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Chapter 5

Chapter 5 Part II

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Queen's University
PSYC 100
Meredith Chivers

Week 8: Chapter 5: Sensation PART II Gustation - we have 2 senses for detecting chemicals in our environment: taste and smell and together they are referred to as the chemosenses - chemosense: one of the two sense modalities (gustation and olfaction) that detect the presence of particular molecules present in the environment - gustation: the sense of taste-> it is the simplest of the sense modalities- taste ≠ flavor flavor includes odor, texture, touch, taste - the flavors of foods diminish when you have a cold not because your taste buds are not operating, but because mucus congestion makes it difficult for odor - laden air to reach your receptors for the sense of smell without odours, onions and apples taste the same Receptors and the Sensory Pathway - tongue has a corrugated appearance: creases and bumps - papilla: a small bump on the tongue that contains a group of taste buds - taste bud: a small organ on the tongue that contains a group of gustatory receptor cells - each receptor cell has hair-like projections called microvilli that protrude through the pore of the taste bud into the saliva that coats the tongue and fills the trenches of the papillae - then molecules of chemicals are dissolved in the saliva, they stimulate the receptor cells, and do so probably by interacting with special receptors on the microvilli that are similar to the postsynaptic receptors found on other neurons - the receptor cells form synapses with dendrites of neurons that send axons to the brain through three different cranial nerves The Five Qualities of Taste - the physical properties of the molecules that we taste determine the nature of the taste sensations - tradition: there are four taste qualities: sourness, sweetness, saltiness, bitterness - there is another taste: umami (“good taste”) umami refers to the taste of monosodium glutamate, we have identified the genes that code for its receptors - there are 5 taste qualities when different molecules stimulate different types of receptors ex. all the substances that taste salty ionize when they dissolve- salty substances include: NaCl,LiCl, KCl, and some other bromides or sulphates but NaCl is the saltiest this leads us to think that salt-tasting receptors identifies NaCl, they respond when sodium enters a taste cell through sodium channels in the membrane there is an influx of sodium, depolarization of the cell, neurotransmitters are released - sodium has a unique role in the regulation of our body fluid if body sodium stores fall, we cannot retain water, so our blood volume will fall result is heart failure - bitter and sweet substances consist of large non0ionizing molecules - look only at molecule shape, we can’t tell if it will taste bitter or sweet or neither - some molecules stimulate both sweet and bitter receptors (like saccharin) - bitterness receptors help us avoid ingesting poisons: most plants produce alkaloids that are poisonous to humans, andmost of them taste bitter - sweetness receptors help us to recognize the sugar content of fruits and other nutritive plant foods when animals that like sweetness eat the fruit, they disperse the seeds and propagate the plant so the sweetness in the fruit is also beneficial to the plant - sour tastes are mostly produced by acids (specifically H+ contained in acid solutions) - sourness receptors are like a warning device against substance that have undergone bacterial decomposition, most of which become acidic back in the day, natural foods tasted sweet or salty, not bitter or sour - monosodium glutamate (chemical that stimulates the umami receptor) is used as a taste- enhancing agent in manyoriental dishes - glutamate is an abundant amino acid and is found in many proteins, which is probably why animals have evolved a ataste for it - there also may be receptors for groups of amino acids to enhance our preference for fuel-rich foods Olfaction - olfaction: the sense of smell - there are 2 ways in which olfaction is different from other sense modalities it’s hard to describe odours in words odours have a strong ability to evoke old memories and feelings, even many years after an event at some time in their lives, most people come across an odour that they recognize as having some childhood association, though they cannot identify it this may be because the olfactory system sends information to the limbic system (which plays a role in emotions andmemories) - there are interesting patterns: women have a more acute sense of smell than men - we may actually have 2 olfactory systems: the second one is called the “accessory olfactory system” - the accessory olfactory system is found in many mammals and detects special chemicals called pheromones - pheromones: chemical signals, usually detected by smell or taste, that regulate reproductive and social behaviorsbetween animals - some evidence: women’s menstrual cycles can be affected by chemical signals - there is no evidence showing that the anatomical units of a human accessory olfactory system are fully functional, and we’ll only look at the primary olfactory system - olfaction is an analytical sense modality (like audition) we sniff air and we can identify the individual components the molecules don’t blend together and produce a single