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Psy280: Perception

Psy280: Perception. Prof. Anderson Department of Psychology Chemical senses. Chemical senses: Your are what you eat (smell). What’s it good for? Chemical composition of our surroundings Olfaction (i.e., smell) Distal/remote sensing Small concentrations of airborne substances

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Psy280: Perception

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  1. Psy280: Perception Prof. Anderson Department of Psychology Chemical senses

  2. Chemical senses: Your are what you eat (smell) • What’s it good for? • Chemical composition of our surroundings • Olfaction (i.e., smell) • Distal/remote sensing • Small concentrations of airborne substances • Gustation (i.e., taste) • Proximal/immediate sensing • Check if appropriate to enter your body • Last sense to use • If it looks like and it smells like, it probably is it

  3. Comparative taste • Not all organisms “taste” with a tongue Moth antennae Fly “feet”

  4. In good and bad taste • Useful for the body • Tend to taste good • Potentially harmful • Tend to taste bad • Tend to taste bitter • Not always the case: Influence of culture • The burn of capsaicin • Bitterness • Compare with vision • All dangerous things ugly? • All ugly things dangerous?

  5. Taste in infancy Neonatal “liking” responses Sweet • Lip smacking • Smiles Bitter • Grimace • Lip retraction • Nose wrinkle

  6. Anatomy of taste: Papillae • Filiform • Cone shaped • All over the tongue • Give rough appearance • Fungiform • Mushroom shaped • Tip & sides • Foliate • Folds at sides • Circumvallate • Flat mounds • At back • Other taste receptors • Palate • Larynx

  7. Anatomy of taste: The bud • All papillae contain taste buds except the filiform • Thus, centre of tongue is “taste-blind” • Taste buds • Multiple taste cells • Create taste pore

  8. Taste sensory transduction • Different taste cell types for different tastes • Specificity at receptor level • Salt • NaCl • Na+ entry into cell • Depolarization • Sour • H+ ions block channels

  9. Taste pathway • Electrical signals carried by 3 pathways • Chorda tympani • Front & side • Glosso-pharyngeal • Back • Vagus • Mouth & larynx • NST (brainstem) • Gustatory thalamus • Primary taste areas • Insular/opercular cortex • Secondary taste areas • Orbitofrontal cortex

  10. Insular cortex and disgust • Disgust = “bad taste” • Anterior insular cortex is primary taste area • Viewing disgust faces increase activation • Lesions impair recognition of disgust Disgust vs fear

  11. Taste experience • What tastes do we taste? • 4 (maybe 5) basic tastes • Sweet (Sucrose), bitter (quinine), sour (HCl), salty (NaCl) • And … umami (MSG) • All taste experience can be described in terms of their combinations • Some substances are primarily 1 taste • Sodium chloride: Salty • Quinine: Bitter • Some are combinations • Sodium nitrate: salty, sour, & bitter

  12. Neural code for taste: Specificity • Different taste receptors carry different dimensions of taste? • Salt receptors related to saltiness? • Block receptors (amiloride)—> impair salt perception • Leaves other sensations intact • Parallel between receptor morphology and taste • E.g., circumvallate (back) = bitter? • Foliate (side) =sour?

  13. Neural code for taste: Specificity • 4 different types of fibers in chorda tympani • Activation of specific fiber tracts responsible for taste sensations • E.g. “sweet”, “bitter” neurons

  14. Problem with taste specificity coding • Taste neurons response are a combination of quality (e.g. bitter) and intensity • E.g., same magnitude of response in “bitter” neuron • A high concentration of sucrose • low concentration of quinine • Similar to colour vision • Neurons response a result of wavelength and intensity • Need 2 or more receptors to resolve ambiguity

  15. Neural code for taste: Distributed coding • Across fiber patterns • Emphasize degree of overlap between fibers • Idea: More overlap—> greater taste similarity • Relative to ammonium chloride (NH4Cl) • NaCl more distinct than KCl • Correlation between taste and across fiber pattern

