The literature proposes sone theories, e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6384527/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6384527/ says c

The literature proposes sone theories, e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6384527/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6384527/ says comprehension is about the same, but that a physical book makes it easier to remember if something happened earlier or later in the book. On a completely unscientific annecdote that seems to match my experience, where with paper I subconciously remember positions in the book, while on a kobo every page feels the same. That said, full text search is sorely missed on dead tree.