motorized sounds, or just sitting in a quiet room with no video. My
video started playing, a simple scene from Yosemite of a summer
meadow, some chirping birds, a blue sky. But a couple of minutes in,
I heard a truck engine, followed by quiet, followed by the sound of a
propeller plane. I’d been assigned to the second condition, and I again
displayed a textbook response: once the nature video started, my heart
rate immediately sank to baseline mid-60s range. When the truck
rumbled, however, my heart rate shot up ten points. It took a while for
it to drop again, but after more quiet nature, it plummeted down to the
mid-50s. Now I was so relaxed I was practically dead. When noise #2
appeared, my heart rate shot back up, though not as high as the first
time. My cortisol levels from this part of the experiment, at 8.2,
reflected this almost-but-not-quite restored state (remember, my
original level was 6.7 and my speech level was 12.1).
Smyth was also recording my heart-rate variability (HRV), which
is fast becoming the darling of physiological stress measurements.
It’s increasingly used by scientists, medical doctors and athletic
coaches. My HRV had also been monitored in Korea before and after
hiking to tell me I had thickening veins. HRV is complicated to
understand, especially in translation. It essentially measures—in real
time—how quickly your autonomic nervous system responds to and
recovers from microevents in the environment. Your heart is like a
dancer—when it’s relaxed, it swans up and down with fluidity. That’s
high variability, and it’s good. But when you’re stressed, that
variability can clench into a much narrower range, the dancer getting
a cramp. Some people have chronically low HRV, which is linked to a
bunch of stress-related health outcomes like cardiovascular disease,
metabolic disease and early death. During the speech test—and the
loud noises—my HRV tightened up.
Noise, at least for me, really is a problem. The test showed that
it’s simply harder for someone who is noise-sensitive to fully unwind
in an urban environment, regardless of its nice parks and nesting