Time perception is an important human skill that allows us to coordinate our actions and anticipate unfolding events. Accurate perception of time is particularly important in tasks that require precise physical actions in response to complex events. Researchers have been interested in understanding situations that alter time perception, including space flight. Studies have shown that the weightlessness and changes in microgravity experienced by astronauts systematically affect their perception of time. After several hours of flight, astronauts showed more variability in their estimates of short-duration lapses of time (like 1-second and 2-second durations) and a greater tendency to overestimate time (e.g. producing a 1.5-second duration when asked to produce a 1-second duration).
Many questions remain about how and why changes in microgravity affect time perception, but the mechanism is likely related to how microgravity changes our interoception, or the perception of our internal bodily sensations. According to prominent theories of time perception, we rely on internal bodily sensations (like our heartbeat and our breathing) to keep time.
Simulating microgravity with head-down tilt
Now researchers may be able to address questions about how microgravity affects time without launching participants into space. It turns out that simply lying down for a while in a head-down tilt (HDT), as shown in the figure below, can cause similar physiological and vestibular changes that are associated with microgravity.
A new study published in this month’s issue of Perception investigated whether a simple change in one’s body posture can result in similar disruptions to our sense of time as experiencing microgravity. In the study, Dr. Weicong Ren and co-authors asked whether exposing participants to 30 minutes of head-down tilt would influence observers’ judgment of time, similar to what has been shown in astronauts.
Participants (16 students from Hebei Normal University) completed a time reproduction task in which they first saw a blue square for a variable amount of time (0.8 seconds, 1 second, or 2 seconds). The blue square then disappeared, and after a brief delay, a gray square appeared on the screen. Participants were instructed to press a button to indicate when the gray square had been on the screen for the same amount of time as the previous blue square. Performance on this time reproduction task was measured in three ways: an absolute error measure; a relative ratio measure; and a coefficient of variation (or how inconsistent responses were from trial to trial). Critically, participants completed the task twice—once before the head-down tilt intervention, and once following 30 minutes of lying in a 30-degree head-down tilt.
As the researchers predicted, performance in the time reproduction task was altered by the head-down tilt manipulation. Participants were more prone to make larger errors after the head-down tilt manipulation than before. Furthermore, participants were more likely to overestimate short durations after the head-down tilt manipulation than before. These results are in accordance with previous findings with astronauts and support the notion that body tilt can lead to similar changes in time perception as experiencing microgravity.
The results of this work suggest that researchers can continue asking questions about microgravity without the expenses and challenges associated with space flight research. For example, researchers can address whether changes in time perception associated with being in a virtual environment are exaccerbated during head-down tilt. Such research will not only address questions about microgravity pertinent to pilots and astronauts, but will also reveal how different mechanisms of time perception interact.