THE EFFECTS OF OLFACTORY STIMULATION ON
SHORT-TERM MEMORY
MARK R. DEETHARDT
DEPARTMENT OF PSYCHOLOGY
LOYOLA UNIVERSITY NEW ORLEANS
ABSTRACT
This research was conducted to assess the possible effects that olfactory stimulation could
have on short-term memory of new information. 44 participants, all above the age of 18,
volunteered for the study (sex and gender of the participants was not recorded). The
independent variable was manipulated by placing various odorants into concealed jars,
and the dependent variable was measured by the number of associated words each
participant remembered. It was hypothesized that participants who received the odorants
would recall more words than participants who did not receive the odorants. The results
were statistically significant but in the opposite direction of the original hypothesis (t (42)
= -3.41, p = .001). Possibly, with a more controlled study, significant results could yield
support for the original hypothesis.
INTRODUCTION
It is common for people to partake in a simple everyday task, and they are suddenly
bombarded with the rush of a past memory that is associated with a certain odor. For
example, the smell of tobacco may remind an individual of their deceased grandparent
who smoked, or the smell of fresh linen might remind an individual of a summer house
they visited as a child. It is logical to ask how the olfactory receptors could evoke such a
strong, vivid memory from an individual’s past. One explanation for the olfactory
system’s powerful effect on human memory is that the olfactory receptors have axons
that terminate in the olfactory bulbs giving the receptors a more immediate connection to
the brain than any of the other senses (Engen, 1991). The point being, unless one has an
impaired sense of smell, our olfactory system plays a pertinent role in human life. An
example of how our olfactory system is believed to play a huge role in human life is
through aromatherapy and osmotherapy. The idea driving both of these therapeutic fields
is that odors affect the psychosomatic roots of mental problems, and these effects are
transmitted to the limbic system where emotional behavior and odor interact (Engen,
1991). It is commonly believed that the nose can identify enormous amounts of odors, but
when people recognize odors, they can only describe them in general terms (Engen,
1991). With these facts in mind, it is obvious that human olfactory receptors interact
frequently with the human mind and our memory, but the pertinent question is how
powerful is the relationships between olfactory stimulation and memory?
Research (Herz, 2000) has been done on the “Proust Phenomenon,” which is the theory
that humans can encode an odor with a certain past event, and later exposure to that odor
will trigger the past memory. Herz (2000) conducted studies were participants had to
associate a certain common odor with a painting or photograph and then record the
emotional response they had to each picture. Two days later, the participants were tested
to see if they could smell the same odors and then recall details about the pictures that
were associated with them (Herz, 2000). In this experiment, Herz (2000) found that equal
number of pictures were correctly recalled with olfactory, visual, tactile, and auditory
cues. The results of this research showed that odors are just as strong as visual, tactile,
and auditory sensory cues in eliciting the details of a past event, but not any more so than
these other sensory cues (Herz, 2000). The only difference found in this research was that
more emotions were associated with recalled memories triggered by odors, but the
amount of detail recalled about the odor memory was no greater than memories triggered
by visual, tactile, and auditory sensory associations (Herz, 2000). This research shows
that indeed olfactory stimulation does play a role in recalling events stored in the subjects
long-term memory, but recollection of memories through olfactory stimulation cannot be
labeled as the best cue to memory (Herz, 2000).
Other relevant research was done in the 70’s (i.e., Engen, Kuisma, & Eimas, 1973; Engen
& Ross, 1973) on short-term memory of odors and on long-term memory of odors with
and without verbal descriptions. In the first study on short-term memory for odors,
participants were tested to see if the duration of the time interval in which they were
presented with an odor had any effect on their memory of the odor (Engen, et al., 1973).
In this research, participants were presented with 100 odorants in four groups of 25. The
odors were presented at three second intervals, and the researcher would randomly make
the participant count backwards from a random number in intervals of three. The
researchers would then wait either 6, 12, or 30 seconds and would randomly introduce
one of the 100 odorants to the participant, and then the participant was asked whether the
odor was new or old. The results of this study were seen as unusual because it showed
that the ability to recall an odor does not dissipate with time like other sensory modalities
(Engen, et al., 1973). Visual and auditory modalities show nearly a 100% recognition
level for short retention intervals where olfactory modalities show around a 90%
recognition level for short time intervals, but this research showed that short term
memory will improve slightly with a retention interval of 12 seconds (Engen, et al.,
1973). The main piece of information this study contributed was that short-term memory
for odors, unlike visual and auditory memories, does not dissipate and will sometimes
improve with time (Engen et al., 1973).
