CHAPTER 4 
Manipulation of Food 
and Fluid Access 
Delivery of food or fluids is commonly used to maintain extended sequences of behavior in 
studies with a wide range of animals. Species as diverse as dolphins, goats, pigs, sheep, 
cows, turtles, fish, octopuses, and crabs, as well as the more often used rats, mice, pigeons, 
and monkeys, have been trained to perform simple to complex tasks under training 
procedures in which small amounts of a food or fluid (referred to as rewards or reinforcers) 
are used to maintain performance. 
REGULATED VERSUS FREE ACCESS TO FOOD AND FLUIDS 
The widespread use of food or fluid reinforcers is due to their well-studied ability to motivate 
the development of a new behavior and to maintain stable responding for extended periods. 
Many experiments require weeks or months of experimental sessions (five to seven days per 
week), and require that stable performance be maintained from day to day. Experimental 
sessions can be very short (e.g., 10 minutes) or long (e.g., 12 hours); some studies conduct 
sessions intermittently or continuously over 24 hours (e.g., time course of drug effects). 
Control of access to food or fluid outside the experimental session ensures response reliably to 
the food or fluid reinforcer in each session. Maintaining performance reliably, even with a 
"treat," is better done in food-restricted animals than those fed ad libitum. There are 
additional reasons to control access to food. Many behavioral experiments seek to maintain 
weights within a constant, narrowly defined range, because fluctuating weights and/or hours 
of food restriction can be potential sources of behavioral variability. When animals have free 
access to food, the amount eaten in the hours just before experimental testing may vary. Also, 
weight regulation per se may be important as one means of minimizing other sources of 
variability in experimental results. In drug studies, for example, control of the animal's 
weight, and in some cases the spacing of meals, helps ensure uniformity of dosing across 
time. 
Restricted food access (either in laboratories or in the wild) is not unusual or undesirable. 
Experiments have demonstrated that a number of species are healthier and live longer if they 
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