Final answer:
The condition described is a Stable and controlled experimental condition, denoted by the stability of the subject, absence of intertrial variability, and a consistent environment, matching option C from the given choices.
Step-by-step explanation:
The experimental conditions characterized by a stable body, no intertrial variability, and a stationary (closed) environment are indicative of a Stable and controlled experimental condition. This means that the variables which could affect the outcome of the experiment are tightly managed. A controlled environment, where the independent variable is manipulated and the dependent variable is measured while all other variables are kept constant, matches these criteria. In such settings, researchers can make more reliable causal inferences about the variables being studied. So, the correct answer would be C) Stable and controlled experimental condition.
Control of extraneous variables in experimental research is essential for developmental psychologists to draw conclusions about the developmental process. Lab-based experiments offer a high degree of control, while natural or field experiments provide contextual accuracy but less control. An essential aspect of experimental research is the ability to manage intertrial variability, ensuring that each trial is conducted under the same conditions, to attain reliable results.