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Psychology 2115A/B
Philippe Chouinard

Principles of Measurement 1 1/9/2013 5:24:00 AM - perception is:  our interpretation  knowledge influences what we see  Ames’ room  Everything we perceive is based on electrical signals in our nervous system Part A – The Perceptual Process 1. environmental stimulus 2. attended stimulus – focus attention for additional processing 3. stimulus on the receptors  light energy on back of retina becomes transformed Transduction - a retinal representation is transformed into electricity - transformation of one form of energy into another - occurs in the nervous system when energy in the environment is transformed into electrical energy by a receptor Transmission - carrying out information through electrical signals to the brain - if these signals don't reach the brain, there is no perception Processing - interaction between neurons in the nervous system so that perception can occur - purpose of perception is to understand the world, not to make exact copies - what we perceive can be distorted Bottom-Up vs. Top-Down Processing - existing knowledge (top-down) - incoming data (bottom-up) - both types are involved in perception, but not always - possible to have without the other Top-Down Processing - duck-rabbit illusion - knowledge of both allows us to see both Part B – Classical Psychophysics Gustav Fechner - psychophysics: the study of the mathematical relationships between a stimulus (physics) and perception (psych) - psychometric function: the mathematical relationship between the stimulus and the perception - classical psychophysics stems from Fechner’s early work and is based on measuring the so-called ‘absolute’ and ‘difference’ thresholds Absolute Threshold Experiment - an absolute threshold experiment is one two approaches that one can use to get a psychometric function - this is done by varying the intensity of a stimulus and asking participants whether or not they can perceive the stimulus - eg., show one stimulus that varies in brightness and ask the subject whether or not they perceive it Absolute Threshold - minimum intensity of a stimulus (I) before it is registered by the brain in the form of a perceptual sensation - defined as 50% correct - subthreshold intensities: below absolute threshold and are not detectable by the sensory system - suprathreshold intensities: above absolute threshold and are detectable by the sensory system - psychometric functions usually follow an ogive (S) function Ideal Detectors - able to consistently fail to detect subthreshold intensities and consistently detect suprathreshold intensities - the resulting psychometric function of an ideal detector follows a step function - humans are not ideal detectors and will never show a step function  the nervous system is noisy; this noise interferes with perception  there are cognitive influences on perception Difference Threshold Experiment - a difference threshold experiment is one of two approaches that one can use to get a psychometric experiment - this is done by varying the difference in the intensity between two stimuli and asking participants whether or not they can perceive a difference - eg., show two stimuli that differ in their brightness and ask the subject whether or not they perceive a difference Difference Threshold - the smallest change in stimulus intensity (I) required to produce a discriminable change in sensation - just noticeable difference (JND): a commonly used measurement of difference threshold calculated in the following manner:  point ‘a’ = 50% correct  point ‘b’ = 75% correct  point ‘c’ = 25% correct - increment threshold = b - a - decrement threshold = a – c - JND = average of increment and decrement thresholds Weber’s Law - we are better at perceiving absolute differences at lower intensities  eg., gum for 10$ vs. 1$  eg., laptop for 899$ vs. 890$ Weber’s Experiments - Weber studied how difference threshold varies for different intensity levels - three different psychometric functions are shown for progressively higher intensity values - bar lengths along x-axis show that the higher the intensity (I), the greater the difference threshold (ΔI) - the difference threshold increases in a linear fashion with stimulus intensity  ΔI = k x I o ΔI = difference threshold o k = Weber’s fraction (a constant) o I = stimulus intensity Weber’s Fraction - a straight line is produced if we make a plot of the difference threshold (ΔI) that was obtained at each of the three intensity (I) levels - this is the graphical form of Weber’s law, and it has been found to hold true for all sensory systems within a broad range of intensities - the Weber fraction (k) is taken from the slope of this line - small values of k imply greater sensitivity in detecting changes of sensitivity Principles of Measurement 2 1/9/2013 5:24:00 AM How to Design the Perfect Chocolate Chip Cookie? - method of constant stimuli: time consuming, extremely sensitive - method of limits: less time consuming, - method of adjustment: less time consuming - Weber’s Law can be applied to baking  1 vs. 2 cups of sugar may not be detectable, but a large difference in the number of chocolate chips could be detectable Fechner’s Law - took Weber’s law one step further by creating another law to describe the relationship between sensation (ie. Perceptual experience) and stimulus intensity - Fechner’s Assumption: a constant change in sensation magnitude (delta S) was needed to produce a difference threshold (delta l) regardless of the actual level of intensity being tested  in case of bubblegum/laptop example, delta S is equivalent to ‘degree of outrageousness’ - sensation (S) = k x log(l)  k = a constant that is related to, but not identical to, the constant in Weber’s law - mathematically, only a logarithmic function allows Fechner’s assumption to hold true  ie. Increasing values of delta l to be mapped on to constant values of delta S Problems with Fechner’s Law - S = k x log(l) only explains a logarithmic function Part C – Modern Psychophysics Stanley Stevens - devised a technique known as magnitude estimation - in magnitude estimation, participants assign ‘values’ to stimuli  values are arbitrary  can only be done for stimuli that are above