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Robert Kurzban

The Evolutionary Psychology Blog

By Robert Kurzban

Robert Kurzban is an Associate Professor at the University of Pennsylvania and author of Why Everyone (Else) Is A Hypocrite. Follow him on Twitter: @rkurzban

If Pee Then Stroop

Published 2 March, 2011

There are, sadly, so few opportunities to discuss research on urinating, I thought I should take advantage of this one.

Coming soon to Psychological Science, a paper that asks that eternal question, are you better at Stroop tasks when you really have to pee?

The research by Mirjam Tuk and colleagues – a version of which is available on SSRN – reports a series of experiments that investigate the effects of a full bladder on performing the Stroop task as well as a discounting task – e.g., would you rather have less money tomorrow or a bit more next week?

The usual framing for self control is that self control relies on a resource, and when one exerts self control, inhibiting some behavior or other, that resource gets depleted, leaving less of it for self control on another task. As the authors put it, “A filling bladder increasingly triggers inhibitory responses (Griffiths & Tadic, 2008). People increasingly have to inhibit their (motor) impulse to void.” So you might expect that as you sit around with an increasingly full bladder, your “self control” gets all used up, and you are worse at tasks that require the putative resource, such as the Stroop task – naming the color of the ink a word is shown in, so that you would have to answer “blue” when you saw the word “green” printed in blue ink.

Tuk and colleagues had people come into the lab, do a Stroop task, and then indicate just how badly they had to “void,” as they put it. People who have to pee more turned out to be faster on the Stroop. In their words, “response times on the color naming blocks decreased with increasing urination urgency.”

Hm. That’s the reverse of what you would expect. You’re supposed to get worse on Stroop tasks after you’ve been “controlling your self.”

They conducted three more studies, this time looking at monetary choices instead of the Stroop. The dependent measure in this case was patience – would you rather have $1 today or $2 tomorrow, or what have you. Again, having to pee led to the outcome that was supposed to require more, not less, self control. People who have to pee can delay gratification more.

The authors explain these results using the very appropriate metaphor, given the content, of hydraulics: it’s a spillover effect. As they put it, “inhibitory signals stemming from increased bladder pressure spill over to the domain of intertemporal choice, reflecting an increasing ability to inhibit the urge to go for the more immediate (but smaller) reward, and opt more often for the reward which is more beneficial in the long term.”

In other words, if your bladder is full, you’re inhibiting peeing, and this inhibition — to choose a different yet similarly fluid metaphor – leaks into other areas.

And a little bonus, since today’s post is a little on the short side. Mark Regnurus at Slate wrote a piece about human sexuality, and alludes to a new idea in the social psychology literature called “sexual economics.” The idea seems to be that there are sex differences surrounding sexuality are driven by the fact that “men want sex more than women do.” Hm. For some reason, that idea sounds vaguely familiar to me…

  • DiscoveredJoys

    That’s intriguing. Does it mean that we ought to test if responses to (say) the Myers-Briggs Type Indicator are affected by physiological state?

  • http://www.psychologytoday.com/blog/homo-consumericus Gad Saad

    Hi Rob,

    Apparently, you beat me to the punch as I put up a post on this exact study a few days after you. Perhaps this is why my post has not received the customary large number of views! 😉


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