Participants were asked to scan a field of characters and indicate when a particular character was identified. Results of that study provided suitable speeds of cursor movement, which could be extrapolated to infer speeds of eye movement, at the different conditions examined in the study.
The conditions of that study which are directly relevant to this study are the density of the background characters and the background characters themselves.
The background characters and character density are similar to the anomalies and casting surfaces examined in this study.