Lecture 26 - The Chemical Senses

Question 1

The chemical senses are construed as “gatekeepers” of the body which:

Answer 1

• Identify things that should be consumed for survival.
• Detect things that would be harmful and should be avoided.
• Cause immediate affective responses to encourage and remember the correct responses.

Question 2

Why do we value the sense of smell?

studies?

Answer 2

Smells have strong emotional content

• Smells (and tastes) can evoke particularly vivid memories.
• People rate personal memories triggered by smells as more emotional when compared to memories triggered by visual images (Herz & Schooler, 2002).
• We also tend to remember more info about an autobiographical event when cued by odor, compared to visual cues (Chu & Downes, 2002).

• However, people are relatively poor at
identifying particular odor objects without context.

Question 3

Proust effect

Answer 3

impacts on memory of smell

We also tend to remember more
information about an autobiographical
event when cued by odor, compared to
visual cues

People rate personal memories
triggered by smells as more emotional
when compared to memories triggered
by visual images

we react stronger and have more vivid memories associated with an odor

Question 4

odor objects

Answer 4

sources of an odor

Question 5

what’s special about chemical senses?

Answer 5

not as though the object leaves an impression but the object actually interacts with your body

smell: some of the molecules ARE INSIDE YOU

Question 6

why are chemical senses “gatekeepers” ?

Answer 6

strong protective role

identify things that could and/or should be consumed

things you want to avoid (tasting bitter, smelling other animals)

smell and taste have immediate affective responsive = encode really deeply so you only have to experience it that once

Question 7

Functions of olfaction

What does olfaction do for us?

Answer 7

• Detect molecules entering the nose in
gaseous form (distal stimulus).

• Many animals are macrosmatic -
• Humans are microsmatic –

Question 8

smell has what kind of learning?

Answer 8

single trial learning = you only need to be exposed to it once

Question 9

even tho smells are so good at producing strong memories, we’re really bad at detecting….

Answer 9

…odor objects

in a crowded room we could smell something, but it would be difficult to figure out what it is

Question 10

macrosmatic

Answer 10

dogs, bears, cats, carnivores

having a keen sense of smell that is
necessary for survival

• Localize other animals/food, find mates,
detect threats, etc.

• Some animals may have a
vomeronasal organ (mainly) used in
detection of pheromones.

Question 11

vomeronasal organ

Answer 11

(mainly) used in detection of pheromones.

This is a part of an accessory olfactory system.

Question 12

microsmatic

Answer 12

humans!

having a less keen sense of smell that seems
less crucial to survival.

− However, olfaction still plays an
important role in many behaviors.

Question 13

What does olfaction do for us?

Not all effects from chemical odors are consciously perceived

Experiment by Stern and McClintock (1998)

Answer 13

– Original work done in 1971 by Martha McClintock.

– Underarm secretions were collected from nine donor women.

– These were applied to the upper lips of recipient women.

Results suggested that menstrual synchrony occurred, shortening the cycles
of some and lengthening the cycles of other recipients: the recipient’s cycles matched the donor’s

• Pheromones in the secretions, even though the women did not report smelling them, may have led to the biological changes. This is known as the McClintock effect.

Question 14

the McClintock effect

Answer 14

menstrual synchrony

an undetected pheromone could have a strong behavioral response

The mechanism and underlying hypothesis are still unclear.

Question 15

Odors have a number of effects on human behavior, some of which
are not always conscious. Most of the studies looking for human
pheromones have focused on the hypothetical role in reproduction.

Answer 15

• Babies prefer odors from their own lactating mothers at birth (they can detect a difference!), and this may help initiate nursing (Porter & Winberg, 1999).
- in utero the baby is constantly taking in amniotic fluid = creates this olfactory connection

• Women tend to prefer the scent of men who have greater body bilateral symmetry. This effect is greatest when nearing ovulation (Thornhill & Gangestad, 1999).
- possibly b/c male is free of genetic injury, malnutrition, disease = evolutionarily important cue

• Both men and women prefer the odors of potential mates who have major histocompatibility complex (HMC) patterns unlike their own (they have different immune systems!!). This indicates that offspring may have healthier immune systems = prevents you from doing your cousin
(Wedekind and Furi, 1997).

Question 16

How do we measure the detection threshold?

Answer 16

yes/no procedure

forced-choice

Question 17

Yes/no procedure

Answer 17

participants are given trials with odors (with
different concentrations) along with “blank” trials.

• Usually with method of constant stimuli.
• do you smell anything?
• PROBLEM: not super reliable: This can result in bias in terms of how the participant decides to respond by default (i.e. always say ‘yes’ or always say ‘no’).

