Psychology Of Interference And Inhibition Research Paper

1. Interference, Inhibition, And Selective Attention

Traditionally, selective attention has been thought to be a function of activation. That is, after initial automatic processing, relevant information is selected (early or late, depending on the locus of the ‘selective filter’) by an activation or facilitation mechanism (Broadbent 1958, Deutsch and Deutsch 1963, Norman 1968, etc.). From then on, irrelevant information is no longer processed, and its effect dissipates passively over time. An alternative conception, the attentioninhibition view (see Bruce and Tipper 1998, Houghton et al. 1996, Neill et al. 1995), has gradually taken over from classical attention-activation theory. In this new approach, the essential mechanism of selective attention is inhibition (or resistance to interference), i.e., the active blocking of irrelevant information. In this case, the cognitive processing of relevant information, after selection, is not seen as being due to specific activation-facilitation, but simply to the fact that processing is no longer adversely affected by interfering irrelevant information.

For psychologists, the question becomes how can these two possible modes of cognitive selection be distinguished experimentally. The paradigm designed to do this is negative priming. Using this paradigm has become the most popular way of measuring inhibition and its interconnection with interference. Take a situation where the subject has to respond first to S1 (the relevant or target stimulus) while ignoring S2 (the irrelevant or distractor stimulus, the one that interferes). Suppose that afterwards the subject unexpectedly has to respond to S2, or in another condition to S3 (a new stimulus). The first part of this procedure is called ‘the prime’ and the second part is called ‘the probe.’ The attention-activation view says that during the prime, S2 dissipates passively over time since it is not selectively activated. If the effect of S2 has not yet completely disappeared from memory when the probe appears, then S2 (now the relevant stimulus) should be easier and faster to process than S3. This is the classic priming effect (positive priming or facilitatory effect), which is measured using mental chronometry (reaction time in ms). Still in the activation view, if the initial effect of S2 has completely faded when the probe arrives, then S2 processing should not differ from S3 processing. Now in the alternative view, attention-inhibition, the prediction for this same prime–probe sequence is exactly the opposite. In this case, S2 is inhibited on the prime, i.e., it is actively blocked in resistance to interference, so it should be more difficult (slower) to process than S3 on the probe. This is the negative priming effect.

Under the impetus of S. P. Tipper (1985), who introduced the negative priming idea into cognitive psychology, a large number of experimental studies on adults have confirmed the existence of this phenomenon in a wide variety of situations, including identification tasks (picture naming, word naming, letter identification), categorization tasks (semantic categorization, lexical decision), matching tasks (letter matching, shape matching), counting tasks, localization tasks, and so on. In Tipper’s (1985) influential study using picture-naming tasks, subjects were shown superimposed line drawings. One stimulus (S1), the relevant one (target), was drawn in red, and the other (S2), the irrelevant one (distractor), was drawn in green (e.g., S1=a kite and S2=a trumpet). So on the prime, interference came from the green stimulus (here, the trumpet). In the negative priming condition, the prime–probe sequence was such that the prime distractor became the probe target (the same trumpet now drawn in red ink). Naming latencies were significantly slower in this condition than when the prime and probe trials were unrelated (that is, when a new stimulus, S3, was introduced as the probe target). Note that the negative priming effect was also observed with a solely semantic relation (i.e., nonidentical) between the prime distractor and the probe target (e.g., a cat and a dog, respectively).

This first work by Tipper, and the many studies that followed (for reviews, see Bruce and Tipper 1998, Neill et al. 1995), have brought the inhibitory control of information into the foreground as an important mechanism of resistance to interference, with the negative priming (observed on the probe) being indicative of the existence and effectiveness of the inhibition (generated earlier on the prime). New and more precise questions then arose, such as: What is the exact nature of interference, and hence, what is in fact inhibited (the response, the perception, the representation)? Does inhibition depend on task requirements? How is episodic memory (retrieval) involved in negative priming? Is there a single inhibition mechanism or are there many? What parameters affect negative priming, knowing that in certain cases the expected effect is not observed? All of these theoretical and experimental questions are now under study in current research.

Initially, the negative priming paradigm was defined in terms of stimuli, with S1 as the target and S2 as the distractor (see the Tipper example above), but current research as illustrated in the following section also uses a variation applied directly to cognitive strategies.

2. Interference, Inhibition, And Cognitive Development

In the study of cognitive development, new experimental research has also been aimed specifically at analyzing interference and inhibition (Bjorklund and Harnishfeger 1990, Dempster 1992, Dempster and Brainerd 1995, Houde 2000, Houde et al. 2000, Pascual-Leone 1988, Tipper et al. 1989). In this framework, the underlying assumption is that cognitive development cannot be reduced to the mere coordination-activation of structural units or scheme (as in Jean Piaget’s 1984 structuralist theory and in the neo-Piagetian models, see Demetriou 1988) but that developing also means learning to inhibit a competing strategy (scheme). To illustrate this approach, two examples are given below in the areas of object construction in infancy and numerical abilities in childhood.

