Difficulties disengaging attention from negative material may reflect deficits in inhibitory control that are associated with depression. Overriding prepotent responses and inhibiting the processing of irrelevant material that captures attention are core abilities that allow us to respond flexibly and to adjust our behavior and emotional responses to changing situations. Cognitive control is related to the functioning of executive control processes, such as inhibition in WM (Hasher et al. 1999
). WM is commonly described as a system for the active maintenance and manipulation of information and for the control of attention (Baddeley 1986
). It is a limited-capacity system that provides temporary access to a select set of representations in the service of current cognitive processes (Cowan 1999
). Thus, WM reflects the focus of attention and the temporary activation of representations that are the content of awareness. Given the capacity limitation of this system, it is important that the contents of WM be updated efficiently, a task controlled by executive processes (e.g., Friedman & Miyake 2004
, Hasher et al. 1999
). Executive processes must selectively gate access to WM, shielding it from intrusion from irrelevant material, and must also discard information that is no longer relevant. In this context, individual differences in the experience and resolution of interference are likely to affect cognitive and emotional functioning. The occurrence of intrusive thoughts might be one consequence of poor interference resolution. Indeed, increased interference from irrelevant representations has been proposed as a source of low WM capacity (Engle et al. 1999
) and has been found to characterize various populations, including older adults (Hasher et al. 1991
), children with attention deficit disorder (Bjorklund & Harnishfeger 1990
), patients with obsessive-compulsive disorder (Enright & Beech 1990
), and patients with schizophrenia (Frith 1979
Several researchers have suggested that depression is associated with deficits in executive functioning (Hertel 1997
, Joormann 2005
). Indeed, there is emerging evidence that depression is characterized by difficulties in the inhibition of mood-congruent material that could result in prolonged processing of negative, goal-irrelevant aspects of presented information and thereby hinder recovery from negative mood and lead to the sustained negative affect that characterizes depressive episodes. Theorists have suggested that deficits in cognitive inhibition lie at the heart of biases in memory and attention in depression and set the stage for ruminative responses to negative events and negative mood states. A number of experimental paradigms have been developed that have the potential to test inhibition models (e.g., Anderson & Bjork 1994
). Below we discuss several of these designs, such as negative priming (Tipper 1985
) and directed forgetting (Bjork 1972
Cognitive inhibition of irrelevant information is crucial in a range of tasks that require selective attention. Negative priming is an experimental task that aims to distinguish activation from inhibition accounts of selective attention (Neill et al. 1995
, Tipper 1985
). In this task, participants are asked to respond to a target in the presence of a distractor. Participants can be asked, for example, to name a word written in red while ignoring a word written in blue that is presented at the same time. The negative priming effect is defined as a longer response latency when the distractor from a previous trial becomes the target on the present trial. Thus, negative priming occurs when, in the following trial, the presented target is identical or related to the previously presented to-be-ignored distractor. The inhibition of the distractor that is activated on the first trial remains activated on the following trial, delaying the response to a target that is identical to or related to the ignored distractor. The delay in responding, therefore, assesses the strength of inhibition of the distractor that was presented on the previous trial.
Negative priming has been observed in a variety of selective attention tasks, including semantically related distractor-target pairs (e.g., a picture of a dog following an ignored picture of a cat; Tipper 1985
). The area of research in which negative priming has been used most widely involves the identification of individual differences associated with the effect. Linville (1996)
was the first to investigate negative priming in depression. She reported that depressed individuals were less likely to inhibit distracting information than were nondepressed controls. Specifically, participants were asked to complete a modified lexical decision task that required them to inhibit the presence of a distractor (i.e., letter string) while identifying whether a second string is a word. Whereas control participants were slower to respond to letter strings that they had been asked to ignore on an earlier trial, depressed individuals failed to show this effect. Similarly, MacQueen et al. (2000)
used a negative priming task in which they systematically varied color and location of prime and target, and reported reduced inhibition of distractors in depressed participants. Although these results support the proposition that depression is related to inhibitory dysfunction, inhibitory deficits might be even more prevalent in the processing of emotional information. In particular, the observation of negative automatic thoughts and ruminations about negative information in depression leads to the hypothesis that there is a valence-specific inhibitory deficit in depression in which inhibition is selectively reduced for negative stimuli.
