Negative Priming

In the incongruent or conflict condition of Stroop color naming, an additional slowing of performance is observed, over and above the usual interference, if the color name to be produced on any given trial is the same as the color word that had to be ignored on the immediately preceding trial. This effect, which has been dubbed negative priming, can be found in a wide variety of task situations in which two stimuli occur on each trial, one to be ignored and the other requiring a response. When a just-ignored distractor becomes the target on the next trial, responding is slowed relative to not having ignored the current target item in the recent past. Similar slowing occurs when there is just one stimulus on each trial to which subjects must produce a newly learned arbitrary response. Suppose that subjects must say "car" whenever they see "bike" or a picture of a bike, "plane" whenever they see "car" or a picture of a car, and "boat" whenever they see "plane"

or a picture of a plane. Now suppose that as a prime the subject sees "car" and correctly says "plane." If the succeeding target is "bike," production of the correct response "car"—the overlearned response that had to be avoided when processing the prime—will be slower than if the prime was an unrelated stimulus that required an unrelated arbitrary response, such as "plane''-"boat."

The dominant interpretation of negative priming invokes a selective process that occurs while processing the prime. To respond appropriately, subjects must select against the distracter item that is the nonimperative component of the prime (or, in a task such as that of Shiu and Kornblum's just described, they must select against the overlearned but contextually inappropriate response that the prime tends to elicit). The act of selection leaves the distractor or the overlearned response in a state that makes it more difficult to process if it recurs as the target.

Two sorts of hypotheses have been offered about how this act of selection could be implemented. According to the distractor inhibition hypothesis, attentional operations actively inhibit either the prime's perceptually activated mental representation, in order to prevent it from competing for access to response selection operations, or the link between the prime's mental representation and the action ordinarily associated with the prime, in order to make that response unavailable. Inhibition takes time to dissipate. Therefore, if the inhibited representation or response link is needed soon thereafter for processing a target, more time and effort will be required for its activation. George Houghton and Steven Tipper constructed a simulation model embodying such processes.

According to an alternative proposal, the episodic retrieval hypothesis of W. Trammell Neill and colleagues, attentional operations mark the distractor item with a "do not respond to this stimulus'' tag or the overlearned response with a "do not produce this response'' tag. The tag provides an instruction that guides decision and response selection, and it remains a part of the experience of having processed the prime that is stored in episodic memory. When the target appears it acts as a cue to retrieve this memory. The tag that served the subject well when the tagged stimulus or response needed to be ignored causes confusion and interferes with performance when the tagged item becomes the target.

Note that the episodic retrieval hypothesis does not propose inhibition in the classic sense of reduction or suppression of activation. Its inhibitory process is

"symbolic" rather than "analog," acting through an influence on a mental representation's informational content rather than its level of activity. Considerable effort has been expended attempting to distinguish these two underlying mechanisms by which an overtly inhibitory behavioral outcome might arise. Arguments have begun to appear that both mechanisms may be at work, and partly as a solution to the dilemma, in 1998 Milliken et al. made an important attempt to reinterpret negative priming in terms of the difficulty of deciding whether retrieved episodic memories of past processing should or should not be used to guide current performance rather than whether they have been inhibited or tagged with negative content. This debate illustrates a crucial point mentioned earlier. Inhibition of behavior (i.e., slowing of overt performance) does not necessarily signal inhibition of mental processing, if what one means by "inhibition of mental processing" is reduction or suppression of activation. Considerable theoretical analysis and empirical investigation are often required to make this determination.

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