More research (Engen & Ross, 1973) was done on long-term memory of odors to
compliment the findings of the short-term memory research. The hypotheses of this
research was that odors are encoded as unitary perceptual events, which leads to lower
levels of immediate retention, but the odors retained by an individual will be less prone to
distortion (Engen & Ross, 1973). In this study, participants were required to smell 48
common odorants, and then at a later time, they were presented with 21 sets of odors, one
new and one old in each set. The participants were then asked to distinguish which odor
was new and which was old in each set. One group received the second set of odors
immediately after the first part of the experiment, a second group received the odors one
day after the initial exposure, a third group received the odors 1 week after the initial
exposure, and a fourth group received the second set one month after the initial exposure.
This study showed that there was no relevant difference between the results of the shortterm memory research results and these results, and that a nearly equal retention level is
maintained across all time periods (Engen & Ross, 1973). The research also showed that
long-term recognition of odors is a large phenomenon that can persevere even through
difficult and distracting test situations (Engen & Ross, 1973). Engen and Ross (1973)
also concluded that neither odor familiarity nor odor labeling enabled participants to
memorize odors more efficiently. In that respect, this research opposes the Proustian view
that the familiarity, due to an emotional experience of an odor, will greatly enable an
individual to remember that odor.
Research done by Davis (1975) showed that olfactory stimulation was distinctively less
effective than the use of geometric figures as catalyst for verbal associations. In this
study, visual cues were compared to olfactory cues in paired association tasks.
Participants were required to either smell odorants and associate a certain number with
each odorant, or they were required to look at geometric figures and associate a certain
number with each figure. The participants were then tested again seven days later to see if
they could recall which numbers were associated with the odors or the geometric figures.
While Davis (1975) did provide evidence to show that visual mnemonic cues are superior
to olfactory mnemonic cues, he also discovered that if the odors were very
distinguishable then they could be just as effective as visual stimuli for verbal
associations. This research refutes Engen et al. (1973) saying that memory for the odor
stimulus and associations were equal to that of visual stimulus and associations after
seven days (Davis, 1975). Similar studies were done by Lawless and Engen (1977) in
which participants associated pictures with odors and were later tested to see if they could
associate the correct odor with the correct picture. A second experiment in this study
required participants to smell odorants, and then they were timed by the researchers on
how fast they could generate a label for each odorant. The results of this experiment
revealed that people would usually have difficulty labeling odors even though they are
familiar with them, which is referred to as the tip-of-the-nose state (Lawless & Engen,
1977; Engen, 1991; Schab & Crowder, 1995). Even though labeling odors is difficult for
a participant to do, the research concluded that generated labels for odors could be used
as mediators in the task of associating pictures with odors (Lawless & Engen, 1977).
In recent research, the effects of labels on odors and a person’s ability to recall odors was
assessed (Bhalla, Marcus, & Cornwell 2000). In this research experiment, subjects were
given various odors to smell and an experimenter generated label was associated with
each odor. Then the participants were asked five minutes after and an hour after their
initial exposure to smell the same and different odors and recall if they had already
smelled the odor, and if they had, they were asked to recall the label associated with the
odor. The results of this research found that experimenter generated labels aided in the
participants’ level of recall for odors, and that recognition of odors was better for odors
with labels than odors without labels. Bhalla et al. (2000) also refuted Engen & Ross
(1973) showing that recognition for odors was better at five minutes than at 60 minutes.
The majority of past research focused on the effects of odor memory and the effects that
labeling has on the memory of odors (Engen et al., 1973; Lawless & Engen, 1977; Bhalla
et al., 2000). Engen & Ross (1973) showed that labeling odors had no subsequent effect
on the memory of odors, but Bhalla et al. (2000) showed that labeling could indeed have
an impact on one’s memory of odors. Another recurring theme in past research is the idea
that individuals will be able to retain odors once they are encoded in their memory much
longer than visual and auditory modalities (Engen et al., 1973; Engen & Ross, 1973).
What the previous research on odor and memory has not covered sufficiently though is
the possibility that a distinct odor may enhance the memory of a word that is associated
with it in a person’s short-term memory. Not much research has been done on odors as
mnemonic devices for words or labels that have no association with that odor. Lawless
and Engen (1977) showed that odors as mnemonic devices were not superior to other
mnemonic devices, but more research should be done to elaborate on this. This research
differed from past research because it did not focus on a participant’s ability to memorize
specific labels that are generally associated with an odor or the odors themselves, but
instead, this research attempted to answer the question of whether or not olfactory
stimulation can help enable people to retain unrelated material more efficiently in their
short-term memory.