Question 18

forced-choice

Answer 18

better than yes/no because it avoids bias

• which one of the two smells stronger?

two trials are given, one with odorant and one
without.

• Participant indicates which smells strongest.
• Some trials compare weak vs. no odorant. Correct performance on 75% of such trials is set as threshold.
• This is more accurate and eliminates some response bias.

Question 19

How sensitive are we?

Answer 19

• Detection varies by source molecule (the odorant) – some require larger concentrations to be detected: more sensitive to certain chemicals and less sensitive to others
• e.g. Methanol requires 141,000 ppb; T-butyl mercaptan requires just 0.3 ppb (added to natural gas).
• Rats are 8 to 50 times more sensitive to odors than humans.
• Dogs are 300 to 10,000 times more sensitive.
• However, individual receptors for all of these animals are equally sensitive - each receptor detects a molecule .
• The difference lies in the number of receptors they each have.

Question 20

Babies prefer odors from

Answer 20

their own lactating mothers at birth (they can detect a difference!), and this may help initiate nursing (Porter & Winberg, 1999).

- in utero the baby is constantly taking in amniotic fluid = creates this olfactory connection

Question 21

Women tend to prefer the scent of men who

Answer 21

have greater body bilateral symmetry. This effect is greatest when nearing ovulation (Thornhill & Gangestad, 1999).
- possibly b/c male is free of genetic injury, malnutrition, disease = evolutionarily important cue

Question 22

Both men and women prefer the odors of potential mates who have

Answer 22

major histocompatibility complex (HMC) patterns unlike their own (they have different immune systems!!). This indicates that offspring may have healthier immune systems = prevents you from doing your cousin
(Wedekind and Furi, 1997).

Question 23

Can we localize odor sources?

Porter et al. (2007)

Answer 23

asked whether humans could be trained to
localize scents as other animals (e.g. dogs) do (can odor be made more important?).

They were also interested in whether we use information differences from each nostril.

– Georg von Bekesy originally suggested this in 1964.

built an odor prism, and have volunteers where things in their nose that either kept the odor stream separate or mixed = worked! = showed a certain degree of PLASTICITY

people faster when the two scent streams were kept separate!!

Question 24

more receptors =

Answer 24

more sensitivity to smells

– Humans have approximately 10 million (?) and dogs have one billion olfactory receptors.

Question 25

While it is true that we are less sensitive to odors than other animals, part of our detection and recognition abilities follow from our

Answer 25

behavioral patterns.

Question 26

It has been shown that bilateral time

differences….

Answer 26

…. in a scent plume reaching the
nostrils is used by some sharks in
orienting toward scents.

the odorant is detected in one side first: so the animal will turn toward the higher concentration and earlier arrival

– Gardiner & Atema (2010) demonstrated
that small time differences in presentation
of odors to shark nares (nostrils) resulted
in strong turning responses.

– This corroborates the Porter study.

Question 27

parallels to hearing with bilateral time difference

Answer 27

sound reaches one ear before the other, we turn to localize

– This may be functionally equivalent to ITD
cues in auditory localization.

Question 28

Humans are ____________ because they have ____________ olfactory receptors.

Answer 28

Microsmatic; fewer

Question 29

Human are sensitive to odors, but can’t always identify or recognize them.

Answer 29

– Recognition threshold

– Humans can discriminate among 100,000 odors, but we cannot always label them accurately.

– This appears to be caused by an inability to retrieve a specific NAME from memory, not from a lack of sensitivity.

Question 30

recognition threshold

Answer 30

concentration of molecule needed to
determine ‘quality’ of an odorant (i.e. floral, citrus, rotten, etc.)

being able to give a name to the “what”

Humans can discriminate among 100,000 odors, but we cannot always label them accurately.

Question 31

Researchers have found it difficult
to map perceptual experience onto
physical attributes of odorants
because:

Answer 31

1. There is no specific language for odor quality (e.g. as color is associated with wavelength).
2. Some molecules with similar structures smell different, and some that have different structures smell the same.
3. There is great variability (~30%) between olfactory receptors in people.

Question 32

links have been recently found between

Answer 32

the structure of molecules, olfactory quality, and patterns of activation in the olfactory system.

Question 33

Niessing & Friedrich (2010) found that the olfactory bulb has

Answer 33

different patterns of activity that suggests a ‘categorical’ perception of odors.

Question 34

Mandairon et al. (2009) found cross-species (humans and mice) similarities

Answer 34

in odor preferences; importantly, ratings of

pleasantness could be predicted by the physiochemical properties of the odorant molecules.