Here's the abstract:
What are the effects of reading fiction? We propose that literary fiction alters views of the world through its presentation of difference—different minds, different contexts, and different situations—grounding a belief that the social world is complex. Across four studies, two nationally representative and one preregistered (total n = 5,176), we find that the reading of literary fiction in early life is associated with a more complex worldview in Americans: increased attributional complexity, increased psychological richness, decreased belief that contemporary inequalities are legitimate, and decreased belief that people are essentially only one way. By contrast, early-life reading of narrative fiction that presents more standardized plots and characters, such as romance novels, predict holding a less complex worldview.
It is notable to me that in their conclusions the authors note that:
In providing capacious labels we have likely obscured important differences within genres that may speak to our hypotheses. We would expect that any reading experience that forces the reader to grapple with difference (e.g., by sketching rich inner lives and complex settings) should lead to a greater sense of complexity in the world. While we expect that those features are more likely to appear in ‘literary fiction’, there is nothing to say other genres of reading do not regularly fill that brief. For example, we suspect that reading ‘soft’ science fiction (which focuses on how characters exist in novel settings, as opposed to ‘hard’ science fiction which places more emphasis on the mechanics of the new setting itself, see e.g. Wilde, 2017) should have similar effects as reading literary fiction. In these studies, we use genre as a shorthand. (page 34 of the preprint)
however, the fact that science fiction is used as an example here, whereas the previous focus was on romance, which was described as
characterized by stock settings, characters, and plots, thereby differing from literary fiction in the degree to which they pose a challenge to a reader’s view of the world (see Modleski, 1982; Radway, 1984 for ethnographies of the relationship between romance novels and their readers, and see Fuchs, 2004; Regis 2003 for the formal elements that are commonly identified with romance novels).To quote one acclaimed romance novelist about the genre, “Successful authors become successful not because of their conventional writing skills, but because of how accessible they make their fantasies.” (Krentz, 1992, p. 4). Accessibility, ease; and not difference, in other words, are the keys to a successful romance novel. (page 6 of the preprint)
might suggest that the authors do not expect "important differences [...] that may speak to our hypotheses" to exist in romance.