letter, each black letter is the same as the gray letter above it. A number of
experiments show that subjects take longer to read the second list (Driver
& Tipper, 1989; Tipper & Driver, 1988).
According to the authors of such experiments, subjects take longer to read
the second column because they actually process the green letters unconsciously
and have to inhibit or prevent themselves from responding to them. When,
after having inhibited a particular letter, subjects are asked to respond to it,
they are slowed down because they have to unblock or disinhibit the letter
and make it available for response. For example, when you read the first black
letter in the second row, you had to ignore, or inhibit, a gray H. The second
black letter in the row happens to be the letter H. Thus, when you try to read
the black H, you have to unblock, or disinhibit, the letter H. Nothing similar to
this happens when you read the first row of letters; the black letters in this row
never appear as gray letters.
Figure 7.11
A test of your attentional mechanism. First, read aloud the black letters in Column one as quickly as
possible, disregarding the gray. Next, quickly read the black letters in Column two, also disregard-
ing the gray. Which took longer?
152 Philip G. Zimbardo and Richard J. Gerrig