Lecture 28 - Taste and Flavor Perception

Question 1

Five basic taste qualities:

Answer 1

detection of molecules in liquids and solids

– Salty
– Sour (how much acid is present - lemons)
– Sweet
– Bitter (poison detector)
– Umami (meety, brothy, savory: cheese)

all have a diff receptor that responds to these elements in the environment

Question 2

Fat

Answer 2

is not currently recognized as a basic taste, but it may have it’s own dedicated receptors.

6th hypothesized taste

no single receptor that responds to it

fat in oils or animal products has its own sensation

Question 3

basic tastes are like the basic colors

Answer 3

Using magnitude estimation, most taste experiences can be described as comprised of
the five elements.

example: things can be salty and sweet and bitter

Question 4

These taste qualities are associated

with

Answer 4

stimulation of different detectors on

the tongue.

Question 5

There are four types of tongue papillae

(surface projections):

Answer 5

NOT taste buds!!!

within these are the taste buds

Question 6

filiform

Answer 6

only ones located in the center of the tongue

• shaped like cones and located over entire surface

Question 7

fungiform

Answer 7

if you get sick they swell up

• shaped like mushrooms and found on sides and tip

have 3-5 taste buds each

Question 8

foliate

Answer 8

• series of folds on back and sides

have more than 100 taste buds

Question 9

circumvallate

Answer 9

• shaped like flat mounds in a trench located at back

have more than 100 taste buds

Question 10

The tongue contains approximately

Answer 10

10,000 taste buds.

distribution is not equal

Question 11

Taste buds are located in all

papillae except

Answer 11

for filiform.

Question 12

taste buds composed of

Answer 12

taste cells (close together but not one unit - like bananas)

Question 13

Only filiform papillae are located

in

Answer 13

the center, so we don’t have

direct taste sensations there.

Question 14

taste pore

Answer 14

where the molecules of food or liquid are making contact

Question 15

transduction takes places

Answer 15

when the molecule comes in and makes contact with the tips of the receptor sites

Question 16

Each taste bud has a variety of

Answer 16

taste cells and receptor types.

Question 17

The taste bud is composed of

Answer 17

50-100 taste cells with tips that

extend into the TASTE PORE

Question 18

Transduction occurs when

Answer 18

chemicals contact the receptor sites on the tips (gustatory hairs).

Question 19

sites on the tips of receptors where chemicals have contact

Answer 19

gustatory hairs

Question 20

there are numerous receptors types

Answer 20

for different tastes

e.g. there are more than 20 ‘bitter’ receptor
types

Question 21

Taste sensitivity may vary

according to the number of

Answer 21

fungiform papillae on the tongue

Question 22

experiment measuring sensitivity

Answer 22

– Blue food coloring is placed on the
tongue.

– Papillae will not take up the dye and will stand out as pink.

– Count the papillae within a specified region to get density.

– You can distinguish three groups of people: nontasters, tasters, and supertasters.

IDEA: nontasters: have very few papillae and if you have a lot (high density) you’re a SuperTaster

Question 23

A recent (2014) crowdsourced
study of papillae density suggests
that the differences are not due to
the number of taste buds.

Answer 23

– Visitors to a museum (n>3,000) volunteered to have their papillae counted.

– Additionally, they tested their sensitivity to bitter chemicals (e.g. PTC).

– Finally, they had genetic testing for a taste receptor gene (TAS2R38) believed to play a part in bitterness detection.

– Variations in the receptor gene were more predictive of supertasters than density!

suggests that density theory is all wrong

Question 24

Behaviorally, there are different individual responses to the
bitter taste of phenylthiocarbamide (PTC) and to 6-npropylthiouracil
(PROP):

Answer 24

– Normal Tasters have specialized receptors for PTC and PROP and detect their presence.

– Nontasters lack these receptors, have fewer taste buds (?), and do not detect PTC.

– Supertasters are especially sensitive to PROP (and PTC) and respond to bitter substances much more strongly than tasters.

Question 25

Signals from taste cells travel along a number of pathways

Answer 25

– Chorda tympani nerve from front and sides of tongue
– Glossopharyngeal nerve from back of tongue
– Vagus nerve from mouth and throat
– Superficial petronasal nerve from soft palate

four separable pathways from the tongue

Question 26

Chorda tympani nerve

Answer 26

from front and sides of tongue

front of the tongue = best access to

Question 27

Taste pathways that the taste signal travels down

Answer 27

make connections in the nucleus of the solitary tract in the spinal cord.

