Automatic attraction of attention to former targets in visual displays of letters.

Shiffrin and Schneider (1977, Experiment 4d) reported that after consistent training in search for particular alphanumeric characters, presentation of one of these characters (former targets) as a distractor impeded detection of simultaneously presented current targets. Even if presented in an irrelevant display location, the former target appeared to attract attention. Here, we analyze weaknesses in the design of Experiment 4d and report four follow-up experiments ranging from a fairly close replication of the original multiframe experiment to a rather conventional single-frame search study. In each experiment, presentation of former targets consistently impeded detection of simultaneously presented current targets. The results suggest that automatic attention attraction to individual alphanumeric characters develops not only in the special experimental paradigm used by Shiffrin and Schneider, but also in standard visual search tasks. The fact that attention appeared to be attracted by shapes as complex as individual letters supports the assumption that simultaneously presented visual stimuli can be compared in parallel against memory representations of alphanumeric characters.