The process of in which information is transported into long term memory is called encoding (Goldstein, 2011). This process can be completed in several different ways using the different senses. Events in one life can be committed to memory via sight. Most would say that sight is the most effective sense in recovering memories because when one tries to remember a past event, they attempt to visualize it. Simple visualizations of past events usually only come in flashes and don’t give an accurate, detailed depiction of the events that occurred. Hearing is the same, if one focuses on the auditory aspects of a memory, they will only recall what was heard and not many other details of the account.
The most detailed and fully formed recalls typically come from memories that are linked with strong emotions. Emotional memories cause a release of hormones from the adrenal glands and these hormones influence the effects or neurotransmitters in the brain, enhancing one’s memory (Wade, 2012). Since emotions are so closely related to memory, one can assume that the sense with the closest relationship to emotions would be the sense that is most able to store and retrieve information accurately. The amygdala is a set of neurons located deep in the brains medial temporal lobe and plays a key role in the processing of emotions (ScienceDaily, 2012).
The primary olfactory cortex, in which the higher level processing of hearing takes place forms a direct link with the amygdala (Herz, 1996). Only two synapses serarate the olfactory cortex from the amygdala, which is involved in experiencing emotion and emotional memory (Herz, 1996). So when one smells something, it immediately triggers an emotional response. That smell is then committed to memory emotionally, and in the future when that particular smell is experienced again, the emotions felt will allow the person to retrieve a detailed account of what was going on when that smell was first experienced.
For example, if one happened to be staring out the window watching a dog chase a squirrel and smelled that their grandmother was baking chocolate chip cookies, years later when smelling those cookies again, that emotional response garnered before could bring about a detailed account of that dog chasing the squirrel.
The hippocampus is a part of the forebrain, located in the medial temporal lobe and is a critical tool used for storing memories (Buzsaki, 2010). The hippocampus has also been considered the brain’s 都earch engine allowing for quick and efficient searches for deposited memories in the brain (Buzsaki, 2010).
The hippocampus provides a storage for information and dedicates it to long term memory, and then later provides the ability to search through that database of information for specific memories and information. Only three synapses separate the olfactory nerve from the hippocampus (Herz, 1996). Given this information, one can see that the sense of smell carries a direct link to the storing of information, and also a direct link with the subsequent retrieval of that information.
Humans tend to underestimate the role of smell in our every day lives. Most mammals actually recognize smell as their most important sense and rely on it constantly for many of their daily activities. Animals use their sense of smell to hunt food, locate members of their family or pack, lure possible mates for reproduction, and even communicate. Members of the canine family often use urine to mark their territories, committing the smell of the urine to memory so they can use that memory to locate their territories and ward off other animals (Ito, 2000). Many animals when they are first born are unable to see, and use their sense of smell to identify their mother (Ito, 2000). Some animals, when they birth their young identify them using their sense of smell, and if that scent is compromised by another animal or person, the parent will reject the young (Ito, 2000).
Animals also learn better using their sense of smell. In a 1993 study, rats were presented with a drinking tube containing quinine hydrochloride (Slotnik, 1993). The hydrochloride had a bad taste and the time it took for the rats to stop going to the drinking tube was recorded (Slotnik, 1993). When the hydrochloride drinking tube was associated with a specific scent, the rats learned to not drink from it much faster than when the water was associated with a different color, sound, or consistency (Slotnik, 1993). The rats learned quicker when the tainted water was associated with smell than any other sense. Humans would be a lot more effective in storing and retrieving their memories if they took the example given my most mammals and utilized the olfactory nerve system more effectively and relied on it more often.
One important aspect of committing information to long term memory is rehearsal. Rehearsal is necessary for commiting things to memory because typically the sensations we see, hear, and feel don’t remain for long. After reading a sentence, the vision of that sentence doesn’t stay there, it passes. So the best way to commit that sentence to memory would be to read that sentence over and over again until it sticks, and even then it only commits it to short term memory (Goldstein, 2010). One could also not read it again, but just repeat it over and over until it is committed to memory using the auditory senses. This shows that committing information to memory using other senses requires work on one’s part.
When it comes to the sense of smell, it is the slowest of all senses. It not only takes the brain longer to perceive olfactory stimuli; the sensation of an odor also persists for greater lengths of time than do sensations of vision or audition (Herz, 1996). One does not have to do any work to commit a smell to memory because the body automatically conducts its own form of rehearsal by allowing the sensation to linger until it is committed to memory. Olfactory receptors most readily receive information from the physical world and therefore are able to code memories for things like emotion or events more efficiently.
Several studies have been conducted with humans to determine what senses have the most effect on memory. One 1990 study examined memory for common odors and odor names encoded with visual, verbal, and olfactory elaborations (Lyman, 1990). In this experiment several groups of people were placed in a room and either presented with a group of odors and the name of that odor, visually given a list of names of objects associated with an odor, or verbally given a list of names associated with an odor (Lyman, 1990).
A week later these groups were brought back in and asked to recall these lists given olfactory, auditory, or visual clues. The group that was presented with the smells again performed a lot better in recalling the name associated with those smells (Lyman, 1990). According to this study and several like it, the olfactory receptors are more effective at storing and retrieving memory; however, studies have also been done to decide whether interference plays a part when storing memory.
When one is listening to a lecture and trying to commit what the lecturer is saying to their long term memory, background noise such as a car outside, another student sneezing, or a phone ringing is known as auditory masking (Goldstein, 2010). This masking reduces the person’s ability to remember what was being said at the time. Visually, if one is watching a television show and there is something moving in their peripheral vision, that distraction could affect the person’s memory of that television show. So in order to determine whether interference also plays a part in the sense of smell and how it is compared to the other senses and their types of interference, a research study was conducted in 2003 by Gesualdo Zucco.
In this study, participants were asked to smell 30 odors while performing other tasks (Zucco, 2003). These tasks included things such as drawing an image, recounting a specific episode from their life, or naming a word and giving the definition (Zucco, 2003). Participants that were asked to conduct these tasks while smelling the odors were later able to recollect these odors just as well as the participants that smelled the odors without having to perform a separate task (Zucco, 2003). In a second study conducted by Zucco, participants were exposed to 15 olfactory stimuli, 15 auditory stimuli, or 15 visual stimuli and all exposed to similar interfering conditions (Zucco, 2003).
After being asked to recall the different stimuli later, it was shown that the interference affected recollection for the visual and auditory stimuli but not at all for the olfactory stimuli (Zucco, 2003). This study shows that not only is memory for odors represented on a separate and unique memory system, but also a more effective memory system than visual and auditory stimuli.
Given the fact that the olfactory system holds closer links to the amygdala and hippocampus, automatically conducts its own form of rehearsal, and is less affected by interference, one can conclude that the sense of smell is the most effective sense in storing and retrieving memories; however, there is one downside to relying on the sense of smell to recall memories. Memories retrieved by the sense of smell are often subject to bias.
A 1987 study showed that women asked to retrieve memories based on specific neutral words while also being exposed to certain odors recalled these memories in a negative or positive light based on the type of odors they were given (Ehrlichman, 1988). Those that were exposed to unpleasant odors recalled their memories as negative, while those exposed to pleasant odors recalled their memories as more positive (Ehrlichman, 1988). Each sense plays its part in memory retrieval and the best way to accurately and in detail commit an event or information to memory and later retrieve that event or information is to use as many senses as possible when encoding. But the most effect sense in storing and retrieving detailed information or events is the sense of smell.