With this research goal in mind, the hypothesis of this research was that conditions where
information to be memorized was accompanied by odors resulted in better recall of the
information than conditions where information was memorized without the
accompaniment of odors. The independent variable that was focused on was olfactory
stimulation, and this was operationalized as the odors presented to participants in the
experiment. The dependent variable was the participants’ ability to recall seven words
that were associated with each of seven odors they were exposed to. This research was
designed with the hopes that olfactory stimulation could be shown as a valuable
mnemonic device which could enable people to remember information more efficiently
in their short-term memory.
METHOD
Participants
This experiment involved 44 participants all above the age of 18. The gender of the
participants was deemed insignificant by the researchers, thus how many males and
females participated was not recorded, but it is known that the majority of the participants
were female. The participants were selected through convenience sampling from
introductory level psychology courses at Loyola University New Orleans. The teachers of
these psychology courses announced a description of the experiment to their classes, and
students were asked to sign up and participate on a voluntary basis. The introductory
psychology course instructors rewarded any student who participated in this research
with bonus points for that class. Any individual who was willing to participate was
allowed to do so regardless of sex or ethnicity. The only volunteers that were not allowed
to participate were those individuals with allergies or cold symptoms.
Materials
Consent forms were used to obtain the participants informed consent before the
experiment began. 42 baby food jars that were cleaned and spray painted black were used
in this experiment. Seven odors were presented to each of the participants in the
experimental group. The materials that produced the odors were various dry teas, spices,
and incense. The odors that were selected were pre-screened by ten individual who rated
the odorants on familiarity and distinctness. The seven odorants that were used in the
experiment were all labeled as unfamiliar and distinct by the ten individuals who
prescreened them. For a complete list of the seven odorants and the words associated
with each odor, refer to Table 1. The words that were associated with the odorants were
simple words picked randomly from a list of frequently used words. The participants
were also provided with a list of 14 words, which contained the seven words they were
required to memorize. The participants were told to use this word list to help them if they
forgot any of the words they were required to memorize. A coffee filter was placed inside
of each jar to ensure that the participants could not see the odorants. A pre-recorded tape
containing instructions for the procedure was played for the participants on a tape
recorder. A small sheet of adhesive paper was in front of each of the ten jars, and the
participants recorded the various words that they memorized on them with a pencil. A
stopwatch was used so that the researchers could ensure that the pause between testing
sessions was exactly five minutes.
Design and Procedure
The experimental procedure used was a single variable between groups design. The 44
participants were randomly assigned into an experimental group consisting of 22
participants or a control group consisting of 22 participants. The independent variable
that was manipulated by the researchers was stimulation of the participants’ olfactory
system. Each participant in the experimental group was presented with seven jars
containing odors, and each participant in the control group was presented with seven jars
containing no odors. The dependent variable was memory retention. Each participant was
given a word to associate with each jar that they smelled, and the number of words that
each participant could memorize and associate with each individual odor was used to
measure whether stimulation of the olfactory system could subsequently aid in an
individual’s memorization process.
It was important to ensure that the participants would not have any other mnemonic cues
that would assist in enabling them to associate the seven odors they were exposed to and
the seven words they were to memorize. Several other controls were implemented in
order to ensure this. One control was that the participants were not allowed to see what
was in the jars they were required to smell. The jars were painted black and a coffee filter
was placed in each jar to ensure that the participants would not be able see any of the
sources of the odors. The participants were also all seated facing the wall to ensure that
they would not make any type of cue with the other participants in the room. Another
control that was implemented was the standardization of all of the instructions for the
experiment. This was achieved by having an individual, who had no affiliation with the
research being conducted, record the instructions on a tape, which was then played for the
participants during the experiment. To avoid the effects of primacy and recency the seven
jars were randomly put into a different order for the recall session of the experiment.
The participants in both the experimental and control group were tested in groups of
three. The participants entered the room that the experiment was taking place in and were
seated by the researchers in desks, which were facing the wall. The participants’
informed consent was obtained and the experiment began.
Next, the researchers played the pre-recorded tape for the participants on a boom box
with the volume turned up sufficiently so that every participant could hear the
instructions. The voice on the tape began by greeting the participants and thanking them
for their participation. The voice told the participants that they were going to smell the
contents of the seven jars that were in front of them from right to left. The participants
were instructed that when they heard the word “START” on the tape, they would pick up
the first jar, unscrew the cap, and smell the odor for 15 seconds seconds. The participants
were instructed to hold the jar about an inch from their nose and to not let their nose
come in contact with the jar. The participants were told that they would hear a word with
each odor and that the word would be repeated three times at a five second interval. Then
the participants were told when they hear the word “STOP,” they were to put the jar they
were smelling back to the position in which they found it in and place the lid back on the
jar. This process was repeated for all seven jars with a 15 second pause in between each
jar.