threshold Stevens’ Power Law - Stevens found that data obtained from the magnitude estimation approach showed a power function - his approach showed that sensation is related to intensity raised by a certain power - S = k x lb  S = sensation (subject’s magnitude estimations)  l = intensity (of real stimulus)  k = scaling constant  b = power value Response Curves from Magnitude Estimation - with power functions, one can have the following three scenarios:  a linear relationship (b = 1)  a response expansion (b>1) o is exponential o as stimulus intensity increases, the magnitude estimates increase more rapidly than the stimulus intensity  a response compression (0 1 is a response expansion  b < 1 is a response compression - no power values (b) serves all senses - different sensory experiences are related to a stimulus intensity raised by a particular exponent - the power value (b) in Stevens’ Power Law can be quite informative How to Design the Perfect Chocolate Chip Cookie? - what is the ideal number of chocolate chips to give the subject a desirable sensational experience when eating the cookie? Cross-Modal Experiments - Stevens also developed cross-modal matching - instead of providing a ‘number’ as an estimate, participants can adjust a ‘sound tone’ to provide an estimation of the perceived intensity of a stimulus from another sensory domain Prothetic vs. Metathetic Sensations - not all sensations can be rated and consequently measured by magnitude estimation - prothetic sensations  sensations that one can assign a rating  obey Stevens’ Power Law - metathetic sensations  sensations that one cannot assign a rating and cannot be measured with magnitude estimation  do not obey Stevens’ Power Law Method of Triads for Measuring Metathetic Sensations - method of triads  a type of multidimensional scaling technique to assess metathetic properties  participants are presented with three stimuli and judge which two are the most similar - similar scaling techniques have been applied to other fields of research in the social sciences Part D – Signal Transduction Theory Ideal Detectors vs. Humans - cell phone is an ideal detector  gives an identical copy of a signal - humans are not ideal detectors Noise Problem - noise can influence data in psychophysics experiments carried out in humans - environmental (minor):  a sudden change in ambient lighting  a computer blip - cognitive (major):  background neural processes related to our thoughts other than the task at hand  shifts in attention/concentration  response criterion Response Criterion - a chosen cut-off point that people use to indicate whether or not they perceive a stimulus - vary among people and can skew greatly the data obtained in psychophysical experiments - a ‘liberal’ person is more likely to respond to noise  can reduce measurements of threshold - a ‘conservative’ persons is more cautious in their responses because they don’t want to make a mistake  can increase measurements of threshold Signal Detection Theory (SDT) - aims to take into account these factors - must first understand the following types of responses and how they relate to ‘signal’ and ‘noise’:  hit: saying ‘yes’ when a stimulus is presented (reflects signal & noise)  miss: saying ‘no’ when a stimulus is there (reflects noise only)  false alarm: saying ‘yes’ when there is not stimulus (reflects noise only)  correct rejection: saying ‘no’ when there is not stimulus (reflects signal & noise) How Do You Modify People’s Response Criterion? SDT Experiment - an SDT experiment will also experimentally manipulate a person’s response criterion by either:  changing the pay-offs o increasing financial gain for hits will cause participants to be more liberal o increasing financial gain for correct rejections will cause participants to be more conservative  changing the probability that a stimulus will appear o if the stimulus appears more frequently, participants will be more liberal Receiver Operating Characteristic (ROC) Curve - ROC curve: plot of hits vs. false alarm rates obtained in an SDT experiment - shifts in response criteria produce different values for hits and false alarm rates  a liberal criteria produce different values for hits and false alarm rates  opposite is true for a conservative criterion Probability Distributions in SDT - SDT: describes the perceptual effect of noise and signal & noise - probability distributions: tell us what the chances are that the perceptual effect is driven by noise or by signal & noise Detection Sensitivity (d’) - is measured as the distance between the peak probability distribution for noise and peak probability distribution for signal & noise - a greater d’ value simply means that there is a stronger signal ROC Curves and d’ - ROC curves depend on d’ - greater values of d’ produce ROC curves that are more ‘bowed’ - ROC curve is a straight line when noise and signal & noise curves overlap exactly and when there is equal probability for hits and false alarms The Somatosensory System: Touch, Feeling and Pain 1 1/9/2013 5:24:00 AM Somatosensory Information 1. cutaneous  responsible for tactile (ie., touch) and nociceptive (ie., pain/temperature) perception  tactile sensation is detected by receptors in the skin  nociceptive sensation is detected by receptors in the skin, muscles, joints, and internal organs 2. proprioception  responsible for perceptions of limb locations  detected by receptors in the muscles and in the tendons 3. kinesthesis  responsible for the perception of limb movements  detected by receptors in the muscles and in the tendons Part A – Neural Basis of the Cutaneous Senses Skin - protects us from foreign elements - provides us with warning signals - divided into two layers  epidermis: outer layer; contains mostly dead skin  dermis: inner layer; contains mostly mechanoreceptors and nerve endings - mechanoreceptors transform a sensory stimulus into a signal that is relayed to the central nervous system Categories of Mechanoreceptors 1. encapsulated receptors  have a specialized capsule that surrounds the nerve ending  eg., Meissner corpuscle, Ruffini cylinder, Pacinian corpuscle 2. receptors with accessory structures  sensory nerve fibre in conjunction with a separate accessory structure  eg., Merkel receptor, hair 