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1. The Senses

2. Special senses
• Smell
• Taste
• Sight
• Hearing
• “Touch” = temperature + pressure + pain
of skin, muscles, & joints
• Equilibrium (in the ear)

3. Sensory Receptors
• Large complex organs (eyes, ears)
• Localized clusters of receptors (taste buds,
olfactory epithelium)

4. Vision Tests

5. Are the squares inside the blue and
yellow squares all the same color?

6. 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).

7. Are the horizontal lines straight or
crooked?

8. 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.

9. Does Lincoln’s face look
normal?

10. 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.

11. Can you see a baby?

12. Illusory Contour
The 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

13. How quickly can you say the
color of the words below?

15. Taste Tests

16. Jellybean Test

18. Flavor = taste + smell

19. 5 Types of Taste Receptors

20. 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

21. Genetics of Taste

22. 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.

23. 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

24. 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

25. 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

26. 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?

27. Substances related to PTC
• Thiourea (thiocarbamide) – very bitter!!!
• Sodium benzoate – sweet, salty, bitter, no taste
• Food preservative

28. Family Pedigree
• Tasters:
• Supertasters (TT)
• Tasters (Tt)
• Non-tasters (tt)