The Senses

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)

Vision Tests

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

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).

Are the horizontal lines straight or crooked?

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.

Does Lincoln’s face look normal?

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.

Can you see a baby?

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

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

Taste Tests

Jellybean Test

Flavor = taste + smell

5 Types of Taste Receptors

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

Genetics of Taste

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

Family Pedigree• Tasters:• Supertasters (TT)• Tasters (Tt)

• Non-tasters (tt)