3. free nerve endings  do not have any specialized terminal structures or other associations Dorsal Root Ganglion (DRG) Neurons - transmit information from the sensory receptors to the spinal cord - bipolar neurons with one central axon branch entering the spinal cord and one peripheral axon branch linking the mechanoreceptor - cell bodies are located in the dorsal root ganglion Afferent Fibers of DRG Neurons - an afferent fiber sends information from the periphery to the more central parts of the nervous system - fibers of DRG neurons can be classified into four categories (A-alpha, A- beta, A-delta, and C) based on the degree of myelination and diameter Transmission Speed of DRG Neurons - transmission speed of a DRG neuron is determined by the diameter of its fiber and its myelination - larger diameter and myelination lead to faster transmission - DRG neurons with encapsulated receptors tend to have fast conducting fibers (mostly A-beta) - DRG neurons with free nerve endings (for temperature and pain) are usually associated with slower conducting fibers (mostly A-delta and C) Adaptation of DRG Neurons - response adaptation: refers to how the neurons respond to sustained stimulation - fast adapting (FA) type: neural firing quickly subsides during continued application - slowly adapting (SA) type: fire as long as the stimulus is maintained Type 1 DRG Neurons - DRG neurons can be classified based on where their mechanoreceptors are located in the skin (type 1: close to the surface; type 2: deeper inside the skin) - type 1 DRG neurons:  Merkel receptors: slow adapting; senses steady pressure  Meissner corpuscles: fast adapting; senses flutter and motion Type 2 DRG Neurons 1. Ruffini cylinders  slow adapting  senses steady pressure 2. Pacinian corpuscles  fast adapting  senses vibration Receptive Field of DRG Neurons - receptive field of a DRG neuron: area of skin that is picked up by the neuron  determined by recording from the neuron’s afferent fiber and surveying the area of skin that generates an electrical signal - smaller receptive fields provide superior spatial resolution - type 1 DRG neurons tend to have small receptive fields - type 2 DRG neurons tend to have large receptive fields Spinal Mechanisms and Signal Transfer - spinal cord: transmits signals between the body and the brain - spinal nerves: bundles of neurons linking the body and the spinal cord - dorsal root: carries sensory signals into the spinal cord - ventral root: carries motor signals out to the muscles - dorsal root ganglion: outside the spinal cord, contains the cell bodies of the DRG neurons Dermatomal Map - there are 31 pairs of spinal nerves, one member of each pair, innervate each side of the body - dermatome: body part that is covered by a sensory nerve - dermatomal map: depicts the body parts devoted to all spinal nerves Ascending Pathways to the Brain - somatosensory information from spinal entry to the brain follows one of two pathways 1. dorsal column – medial lemniscus pathway:  transmits to the brain tactile signals received by fast conducting DRG neurons 2. anterolateral pathway:  transmits to the brain temperature and pain signals received by slow conducting DRG neurons - modality segregation: a division or labor in the transmission of two types of sensory information - both pathways are somatotopically organized; namely, fibers going up the spinal cord are arranged by body part - both pathways cross to the opposite side so that the left brain receives signals from the right side of the body, and vice versa - both pathways reach the thalamus before entering the primary (S1) and secondary (S2) somatosensory cortex Somatotopic Organization of S1 - first shown in humans by Penfield - stimulated different parts of S1 during surgery and asked patients what part of the body that they felt Homunculus in S1 - homunculus representation:  some body parts are represented by larger cortical areas in S1 than other body parts  a similar homunculus representation can be found in S2 Experience-Dependent Plasticity - cortical representations of sense in S1 can become larger if that function is used often - the opposite is true if that function is used less frequently Other Properties of S1 - S1 is organized as columns according to receptor type (eg., one column for information conveyed by FA-fibers and another column for information conveyed by SA-fibers) - composed of four cortical Brodmann areas: 1, 2, 3a, and 3b - neurons in S1: smaller receptive fields for more sensitive body parts Somatomotor Circuits - somatosensory information can influence the motor system at the spinal level  somatosensory input into the spinal cord interact with spinal circuits that influence spinal motor output  this circuitry is used for rapid withdraw reflexes - somatosensory information can influence the motor system at the cortical level  the primary motor cortex, or M1, which innervate limb movements, neighbors S1  S1 and M1 work closely together in controlling limb movements - tactile processing is important for grasping objects that differ in their surface properties  smooth objects have less friction and therefore require more ‘fingertip’ forces for grasping  S1 and M1 work closely together to regulate ‘correct’ fingertip forces on objects Part B – Perceptual Aspects of Touch Absolute Thresholds - absolute thresholds (*) vary as a function of a number of factors 1. body parts: facial areas around the mouth are more most sensitive 2. gender: women are more sensitive than men 3. age: sensitivity decreases with age *minimum intensity of a stimulus before it is registered as a sensation Difference Thresholds - difference thresholds (*) also vary as a function of a number of factors 1. body part: fingers are most sensitive 2. hairless vs. hairy skin: hairless skin is more sensitive - usually measured with a compass-like instrument *the smallest change in stimulus intensity required to produce a discriminable change in sensation Cortical Mechanisms for Sensory Acuity - S1 neurons representing parts of the body with better acuity, such as the fingers, have smaller receptive fields - smaller receptive fields, in turn, enhances the ability to feel two points that are close together Law of Outward Mobility - difference threshold