odour like if you mix many different lights together - for the number of sensory receptor cells, visual system is first place, olfactory system is second place olfactory system has around 10 million receptor cells we can smell some things at lower concentrations than laboratory instruments can detect - dogs have more sensitive olfactory systems than humans do they put their noses where odours are the strongest, just above ground level a dog’s nose would not be useful if it were 2 m high like ours is a human’s nose at ground level works much better - experiment: made a scent trail in a grassy field people wore blindfolds, earmuffs, kneepads and gloves so that they could only rely on their sense of smell they followed the scent trail quite well and used the same zigzag strategy used by dogs - but it is true that dogs have many more sensory receptors Anatomy of the Olfactory System - the receptor cells lie in the olfactory mucosa olfactory mucosa: the mucous membrane lining the top of the nasal sinuses (just under the base of the brain);contains the cilia of the olfactory receptors - the receptor cells have cilia that are embedded in the olfactory mucosa, they also have axons that pass through smallholes in the bone above the olfactory mucosa and form synapses with neurons in the olfactory bulbs - olfactory bulbs: stalk-like structures located at the base of the brain that contain neural circuits that perform the firstanalysis of olfactory information - interaction between odour molecule and receptor ≈ interaction between transmitter substance an d postsynaptic receptor - molecule of a substance fits a receptor molecule on the cilia of a receptor cell-> cell is excited this excitation is passed on to the brain by the axon of the receptor cell - so similar mechanisms detect the stimuli for taste and olfaction - olfactory information is different because it is not sent to the thalamus and then relayed to a specialized region of thecerebral cortex olfactory information is sent directly to parts of the limbic system (mostly the amygdala and the limbic cortex of thefrontal lobe) - olfaction also shows cross-modal integration with taste stimuli - experiment: they tested people’s sensitivity to benzaldehyde (smells like cherry and almonds) the threshold for detecting the odour was lower when the participants in their study held a sweet solution of saccharin in their mouths - suggestion: connections in the amygdala may be responsible for the increased sensitivity to the odour when it ispaired with a relevant flavor The Dimensions of Odour - so there are five qualities of taste, and a colour can be specified in terms of hue, brightness, and saturation - research in molecular biology: the olfactory system contains several hundred different receptor molecules, located inthe membrane of the cilia of the receptor cells these receptor molecules detect different categories of odours humans have 339 different types of olfactory receptors, mice have 913 humans can recognize up to 10 000 different odorants - we have a small number of receptors compared to so many different odorants - ans. A particular odorant binds to more than one receptor the brain eventually receives signals from several receptors - so to recognize a particular odour, we have to recognize a particular pattern of activity so chemical recognition is like pattern recognition - so you have an odorant and many odorant receptor molecules - if a part of the odorant molecule fits the binding site of the receptor molecule, it will activate it, stimulate the olfactoryneuron - each odorant molecule fits into at least one receptor, and most of the time fits in more than one - if we know which pattern of receptors is activated, we know which odorant is present - but, even though an odorant can bind with many receptor molecules, it might not bind equally well with each of them it can bind very/moderately/weakly well with a receptor molecule-> the pattern of activation is recognized by the brain The Somatosenses - somatosense: bodily sensations; sensitivity to such stimuli as touch, pain, and temperature it includes our ability to respond to touch, vibration, pain, warmth, coolness, limb position, muscle length and stretch, tilt of head, changes in speed of head rotation - depending on how you use the term of sense modality, we could respond to warmth and coolness by means of one sense modality, or two different ones - many experiences need stimulation of several different sense modalities at the same time - ex. when you determine the flavor of spicy food, not only odour and taste let you do that mild stimulation of pain detectors in the mouth and throat also help - ex. the sensation of a tickle or an itch- mixtures of varying amounts of touch and pain - ex. our perception of the texture and shape of a 3D object that we touch-> there is cooperation among senses of pressure, muscle and joint sensitivity, as well as motor control object moves smoothly in our hand= slippery object moves without much resistance= a feeling of oiliness object gives us vibrations= rough - there are 3 major categories for the Somatosenses groups: the skin senses, the internal senses and the vestibular senses The Skin Senses - the surface of the human body is innervated (supplied with nerve fibres) by the dendrites of neurons that transmitsomatosensory information to the brain - cranial nerves for information transfer: between the face and