Theories of mental time keeping are not merely of philosophical interest—they may also have clinical significance. A well-documented observation in psychiatry is that people suffering from depression commonly describe feeling ‘stuck in time’. This symptom may be related to anxiety speeding up the mental watch or it may be that depression in itself reduces the occurrence of events. People who are depressed are more likely to remain in bed (even though insomnia is a frequent symptom), go out less, and rarely meet new people or have memorable experiences. The result may be that relatively few memories of events are encoded with an endless supply of mental seconds.
Yet despite the apparent consistency of the events-per-mental-second model as a way of explaining time perception in depression, the evidence is lacking. When psychologists applied their standardized tests of time perception to people with and without depression, they found no indication that the former had disturbances in time perception. This caused us to ask the question: Is there something about emotion and time other than the mental watch?
Most people, including psychologists, define events by what we see and hear, but, critically, events involve doing things. Staying in bed is a lack of activity, as much as standing there and waiting for the bus is. The things that people see and hear often result from moving around. Actions are, in other words, more than just body movements; they involve the relationship between the self, body movements, and the resulting sensations. For example, the action of grabbing a cup of coffee involves me, reaching out, and the resulting warm feeling in my hands as I hold the cup. Could it be that the key to mental time lies in exactly this relationship? And if so, could it be that the temporal disturbances in depression are not so much due to the number of events happening to them, but how much they themselves act?
To start with the first question, as to whether actions change time perception, we made use of a known effect in psychology: actual body movements and imagined body movements are remarkably similar. Indeed, research suggests that motor imagery uses similar brain structures to actual motor movements. This enabled us to investigate whether different types of imagined movements result in an altered sense of time. If imagined movements cause people to time the same visual stimulus as either longer or shorter, then this suggests what we do (at least mentally) is at least as important for subjective time as what we see.
We asked volunteers to estimate the duration of a video of a ‘star field’ in whole seconds, with a range of up to a minute. They were not aware, but the video was always either 7, 10, or 16 seconds. The results showed that they were quite good at estimating its length, although short durations were overestimated, and long ones underestimated. Critically, however, prior to timing each video, participants were instructed to imagine moving, to feel their body as if perhaps they were themselves floating in space. The instructions were to specifically imagine moving slower and slower, imagine moving faster and faster, or to merely watch the stars. The results were clear-cut: Imagining moving slower resulted in the same video being rated as shorter, while imagining moving faster had the opposite effect. Importantly, since the movement was only imagined, and each video was the same (each video was timed for each type of movement condition), we can rule out all perceptual effects. Thus, actions, even only imagined actions, change time perception.
Now, to go back to the question of depression, we aimed to test whether these effects might be different for people who were having symptoms of depression. For this, of course, it was necessary to obtain a much larger and more diverse sample than involved in our previous, lab-conducted study that included 35 participants (23 female, 10 male, 2 non-binary), mostly students at the University of Helsinki. To conduct the larger study, we were awarded a CloudResearch grant, by which we obtained 91 volunteers (73 from the USA). CloudResearch was very helpful in providing a representative sample of young and old adults, of equal male and female proportions. Participants were each sent a link to a downloadable executable, which started the experiment. The experiment was about the same as the Finnish version, but started with a standardized inventory for symptoms of depression and also included several questions about what exactly they imagined. After finishing, about an hour later, the software sent the data back to the server. For an experimental psychologist, it’s truly a magical sight to see dozens of participants suddenly uploading their data rather than us begging each one individually to do our study!
The results were remarkable. To begin, the Finnish results were replicated – no longer a given in psychology studies. Again, short durations were overestimated, and longer ones underestimated. More importantly, the same durations were reported as taking shorter if participants were imagining slower movements but faster if they imagined faster movements. So, what happened when people were depressed? It turned out that the more symptoms of depression someone reported, the greater was their effect of imagery on time perception. Interestingly, the effect was strongest for slow movement imagery: people with more symptoms of depression saw the video as even shorter when they imagined moving slower and slower than those without these symptoms. This could give a new clue as to how depression and time perception are related: Perhaps people with depression are driven towards slower movements and can therefore more easily imagine moving less rather than more. If this results in a stronger effect of time perception for them than with other people, this could explain the reports of feeling ‘stuck in time’.
Potentially, continued research might improve our experiment to become a diagnostic tool for detecting depression, but we believe there could be more important implications. Another potential application of our findings is to apply it to create novel treatments that focus on the relation between imagination, time perception, and clinical symptoms. Indeed, some treatments already exist that seem to involve actual or mental movements. Physical exercise has been proven time and time again to prevent or reduce symptoms of depression. Mindfulness therapy has also been offered as effective in some instances of depression, and certain meditation techniques of mindfulness involve controlled movement of one’s attention from one body part to the next. Perhaps, by training this kind of controlled actual or mental movement, the illusory relationship between our inner body movements and events occurring in the outer world is reduced, such that people get ‘unstuck in time’. But such a vague theory remains just speculation until we have more evidence!
In the meantime, why hasn’t the bus arrived yet? Waiting for the bus normally involves little movement, so should the time pass very slowly, or quickly? According to what we just discussed, moving slowly causes underestimation, so if you waited for 5 minutes, you will have experienced much less, and your mental timing may have counted only 3 minutes. But remember again that time perception isn’t just about perception, but also about what you were doing. Did you imagine the bus moving, did you perhaps even try to will it to go faster and appear around the corner? If so, in your impatient imagination, by imagining the bus moving fast, you might quite ironically have made the time appear to pass slower than just passively waiting. Instead, try to relax, breathe steadily, and imagine the bus-driver slowing down to take a much-needed break. That way you should underestimate the time you have been waiting and the bus should arrive sooner than expected. Of course, if you happen to enjoy waiting, you should try to get up and start moving, run in circles while you wait. Not only does moving fast make us overestimate time, it is also generally healthy advice.