Drinking in a patchy environment: the effect of the price of water.
Rats divide drinking time between water sources exactly as the matching law predicts, giving another clear animal model of choice.
01Research in Context
What this study did
Scientists let rats drink from two water spouts in a box.
One spout gave water only after many lever presses. The other gave water after fewer presses.
The team counted how rats split their drinking between the two spouts when the cost changed.
What they found
Rats matched their time to the payoff. They spent more time at the cheaper spout.
The animals followed the matching law: time tracked water per minute, not just total sips.
How this fits with other research
Anonymous (1995) saw the same matching pattern when rats worked for food pellets.
Together, the two studies show the rule works for both water and food.
Collier et al. (1986) first framed lever pressing as buying food. Evans et al. (1994) stretched the same idea to drinking, proving the economic view holds across commodities.
Why it matters
The matching law is a core tool for understanding choice. This water study gives you one more clean demo to share with staff or parents. Use it to explain why clients may switch to the easier task when you raise the response requirement on another.
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02At a glance
03Original abstract
Rats in a laboratory foraging paradigm searched for sequential opportunities to drink in two water patches that differed in the bar-press price of each "sip" (20 licks) of water within a bout of drinking (Experiment 1) or the price and size (10, 20, or 40 licks) of each sip (Experiment 2). Total daily water intake was not affected by these variables. The rats responded faster at the patch where water was more costly. However, they accepted fewer opportunities to drink, and thus had fewer drinking bouts, and drinking bouts were smaller at the more costly patch than at the other patch. This resulted in the rats consuming a smaller proportion of their daily water from the more costly patch. The size of the differences in bout frequency and size between the patches appears to be based on the relative cost of water at the patches. The profitability of each patch was calculated in terms of the return (in milliliters) on either effort (bar presses) or time spent there. Although both measures were correlated with the relative total intake, bout size, and acceptance of opportunities at each patch, the time-based profitability was the better predictor of these intake measures. The rats did not minimize bar-press output; however, their choice between the patches and their bout sizes within patches varied in a way that reduced costs compared to what would have been expended drinking randomly. These data accord well with similar findings for choices among patches of food, suggesting that foraging for water and food occurs on the basis of comparable benefit-cost functions: In each case, the amount consumed is related to the time spent consuming.
Journal of the experimental analysis of behavior, 1994 · doi:10.1901/jeab.1994.62-169