Final answer:
The brain increases blood flow to active regions during tasks like recognizing faces; this physiological response serves as a measure of neural activity. Observing reactions to stimuli provides insight into brain processes and conditioning effects.
Step-by-step explanation:
The brain responds to stimuli by increasing blood flow to active neural tissue during certain tasks, such as visual recognition. When a person recognizes a face, as in the experiment where subjects look at photographs and press a button for recognition, specific areas of the brain related to memory, pattern recognition, and decision-making are activated. This results in increased blood flow, which can be measured and used as an indication of brain activity.
In the context of the given study, observing Little Albert's reactions to stimuli before and after conditioning would show changes in neural activity. If conducting such an experiment today, ethical considerations would be of utmost importance due to the distress caused to Little Albert in the original experiments by Watson and Rayner.