front parts of the head + the brain spinal nerves for the rest of the body’s surface + the brain - for the somatosensory system, there are no separate receptor cells, all sensory information is detected by the dendrites - dendrites have specialized endings that modify the way they transduce energy into neural activity - free nerve ending: a dendrite of somatosensory neurons it is the most common type of skin sensory receptor, it resembles the fine roots of a plant free nerve endings infiltrate the middle layers of both smooth and hairy skin they surround the hair follicles in hairy skin - pacinian corpuscle: a specialized somatosensory nerve ending that detects mechanical stimuli, especially vibrations the largest of the special receptive endings, visible to the naked eye very sensitive to touch; when they are moved, their axons fire a brief burst of impulses - other specialized receptors detect other sensory qualities like pressure, warmth, coolness, pain Touch and Pressure - psychologists look at touch and pressure as 2 separate sensations touch: light contact of object on skin pressure: produced by more forceful contact - sensations of pressure are only when the skin is moving (being pushed in) this means that the pressure detectors respond only when they are being bent - put a weight on your arm, you will feel pressure and if you don’t move then nothing at all: no because your brain ignores it, but because the sensory endings no longer send impulses to your brain - experiment: looked at very slow minute movements of a weight sinking down into the skin finding: sensory transmission stops when the movements stop sensory transmission began again when we placed another weight onto the first one - of course if you put a heavy weight, the person will feel something, but that will be pain, and not pressure - the most sensitive regions: lips and fingertips - the most common measure of tactile discrimination (the ability to tell touches apart) is the two-point discriminationthreshold - two-point discrimination threshold: the minimum distance between two small points that can be detected asseparate stimuli when pressed against a particular region of the skin you touch someone with the legs of the caliper and ask if the sensation is coming from 1 or 2 points farther apart the legs to feel 2 sensations = lower the sensitivity of that region of skin Temperature - we can detect thermal stimuli from less than 8 degrees to more than 52 degrees (noxious cold – noxious heat) - there is no one single receptor that could detect the whole range of temperatures; we know of six mammalianthermoreceptors - one of the receptors that is sensitive to ranges of temperatures close to body temperature is found in the anteriorhypothalamus (responsible for measuring and maintaining our body temperature) - some of the thermal receptors respond to particular chemicals, as well as changes in temperature - ex. menthol, found in the leaves of the mint family, gives a cooling sensation it binds with and stimulates this thermal receptor and produces neural activity that the brain thinks of as cool - chemicals can also produce the sensation of heat Pain - like temperature reception, pain reception is accomplished by the networks of free nerve endings in the skin - there are at least 3 types of pain receptors (called nociceptors, detectors of noxious stimuli): high-threshold mechanoreceptors: respond to intense pressure (ex. something striking, stretching, pinching skin) respond to extremes of heat, to acids, to the presence of capsaicin (ingredient in chile peppers they found that mid with targeted mutation against this receptor showed less sensitivity to painful high-temperaturestimuli and would drink water to which capsaicin had been added a drug that blocks this type of receptor reduced the pain in patients with bone cancer (the pain is from acid) are sensitive to ATP (cell energy source, is released when the blood supply to a region of the body is disrupted, orwhen a muscle is damaged, released by rapidly growing tumours) these receptors are partly responsible for the pain made by angina, migraine, damage to muscles, some kinds of cancer - pain is involved with intense sensory stimulation, but it also has an emotional component - a given sensory input to the brain may be interpreted as pain in one situation and as pleasure in another ex. when people are sexually aroused, they are less sensitive to some kinds of pain and may find it pleasurable - suggestion: the physiological sensation of pain ≠ the emotional reaction to pain - opiates (like morphine) diminish the sensation of pain (it stimulates opioid receptors on neurons in the brain, thesesneurons block the transmission of pain information to the brain) take opiates = you feel no pain - some other tranquilizers (like Valium) depress neural systems that are responsible for the emotional reaction to pain, but don’t diminish the intensity of the sensation some tranquilizers = you feel the pain, but it doesn’t bother you - we do operations of prefrontal lobotomy to treat people who have chronic pain that we can’t fix in any other way prefrontal lobotomy is like tranquilizers: it blocks the emotional component of pain, not the primary sensation - there are 2 kinds of pain: an immediate sharp or bright pain, or a deep, full, throbbing pain - most noxious stimuli elicit the first one then the second one, other stimuli elicit only one