  16. Tastes differ • Taste is dynamic • Depends upon internal state: Hunger • Adaptation/Sensory-specific satiety (SSS) • Peripheral • Chewing, smelling induces SSS • Sweet desserts follow savory meals • Alliesthesia • Central • Changed pleasantness that is not sensory based • Decreased pleasantness of sucrose when tubed into stomach • Animals change diet based on nutritional needs • Individual differences • Experience: culture • Genetics: tasters and nontasters • saccharin (bitter or tasteless)

  17. Flavor = Taste+smell • Eating chocolate with a stuffed nose • Where’s the flavor? • Taste Identification is impaired without smell • What we call taste is really an interaction between our chemical senses • Locate taste as occurring in the mouth • Taste nerves carry somatosensory/texture info as well Like visual capture

  18. Distal chemical sensing: Olfaction • For many mammals it is the most important sense • Identification • Smell “face” • localization • We are vision/hearing dominate mammals • Under-appreciate/under-use our sense of smell

  19. Olfactory epithelium • Olfactory mucosa • Mucus! • High in nasal cavity • Site of transduction • Contains olfactory receptor neurons (ORN)

  20. Nose hair: Olfactory cilia • ORN have cilia • Cilia contain olfactory receptor proteins • Similar to visual pigment • Transduction • Odorants bind to ORs • Change shape of protein • Ion flow across OR • Electricity

  21. Smell blind • Olfactory nerve passes through cribriform plate (skull) to reach OB

  22. Smell antennae: Olfactory bulbs • An outcropping of the brain • Its like a snail in your brain! • Electrical responses in cilia passed through olfactory nerve to OB Chemotaxis

  23. How many receptor types are there? • 1000 different kinds of olfactory receptors (OR) • 10 million OR neurons • 10,000 of each type of OR • Each OR neuron has only one type of receptor • 1000 neuronal chemical detectors • Compare to visions 4 receptor types (3 cones, 1 rod)

  24. Mapping onto the bulb • Similar ORN axons go to similar portions of the bulb • Glomeruli (1000-2000) • Inputs mainly from 1 ORN • Thus, each glomerulus responds to similar compounds • Like orientation columns in visual cortex • Glomeruli coding • Similar structure, not smell • Odotope maps • Mapping of similar chemical features

  25. Distributed coding of smell • Olfactory code is a complex pattern • Overlap across 1000 ORN types represents smell quality • Number of receptors would suggest specificity coding • Millions of colours can be perceived with 3 cones • How many odors?

  26. Experience and identification of odors • Can tell the difference between 10,000 odors • Distributed coding suggests much greater number • Poor at identification • Vision dominates • Get better with experience

  27. Of mice and men • Rats up to 50 times more sensitive to odors than humans • Dogs can be 10,000 times more sensitive • Yet olfactory receptors equally sensitive • 1 molecule can stimulate an olfactory receptor • Can’t get more sensitive than that! • Many more receptors (1 billion compared to 10 million) • Decreases # of molecules needed for neural response • Expertise • Wine tasters don’t get more sensitive w/ their nose • Better at retrieving labels from memory

  28. Rebuilding your neural nose: Olfactory neurogenesis • Mucosa is exposed • Not safely protected like photoreceptors or auditory cilia • Unlike vision/audition receptors regenerate • Every 5-7 weeks • Axons have to find way to bulb • Create new synapses • Constant rebuilding olfactory system

  29. What special about neural transmission in olfaction? • Unlike other senses, short distance to brain • Vision/audition have many synapses between retina and brain • Central destinations of olfactory information from bulb • Primary olfactory cortex (piriform cortex) • Secondary olfactory cortex (orbitofrontal cortex) • Amygdala • Unlike other senses, no mandatory thalamic relay

  30. What’s the neural code for smell? • How does the brain know what of hundreds of chemicals are entering the nose? • Don’t really know • Odor quality • Related to physical/chemical properties? • e.g., structure of molecule • Odotopes in olfactory bulb (OB) • Similarly structured molecules smell the same? • Not necessarily • Differently structured molecules smell different? • Not necessarily • Thus, not easy to relate smell with physicochemical properties of stimulus or OB maps

