Writing with AI Lowers Psychological Ownership, but Longer Prompts Can Help

Feelings of something belonging to someone is called "psychological ownership." A common assumption is that writing with generative AI lowers psychological ownership, but the extent to which this occurs and the role of prompt length are unclear. We report on two experiments to better understand the relationship between psychological ownership and prompt length. Participants wrote short stories either completely by themselves or wrote prompts of varying lengths, enforced through word limits. Results show that when participants wrote longer prompts, they had higher levels of psychological ownership. Their comments suggest they felt encouraged to think more about their prompts and include more details about the story plot. However, these benefits plateaued when the prompt length was 75-100% of the target story length. Based on these results, we propose prompt entry interface designs that nudge users with soft and hard constraints to write longer prompts for increased psychological ownership.