of the two kinds (pinprick, blunt object hit a muscle) - phantom limb: sensations that appear to originate in a limb that has been amputated 70% of amputees say it feels like their limb still exists and that it often hurts pain, pressure, warmth, cold, wetness, itching, sweatiness, prickliness - suggestion: the phantom limb sensation is inherent in the organization of the parietal cortex (the part that has to dowith our awareness of our own bodies) - people with sensory neglect (lesions in the right parietal lobe) push their own legs off the bed, thinking it’s not theirs - some people who were born missing limbs still experience phantom limb sensations, which suggests that our brains were programmed to provide sensations for all 4 limbs, even when we don’t have them The Internal Senses - there are also sensory endings in our internal organs, bones and joints they can convey painful, neutral, pleasurable sensory information - ex. internal senses: pain of arthritis, perception of the location of our limbs, pleasure of a warm drink in our stomach - muscles contain special sensory endings - there is a class of receptors called joint receptors: found at the junction between muscles and the tendons that connect them to the bones give information about the amount of force the muscle is exerting this way, they protect us from making muscular contractions that are too forceful - weightlifters have a local anaesthetic injected near the tendons to eliminate this protective mechanism so they can liftheavier weights (but tendons or bones may snap) - there is another set of stretch detectors found throughout the muscle, it is made up of receptors called muscle spindles - muscle spindle: a muscle fibre that functions as a stretch receptor; arranged parallel to the muscle fibres responsiblefor contraction of the muscle, it detects muscle length - brain uses information from these receptors and from joint receptors to keep track of the location of parts of the body and to control muscular contractions The Vestibular Senses - having our sense of balance actually involves many senses - vestibular apparatus: the receptive organs of the inner ear that contribute to balance and perception of head movement it provides us with part of the sensory input that helps us remain upright - we have 3 semicircular canals: organs in the inner ear that respond to rotational movements of the head they are oriented at right angles to one another these canals contain a liquid rotation of the head makes the liquid flow, stimulating the receptor cells in the canals - we have another set of inner ear organs: vestibular sacs - vestibular sac: one of a set of two receptor organs in each inner ear that detect changes in the tilt of the head contains crystals of calcium carbonate embedded in a gelatin-like substance attached to receptive hair cells - in one sac: the receptive tissue is on the wall in the other sac: the receptive tissue is on the floor- - head tilts-> weight of CaCO3 shifts-> different forces on the cilia of the hair cells-> change in activity of the haircells-> information transmitted to the brain - this information from the vestibular sacs must be coordinated with information from the semicircular canals - rapid step forward and tilting your head back both shift the crystals in the same way, but in the latter situation, you don’t feel as if you’ve accelerated forward - semicircular canals helps us disambiguate the information from the vestibular sacs - vestibular sacs: very useful for maintaining an upright head position also participate in a reflex that enables us to see clearly even when the head is being jarred they stimulate reflex movements of the eyes to compensate for the head movements - the reflexive eye movements are linked to the specific vestibular information from the head if you have a problem with this reflex, you need to stop talking to see things clearly Week 9: Chapter 6: Perception pp. 166-193 - sense organs are there to provide information to guide behaviour, but it doesn’t do it by itself - ex. our vision: the brain receives information from approx 1 million axons in each of the optic nerves and it organizes everything into a perception of a scene- and even when our bodies or eyes move, so the photoreceptors are exposed to entirely new patterns of visual information, our perception of the scene stays the same, we see a stable world - ex. when we hear someone talking, we locate the person using the sensations of Chapter 5, but even when we move our head, change our position, it doesn’t change what we know about the speaker’s location - so even when sensation can change, perception could stay the same - perception: a rapid, automatic, unconscious process by which we recognize what is represented by the information provided by our sense organs the process of perception gives unity and coherence to the input it is not deliberate or effortful, we don’t have to puzzle out the meaning of what we see - it’s not that we see the object, then perceive it, we just perceive the object - once in awhile, what we see may require us to reflect on what it might be, or get more evidence to decide what it is,but this has to do more with problem solving than perception - if we look at a scene, we can describe some of the elements that are present - we don’t necessarily become aware of the elements first, then perceive the objects and the background - ex. when you see a