The negative affective priming (NAP) task was designed to assess inhibition in the processing of emotional information (Joormann 2004
). This task assesses response times to positive and negative material that participants were instructed to ignore. Joormann (2004)
found that dysphoric participants and participants with a history of depressive episodes exhibited reduced inhibition of negative material. Thus, these participants responded more quickly when a negative target was presented after a to-be-ignored negative distractor on the previous trial. As predicted, no group differences were found for the positive adjectives. In a related study, participants who obtained high scores on a self-report measure of rumination exhibited a reduced ability to inhibit the processing of emotional distractors, a finding that remained significant even after controlling for level of depressive symptoms (Joormann 2006
). Importantly, these findings were replicated using a negative priming task with emotional faces (Goeleven et al. 2006
). Compared to nondepressed controls, depressed participants showed impaired inhibition of sad facial expressions but intact inhibition of happy expressions. Never-depressed individuals exhibited a stronger NAP effect for both sad and happy faces compared to neutral faces, indicating successful inhibition of emotional information in general.
Negative priming tasks assess only one aspect of inhibition: the ability to control the access of relevant and irrelevant material to WM. Most contemporary theories postulate that inhibition is not a unitary construct, but instead involves several components such as response inhibition, cognitive inhibition, and emotional inhibition (e.g., Friedman & Miyake 2004
, Nigg 2000
). In addition, cognitive inhibition operates at different stages of the processing of information, for example, by preventing off-goal information from having access to WM or by reducing the activation of information that was once relevant, but now is irrelevant because of a change in goals. Whereas results from NAP studies suggest that depression involves difficulties keeping irrelevant emotional information from entering WM, it is unclear whether depression is also associated with difficulties removing previously relevant negative material from WM. Difficulties inhibiting the processing of negative material that was, but is no longer, relevant might explain why people respond to negative mood states and negative life events with recurring, uncontrollable, and unintentional negative thoughts.
To test this hypothesis, Joormann & Gotlib (2008)
used a modified Sternberg task that combines a short-term recognition task with instructions to ignore a previously memorized list of words to assess inhibition of irrelevant positive and negative stimuli. In this task, two lists of emotional words are presented simultaneously. After the lists are memorized, a cue indicates which of the two lists is relevant for the recognition task on the next display, in which participants indicate whether the probe that is presented came from the relevant list; probes from the no-longer-relevant list must be rejected, as must new probes. The difference in reaction times to an intrusion probe (i.e., a probe from the irrelevant list) and reaction times to a new probe (i.e., a completely new word) reflects the strength of the residual activation of the contents of WM that were declared to be no longer relevant and, therefore, assesses a person’s ability to remove irrelevant information from WM (Oberauer 2005a
). We found that participants diagnosed with MDD exhibited difficulties removing irrelevant negative material from WM. Specifically, compared to never-depressed controls, depressed individuals exhibited longer decision latencies to an intrusion probe (i.e., a probe from the irrelevant list) than to a new probe (i.e., a completely new word), reflecting the strength of the residual activation of the contents of WM that were declared to be no longer relevant. Importantly, this pattern was not found for positive material. Joormann & Gotlib (2008)
also found that difficulty removing negative irrelevant words from WM was highly correlated with self-reported rumination, even after controlling for level of depressive symptoms.
In sum, therefore, these findings indicate that depression is associated with inhibitory impairments in the processing of emotional material, specifically, with difficulties removing irrelevant negative material from WM. We recently replicated these findings using a task developed by Nee & Jonides (2008)
that allows us to assess two aspects of inhibition within the same task: access of information to WM and discarding irrelevant material from WM. Interestingly, in this task, depressed participants did not differ from nondepressed controls in their ability to keep irrelevant negative material from entering WM. We did, however, obtain a group difference in the ability to discard negative material from WM; no group differences were obtained in the processing of positive or neutral material. Difficulties discarding negative material in the depressed group were also correlated with self-reported rumination. Finally, using a task that requires participants to resort material in WM, Joormann et al. (2009b)
demonstrated that MDD participants had difficulties manipulating negative material in WM, and that this deficit was associated with self-reported proneness to rumination.
