones are at the back and feed into bipolar and amacrine cells which then feed into ganglion cell • Axons of the ganglion (from the optic nerve - 1 of the cranial nerves) leaves the eye and goes to the thalamus Light goes through retina --> rods and cones --> bipolar and amacrine cells --> ganglion cells --> thalamus •Optic disk - place where optic nerve leaves the eye o Has no photoreceptors - blind spot! •Optic nerves from each eye exchange fibers at the optic chiasm so that info from left visual field goes to right visual cortex and info from right visual field goes to left visual cortex Dark adaptation •Eye becomes more sensitive to light in a dark environment • Cones allow perception of colour •Rods cant perceive colour - work best in dim-light conditions o Why you don’t see colour in the dark Purkinje shift •Bright sunlight: cones are active and rods are inactive (most sensitive to yellow and red) •Twilight: rods become active as cones lose their sensitivity (cant perceive colour but most sensitive to yellow-green wavelength) Rods and Cones •When exposed to light photopigments change their chemical structure and gradually become more white (bleaching) o Generates neural impulse o Causes photoreceptor to be less receptive to light •If sufficiently bleached photoreceptor will bounce light away and stop processing (photoreceptors are inactive in bright conditions) •If you put photoreceptor back in dark it will gradually unbleach o Unbleaching follows same time-function as dark adaptation curve o Cone unbleaches before rod o Rods sensitive to dim light and cones sensitive to colour in bright light •4 kinds of photopigments in a normal human retina - each directly sensitive to a specific wavelength o 3 of 4 found in cones (trichromatic theory of colour vision) • Long-wavelength cones (red-cones) • Medium-wavelength cones (green-cones) • Short wavelength cones (blue-cones)  People with colour defects lack specific types of cones  Tetrachromats - people that express 4 different types of photopigments in their retinas o 1 in rods • Most sensitive to medium wavelength • Slightly different sensitivity to green cones Sensitivity and convergence •Sensitivity to light also a function of the distribution of photoreceptors on the retina and their neural connections •Convergence o Many rods converge their outputs onto a few ganglion cells o Activity of single rods is added together to generate a signal o Problem: no way of telling where the signal came from •Cones have little convergence (1 to 1 ratio between cones and ganglion cells) o Reduces ability of cones to respond to dim light o Increases ability of cone system to register fine spatial detail Distribution of rods and cones • Most light focused on fovea - area directly behind pupil • Fovea has a lot of cones packed together but no rods • Outside fovea: many rods, no cones • Fovea is where you see fine detail • What you're looking at goes through fovea - fine detail • Peripherals doesn’t see fine detail but is more sensitive to light (because of convergence of rods) • Ex: if you want to see a dim star, look at it through peripherals Colour vision • Different types of photoreceptors allow you to signal colour as well as brightness • Young - shows that you can make any wavelength by mixing colours • 2 way to vary colour of a stimulus o Additive colour mixing - create new colours by adding colours together o Subtractive colour mixing - adding pigments increases absorbing quality which reduces the number of wavelengths from the reflected light Hering's opponent processing theory of colour vision • Trichromatic theory does not explain why staring at a stimulus gives afterimages o Green gives red o Blue gives yellow o Black gives white (vis versa) • Suggested that perception is an opponent process • Perception of colour is the result of 3 opponent-process channels Combining both theories • When light is presented to eye, cones produce signals of different strength and the relates strengths signal the colour of the light o Done at the level of the ganglion cells in the retina • Opponent processes directly compare the strengths of the inputs coming from yellow and green cones o To determine redness or greeness of light • Opponent process directly compares input of blue cones to the combined input of green and yellow cones o To determine blueness or yellowness of the night • Opponent process adds up total activity in the green and yellow cones o To determine how much light there is (brightness/dark vs light) •Colour aftereffects o Stare at green - red/green process tells you way more green activity then red activity so you see green o After time: green cones become fatigued and fire less (still more than red though) o When you move gaze to white surface (stimulates cones evenly) fresh red cones fire happily - you see red! Eye movement •Our eye moves constantly - necessary •Resolution varies by orders of magnitude across the visual field •Fine spatial detail only available in smaller area in the centre of retina - must move to point to objects Audition (Hearing) Sound •Result from vibration of air molecules •Source causes adjacent air molecules to become compressed into local regions of increased pressure and rarified in areas of decreased pressure •Pressure changes travel through