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PSY 280 L09.19

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University of Toronto St. George
Matthias Niemeier

PSY 280 – Perception M. Neimeier 09/19/12 Olfaction and Taste; Spatial Orientation and the Vestibular System **Midterm 1 = chapters 9-15 (Oct. 17) Q: Mention and describe 4 psychophysical methods. Describe one of them in more detail using an example - Method of limits >> staircase method; high level to low level of intensity, or vice versa (when do they detect it, when do they go numb, etc.) - Magnitude estimation >> headache, how painful in a scale of 1-10 - Method of constant stimuli >> repetition of different levels of stimuli (higher intensity usually means higher chance of detection) - Signal detection theory >> phone-in-the-shower situation - Cross modality detection Olfaction - “One of 2 chemical senses” – wrong! Chemical senses are very common in our body o E.g., hormones, neurotransmitters; sensors in blood vessels that tells us how much oxygen is in blood - Kant: smell is not an important function of the body - CEO of IKEA: smell is very important o Perfume of fresh wood (pleasant odor) = freshness, high quality ~ associated with a positive reaction - Attention: smell catches attention and leads to you associating it with ether a positive or negative idea - Language: very difficult to express smell in words - Odors = olfactory sensations o Chemical compounds that are volatile, small and hydrophobic  But not all … o Smaller compounds are easier to smell, e.g., menthol - The human olfactory apparatus: o Nose: small ridges, olfactory cleft, olfactory epithelium st o Secondary purpose of the nose (1 is breathing) o Sniffing makes the nose more sensitive to smells – better detection o Autonomic system controls the alternate flaring of the nostrils for maximum olfaction (nasal cycle) --- air flow matters o Olfactory bulb is the “toothbrush” thing at the top of the olfactory epithelium o Olfactory epithelium is the “retina” of the nose  3 cells – supporting, basal and olfactory sensory neurons (OSNs)  OSNs have cilia protruding into the mucous covering the olfactory epithelium  Basal cells are precursors to OSNs o Olfactory receptors (ORs) interact with odorants  action potential along the olfactory nerve  Olfactory nerve is the cranial nerve I – thin axons, slow • Enters the skull through cribriform plate o Lesions caused by head trauma (that affects the cribriform plate) and/or infections to the olfactory nerve can cause anosmia – permanent loss of smell  Causes great suffering – loss/diminished sense of taste / flavour; diminished danger warning system  Anosmia quite a common early symptom of Alzheimer’s and Parkinson’s o Olfactory bulb – ipsilateral projection o Glomeruli – spherical structures in which OSNs synapse with mitral cells and tufted cells o Chemo-topography – glomeruli sort according to ORs o Olfactory cortex o Amgydala-hippocampal complex o Entorhinal cortex - The genetic basis of olfactory receptors o ~1000 different olfactory receptor genes, each codes for single type of OR o Pseudogenes – dormant, don’t produce proteins (i.e., ORs), 20% in dogs, 60-70% in humans o Trade-off between vision and olfaction? - Multisensory perception – a feel of scent o Odorants can stimulate the somatosensory system (touch, pain, temperature receptors) o These sensations are mediated by the trigeminal nerve (cranial nerve V) o Also see taste! - Shape pattern theory o Match between shapes of odorants and odor receptors (key and lock)  Dominant biochemical theory o Recent molecular research – scents are detected by means of combinatorial codes o ORs can be maximized – detect more odorants - Importance of patters: o We detect a multitude of scents based on ‘only ‘ 300-400 olfactory receptors – how? o We can detect the pattern of activity across various receptor types o Similar to metameres in colour vision – phenyl ethyl alcohol = rose  Any two types of stimuli that result in the same pattern - Odor mixtures o We rarely smell “pure odorants” – rather we smell mixtures o How do we process the components in a mixture of odorants  Analysis – e.g., audition: hi/low pitched tones  Synthesis – e.g., metameres in colour vision o Olfaction rather synthetic but can be trained - Olfactory Psychophysics o Differences between detection, discrimination and recognition  Detection of the presence of odors and recognize the components from memory - Olfactory detection thresholds – depends on several factors, e.g., length of carbon chains (vanilla!) o Women – lower thresholds than men, depending on menstrual cycles but not pregnancy - Professionals can distinguish up to 100 000 odors (e.g., professional perfumers, wine tasters) - Recognition is smell and memory o Durability – our recognition of smalls is durable even after several days, months or years - Identification – smell and language o Attaching verbal label to smell is not easy – few words for smell o “Tip of the nose” phenomenon o Disconnect between language and smell (left VS. right brain) o Patrick Süskind – the Perfume (book / movie) - Adaptation o Sense of smell is essentially a change detector  E.g., walking into a bakery o Odors bind to G protein-coupled receptors that indirectly open the Na + channels o Receptor adaptation – continuous stimulation; GCPRs bury themselves inside cells  Intermittent stimulation – e.g., wood smell at IKEA o Cross adaptation – reduces detection of odor after exposure to odors that stimulate the same ORs - Cognitive (and other kinds of) habituation – after long-term exposure to an odorant, one has very diminished detection ability o After returning from vacation, the house has a smell o Long-term (not necessarily cognitive) mechanisms  Longer term receptor adaptation  Odorant molecules may be absorbed into bloodstream causing adaptation to continue  Cognitive-emotional factors  **Odors believed to be harmful won’t adapt - Odor Hedonics o The liking dimension of odor perception  Typically measured with scales pertaining to an odorant’s perceived pleasantness, familiarity and intensity o We tend to like odors we’ve smelled many times before (nurture!) o Influence of intensity o They either start off “neutral,” peak into “pleasant,” then slope off to “unpleasant” as intensity increases OR they start off as “neutral” and descends to “unpleasant” as intensity increases (based on Intensity VS Pleasantness graph) Taste - Anatomy o Taste buds  Create neural signals conveyed to the brain by taste nerves  Embedded in structures called papillae (i.e., bumps on the tongue)  Each taste bud contains taste receptor cells  Information is sent to brain via cranial nerves o 4 forms of papillae  Filiform – anterior portion of the tongue, without any taste function  Fun
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