R5 — Pair interactivity with restraint: add interactive features ONLY where they let the user do something they need to; "too much interactivity" reduces deep elaboration

Rule: Add interactive features only where they let the user accomplish something necessary to the tool's purpose. Decorative interactivity (sliders, animations, drag-zooms for their own sake) reduces deep elaboration and can net-decrease engagement quality.

Why: Oh & Sundar 2015 (COUNTER-finding: Oh & Sundar 2015 also showed modality interactivity REDUCED the number of message-related thoughts — absorption can come at the cost of deep elaboration; Sundar warns of "too much interactivity") — modality interactivity reduced message-related thoughts; absorption can come at the cost of deep elaboration. Sundar broader work warns of "too much interactivity" cost. ICAP's behaviour-based coding limit (Chi & Wylie (2014), Educational Psychologist 49(4) — ICAP framework: Interactive > Constructive > Active > Passive engagement; ~8-10% learning improvement per step) — overt behaviour ≠ guaranteed cognitive engagement.

How to apply:

• Every interactive feature must answer "what user task does this enable?" If the answer is decorative, remove it.
• Prefer message interactivity (the system responds contingently to user input — calculator core) over modality interactivity (sliders, zooms, drags) when they compete for screen space.
• When stakes are high (the user needs to understand the output, not just see it), reduce interactivity around the result to support elaboration.