  31. The hedonic primacy of olfaction • Sensory and emotional experience • Not the same for vision/audition • Seeing and feeling more distinct • More intertwined in the chemical senses • Why? • Orbitofrontal cortex • Plays dual role • Critical for emotional experience • Secondary sensory cortex for olfaction

  32. What makes a bad smell smell bad? • Amygdala/piriform = intensity • Medial OFC = good • Lateral OFC = bad

  33. The smell of attraction • Attraction and symmetry • Symmetry associated with • immune system health, healthy development • Pleasant odor

  34. Does the world smell different to each nostril? • Nostrils are different sizes • Alternate every few hours which is bigger! • Airflow in each nostril differs • Odorants attachment to mucosa depends on airflow • Some better at low vs high and vice versa • Provides two olfactory images of the world • Result: better olfactory acuity

  35. Smell constancy:Little and big sniffs • Intensity and concentration constancy • Do big sniffs make for more intense smells? No • Sniff activity in piriform cortex Magnitude estimation for odor strength equal

  36. Olfactory subliminal perception: Pheromones • Odorless airborne chemicals can powerfully influence behavior • Sexual behaviour • Mood • Menstrual synchronization • Bruce effect: Aborted fetus • Accessory olfactory system • Vomeronasal organ (VNO) • Not sure if functional in humans • Like extrageniculostriate visual pathway • Nonconscious vision

  37. ESP

  38. Extrasensory perception: ESP • The feeling of presences, being, or energy without use of the 5 basic senses • The problem with ESP is that it is “extrasensory” • Sensory systems are the receivers of environmental stimulation • Without a receiver there is no perception • Tree falls in a forest • Subliminal is sensory (e.g., visual, olfactory, auditory), but nonconscious • Below subjective threshold for perception • Brain can discriminate thingsto which we don’t have conscious access • E.g., amygdala and “unseen” fear

  39. Why is it possible? • What have we learned? • All about conscious perception • Guides our own investigations • Colour, motion, depth, pitch, smell, taste, etc. • Bias in what “phenomena” we investigate • ESP might represent sensory systems that are functional but unknown • Don’t represent conscious information processing • E.g. discovery of new photoreceptor that regulates circadian rhythms • Electromagnetic waves outside the visual spectrum

  40. trees... buildings... clouds... sender receiver attempts to ‘psychically’ send target to receiver reports imagery Experiments on ESP: Ganzfeld research Target randomly chosen • All “sensory” information reduced • Receiver in sound proof chamber with ping pong balls on eyes, earphones w/ white noise • Reduce external sensory “noise” to enhance sensitivity to weak signal • Progressive relaxation: Decrease internal somatic noise

  41. At end of session… • Receiver shown 4 pictures (3 decoys plus target) • Must rate each picture in terms of matching imagery • 25% chance of rating target picture highest Experiments on ESP: Ganzfeld research

  42. Results • 1974-1997 • 50+ studies from 15 different labs • Hit rate = 33.2%, significantly different from chance (25%) • Dynamic targets better than static (37% vs 27%) • Higher rates when a friend versus stranger is the sender (44% vs 26%) • 50% hit rate for “artistic” students (n=20) • Julliard students

  43. Problems • Experimenter needs to be blind to target • Sensory “leakage” • Sensory cues from use of same target • The file drawer problem • How many studies not showing effect unreported? • What are the limits of this perception? • Send over telephone wire? • Reading other minds • Would be difficult to home in on one signal • Potentially insulting too!

  44. Magnetoreception • Diverse animals can use the earth’s magnetic field as orientation cue • North/south axis, and local magnetic fields • Magnetic map sense • Like having an internal GPS • Homing pigeons, spiny lobsters • Placed in novel location • Don’t monitor outward journey • Can navigate back • Know very little about the physiological mechanisms • No obvious receptors • Accessory structures usual focus sensory stimuli on sensory surface • Lenses: vision • Outer ear: audition • Biomaterials don’t affect magnetic field lines

  45. THE END

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