Figure 16.4
Presence of absence of a feature can have remarkably different effects on the time it takes to find a
target in the midst of distractors. In one experiment (a) the target was a circle intersected by a ver-
tical line segment or a circle without that feature. The search time for the intersected circle (solid)
proved to be largely independent of the number of items in the display, suggesting that the feature
popped out. The search time for the plain circle (dashed) increased steeply as distractors were
added, suggesting that a serial search of the display was being made. A second experiment (b)
required subjects to search for a vertical line (dashed) or a tilted line (solid). The tilted line could be
found much faster; evidently only the tilted line popped out of the displays. A third experiment (c)
tested an isolated line segment (dashed) or intersecting lines in the form of a plus sign (solid). Evi-
dently neither popped out.
406 Anne Treisman