Shaping the "Episodes" of Our Memory

Source: Mariya / Pixabay

One weekday evening when I was 5 years old, my parents surprised my sisters and me with dinner at our small town’s most popular burger joint (a rare splurge on their limited budget). I ordered a cheeseburger and a strawberry shake, and just as the food arrived at our table, my absolute favorite song at the time came on the jukebox. In a state of happiness bordering on ecstasy, I bathed in the familiar notes of the tune, lifted the burger to my mouth, took a great big juicy bite, and then it happened. A big greasy blob of mustard squirted out from between the meat and bun and landed right in the middle of the brand-new shirt I was wearing for the special occasion. The perfect night, like my brand-new shirt, was ruined.

To this day, the mustard stain incident is indelibly seared into my memory. As crystal clear as the incident is in my mind, however, I strangely have no recollection of anything that happened before or after the event. The memory stands alone, an island of momentary awareness in the sea of my 5-year-old life.

Autobiographical memory is episodic

The isolated quality of this incident illustrates an interesting characteristic of our remembered lives. While we live life in real-time as a more or less continuous stream of sensations and experiences, we tend to remember it, not as a single coherent autobiographical record, but as a collection of discrete, loosely related episodes, less like a movie than a long-running TV series. This impression is so universal, that we have of our remembered lives as being divided up into episodes that psychologists refer to our autobiographical memory as “episodic” (as opposed to semantic, which is our memory of facts).

External, spatial transitions can segment our memories

Psychologists exploring the episodic nature of autobiographical memory have identified one possible source of our segmented past in various transitions we encounter in our external world. Several studies have revealed that items encountered in a shared or stable context, such as a room, become linked together in our memory. A sudden change in context, however—such as walking through a doorway into another room—is thought to create an “event boundary” that separates items in our memory.

My unhappy mustard memory is not bounded by space, however—between my entrance into, and my exit from, the drive-in. It begins and ends with my emotional responses to the incident, so some other type of transition must have been involved in isolating the episode.

Do emotional fluctuations also segment memory?

Looking for other types of transitions that might be at play in segmenting our memory into episodes, psychologists at UCLA and Columbia University conducted a study to explore the role that fluctuations in our internal world play in this process. Specifically, they wanted to know if fluctuations in emotional states segment memories in the same way that transitions in physical space do.

With the primary goal of determining “if meaningful shifts in emotional states function as event boundaries that segment memory,” the team hired film score composers to write new musical pieces designed to evoke a range of emotional states (joyous, anxious, sad, and calm.) These pieces were spliced together into 10 “songs,” each consisting of three emotional segments separated by a 6-9 second musical transition period.

While listening to each of these songs, participants in the study viewed a series of 24 random object images. After each image sequence, participants were tested on two aspects of episodic memory: temporal order and temporal distance.

Temporal order was tested by showing the participants 10 pairs of objects from the prior sequence, and then asking them which of the two objects in each pair appeared first in the series. Temporal distance was tested by asking the participants how far apart the two items appeared in the series. (In reality, each pair of items had been separated by the same three intervening items during the encoding session; any variation in perceived separation was purely subjective.)

Participants were once again presented with the images and tested on their item recognition and “temporal source memory” 24 hours later.

Emotional fluctuations serve as “event boundaries”

The findings revealed that fluctuating emotional states “may function as a strong feature of an internal context that links and separates memories across time.” Changes in our emotions play a role in segmenting our experience into the “episodes” that make up our autobiographical memory.

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Regarding the question of temporal memory, the researchers found that image pairs that fell on different sides of musical-emotional transitions were judged to have appeared farther apart in time than pairs that did not span such an “event boundary,” even though they were all the same distance apart. Participants’ memory of the order in which items originally appeared was also impaired for items spanning perceptual boundaries. The “time dilation effects” and impaired temporal order memory displayed by participants suggest that internal event boundaries (shifts in emotion) segment autobiographical memory in the same way that external boundaries do.

Another interesting finding of the study was that emotional shifts in a positive direction appear to bind sequential memories together, while shifts in to negative direction (such as might be experienced, say, by a small boy dropping mustard on his new shirt) help to segment memories into episodes. This finding would go a long way toward explaining the stand-alone quality of my drive-in burger memory, with my sudden emotional shift from elation to despair isolating the episode from all the myriad other things that were going on in my life before or after it.

Autobiographical memory is a dizzyingly complex phenomenon, and no one factor can fully account for any single aspect of it. Regarding the question of why we experience our memories as episodes instead of a continuous stream of sensory data, however, this study sheds a lot of light on the role that our emotions play in this process. The moment-to-moment emotional fluctuations that occupy a large portion of our daily lives, it appears, “can sculpt unfolding experiences into memories of meaningful events.”