improves as one moves from the shoulder toward the fingertips - this is because of the smaller receptive fields for the fingers and because there are more mechanoreceptors on the fingers Sensing Vibration - Pacinian corpuscle receptors are important for sensing vibration - as fast adapting fibers, they respond to changes in pressure but don't respond to continuous pressure - mechanoreceptors differ in sensitivity to vibrational stimuli - Meissner’s corpuscles are more sensitive to lower frequencies and produce a sense of flutter - Pacinian corpuscles are more sensitive to higher frequencies and evoke a diffuse sense of vibration in deep tissue Sensing Texture - temporal cues, such as when the finger goes over a surface, are important for sensing fine details - people are better at differentiating surfaces when they move their fingers - one can decrease the effectiveness of Pacinian corpuscle receptors by vibrating the hand at 250 Hz such that these receptors adapt and are no longer sensitive - following this experimental adaptation, people are less able to differentiate differences between fine textures - thus, vibration is important for sensing texture Reading by Texture - blind people can read using two ‘tactile’ language systems 1. Braille system:  Braille alphabet is produced by different combinations of raised dots with a 2x3 grid  Dot patterns represent full alphabet and punctuation marks 2. Moon system:  easier to learn but has limitations  namely, their embossed letters produce mechanical blurs that makes letters difficult to distinguish The Somatosensory System: Touch, Feeling and Pain 2 1/9/2013 5:24:00 AM Part C – Pain Nociceptors - transduce noxious stimuli from mechanical, thermal, or chemical aggression, into an electrical signal that then foes into the central nervous system - these receptors are located in the free nerve endings of DRG neurons in the skin, joints, muscles, and internal organs - DRG neruons with nociceptors have A-delta or C fibers Ascending Pathway - nociceptive information travels from the spinal cord to the primary somatosensory cortex (S1) via the anterolateral pathway - first synapse occurs in the dorsal horn of the spinal cord, and then fibers cross over to the opposite side of the spinal cord and enter into the ascending tracts of the anterolateral system Temperature - physiological zero: a range of temperature in which we feel neither warm or cold - thermoreceptors in the skin provide signals when temperature deviates from physiological zero - cold-type thermoreceptors: increase firing when temperature is lowered  DRG neurons with these receptors have A-delta fibers - warm-type thermoreceptors: increase firing when temperature is increased  DRG neurons with receptors have C fibers - rate of temperature change influences firing rate - thermal sensitivity is related to the area stimulated  eg., putting your whole hand in warm water will feel warmer than putting one finger - thermal adaptation is faster if the stimulus is closer to physiological zero  eg., a warm bath will not feel so warm after a while Referred Pain - arises when pain in one part of body is mistakenly attributed to another site - convergence of pain fibers from different sites onto same neuron in dorsal horn of spinal cord - eg., some people will experience pain in their left shoulder/arm during a heart attack Cognitive Elements of Pain 1. pain can be affected by mental states  eg., soldiers/athletes not feeling pain during battle/sporting events despite injury  reduced perception of pain during instance of extreme stress may be important for survival 2. pain can increase/decrease with attention  eg., burn centers will sometimes use video games to distract burn victims from their pain 3. pain can occur when there is no stimulation on the skin  eg., phantom limb pain Phantom Limb Pain - pain found in many amputees who had a limb amputated and continue to experience the former limb as well as pain in it - dorsal horn neurons become hyperactive when sensory input is removed - this is an example of ‘central pain’ where the nociceptive signals are not being generated at the peripheral nerve terminals but at a more central site (brain or spinal cord) Gate Control Theory - devised by Melzach - circuits in the spinal cord serve as a ‘gate’ to allow or not allow information about pain from the spinal nerves to reach the brain - this ‘gate’ is controlled by inputs from the brain and by sensory inputs that are not painful  these inputs can close the gate such that nociceptive signals to the brain is dampened Pain Management 1. anti-inflammatory drugs: inflammation of tissue makes nociceptors more sensitive  Eg., Aspirin, Tylenol, and Ibuprofen relieve pain by reducing inflammation 2. analgesic drugs: used to achieve analgesia, relief from pain (eg., opiates)  these drugs bind to receptors that ordinarily interact with endorphins, which are substances that or body produces naturally to relieve pain  relieves pain without eliminating sensation 3. anesthetic drugs: used to achieve anesthesia, reversible loss of sensation by blocking transmission (either locally or generally)  relieves pain by eliminating sensation 4. other drugs: a number of other drugs (eg., anti-depressants, anti- convulsants) relieve pain for reasons that we still don't fully comprehend 5. surgery: used in severe cases and include procedures at various levels from peripheral nerves, to the spinal cord, or the brain  eg., cordotomy: a surgical procedure that disables selected pain- conducting tracts in the spinal cord 6. neurostimulatory procedures: uses electrodes to deliver electric currents and stimulate tissue to actively suppress nociceptive signal transmission and/or increase endorphin production 7. psychological approaches: given that pain has a cognitive element to it, psychological management can be effective  these methods include relaxation training, distraction techniques, and hypnosis Opiates, Endorphins, and Pain - endorphins: substances that our body produces naturally to relieve pain 1. naloxone reduces the effects of heroin by occupying receptors that normally bind with endorphins 2. stimulating sites in the brain that cause the release of endorphins can reduce pain 3. naloxone decreases pain reduction