tall, cylindrical object on a countertop, you immediately perceive: a glass you then perceive the smudges, the lettering, the beverage, etc. - note: our awareness of the process of visual perception comes only after it is complete - the line between sensation and perception is not too clear - for some sensory systems like pain and vestibular sense, the distinction is arbitrary since they help us to react rather than to provide a representation of the world around us - we will focus on visual perception Brain Mechanisms of Visual Perception - visual perception is often looked at as a hierarchy of information processing - circuits of neurons analyze particular aspects of visual information and send the results of the analysis to another circuit which performs even more analysis - more and more complex features are analyzed during the process - eventually, the process leads to perception of the scene and all the objects in it - the higher levels of perceptual process interact with memories: we can recognize familiar objects, and learn the appearance of new unfamiliar objects The Primary Visual Cortex - Hubel and Wiesel: inserted microelectrodes into various regions of the visual systems of cats and monkeys and looked at the APS produced by individual neurons - after inserting a microelectrode, they would present various stimuli on a screen in front of the open-eyed unconscious animal (neurons in the visual system still respond) - the stimulus was moved around on the screen and found the point where the neuron would be most affected they also presented stimuli of different shapes and saw which shape affected the neuron the most - conclusion: the geography of the visual field is retained in the primary visual cortex; the surface of the retina is mapped on the surface of the primary visual cortex the map is distorted, the largest amount of area is given to the centre of the visual field where our vision is most precise - the map is like a mosaic with many tiles, and each tile is called a module - module: a block of cortical tissue that receives information from the same group of receptor cells all the neurons within a module receive information from the same small region of the retina the primary visual cortex has about 2500 modules - each module receives information only from a small region of one retina, and so information from only a small region on the visual field (the scene projected on that part of the retina) - neural circuits within each module analyze their own particular part of the visual field, their receptive field - receptive field: that portion of the visual field in which the presentation of visual stimuli will produce an alternation in the firing rate of a particular neuron ex. some circuits detected the presence of lines passing through the field, and also signaled the orientation of these lines or the width or the movement or the direction of the movements or the colours - a certain cluster of neurons receives information from a small portion of the visual field - one of the neurons respond to lines oriented at 50 degrees to the vertical - other neurons in this cluster that share the same receptive field respond to lines of different orientations - conclusion: the orientation of lines that pass through this receptive field is signaled by an increased rate of firing particular neurons the cluster The Visual Association Cortex - an individual module of the primary visual cortex receives very little information - so for us to perceive objects and entire visual scenes, the information from all the individual modules must be combine, and this happens in the visual association cortex Two Streams of Visual Analysis -visual information analyzed by the primary visual cortex goes to be analyzed even further in the visual association cortex - we found more than 2 dozen distinct regions and sub-regions of the visual cortex of the rhesus monkey these regions are arranged hierarchically and it starts with the primary visual cortex - information is sent from one circuit of neurons to the next, where more and more complex features are analyzed - only a few milliseconds later, there is perception of the scene and the objects in it - so information goes from the primary visual cortex to the visual association cortex - the visual association cortex divides into two pathways: the ventral stream and the dorsal stream - ventral stream: the flow of information from the primary visual cortex to the visual association area in the lower temporal lobe; used to form the perception of an object’s shape, colour, and orientation (the “what” system) what is the object? What form does it have? What colour? - dorsal stream: the flow of information from the primary visual cortex to the visual association area in the parietal lobe; used to form the perception of an object’s location in 3D space (the “where” system) where is the object located? Is it moving? The Ventral Stream: Perception of Form - animals studies: The recognition of visual patterns and identification of particular objects takes place in the inferior temporal cortex, at the end of the ventral stream - this is where analyses of form and colour are put together and perception of 3D images emerge - functional-imaging studies and study of people with damage to the visual association cortex confirm these things - brain damage can cause a group of deficits called visual agnosia - visual agnosia: the inability of