Fleeting cues are typically used to introduce particular objects. However, more than an introductory cue is needed when rendering complex structures. For instance, a fleeting cue at the beginning of each item is not sufficient when rendering an itemized list -the listener is likely to forget the current context if the items are complex.
In the visual setting, the logical structure of a list is displayed by super-imposing indentation, an implicit layout cue, on the text. AsTeR uses persistent audio cues to achieve a similar effect. These cues consist of either a change in some characteristic of the speaking voice or a sound that repeats in the background and have the advantage of being present during the entire rendering, without detracting from the flow of information.