It is likely that deficits in cognitive control not only affect people’s ability to disengage attention from irrelevant material, thereby increasing unwanted thoughts, but also make it difficult for them to intentionally forget unwanted material. As we described above, investigators have consistently documented the operation of memory biases in depression. Theorists have suggested that analogous processes underlie both selective retrieval of target items from memory and selective attention to objects in the external environment (Anderson & Spellman 1995
). Consequently, if inhibitory dysfunction is found in depressed individuals on selective attention tasks, it may also be detectable on memory tasks. The postulation that depression is associated with such deficits in executive control has been tested in directed-forgetting tasks in which participants are instructed to forget previously studied material at some point during the experiment. Later recall is tested, however, for material that was to be remembered and material that was to be forgotten (Bjork 1972
). In a study using neutral material, Cottencin et al. (2008)
reported increased recall of to-be-forgotten words and decreased recall of to-be-remembered words in depression. Using positive and negative words, Power et al. (2000)
reported differential directed-forgetting effects for depressed and nondepressed participants. Specifically, the depressed participants exhibited a facilitation effect for negative words after the “forget” instruction. It is important to note that the effect was only found when the adjectives were processed in a self-relevant manner. Similar findings were obtained by Joormann & Tran (2009)
, who demonstrated that participants who scored high on a trait measure of rumination exhibited reduced forgetting of negative material in this task. These participants also exhibited increased recall of negative words that were not presented during the learning phase. These results remained stable when depression scores were included as a covariate. Interestingly, a recent study reported that depressed participants were more likely to falsely recall negative material that had never been presented during the learning trials (Joormann et al. 2009c
Hertel & Gerstle (2003)
reported additional evidence for reduced inhibition of negative words in dysphoric students. These authors used a paradigm that was originally proposed by Anderson & Green (2001)
. Dysphoric and nondysphoric students learned word pairs, each consisting of a positive or negative adjective and a neutral noun. In subsequent practice trials, participants practiced either recalling the target word or suppressing (i.e., making an active effort not to think about) the target word when given the adjective as a cue. On the final test, recall for all words was tested. Hertel & Gerstle (2003)
found that recall from sets assigned for suppression practice was greater in the group of dysphoric participants, with a tendency toward increased recall of to-be-suppressed negative words. Moreover, the degree of forgetting was significantly correlated with self-report measures of rumination and unwanted thoughts. Again, these results suggest a close relation between self-reported rumination and inhibitory difficulties. Using a slightly modified version of the Anderson & Green (2001)
task in which participants were instructed to remember or forget positive and negative nouns, Joormann et al. (2005)
investigated intentional forgetting of positive and negative adjectives that depressed and control participants had learned to associate with neutral nouns. In contrast to directed forgetting studies, the authors provided multiple opportunities for the participants to practice the active suppression of the items to examine whether forgetting would increase with suppression training. Importantly, depressed participants could be trained to forget negative words, suggesting intriguing implications of this research for interventions (see also Joormann et al. 2009e
In sum, the literature reviewed above does not indicate that depression is associated with biases in all aspects of information processing; rather, it suggests a very specific difference between depressed and nondepressed individuals in cognitive functioning. Depression is not necessarily characterized by a general cognitive deficit or by a high level of alertness in the processing of negative material. Instead, whereas anxiety disorders are associated with quick detection of and fast orienting toward threat-related stimuli, results of studies investigating the automatic processing of negative material in depression are equivocal. Once negative material has become the focus of attention, however, depressed individuals are prone to elaborate on it and have difficulty stopping or inhibiting the processing of this material. This specific difficulty is likely to have important consequences for depressed people’s ability to recover from negative affect and, consequently, may represent an important link between cognition and emotion dysregulation in this disorder.