• Signals then travels up to the thalamus (just like everything else except for odor)

• From there the signals go to cortical
areas:
– Insula (primary area): heavily involved in disgust responses = SPIT IT OUT
– Frontal operculum cortex (primary)
– Orbitofrontal cortex (secondary): one of the earliest areas that odor goes to: quality, qualitative element of some odor

Question 28

structure

Answer 28

receptors in cells in taste bud in papillai

Question 29

Flavor

Answer 29

isn’t as nearly determined by taste

qualitative element has more to do with odor than the taste

is a complex construction: multi-model: associations with other things

is the subjective experience associated with ingesting food or drink.

– Combination of smell, taste, touch
and other sensations (such as
‘burning’ of hot peppers and alcohol –
nociceptors).

– Odor stimuli from food in the mouth
reaches the olfactory mucosa through
the retronasal route.

Question 30

Getting to know your coffee

Answer 30

– “The beans are hand-picked at the
peak of harvest, fully washed then
sun-dried on patios. The result is a
sweet aroma, smooth texture;
notes of almond, milk chocolate
and cherry with a lingering finish.”

– Scales of ‘body” (medium to very
full) and ‘liveliness’ (smooth to bright) provide some measures for comparison.

– Note how tastes, smells, and textures are mixed together.

Question 31

why is odor so important for flavor?

Answer 31

Odor stimuli from food in the mouth
reaches the olfactory mucosa through
the retronasal route.

air travels through the back of the throat and the molecules in gaseous form can go up to the olfactory mucosa

odor associated with what’s happening on the tongue

Question 32

If flavor has a strong olfactory component, why do we experience it in our mouths?

Answer 32

• Flavor begins with spatial information: things are mapped on the tongue have a large representation in the cortex (it’s very sensitive)

• Tactile receptors in the mouth localize other
sensory components to place flavor in the oral
cavity.

• This is known as the oral capture illusion.

you’re smelling something but you think it’s coming from the tongue because the tongue is very sensitive and has good sensory info whereas the nose does not

Question 33

Taste tests with the nose open and closed reveal that most

flavors are strongly affected by olfaction.

Answer 33

A few, such as MSG are not (umami taste).

meaty or brothy occurs whether the nose is closed or not

Question 34

How is flavor constructed?

Answer 34

Responses from taste and smell
are first combined in the
orbitofrontal cortex (OFC).

Question 35

OFC

orbitofrontal cortex

Answer 35

also receives input from the primary somatosensory cortex and the inferotemporal cortex in the visual what pathway.

– Bimodal neurons in OFC respond to taste and smell, as well as taste and vision.

– Firing of these neurons is also affected by the level of hunger of the animal for a specific food
(firing increases with how hungry you are).

this whole experience of flavor is being rated by OFC

convergence! all these diff associations activity the flavor representation

Question 36

Common themes

Answer 36

perception is an active process: not just receiving info and it’s continually happening

perception is studied at multiple levels: Marr’s levels as a scaffolding

perception is a hard problem: how do we filter and make sense and transduce and make sense of all this sensory information and faithfully represent what’s going on

Perception is a hard problem, with lots of sources of stimulus ambiguity or signal variation.

• Transduction uses different mechanisms, but we seem to use similar transmission and processing strategies (e.g. hierarchical processing).
• Perception is shaped and altered through experience dependent plasticity.

• We segregate information during initial processing, but combine it for identification and action (e.g. from streams of
processing to multisensory interaction to categorization).

Question 37

computational level

Answer 37

What problems does the system solve? How is the

output related to the input?

Question 38

algorithmic level

Answer 38

How does it solve these problems? What steps does

it take? What representations does it use?

Question 39

implementational level

Answer 39

How is this instantiated in the brain or system?

most concrete

Question 40

perception can be manipulated

Answer 40

heuristics: quick and dirty solutions to make estimates about what we’re dealing with

so senses can be tricked

This can be done within a sense or between senses.

Question 41

perception is affected by knowledge

Answer 41

Studying perception has changed your brain. This also means you have changed your perceptual abilities.

Question 42

perception is fading…

Answer 42

Presbycusis

Changes in touch and pain sensitivity

Presbyosmia