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