  Social media platforms depend on algorithms to select, curate, and deliver
content personalized for their users. These algorithms leverage users' past
interactions and extensive content libraries to retrieve and rank content that
personalizes experiences and boosts engagement. Among various modalities
through which this algorithmically curated content may be delivered, the
homepage feed is the most prominent. This paper presents a comprehensive study
of how prior user interactions influence the content presented on users'
homepage feeds across three major platforms: YouTube, Reddit, and X (formerly
Twitter). We use a series of carefully designed experiments to gather data
capable of uncovering the influence of specific user interactions on homepage
content. This study provides insights into the behaviors of the content
curation algorithms used by each platform, how they respond to user
interactions, and also uncovers evidence of deprioritization of specific
topics.
