The Senses
Jul 24, 2015
Special senses
• Smell• Taste• Sight• Hearing• “Touch” = temperature + pressure + pain
of skin, muscles, & joints• Equilibrium (in the ear)
Sensory Receptors• Large complex organs (eyes, ears)• Localized clusters of receptors (taste buds,
olfactory epithelium)
Bezold effect
The smaller squares inside the blue and yellow squares are all the same color.
They seem different (magenta and orange) because a color is perceived differently depending on its relation to adjacent colors (here blue or yellow depending on the outer square).
Café Wall Illusion
The horizontal lines are straight, even though they do not seem straight. In this illusion, the vertical zigzag patterns disrupt our horizontal perception.
Some neurons in the brain seem specialized in processing faces. Faces are usually seen upright. When presented upside down, the brain no longer recognizes a picture of a face as a face but rather as an object. Neurons processing objects are different from those processing faces and not as specialized. As a consequence these neurons do not respond to face distortions as well. This explains why we miss the weird eyes when the face is inverted.
Illusory ContourThe baby’s head is on the left, the baby’s feet are
against the trunk of the tree on the right.Illusory Contour: a form of visual illusion where
contours are perceived without a luminance or color change across the contour
Aging
• After age 50, ability to smell and taste decrease• Membranes lining nose become thinner & drier olfactory nerve deteriorate• # taste buds decrease with age more difficult
to detect sweet/salty foods taste more bitter• As people age, their food tastes more bland
eat less possible malnutrition
PTC = phenylthiocarbamide
• Discovered in 1931 by when a DuPont chemist named Arthur Fox accidentally released a cloud of fine crystalline PTC in the lab.• A nearby colleague complained of the bitter
taste, while Dr. Fox tasted nothing.• Fox continued to test the taste buds of family
and friends, setting the groundwork for future genetic studies.
Genetics of PTC Tasting
• Gene for tasting PTC (Tas2r38) is located on Chromosome 7.• PAV = taster (T), AVI = nontaster (t),
AAV = another allele• PAV-PAV = TT = very bitter• PAV-AVI = Tt = somewhat bitter• AVI-AVI = tt = nontaster
• General Population: 70% Tasters, 30% Nontasters
TAS2R38
Bitter tastes = Result of selection pressures?• Thiocynate Compounds (bitter taste) found in
broccoli, cauliflower, mustard family• Tasters: avoid these foods in diet• Nontasters: more varied diet, include green
leafy veggies• Thiocynates might inhibit thyroid function
tasters may have protection against thyroid diseases
Bitter tastes = Result of selection pressures?
• Poisons = bitter taste• Tasters: part of hunter-gatherer societies?
• Genetic Drift• Europeans: all 3 alleles (PAV, AVI, AAV)• Asians: AAV allele rare• Native Americans: 98% have PAV allele only
Denver Museum of Nature and Science• Expedition Health: Genetics of Taste Study• Purpose of Study:• Is ability to taste bitter compounds related to
what foods you eat, your % body fat, and BMI?• Is your ability to taste bitter compounds
related to your genetic ancestry?
Substances related to PTC
• Thiourea (thiocarbamide) – very bitter!!!• Sodium benzoate – sweet, salty, bitter, no taste• Food preservative