caused by endorphins by keeping the endorphins from reaching the receptor sites Part D – Proprioception and Kinesthesis - proprioception: information about limb position - kinesthesis: information about limb movement - both are detected by proprioceptors that reside in muscles and tendons, and are found in nerve endings of DRG neurons with A-alpha fibers that feed into the central nervous system - two types of proprioceptors:  muscle spindle receptors, which are sensitive to stretch, are located in the muscle  golgi tendon organs, which are sensitive to tension, are located in the tendon Ascending Pathway - proprioceptive and kinesthetic information travel from the spinal cord to the primary somatosensory cortex (S1) via the dorsal column – medial lemniscus pathway - first synapse occurs in the dorsal horn of the spinal cord, goes up the spine, then crosses over in the brainstem (ie., medulla oblongata), goes to the thalamus, and enters S1 Brodmann Areas of S1 - Brodmann area: a region of the cerebral cortex defined by its cytoarchitectonics, or structure and organization of cells - S1 contains four Brodmann areas:  areas 3a (closest to M1) and 2 receive proprioceptive signals  in contrast, areas 1 and 3b receive tactile signals Higher-Order Cortical Areas - S2 receives input from S1 for additional somatosensory processing - Brodmann areas 5 and 7 in the posterior parietal cortex also receive input from S1 for further somatosensory processing - the posterior parietal cortex also processes sensory input from other modalities (eg., auditory, vision) Passive vs. Active Movement - passive movement: somebody else moves the limb - active movement: person moves the limb themselves - corollary discharge: during active movements, the motor centers in the brain not only send motor commands to the limbs but they also send a single to other parts of brain (called corollary discharge) to inform them what is being made Haptic Perception - haptic perception: the combined tactile and kinesthetic experience from exploring an object by active touch - people are better at identifying objects by active touch than by passive touch - Gibson proposed that this was because movements on an object engage the mind and because kinesthesis provides information about 3D structure - haptic perception requires that the somatosensory, motor, and cognitive systems in the brain work together Haptic Exploration - different types of motions on objects provide different types of information - lateral motions: provide information about texture - enclosure and contour-following motions: provide information about shape Cortical Mechanisms of Haptic Perception - as we move from mechanoreceptors in the fingers towards the brain, we see that neurons become more specialized - some S1 neurons respond to specific orientations of stimulation and some S1 neurons respond to specific shapes - the S1 neurons are also greatly influenced by attention indicating that cognitive system Part E – Illusions - our perceptual experience with illusions demonstrate that sensation can be very different that what the brain receives ‘bottom-up’ (ie., by sensory input) due to ‘top-down’ processing Illusions - tactile illusions: 1. tactile funneling illusion:  producing it involves short and simultaneous vibratory signals at two different locations of the skin  one pulse (not two) is felt half way between the two locations 2. cutaneous rabbit illusion:  producing it involves short vibratory signals at two different locations of the skin spaced at different times  what is felt is a progression of pulses on the path form one location to the next S1 and Tactile Funneling Illusion - in the monkey, S1 activation during the tactile funneling illusion reflect ‘perceived’ not ‘tactile’ somatotopic responses in S1 (ie., D3 + D4 stimulation invokes S1 cortex between D3 and D4 representations) - this can only reflect a ‘top-down’ influence from higher-order areas in the brain and S1 Size-Weight Illusion - when two objects are lifted that have equal weight but differ in size, people will perceive the small one as being much heavier - why? We judge weight based on the density of objects  although proprioceptive signals tell us that both objects weight the same, ‘higher-order’ centers in the brain tell us that the smaller object has a greater density Rubber Hand Illusion - one begins to feel sensations in the ‘rubber’ hand after stroking the ‘real’ hand and the ‘rubber’ hand simultaneously for a while The Chemosensory Systems: Taste and Smell 1 1/9/2013 5:24:00 AM Part A – General Characteristics of Chemosensory Perception Chemosensory Systems - taste and smell are triggered by chemicals - when you drink something:  you taste it because chemicals in the liquid stimulate your tongue o this is carried out by the gustatory system  you smell it because chemicals in gas stimulate your nose o this is carried out by the olfactory system Taste and Smell are Gatekeepers - taste and smell are gatekeepers  they identify substances that the body needs for survival and that should be consumed  they identify substances that are bad for the body and that should be rejected for consumption Evolutionary Development - the chemosensory systems is the first sensory sense to have emerged in evolution so that primitive marine organisms could find food and avoid danger - chemotaxis: organisms direct their movements according to certain chemicals in the environment - chemoattractant: chemicals that attract motility towards it - chemorepellant: chemicals that cause motility to flee away - as life moved away from the water:  smell served as a distant detector of chemical stimuli  taste served as a close detector of chemical stimuli  these senses evolved also as a way to communicate (eg., ability to mark territory boundaries, interact with other species, signal sexual receptiveness, etc) Neurogenesis of Chemosensory Sensory Cells - as gatekeepers, sensory cells in our tongue mediating taste and sensory cells in our nose mediating smell are constantly exposed to chemicals and harmful material (eg., bacteria, dirt, etc) - high turn-over rates for sensory cells that pick up chemicals:  every 1 to 2 weeks for sensory cells on the tongue  every 5 weeks for sensory cells in the nose - neurogenesis = renewal of neural cells Are Humans Sensitive to Chemicals? - chemical signals are very important for many mammalian species but humans rely much more on vision and hearing - for many mammalian species, smell is a matter of life and death  not so in humans - macrosmatic species: species with a keen sense of smell that is important to their survival - microsmatic species: species with a less keen sense of smell that is not crucial for survival Pheromones and Vomeronasal System - pheromones: chemicals that many mammalian species release to affect the physiology and behavior of other animals - vomeronasal system:  a system that exists in parallel to the main olfactory system that is used for detecting pheromones  vomeronasal organ is located in the nose and contains sensory cells that synapse in the accessory olfactory bulb which in turn projects signals to the brain  this system has yet to be identified anatomically in humans Claims of Human Pheromones - menstrual synchrony: women who live or work together often have menstrual periods at about the same time - McClintock experiments:  showed that menstrual synchrony could be the result of pheromones  sampled armpit secretions of women at various times in their cycle and had other women smell these samples  McClintock could shorten a cycle by having recipients smell samples taken during menstruation  McClintock could lengthen a cycle by having recipients smell samples during ovulation Part B – The Gustatory System: Biological Mechanisms Five Categories of Taste 1. sweet: usually associated with substances that have nutritive value 2. bitter: usually associated with substances that are potentially harmful 3. salty: indicates Na+ (sodium)  something the body needs especially after sweating 4. sour 5. umami (or MSG): is contained in many Asian dishes Chemotopic Organization of the Tongue - tip of the tongue: tends to be more sensitive to sweet and salty tastes - back of the tongue: tends to be more sensitive to sour and bitter tastes - the so-called ‘tongue map’ can be a little misleading however..  the reality is that all parts of the tongue are sensitive to all tastes  some tend to be more sensitive than others Taste Reception in the Tongue - papilla: small mounds or projections of tissue on the surface of the tongue  fungiform papillae: look like mushrooms o located near the tip of the tongue  vallate papillae: large and their grooves are deep o located at the very back of the tongue  foliate papillae: have deep grooves o located at the back and along the sides of the tongue - tastants: dissolved chemicals in saliva that enter the taste buds - taste buds: each contain 50-150 sensory cells  embedded within the grooves of the papillae - taste sensory cells: contain microvilli that project towards the surface of the tongue  microvilli interact with tastants to allow transduction  synapse to neurons that transmit electrical signals to the brain Transduction of Tastants - salt and sour tastants are transduced by ionic channel mechanisms  salt tastants: o contain Na+ (sodium) ions o Na+ enters an ion channel which causes the sensory cell to depolarize and project electricity  sour tastants: o acidic, contain H+ (hydrogen) ions o H+ enters an ion channel which causes the sensory cells to depolarize and project electricity - sweet and bitter tastants are transduced by receptor-mediated mechanisms  sweet tastants: o bind to receptors o this binding triggers a G-protein to release a secondary messenger called cAMP in the cell o cAMP then bind to ionic channels to depolarize the cell  bitter tastants: o bind to receptors o this binding results in a similar cascading of events that will depolarize the cell ‘Labeled-Line’ vs. ‘Cross-Fiber’ Coding - labeled-line system:  each nerve fiber is responsible for transmitting information that is highly specific and restricted to a particular sensory modality  the somatosensory system is fully labeled-lined - the gustatory system is not fully labeled-lined:  individual sensory cells can respond to several taste stimuli  a single nerve fiber can receive signals from more than one taste bud  each taste bud can send its signals through to more than one single nerve fiber - how can taste be coded with these ‘crossovers’?  answer: firing patterns of the neurons can code the taste – similar idea as in Morse code - cross-fiber coding:  different taste qualities are coded by the pattern of discharges across a large population of fibers  different taste intensities are coded by the intensity of firing Electrical Signals to the Brain - sensory cells in the tongue (and throat) innervate one of the three cranial nerves that transmit signals to the brain  facial nerve: aka cranial nerve Vll o transmits signals from the front 2/3 of the tongue  glossopharyngeal nerve: aka cranial nerve Xl o transmits signals from the back 1/3 of the tongue  vagus nerve: aka cranial nerve X o transmits signals from the back of the throat - two intermediate subcortical structures are involved in transmission before these signals are sent to the cortex  nucleus of the solitary tract (NST) in the brain stem o first subcortical ‘weigh station’  VPM nucleus in the thalamus o Second subcortical ‘weigh station’ Primary Gustatory Cortex - from the VPM nucleus, the taste signals enter the primary gustatory cortex in a part of the brain called the insula - neurons in the primary gustatory cortex are more specifically tuned to individual tastes than neurons in earlier structures - a greater proportion of neurons in the primary gustatory cortex show a preference for sweet and salty sensations - note that sweet and salty sensations are usually associated with foods that the body needs and that we have formed, through experience, pleasant associations Secondary Gustatory Cortex - from the primary gustatory cortex, the taste signals enter the secondary gustatory cortex in a part of the brain called the orbitofrontal cortex - secondary gustatory cortex:  processes taste signals further  also receives information from other modalities to (eg., small, somatosensory, vision) that can enhance (or diminish) the gustatory experience  also serves as gateway for taste signals to enter other areas in the brain involved in emotions and in forming memories