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A Unique Stench

Do you ever catch yourself thinking back to experiences from your past – happy, triumphant, gloomy memories? Perhaps, you sometimes imagine what life could present you down the road, where you’ll be 5, 10, 15 years down the line. Research into mental time travel (MTT) – the manner of mentally travelling back in time to relive past personal events or forward in time to imagine possible autobiographical events in the future, suggests that past and future MTT operate along similar principles, mostly in that people tend to recall events dated close to the present regardless of direction. However, differences have been observed as well; future events have been found to involve more of an observer perspective (as opposed to first-person) and refer less frequently to specific events, while they’re generally more personally important and relevant to the person’s self-identity. In other words, MTT into the future is based more upon the creation of potential circumstances in terms of one’s own personal representation of the world based on prior experiences, while MTT into the past is based on actual recollection of past events. The present study (Miles and Berntsen, 2011) aimed to further investigate future versus past MTT in response to different types of sensory cues. It focused on odor cues, as it has been claimed that odors are uniquely encoded and maintained in memory. Thus, it was expected that memories evoked in response to various smells should be different from those evoked via verbal or visual cues.

Prior research suggests that recall of autobiographical memories resulting from odor cues tend to be older, childhood memories from the first decade of life. In addition, odor-induced memories were found to refer less often to specific events than memories in response to verbal and visual cues. For instance, while the sight of fresh, vine-ripe tomatoes may evoke memories of recent, specific experiences of eating tomatoes, or perhaps planting a garden of your own, the smell of that same vegetable (or fruit, if you want to get technical), may send you back into the archives of your youth – you may be taken back to the general memory of eating your mother’s homemade tomato sauce when you were a child.

Two potential explanations have been suggested to explain the tendency for odors to evoke more distant, remote memories. The “uniqueness explanation” suggests that one’s first experience with a particular odor may have a privileged position in memory, possibly because initial experiences with odors prevent the formation of new, distinct memories for those same odors. This effect may be more pronounced with odors as opposed to verbal or visual experiences. If this explanation is accurate, odor cues should evoke more remote memories (because these memories occurred first), but should not induce more distant representations of future events (once again, because the older memories hold a privileged, unique position in a person’s own memory “bank”). Alternatively, the “remoteness effect” suggests that due to the very nature of odor cues accessing more generic memories, these memories are more likely to refer to remote events, as recall becomes less specific as time passes. Evidence in support of the remoteness effect should reveal a mirroring effect, in that creation of future events should be just as distant from the present (albeit opposite in direction) as recall of memories – a 20 year old should be just as likely to recall his 10th birthday party, as he is to imagine what his 30th might be like.

Miles and Berntsen recruited 89 university students to participate in their study; each was compensated with a gift valued at approximately $20. They were randomly assigned to one of three cue conditions: verbal, visual, or odor-induced. In the verbal condition, participants were read cue words, in the visual condition the words were presented on a card, and in the odor condition the participant was asked to smell an odor from a jar. Twelve stimuli were chosen based on a pilot study that identified cues that were particularly memory-inducing and highly identifiable to participants. For example, chocolate was chosen as one of the stimuli. In this trial, participants in the visual condition were presented with an index card with the word “chocolate” written on it, in the verbal condition participants were read the word aloud, and in the odor condition they were asked to smell the contents of a jar filled with chocolate. Each participant was exposed to stimuli in both past and future conditions. In the past condition, participants were asked to recall an autobiographical event from their past. In the future condition, they were asked to construct an event that could potentially happen in their own personal future. Following the retrieval/construction phase, participants were asked to write a brief description of the event and to answer several additional questions.

Ultimately, odor-induced events were found to be less specific than those in the verbal and visual conditions, and memories of past events were more distant from the present than constructed future events. Past events were also rated as higher on visual imagery- they were recalled in greater detail, and were considered more specific and coherent, whereas future events tended to be recalled from the perspective of an observer (rather than a first-hand experience), and were rated as more influential to the individual’s life and more relevant to personal identity. A larger portion of memories were reported in the early stages of life in the odor condition than in the verbal and visual conditions. Critically, odor-induced future events were more concentrated in the upcoming year. In terms of visual imagery, higher ratings were reported in the verbal and visual conditions for memory recollection, but not for creation of future events, under which condition the odor condition was rated slightly higher. Past events were also found to be more clear and complete than future events in the verbal and visual conditions, but this trend was reversed in the odor condition.

These findings support the uniqueness explanation; one’s first experience with a particular odor may have a privileged position in memory, possibly because initial experiences with odors prevent the formation of new, distinct memories for those same odors. This effect is unique to odor-induced memories, at least in comparison to verbal and visual cues. The tendency for constructed future events to be concentrated within the first year in the odor condition supports this idea, and is in direct opposition to the remoteness effect.

This study explored a new method for investigating sensory cuing, one in which both past and future MTT were analyzed. In addition, various cue modalities were explored, some of which had previously received little attention. Generally, evidence was found in support of the idea that different types of cues have different influences on remembering personal events in the past versus constructing future events. So, if you ever find yourself frustrated that you can’t remember events from your childhood, don’t simply ask your mother what it was like, sniff around a little bit and see what you can discover on your own!



Miles, A.N., & Berntsen, D. (2011). Odour-induced mental time travel into the past and future: Do odour cues retain a unique link to our distant past?. Memory,19(8), 930-940.

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  1. May 18th, 2013 at 11:40 | #1

    This idea is a really fascinating new take on memory studies. This idea of older, vaguer memories for odor makes sense, when I think back to different smells I’m instantly brought back to childhood (maybe when I first experienced these smells and was most likely to perceive them as important?). It would be interesting to do a study on food memory not in terms of how well we remember food, but in terms of how sharply we link past memories to taste. It would be interesting to see which scents have the strongest links to memory, which ones invoke more future-focused memories and which ones take us farthest into our pasts. This would also be an interesting cross-cultural study. Do the same smells transport people around the world to their early childhoods? Do immigrants have sharper childhood memories using culturally specific smells not present in the new country they live in? Researchers could also examine differences in age–the distance mentally time traveled might vary for older adults. This could also have implications in Alzheimer’s memory research.

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