1. Evolution and the Theory of Games 1982
2. Choices Values and Frames 2000
3. Foraging Theory 1986
4. Behavioral Ecology: An Evolutionary Approach 1997
5. Value is an inherently subjective concept. To study value it is necessary to first operationalize it in terms of variables that can be directly observed. One external determinant of value is reward which we define as anything that an animal will work to acquire (a squirt of juice in the case of our thirsty monkeys). At an intuitive level the value of a behavioral option to our monkeys could be related to several aspects of the liquid reward including its size or its inherent desirability (e.g. sweet juice versus water). In the matching task used in this study value is related to the frequency with which an option results in reward. This concept is captured by the economic term “income ” defined as the number of rewards earned over some period of time. We show that we can effectively quantify an option's value in terms of the income experienced by the monkey over a well-defined recent period of time which we term “local income.” Because the matching task is a two-alternative forced-choice task the local income associated with a single behavioral option is only a fraction of the total income earned as the monkey distributes its choices between the two options. We therefore use the term “local fractional income” (defined formally in Fig. 2) to refer to the local income associated with a single behavioral option.