A researcher gives participants a list of words referring to concrete objects (e.g., car, apple, box). She tells the first group of participants to form a vivid mental image of each object. She tells the second group to think of a story using all the words from the list. Both groups then completed a memory test. What concept is the researcher most likely testing with the first group of participants?

a. Semantic encoding
b. Visual encoding
c. Acoustic encoding
d. Simultaneous encoding