Nociceptive Information and Taste - capsaicin: active ingredient in chili peppers - a number of ‘hot spices’ add flavor by binding to nociceptive (ie., thermal/pain) receptors - what we perceive as ‘hot’ is an example of how the somatosensory system can influence taste The Chemosensory Systems: Taste and Smell 2 1/9/2013 5:24:00 AM Part C – The Gustatory System: Perceptual Characteristics How Does One Measure Taste? - electrogustometry: delivers a small electric current through an electrode to a specific region of the tongue - chemogustometry: application of a chemical solution to either a restricted part of the tongue (regional chemogustometry) or in the whole mouth (whole-mouth chemogustometry) Taste Abnormalities - these methods are used clinically to assess taste abnormalities  ageusia: total loss of taste o can arise form injury to the gustatory nerves  hypoguesia: reduction in taste sensitivity o can arise from smoking, dry mouth, influenza, diabetes and hypertension  dysgeusia: taste distortions occur o namely, one category of taste will be perceived as belonging for a different category Factors That Influence Taste Sensitivity 1. type: bitter tastes (usually associated with substances that are potentially harmful) tend to be most sensitive, followed by sour, salt, and sweet tastes 2. temperature: relationship between sensitivity and temperature is a U- shaped function for all the taste primaries  sensitivity is best somewhere between room temperature (22C) and body temperature (37C) 3. age: sensitivity decreases with age 4. location: sensitivity for salty and sweet tastes are lowest near the front of the tongue  sour tastes are lowest at back  bitter tastes are lowest on the soft palate 5. surface area: the greater the area of stimulation, the greater the sensitivity 6. temporal factors: how rapidly the taste is presented on the tongue  how long the taste may linger after being detected  adaptation and cross-adaptation Measuring Taste Quality 1. multi-dimensional scaling  techniques to measure similarity between stimuli (eg., Method of Triads) so that one can construct a 3D similarity map  closely spaced points represent tastes that are perceptually similar  experiments using multi-dimensional scaling have shown that not all tastes are contained within the space of the four ‘classical’ primary qualities (ie., sweet, sour, bitter, and salty) 2. rating scales of different descriptors  namely, subjects taste the stimulus (eg., a beer), are given a list of descriptors (eg., bitter, sweet), and provide a rating for each  taste quality can be shown through ratings on a number of taste descriptors  in the food industry, taste maps can be used for making comparisons and establishing quality goals Taste Hedonics - taste hedonics: the evaluation of foods with regard to its positive or negative appreciation - influenced by early exposure and culture Part D – The Olfactory System: Biological Mechanisms Olfactory Epithelium - olfactory epithelium: receptor organ for the sense of smell  located at the upper margins of the nasal cavity where odorants (airborne chemicals) trigger the neural signals - two routes to get to the olfactory epithelium:  orthonasal route: through the nostrils  retronasal route: through the back of the throat Olfactory Sensory Neuron - olfactory sensory neuron: bipolar neuron transducing an odorant into an electrical signal - dendrites contain cilia, which is where the odorant binds to a receptor - approx. 1000 different types of receptors exist, each being sensitive to a broad set of odorants with some affinity for specific chemical structures - each olfactory sensory neuron expresses only one type of receptor Transduction of Odorants - binding of the odorant molecule to the receptor triggers the G protein, which produces cAMP, which increases the entry of Na+ ions into the neuron and produces membrane depolarization - signal then travels to a structure called the olfactory bulb Olfactory Bulbs - olfactory bulbs: paired oval structures that reside below the frontal lobe - all incoming axons converge on a small area called the glomerulus - each olfactory sensory neuron projects to only one glomerulus but each glomerulus can receive input from sensory neurons over widespread areas of the olfactory epithelium ‘Labeled-Line’ vs. ‘Cross-Fiber’ Coding - label-line coding:  is supported because an olfactory sensory neuron goes to one glomerulus in the olfactory bulb - cross-fiber coding:  is supported because odorant receptors are capable of binding to different odorants  is supported because a single odorant can activate several difference glomeruli - similar to the gustatory system, the olfactory system relies on the pattern of discharges across a large population of fibers  different smell qualities are coded by the pattern of firing  different smell intensities are coded by the intensity of firing Cortical Processing of Olfaction - signals from olfactory bulb are transmitted to five areas that together make up the primary olfactory cortex - piriform cortex is believed to process fundamental sensory aspects of olfaction - limbic structures (amygdala, hippocampus) process emotion- and memory- related aspects of smell - simiar to gustation, highest levels of perceptual and cognitive processing related to olfaction take place in the orbitofrontal cortex Olfaction and Memories - Proust phenomenon: a vivid recollection of an experience that happened many, many years ago triggered by a particular odor - named after French novelist Marcel Proust for a famous passage in his novel ‘Swann’s Way’ about a memory invoked by the smell of a madeleine cookie Aromatherapy - tries to invoke memories of things that we commonly associate as being pleasant (eg., smell of the forest, the smell of the beach) - fragrance industry is a 1 billion dollar a year industry Taste and Olfaction Interactions - taste and olfaction interact together to boost our sense of flavor - odorants released by food in the mouth can reach the olfactory epithelium through the retronasal route - people with anosmia (total loss of smell) often complain of the great void in sensing flavors in foods Part E – The Olfactory System: Perceptual Characteristics How Does One Measure Smell? - olfactometer: device that