A recent paper in Cortex describes how caloric vestibular stimulation (CVS), i.e., rinsing of the ear canal with cold water, reduces unrealistic optimism. Here are some bits from the paper:

Participants were 31 healthy right-handed adults (15 men, 20–40 years)...

Participants were oriented in a supine position with the head inclined 30° from the horizontal and cold water (24 °C) was irrigated into the external auditory canal on one side (Fitzgerald and Hallpike, 1942). After both vestibular-evoked eye movements and vertigo had stopped, the procedure was repeated on the other side...

Participants were asked to estimate their own risk, relative to that of their peers (same age, sex and education), of contracting a series of illnesses. The risk rating scale ranged from −6 (lower risk) to +6 (higher risk). ... Each participant was tested in three conditions, with 5 min rest between each: baseline with no CI (always first), left-ear CI and right-ear CI (order counterbalanced). In the latter conditions risk-estimation was initiated after 30 sec of CI, when nystagmic response had built up. Ten illnesses were rated in each condition and the average risk estimate per condition (mean of 10 ratings) was calculated for each participant. The 30 illnesses used in this study (see Table 1) were selected from a larger pool of illnesses pre-rated by a separate group of 30 healthy participants.Overall, our participants were unrealistically optimistic about their chances of contracting illnesses at baseline ... and during right-ear CI. ...Post-hoc tests using the Bonferroni correction revealed that, compared to baseline, average risk estimates were significantly higher during left-ear CI (p = .016), whereas they remained unchanged during right-ear CI (p = .476). Unrealistic optimism was thus reduced selectively during left-ear stimulation.

(CI stands for caloric irrigation which is how CVS was performed.)

It is not clear how close the participants came to being realistic in their estimates after CVS, but they definitely became more pessimistic, which is the right direction to go in the context of numerous biases such as the planning fallacy.

The paper:

Vestibular stimulation attenuates unrealistic optimism

  • Ryan McKay
  • Corinne Tamagni
  • Antonella Palla
  • Peter Krummenacher
  • Stefan C.A. Hegemann
  • Dominik Straumann
  • Peter Brugger

(paywalled, but a pre-publication version is available

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FWIW I already summarized this study in a LessWrong comment 3 weeks ago.

Squirting water into ears has come up on LW before in connection with anosognosia, e.g. The Apologist and the Revolutionary. So this is at least somewhat consistent with my model of reality.

I read somewhere on here that it also makes you vomit.

That would indeed briefly diminish my optimism.

No, it's not that bad. But it does give you genuine vertigo - I was surprised when I did it that it wasn't just a little vertigo but closer to roller coaster vertigo. Apparently shocking your inner ear really does stuff!

Indeed anosognosia is mentioned multiple times in the paper, perhaps serving as the motivation.

I don't think that adding a bias is "more rational" than not adding one, even if you are adding a bias that is in the opposite direction as a known one, unless you can estimate the total direction and magnitude of all of your biases and offset by that much.

Idle curiosity: I wonder if one can become happier by squirting water in one's right ear?

First, this is equivocating rationality and accuracy. Second, just because something results in more rational decisions, that doesn't mean that it is valid to characterize it as increasing rationality. If I observe a compass, and see that the direction is pointing coincides with the direction that Oregon is from my current location, it would be an error to conclude that compasses point towards Oregon.

So, people who habitually swim in cold water without earplugs should be more rational?

It's not that simple to get water that deep into your ears.

If you're interested in increasing your rationality, I have a homeopathic treatment specifically formulated for that purpose.

As long as the net effect of this isn't to make me cynical...

Even with the risk assessment metric based upon financial concerns, water to the ears may still trigger feelings of vulnerability - can anyone think of a way to mitigate this confound? Though I am curious why this effect would be more pronounced in the right hemisphere.


Subjects who know nothing of the study, control group gets right ear.

If the effect is truly only expressed in the right hemisphere, that would not clarify whether feelings of vulnerability or vestibulo-sensory signalling produce the lowered 'unrealistic optimism'.

Low sample size, not reproduced (unless I'm wrong?), unclear that results would generalize even if true. I'm not sure it's fruitful to pay attention to such studies.

There was previous evidence that indicates that putting water into your left ear makes you more rational ( http://lesswrong.com/lw/20/the_apologist_and_the_revolutionary/ ). This study basically encourages it to treat the idea of putting water for rationality purposes in your left ear more seriously than we did based on previous evidence.

The study is in press and you expect it to be reproduced already?

No. I just don't think a result should count as much evidence until it has been reproduced (unless perhaps the original study has met particularly rigorous experimental standards).

Maybe if somebody came up with a nice self-experiment protocol...

The experiment didn't compare cold water in the ear to other sorts of pain/distraction.

No, they did something even better than that..

Compared to baseline, average risk estimates were significantly higher during left-ear stimulation, whereas they remained unchanged during right-ear stimulation.

Say that the Wright brothers had played with this cold water in the left ear. They wouldn't even bother to travel to Kitty Hawk, would they?

They weren't taking a stab in the dark requiring optimism. Now, Columbus might be a different story.