Final answer:
The recency effect occurs when material presented later in a message is most impactful, often due to the temporal proximity to the decision-making moment.
Step-by-step explanation:
The type of effect said to occur when material presented later in a message has the most impact is known as the recency effect. This effect has been studied in the context of persuasion and memory, and suggests that items presented last in a series are often remembered most readily or have the greatest influence on opinions and decisions. Findings by Miller & Campbell (1959) contribute to this understanding, indicating that when there's a delay after the first message and before the need to make a decision, the last message presented tends to be more persuasive.