Semantic encoding refers to the processing of:

Semantic encoding is the cognitive process that involves the interpretation and understanding of information based on its meanings. This type of encoding focuses on attaching significance and context to the information being processed, which facilitates better retention and retrieval from memory. For example, when learning a new word, understanding its meaning and how it relates to concepts you already know helps to embed that information into long-term memory.

In contrast, processing sounds relates more to auditory encoding, capturing the phonetic aspect of information rather than its significance. Visual imagery pertains to visual encoding, which involves creating mental images of stimuli, focusing on how they appear rather than what they mean. Processing unfamiliar units refers to various forms of encoding that may not specifically focus on semantic understanding, such as rote memorization of facts without grasping their meanings. Thus, the essence of semantic encoding is its emphasis on meaning, making it the most relevant choice in this context.