‘Classical’ response
“Participants exhibited an increased heart period after tone onset, which returned to baseline following an average canonical bell shape,” the authors reported.
The researchers performed regression analyses to determine how, on average, the heart rate before the tone was related to perceived duration or how the amount of change after the tone was related to perceived duration.
They found that when the heart rate was higher before the tone, participants tended to be more accurate in their time perception. When the heartbeat preceding a tone was shorter, participants experienced the tone as longer; conversely, when the heartbeat was longer, they experienced the duration of the identical sound as shorter.
When participants focused their attention on the sounds, their heart rate was affected such that their orienting responses actually changed their heart rate and, in turn, their temporal perception.
“The orienting response is classical,” Ms. Sadeghi said. “When you attend to something unpredictable or novel, the act of orienting attention decreases the HR.”
She explained that the heartbeats are “noise to the brain.” When people need to perceive external events, “a decrease in HR facilitates the intake of things from outside and facilitates sensory intake.”
A lower HR “makes it easier for the person to take in the tone and perceive it, so it feels as though they perceive more of the tone and the duration seems longer – similarly, when the HR decreases.”
It is unknown whether this is a causal relationship, she cautioned, “but it seems as though the decrease in HR somehow makes it easier to ‘get’ more of the tone, which then appears to have longer duration.”
Bidirectional relationship
“We know that experienced time can be distorted,” said Dr. Arslanova. “Time flies by when we’re busy or having fun but drags on when we’re bored or waiting for something, yet we still don’t know how the brain gives rise to such elastic experience of time.”
The brain controls the heart in response to the information the heart provides about the state of the body, she noted, “but we have begun to see more research showing that the heart–brain relationship is bidirectional.”
This means that the heart plays a role in shaping “how we process information and experience emotions.” In this analysis, Dr. Arslanova and colleagues “wanted to study whether the heart also shapes the experience of time.”
To do so, they conducted two experiments.
In the first, participants (n = 28) were presented with brief events during systole or during diastole. The events took the form of an emotionally neutral visual shape or auditory tone, shown for durations of 200 to 400 ms.
Participants were asked whether these events were of longer or shorter duration, compared with a reference duration.
The researchers found significant main effect of cardiac phase systole (F(1,27) = 8.1, P =.01), with stimuli presented at diastole regarded, on average, as 7 ms longer than those presented at systole.
They also found a significant main effect of modality (F(1,27) = 5.7, P = .02), with tones judged, on average, as 13 ms longer than visual stimuli.
“This means that time ‘sped up’ during the heart’s contraction and ‘slowed down’ during the heart’s relaxation,” Dr. Arslanova said.
The effect of cardiac phase on duration perception was independent of changes in HR, the authors noted.
In the second experiment, participants performed a similar task, but this time, it involved the images of faces containing emotional expressions. The researchers again observed a similar pattern of time appearing to speed up during systole and slow down during diastole, with stimuli present at diastole regarded as being an average 9 ms longer than those presented at systole.
These opposing effects of systole and diastole on time perception were present only for low and average arousal ratings (b = 14.4 [SE 3.2], P < .001 and b = 9.2 [2.3], P <.001, respectively). However, this effect disappeared when arousal ratings increased (b = 4.1 [3.2] P =.21).
“Interestingly, when participants rated the events as more arousing, their perceived durations contracted, even during the heart’s relaxation,” Dr. Arslanova observed. “This means that in a nonaroused state, the two cardiac phases pull the experienced duration in opposite directions – time contracts, then expands.”
The findings “also predict that increasing HR would speed up passing time, making events seem shorter, because there will be a stronger influence from the heart’s contractions,” she said.
She described the relationship between time perception and emotion as complex, noting that the findings are important because they show “that the way we experience time cannot be examined in isolation from our body,” she said.