It's a Jungle in There: How Competition and Cooperation in the Brain Shape the Mind by David A. Rosenbaum

shirt, gazing where you shouldn’t, the slow return look is an example of inhibition of return. Your tendency to look more slowly at a site you weren’t supposed to illustrates
negative priming
. 24 In experiments where people have to ignore distracting stimuli (not encased in tee shirts), if those stimuli later become targets for visual searches, it takes longer to respond to the targets than if they weren’t distracters before. The distracters become stigmatized, so to speak, or negatively primed. In the parlance of cognitive psychology, they become inhibited. The inhibition sticks, at least for a while.
    Here’s another example of the importance of inhibition in attention. Suppose you agree to participate in an experiment in which you’re supposed to detect letters in the middle of a display. You’re supposed to pressone button as quickly as possible if you see the letter S and a different button if you see the letter
T
. The experiment has a devilish twist, however. You’re not shown one letter—just the
S
or the
T
. Instead, you’re shown the one target letter flanked by others. The flanker letters can complement or contradict the target. If the flankers complement the target and the target is
S
, you’re shown two pairs of
S
s on either side of the
S
in the middle, as seen in the first line below. On the other hand, if the flankers contradict the target and, again,
S
is the target, you may instead be shown two pairs of
T
s on either side of the middle
S
, as seen in the middle line below. There’s also a control condition where, as shown in the third line below, the middle
S
is flanked by pairs of neutral letters, like
X
, for which you don’t have a specific associated response. 25
    SSSSS
    TTSTT
    XXSXX
    What happens in this set of conditions? When the
S
is surrounded by
S
s, reaction times are short, but when the
S
is surrounded by
T
s, reaction times are long. Finally, when the
S
is flanked by
X
s, reaction times are middling.
    How can you explain this outcome? If the presence of non-
S
flankers (
T
s or
X
s) merely reduced the activation of the
S
response, you’d expect the reaction times to be no different when the
S
is surrounded by
T
s or by
X
s. But because
S
responses are longer when
S
is surrounded by
T
s (to which another response is assigned) than when
S
is surrounded by
X
s (to which
no
response is assigned), the
T
flankers lead to inner conflict. When an
S
appears, its inner agents are activated and they try to launch their associated response while also trying to inhibit the response of the “enemy”
T
s. When the
T
s appear, their inner agents are activated, and they try to generate their associated response while inhibiting the response associated with
S
. The correct response comes out only after the battle has been waged.
    Positing an inner battle isn’t just borne of a shoot-’em-up mentality. Direct evidence for such skirmishes in the flankers task has been obtained from studies of muscle activity. 26 Using electrodes that picked up muscle activity of participants performing the flankers task, Michael Coles and colleagues at the University of Illinois (in the same department where the flankers task was developed) showed that the muscles of the two hands become active when participants were shown competing stimuli. If the target stimulus called for a response with one hand and the flankers called for a response of the otherhand, the muscles of
both
hands came on. Only gradually did the muscles of the wrong hand quiet down while the muscles of the correct hand contracted more intensely. Cognitive psychologists call this process
response competition
.
    For response competition to be inferred, you don’t have to see muscle co-activation in competing responses. Whenever decision times are elevated because mutually exclusive responses are called for, response competition is likely to play a role. Appealing to response competition is hardly controversial in studies of attention and