the air to our ears in a wave •3 characteristics o Frequency • Pitch • Sensitivity to sound depends on frequency (most sensitive to 1000- 4000Hz • Range of hearing decreases as you age o Amplitude • Loudness (dB) • Because we are sensitive to different frequencies, the same amplitude at a different frequency does not sound equally loud o Complexity • Psychological property associated with complexity = timbre  What allows us to distinguish the different qualities of different instruments when playing the samenote • Pure tone = sine wave produced by striking fork • Pure tones not very common in nature The ear •Can be broken down into 3 parts 1. Outer ear •Includes pinna, ear canal and ear drum o Pinna - holds sunglasses, locates sound in space • Leads to ear canal • Pinna and ear canal funnels sound into the ear so that it can vibrate the ear drum 1. Middle ear • Between outer and inner ear • Includes ossicles - smallest bone in your body • Sound waves vibrate ear drum and cause vibration of these 3 ossicles • Ossicles function: o Outer and middle ears filled with air o Inner ear filled with fluid o When soundwave travels from air to fluid (less dense to more dense) it tends to be reflected • Why you can't hear noise from outside underwater o Ossicle = amplification system that overcomes reflection • Pushes energy of the in-out vibration of the eardrum into and in-out vibration of the oval window of the inner ear 1. Inner ear • Made up of cochlea and vestibular apparatus o cochlea - where auditory transduction occurs • Vibration of oval window causes fluid to vibrate in cochlea • Cochlea coiled up - along length runs the basilar membrane with the tectorial membrane above it • Sandwiched between these 2 membranes are 4 rows of hair cells o 1 row of inner hair cells - sensory in nature o 3 rows of outer hair cells - serve motor function • Inner hair cells transduce the sound into electrical activity • Inner hair cells connect to auditory nerve fibers which become part of the 8th cranial nerve that travels from the ear to the brainstem where info is processed through many brainstem relays before it finally reaches the thalamus, the primary auditory cortex and other cortical processing areas • Hair cells have cilia that sway back and forth • Movement in 1 direction causes a depolarization of the hair cell, resulting in an action potential in the auditory nerve going to the brain •Von Helmholz: thought that cochlea acts as frequency analyser that break down complex sound into their discrete frequency component. Parts of cochlea sensitive to different frequencies - that part relays info to brain. •Georg von Bekesy: the travelling wave o Vibration of oval window causes wave to travel down the basiliar membrane o Different parts of the basiliar membrane become deflected more than others depending on the frequency of the sound • High f doesn’t travel far - peak close to oval window • Low f travels far - peak further from oval window o Degree of deflection determines how strongly the inner hair cells are stimulated at that place + how strong the resulting signal to the auditory nerve is • Different parts of basiliar membrane are responsible for coding different frequencies •Outer hairs --> work like little motors o When they detect movement in basiliar membrane they 'jump up and down', serving to selectively amplify the up-down movement of the basiliar membrane where they are active o Causes inner hair cells at that location on the basiliar membrane to fire more o Amplification is highly selective - only happens at specific area on basiliar membrane • 1 particular frequency is singled out and amplified o This increases frequency resolution - ability to tell similar frequencies apart o Outer hair cells also cause the ears to produce sound Hearing Loss •Outer hair cells deteriorate with age and cause hearing loss •Hearing aids amplify sounds but don’t fix problem with frequency resolution •Deaf ear: inner and outer hair cells aren't working •Cochlear implant - long electrode array that approximates the shape of the basiliar membrane (inserted into cochlea) • Microphone outside head picks up sound from environment • Processor converts the sound to electrical pulses • Relay couples magnetically with a receiver inside the head which connects to the implanted electrode array • The electrodes of the array squirt the pulses out to the auditory nerve Chemical Senses • Include gustation and olfaction • Each have distinctly different pathways into the brain (localization of function in different structures) and have differently specialized sensory neurons Olfaction • receptors in the olfactory muscosa project their axons into the olfactory bulbs in the brain • Olfactory info travels from the bulbs along the olfactory nerve (cranial nerve) directly to the underside of the frontal cortex (where primary olfactory cortex lies) • Anosmia: sharp movement of head prevents olfactory info from getting to the brain • Odors identified based on population code o Different odorants bind differently to different olfactory receptor cells thus activating unique patterns of receptor fibers o These receptors cause a unique pattern of firing across the fibers of the olfactory nerve • Primary olfactory complex - between the orbitofrontal cortex and the rhinal