When this process was finished, the participants were asked to take a five-minute break,
which was timed by the researchers on a stopwatch. They were instructed not to
communicate about the experiment with each other, and they were also asked not to eat
anything and if they must drink something to drink only water. During this time, the
researchers rearranged each set of seven jars in a random order. Small sheets of paper
were placed in front of each jar by the researchers for the participant to record their
answers. The participants returned to the room, and the memory recall phase of the
experiment began.
Upon being seated again, the participants were instructed that they had a word list of 14
words, which contained the seven words they were required to memorize as well as seven
unrelated words. They were instructed to use the word list to prompt them to remember a
word if they had forgotten one them. The researchers then started the tape of instructions
for the participants. This time, the participants were instructed by the tape that when they
heard the word “START,” they were to pick up the first jar on their right and smell it for
15 seconds, but this time they were instructed to write the word they heard while smelling
the stimulus in the first half of the experiment. When the participants heard the word
“STOP,” they were to return the jar and replace the jar’s cap. This process was repeated
for all seven jars with the participants recording the word that was associated with each
smell.
When the experiment was completed, the researchers debriefed the participants telling
them that they had just participated in a research project to asses what effect olfactory
stimulation could have on memory retention. The participants were given an opportunity
to ask the researchers any questions they felt compelled to ask and then exited the room.
Their responses were then collected by the researchers, and each participant’s individual
responses were stapled together and placed in an envelope. Both the experimental and the
control group’s data were placed in separate envelopes so that the researchers could
distinguish between the two sets of data.
The same process was repeated separately for 22 participants in a control group. The
control group was given the same recorded instructions. The only difference was they
were given jars containing no odor, and they were tested strictly for memorization.
RESULTS
The hypothesis of this research experiment was that an experimental group, that had to
smell an odor and memorize a word with the odor, would be able to recall more words
than a control group that did not smell any odor. An independent samples t test was used
to compare the means of the experimental (M = 2.36, SD = 1.84) and the control group
(M = 4.41, SD = 1.82). The results of the t test showed the difference between the mean
score of the experimental and control group to be significant (t (42) = -3.71, p = .001) but
in the opposite direction of the original hypothesis.
DISCUSSION
The results of this research were significant, but the original hypothesis that odorants
would actually enhance a participant’s memory of words was not supported. The results
of this research supported the exact opposite of the original alternative hypothesis. While
the intended hypothesis is not supported by these findings, the results do support a
hypothesis that states participants will memorize less with the aid of odors than
participants with the aid of no odors.
Much of the past research that was done related to odor and memory confirms the
conclusions of this study (i.e., Engen, et al., 1973; Engen & Ross, 1973; Davis, 1976).
Engen et al. (1973) and Engen & Ross (1973) both supported a hypothesis that odors are
encoded as unitary perceptual events, which lead to lower levels of immediate retention,
but the odors retained by an individual will be less prone to distortion. This previous
research hypothesis can help explain why the current research failed to support the
alternative hypothesis. Engen et al. (1973) and Engen & Ross (1973) showed that
immediate retention for odors was very poor, and this research experiment demanded
participants to immediately encode an odor in their memory and then associate this
encoded odor with a random word. According to these two past research experiments, the
current research experiment would not yield supportive results because it required
participants to mange the difficult task of retaining an odor in their immediate memory.
Research done by Davis (1975) also supported the results of this experiment. Davis
(1975) provided research that supported the hypothesis that visual cues are far superior to
olfactory cues in paired association task. According to the research done by Davis (1975),
this research experiment would not yield positive results, because it was attempting to use
olfactory stimulation, which is a poor associative cue, to help participants associate a
word with an odor.
Along with the past research that supports the conclusions of this study, there are several
serious problems with the study that may have affected the internal validity and the
external validity of the study. The first and most obvious problem that may have
decreased the external validity of this study is the fact that convenience sampling was
used to obtain the participants for this research. This research was conducted for
introductory level research and statistics classes, and due to the time restraints in which
the research was conducted, the only way to obtain a significant number of participants
was to use convenience sampling. All of the participants obtained were Loyola students
who volunteered for the study. This seriously impaired the generalizability of the
research due to the limited sample of the population.