The question of the relationship between cognitive development, interference, and inhibition becomes a relevant one as soon as the basic unit of reality, the permanent object, is in place in the infant. Research on infant oculomotor activity, which uses the violation-of-expectancy paradigm, has shown that early object permanence already exists at the age of four or five months. How, then, can one explain the well-known A-not-B error, observed by Piaget (1954) at eight months and present until the age of one year? To demonstrate this error, the experimenter puts an infant in front of two covers that are equally easy to reach (A and B), and then puts an object under cover A. The infant has no trouble finding it. After a few repetitions (A-A-A…), the object is conspicuously moved under cover B. The infant who continues to search under A makes the A-not-B error.

According to Piaget, this error is a testimony to the lack of object permanence, in the sense that infants should know that the object continues to exist under cover B because that is where they lost sight of it. But this explanation is no longer tenable today. As indicated above, new research has shown that the object permanence scheme (acquired by the early age of four or five months) clearly precedes the A-not-B error. (Certain authors (Smith et al. 1999) even indicate that there are circumstances in which older children and adults make a similar error.) An interference-and-inhibition-based analysis is better able to resolve this paradox. Situations where oculomotor reactions to unexpected events are observed (events where object permanence is violated) can indeed be considered as optimal contexts where the ‘simple’ activation of object permanence suffices. The Piagetian situation, on the other hand, where the object disappears under A-A-A… and then under B, is a misleading situation which, according to neuropsychological analyses of the connection between frontal cortex maturation and the A-not-B error, requires the inhibition of a dominant motor tendency, i.e., the interfering preprogrammed gesture towards A (Diamond 1991, 1998). The A-not-B error is thus considered to be the outcome of an executive failure to inhibit a motor response—which leads to perseveration—and not the lack of the object permanence scheme. More exactly, Diamond (1991, 1998) defends a ‘memory inhibition’ interpretation. Already in infancy, then, being intelligent (no longer making the A-not-B error) means inhibiting an interfering scheme. In agreement with Diamond (1991), ‘Cognitive development can be conceived of, not only as the progressive acquisition of knowledge, but also as the enhanced inhibition of reactions that get in the way [interference] of demonstrating knowledge that is already present [here, object permanence]’ (p. 67).

In the area of numerical development, new research has also revealed the existence of early abilities that were unknown to Piaget. By recording oculomotor behavior, recent studies have shown that four and five-month-olds are capable of detecting the violation or conservation of number when presented with unexpected or expected numerical events. It has also been shown that these early numerical abilities undergo a cognitive-linguistic reorganization process and then re-emerge in preschoolers after a temporary drop in performance (Houde 1997). So why, then, do children at this age answer incorrectly on Piaget’s (1952) conservation of number task? When shown two rows of objects that contain an equal number of objects but differ in length (because the objects in one of the rows have been spread apart), these children think the longer one has more objects.

We know that Piaget’s interpretation was that preschool children are still fundamentally intuitive, or as he called them, ‘preoperational,’ and hence limited to a global and holistic perceptual way of processing information (here, based on length or, in certain cases, on density). In this view, they have not yet integrated the number strategy that enables them to perform an analytic process involving an exact calculation. The new studies mentioned above cast doubt on this interpretation, suggesting that the conservation of number task is a number length interference task more than anything else, one that reflects the ability to resist the visuospatial length-equals-number strategy (an often relevant quantification heuristic still used by adults). As Dempster (1995) said, ‘Conservation and class inclusion have more to do with the ability to resist interference than they do with the child’s ability to grasp their underlying logic’ (p. 15).

Here again, as in the A-not-B error in object construction, being intelligent (resisting the visuospatial interference) is essentially being capable of inhibition. This interpretation was recently confirmed using a negative-priming adaptation of Piaget’s numerical task (Houde and Guichart 2001). A chronometric paradigm (adapted from Tipper 1985; see above) was used with nine-year-olds, who succeed in Piaget’s conservation of number task, to test the role of cognitive inhibition in a priming version of this classical task. The experimental design was such that the misleading strategy ‘length-equals-number’ to be inhibited on the prime (a Piaget-like item with number length interference) became a congruent strategy to be activated on the probe (a subsequent item where number and length covaried). A negative priming effect, manifested by slower reaction times, was observed for the prime–probe sequence (compared to an unrelated condition). This result thus confirmed that, first and foremost, success on Piaget-like tasks requires an inhibitory process. In this light, the solution to the enigma of cognitive development could be found by looking mainly at the interference-and-inhibition side of cognition rather than searching solely on the scheme-coordination or coactivation side, as Piaget did.

Thus, whether it be in the study of cognitive development in infancy and childhood, or in the study of selective attention in adulthood, interference and inhibition are key concepts for new approaches in cognitive psychology (and also in the field of cognitive aging, following Dempster’s 1992 theoretical input). One of the most exciting research trends for addressing these questions is neurofunctional imaging, a new field where the cerebral bases of cognitive interference and inhibition are beginning to be explored (Ghatan et al. 1998), particularly in the anterior cingulate cortex (Bush et al. 2000) and in its strong reciprocal interconnections with the lateral prefrontal cortex. Another exciting perspective is the current evolutionary framework (Bjorklund 1997, Bjorklund and Harnishfeger 1995, Cosmides and Tooby 1987), where inhibition is regarded as a possible ‘Darwinian algorithm.’

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