Final answer:
The correct answer to the question is 'salience.' Salience is what makes a stimulus stand out and captures attention due to its distinct physical properties such as color, contrast, or movement.
Step-by-step explanation:
The physical properties of a stimulus, including its color, contrast, or movement, define its salience. Salience refers to the feature of a stimulus that stands out and is likely to attract attention due to its distinctiveness or intensity compared to the surrounding environment. The other options provided (reliability, specificity, and instrumentality) do not accurately describe the physical characteristics of stimuli that make them noticeable or prominent.