When are nonwords easy to see?

The influences of presentation mode (mixed vs. blocked trials) and target variability on the detection of targets in words and in random letter strings were examined. The results indicated that there was a substantial word superiority effect in mixed lists of words and nonwords, but that this effect was eliminated when pure lists of words and nonwords were compared. Also, target variability affected the shape of the serial position curve. When subjects searched repeatedly for a single target, the serial position curve had only a significant linear component. However, when the identity of the target varied from trial to trial, the serial position curve had a significant quartic component (i.e.. it was M-shaped). These results were interpreted in terms of strategies and feature learning.