Which concept refers to the panelist's adaptation to a stimulus over time?

The correct choice refers to the concept of habituation, which describes the process by which a panelist gradually reduces their response to a stimulus after repeated exposure to it. This adaptation occurs because the sensory system becomes accustomed to the stimulus, resulting in a decreased sensitivity and response over time.

Habituation is particularly relevant in sensory testing, as it helps to explain why repeated exposure to the same sensory information may lead to a less intense perception of that stimulus. For instance, in a taste panel, a panelist may initially find a particular flavor strong but may perceive it as milder after multiple tastings.

The other options involve different concepts. Desensitization generally refers to a reduction in emotional responsiveness or sensitivity to specific stimuli, often used in psychological contexts. Calibration involves adjusting scale settings or responses to ensure accurate measurements in sensory evaluations. Normalization refers to the process of adjusting data to bring it into a standard format, ensuring consistency across different measurements or assessments. These concepts, while related to sensory analysis, do not specifically address the adaptation to stimuli that habituation describes.