Experimental conditions are the subsets of an experiment that define the relevant experimental manipulation.
In the Cognitive Atlas, we define a contrast as any function over experimental conditions. The simplest contrast is the indicator value for a specific condition; more complex contrasts include linear or nonlinear functions of the indicator across different experimental conditions.
An indicator is a specific quantitative or qualitative variable that is recorded for analysis. These may include behavioral variables (such as response time, accuracy, or other measures of performance) or physiological variables (including genetics, psychophysiology, or brain imaging data).