a person who is not blind to recognize the identity of an object visually; caused by damage to the visual association cortex agnosia = “failure to know” ex. you can’t identify common objects by sight even though they have normal vision when you hold the object, for ex., you could recognize it by touch - a common symptom of visual agnosia is prosopagnosis - prosopagnosia: a form of visual agnosia characterized by difficulty in the recognition of people’s faces; caused by damage to the visual association cortex they see eyes, noses and mouths, but can’t recognize the particular configuration that identifies a specific person’s face they still remember who they are, just can’t recognize them by just their face - face-recognizing circuits are found in the fusiform face area (FFA) fusiform face area (FFA): a region of the ventral stream of the visual system that contains face-recognizing circuits located at the base of the brain - much evidence: face-recognition circuits develop as a result of experience with seeing people’s faces ex. brain lesions that produce prosopagnosia can also impair the ability of a farmer to recognize his cows, or the ability of a driver to recognize their own car - so the failure of recognition is not confined to faces - experiment: bird or car experts viewed pictures of birds or cars and the FFA was activated the FFA was not activated when non-experts looked at the pictures - suggestion: the FFA can be actually called the flexible fusiform area, since it has to do with the visual recognition of diverse objects - people with autistic disorders can’t develop normal social relations and in severe cases, they give no indication that other people exist - they showed a deficit in the ability to recognize faces and looking at faces didn’t activate the FFA - it may be that other brain abnormalities associated with autistic disorder may result in a lack of interest in other people and therefore the failure to acquire face recognition during childhood - functional-imaging studies: there are several additional regions of the ventral stream that respond differently to particular categories of visual stimuli ex. the extrastriate body area (EBA) - extrastriate body area (EBA): a region of the occipital cortex, next to the primary visual cortex, that responds to forms resembling the human body activated by photographs, silhouettes, stick figures of human bodies or human body parts it is not activated by photographs or drawings of tools, scrambled silhouettes, scrambled stick drawings of bodies - the EBA can be temporarily inactivated by transcranial magnetic stimulation: when they did that, people lost the ability to recognize photographs of body parts, but not parts of faces or motorcycles - parahippocampal place area (PPA): a region of the ventral stream, below the hippocampus, that is activated by visual scenes activated by visual scenes (collections of several objects) and backgrounds - a woman had bilateral damage to the ventral stream so she had visual agnosia for objects - her PPA was still intact so she can still recognize both natural and human-made scenes like beaches, forests, deserts,markets, etc. she couldn’t recognize the specific objects that belonged to these scenes The Ventral Stream: Perception of Colour - individual neurons in a region of the ventral stream respond to particular colours so this region probably has to do with combining the information from the red/green and yellow/blue signals that originate in retinal ganglion cells - damage to this area in monkeys caused them to be unable to distinguish different colours, but they could still distinguish between shades of grey-> this must mean that the deficit was not caused by a more general impairment of visual perception - lesions of a particular part of the ventral stream in humans can also cause loss of colour vision without affecting visual acuity - some say that their vision is like a black and white film - cerebral achromatopsia: vision without colour, the inability to discriminate among different hues; caused by damage to the visual association cortex if the brain damage is only to one side of the brain, people will lose colour vision in only half the visual field if the damage is bilateral, they lose all colour vision: they can’t imagine colour and they can’t remember the colour of objects they knew before the damage - fMRI: they found a colour-sensitive region in the human ventral stream - lesions that cause achromatopsia must damage this region or other regions that provide input to it The Dorsal Stream: Perception of Spatial Location - the parietal lobe receives information: visual, auditory somatosensory, vestibular it is also involved in spatial and somatosensory perception - damage to the parietal lobe disrupts performance that require perceiving and remembering the location of objects controlling the movement of the eyes and the limbs - the end of the dorsal stream is in the posterior parietal lobe - studies with monkeys, fMRI with humans: neurons in the dorsal stream are involved in: visual attention and control of eye movements the visual control of reaching and pointing the visual control of grasping and other hand movements the perception of depth - primary function of the dorsal stream of the visual cortex: to guide actions rather than simple to perceive spatial locations this is suggesting tha
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