The sensory details that the text "suggests" but doesn't fully describe (like the specific shade of a character's blue eyes). The Stratum of Represented Objectivities:

Locating a PDF of Roman Ingarden’s The Literary Work of Art is easy. Mastering its insights is a lifetime’s work. But even a partial understanding reshapes how you read: you become aware of the gaps your mind fills, the strata your attention moves through, and the metaphysical qualities that emerge from a successful concretization.

The reader performs by filling in these gaps. This explains why two people can read the same book and "see" different things. The work itself remains a schema, while the concretization is the individual experience of that work. Polyphony and Aesthetic Value