A second problem that may have affected the outcome of the study is the amount of time
that the participants were actually allowed to smell the odorants with which they were
required to associate a word. In this research, the participants were only allowed to smell
each odor for 15 seconds. Then they were given a five minute break and then tested again
to see if they could remember the odor and the word that was associated with it.
According to past research, odors are not immediately retained very well, but they may
be retained significantly better over time. This research could have yielded stronger
results in favor of the original alternative hypothesis if the participants were given more
time to encode the actual smells and then given a longer amount of time to process the
smells in their memory. All of the odors that were presented to the participants were very
novel and distinct odors that the participants had probably never been exposed to. Since
the odors were very new to the participants, they probably needed much more time than
15 seconds to encode the odor and much more time than five minutes to let their
memories process the odors. It was also possible that the participants were so concerned
with trying to process the novel odors that this task interfered with the participants’
memorization of the words associated with each odor. Since the amount of time the
participants were exposed to each odor was a serious shortcoming of this research, it is
hard to assess if the experiment accurately recorded the effects of olfactory stimulation
on a participant’s ability to memorize information.
A final factor that was a shortcoming of this study was that the gender of the participants
was not controlled for. Research done in the past by Engen (1987) showed that females
performed far better than males on test where they were required to memorize new or
novel odorants. Since convenience sampling was used in this experiment, gender was not
controlled for. A majority of the participants in this experiment were female, but several
males participated as well. While this was not the most major shortcoming of the study,
the fact that the gender of the participants was not controlled along with the problem of
the time interval in which the odors were encoded could have seriously affected the
internal validity of this study.
Even though this experiment failed to support the intended hypothesis, it still has some
significant practical and theoretical implications. The practical implication of this study is
that is can be used as a guide for other researchers, who wish to conduct similar research,
to not make the same mistakes that were made in this experiment. Hopefully this research
can be used as a tool to show many of the possible mistakes that could be made when
testing the effects of olfactory stimulation on short-term memory. Secondly, the
researchers who conducted this experiment were novices in the field of research and
statistics. This research has provided the researchers with the building blocks for
conducting future research in this and other areas, and since this research did produce
significant results, it should prompt other interested researchers to conduct similar
research to see if they yield the same results.
The theoretical implication of this study is that the results, even though they were not
intended to, complement the already existing body of research on odor and memory. The
majority of past research has shown that odorants are inferior in helping individuals
associate words or memorize words associated with them, and this study supports those
findings. Theoretically, this research shows that odorants to do not aid in short-term
memory recall, and that odorants, as mnemonic cues, actually impair individuals from
memorizing and recalling newly acquired information.
With much improvement this experiment could hopefully be conducted again and yield
support for the intended hypothesis. First, the experiment would have to be much more
lengthy. The amount of time that the participants were given to smell the new odorants
and encode them in their memory would have to be much longer. Another improvement
would be to give the associated word after the participants had finished smelling the
odorants, because it appears that if the participants are smelling a new odorant and trying
to memorize a word to associate with it at the same time, to much interference is caused
in their memory. A better method of participant recruitment would have to be
implemented, such as asking for only a certain number of males and females to sign up.
Since females perform significantly better on test involving odor memory, it seems
logical that controlling for gender would be an improvement in future studies. Either
making the number of males and females even or testing them each as separate groups
would eliminate gender differences as a confound. With all of the extraneous variables
controlled, it might be possible to conduct an experiment that would support the original
research hypothesis.
The fact remains that olfactory stimulation is a huge part of human existence. Unless an
individual’s olfactory system is impaired, one is bombarded with hundreds of smells each
and every day, which range from pleasant flowers to grotesque smoke. It is important to
know how such a huge physiological process, such as smell, pertains to the psychological
concept of memory. Many research experiments have shown the intricate relationship
between these two processes, and hopefully this research experiment has added to that
knowledge by showing that olfactory stimulation does not effect short-term memory
retention of new information and may in fact impair short-term memory of new
information.
TABLE 1
List of Odorants and Their Associated Words
Odor #/ Odor Name/ Associated Word
1. Chamomile Green Tea/ Advertise
2. Strawberry Kiwi Fruit Tea/ Piano
3. Lapsang Souchang Tea/ Vegetarian
4. Thai Tea & Jasmine Olfactory Sachet/ Condense
5. Incense Stick/ Editorial
6. Brandy Cognac Tea/ Frontier
7. Thai Chicken Spice, Cinnamon, & Muling Spice/ Skeleton
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