cortex covering the amygdala and hippocampus o Amygdala - assigns emotional value to events (respond emotionally to smells) o Hippocampus - involved in long term memory (remember smells) • Pheromones - special chemicals processed by the olfactory system o Signal info related to social and sexual behaviour Gustation • Humans only responsive to 5 general types of taste: sweet, salt, sour, bitter and umami (respond to glutamate and MSG) • Taste receptor cells - found on taste buds of the tongue • Taste info conveyed along a variety of cranial nerves from the tongue and mouth to the brainstem and thalamus and then to the primary gustatory cortex in the brain • Taste info combined with smell to yield perception of flavour • Both gustatory and olfactory lose sensitivity due to sensory adaptation and habituation • Adaptation and habituation are different o Both change in behaviour to a repeatedly present stimulus o Habituation = diminished response to a stimulus as a result of learning that it is meaningless or irrelevant • Happens slowly and can last a lifetime o Adaptation: change in behaviour to a repeated stimulus that results from fatigue - usually neural fatigue • Happens quickly, recovered from quickly The somatosenses • 3 types: skin, internal and vestibular Skin senses • Conveys 3 general classes of sensations: touch, temperature and pain • Each sensation class has special receptors that detect intensity of different types of sensation Touch • Skin surface across body is projected to the primary somatosensory area of the cortex o Has a topographic map of the body - the homunculus • Each body part represented next to adjacent areas - somatotopic representation • Biggest body parts (in picture above) have highest sensitivity to touch Temperature • Sensed through thermoreceptors in the skin o Are free nerve endings • Warm fibres - signal T over 30C • Cold fibres - signal T below 30C • If constantly exposed to a certain temperature they will stop signaling o Ex: entering a cold swimming pool Pain •Sensory receptors are free nerve endings in the body (same as T) •3 types of peripheral receptors o Extreme pressure o Extreme hold and cold o Tissue damange • Stimuli from these receptors relayed through the thalamus to the somatosensory cortex, limbic system and prefrontal cortex o Pain experienced depends on processing in these parts The internal senses •Muscles contain stretch detectors - tell brain about degree of contraction of muscles •Pressure receptors in joints - stimulated by contact within joint surfaces •Continually provide us info about position, posture and movement of limbs in space The vestibular senses •The cochlea mediates general body orientation •Gravity = basic plane of reference •Organs and receptors sensitive to gravitational force all work the same way (above) - evolutionarily very old •Fluid filled cavity lined with receptor cells contains little 'rocks' with mass •Depending on pull of gravity the rocks will fall to bottom of the cavity and press on receptors o Tells the organism which way is up or down •Vestibular apparatus in the inner ear is 5 different accelerator detectors o 2 detectors in the vestibule inform about • Forward/backwards movement • Upward/downward movement o 3 semicircular canals indicate rotational movement (in each of the 3 dimensions) - rotational movements are similar to • When you nod your head • When you shake your head • When you tilt your head from side to side Perception November-06-11 12:03 PM Perception •Study of the higher-level processes that the brain uses to interpret, organize and select sensations •Knowledge and experience also factors Relating sensation to perception: psychophysics • Psychophysicist: measures the relationship between the physical characteristics of stimulus and the sensory experience •Difference threshold - the just noticeable difference between 2 stimul •The 'just noticeable difference' (JND) for a stimulus goes up as its intensity goes up o Taste: 20% • Ex: can take out 20% of sugar from sunny D before people notice o Sound intensity : 15% o Light intensity: 1% •Weber's Law: JND/initial intensity = constant •Fechner's Law: relationship between physical intensity of a stimulus and psychological magnitude in units of JND o Bringing sugar down from 10g to 8g is a decrease of 1 magnitude •Steven's power law: accounts for the sensation over a greater range of physical stimulus intensities •Absolute threshold - minimum intensity of stimulation that must occur before we can experience a sensation Signal detection theory (SDT) •Absolute threshold - observers say they detect stimulus on about 50% of trials (you won't hear a faint noise every time) •Why do we not always hear faint stimulus? o Stimulus doesn't just depend on sensitivity, it depends on expectations • If you're expecting a call (while you're in the shower) you're more likely to hear it than if you're not o Have to do with cognitive factors - changes in attention, expectation alertness.. •Response bias - observer's willingness to say yes, independent of their sensitivity •2 errors you can make when trying to detect a stimulus o False alarms o Misses •Bias causes you to make these errors •Need a way to account for both sensitivity and bias
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