experimenters use to deliver smells while controlling for duration of delivery, temperature, and humidity Smell Abnormalities - this instrument is used clinically to assess smell abnormalities  hyposmia: reduced smell perception o can arise from an infection or inflammation of the nasal passages causing obstruction o eg., when we have a cold  anosmia: total loss of all smell sensation o can arise from traumatic injury  specific anosmia: loss of smell for a particular odor Smell Sensitivity in Different Species - rats are 8 to 50 times more sensitive to odors than humans - dogs are 300 to 10 000 times more sensitive - however, individual olfactory receptors for all animals are equally sensitive  the difference lies in the number of receptors they each have - humans have ten million and dogs have one billion olfactory receptors Factors That Influence Smell Sensitivity 1. gender: some gender differences have been found in terms of sensitivity to certain odorants that may be linked to hormones 2. age: increasing age is accompanied by a reduction in sensitivity 3. adaptation: continued exposure to an odor reduces perceptual intensity  sensitivity to our own bodily smells 4. cross-adaptation: sensitivity to one odorant can be reduced by exposure to a different one Measuring Smell Quality - researchers have found it difficult to map perceptual experience onto physical attributes of odorants because:  often, there is no specific language to describe odor quality  some molecules that have similar structures smell different, and some that have different structures smell the same - similar to measuring taste, one can use techniques that employ multi- dimensional scaling and rating scales of different descriptors Perception of Odor Mixtures - mixtures can result in: 1. retaining their individual qualities 2. masking effects:  ie., the effects of one aromatic substance suppressing our ability to perceive others  eg., deodorants and air fresheners 3. blend together to create an entirely new fragrance The Auditory Systems: Sound and the Ear 1/9/2013 5:24:00 AM If a tree falls in a forest and no one is there to hear it, will it create a sound? - physicist’s point of view:  yes  sound is a vibrational disturbance in air or in another medium - psychologist’s point of view:  no  sound is an event that leads to a perceptual experience we know as hearing. - three requirements for us to hear sound:  there must be something that creates the sound  sound must propagate through air, or another medium, from its source  there must be a mechanism to translate sound energy into a biological signal Part A – Physics of Simple Harmonics Vibrational Properties of a Sound Source - two competing forces are at play on a sound-producing object: 1. inertia: the tendency of an object to resist any change in its motion o ie., it wants to keep moving 2. elasticity: the tendency of an object to return to its original state o ie., it wants to return to its starting position - the back and forth movement of a tuning fork is the result of inertia and elasticity:  the force applied to the prongs cause them to initially move in the direction of the force  elasticity produces a restoring force that opposes this motion in the opposite direction returning it to equilibrium  the two forces oscillate and decays over time as the result of air resistance, which is known as dampening - simple harmonic function:  when we plot the physical displacement of the prongs over time, we see that it follows a sinusoidal function  this function is known as a simple harmonic function Impact on Air - impact of a sound-producing object on air:  causes a corresponding vibrational disturbance to the air particles that surround the source  causes variations in air pressure from high concentration (compression) to low (rarefaction) concentration of air molecules - propagating regions of increased and decreased air pressure also show a sinusoidal profile of pressure change  resulting sound wave that follows this sinusoidal profile is called a pure tone Sound Amplitude - amplitude relates to the amount of change in air pressure - more intense sounds can be produced by heavier tapping of the tuning fork compared to softer tapping - amplitude is taken as the pressure difference between baseline and the maximum peak or trough value Frequency - frequency is measured in terms of how many cycles are completed in one second (denoted as Hz)  1 cycle in 1 second = 1 Hz  2 cycles in 2 seconds = 2 Hz, etc. Sound Frequency - one complete cycle of sound wave is defined as the region between two identical points - frequency of a sound wave is defined by the number of cycles of pressure change per second (Hz) - higher frequency sound will have a shorter time span to complete a cycle Loudness and Pitch - loudness: our perception of the amplitude of a sound wave  loudness is associated with larger amplitudes of a sound wave - pitch: our perception of the frequency of a sound wave  higher pitch is associated with higher resonant frequencies of a sound wave Loudness - dB = 20log(Ps/Pr) - decibels (dB) is used to index the loudness of a sound  Ps = peak pressure of air displacement  Pr = peak pressure of air displace for the softest sound that humans can perceive (20 micropascals) - the pressure and intensity ratios are taken with respect to the minimum audible sound as the reference point (Pr) Pitch - across species:  range of frequencies that we can hear is 20 to 20 000 Hz  elephants can hear below 20Hz  dogs can hear up to 40 000Hz  cats can hear up to 50 000Hz  dolphins can hear up to 150 000Hz - musical instruments:  every musical note that we perceive corresponds to a sound wave that oscillates at a specific resonant frequency  lower notes correspond to lower resonant frequencies Musical Scales - letters in the musical scale repeat - an octave is the interval between two points where the frequency at the second point is twice the frequency of the first - notes with the same letter name (separated by octaves) have resonant frequencies that are multiples of each other - we perceive such notes as similar to one another Physics of a Piano - when a key is struck, a hammer hits a wire and this wire vibrates, which causes
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