Individual differences

Geiselman & Panting (1985) investigated the interaction of personality dimensions and directed forgetting. They found that the more people tended to respond in a socially desired way the less unpleasant to-be-remembered items were recalled. Further, the higher scores individuals had on an empathy scale, the more unpleasant to-be-forgotten words were recalled. The author claimed that the empathy scale measured sensitization as sympathy for others and expected people with high empathy scores to be sensitive to negative concepts. Thus, this outcome was interpreted as reflecting the limiting effects of sensitization on directed forgetting.

Several studies used directed forgetting paradigms to investigate repressive coping styles which are thought to be involved in some mental disorders as for example trauma-related disorders. There is evidence that people who exhibit a repressive coping style (repressors) typically show specific memory performances like reduced recall of unpleasant material (Davis & Schwartz, 1987). Because repressors are thought to inhibit the retrieval of certain memories this was further investigated using list method directed forgetting as retrieval inhibition is assumed to play a role in this paradigm. Two studies from Myers and colleagues (Myers, Brewin, & Power, 1998; Myers & Derakshan, 2004) examined whether repressors show superior retrieval inhibition and therefore enhanced forgetting of unpleasant material. Both studies used lists of intermixed pleasant and unpleasant words that had to be rated for self-descriptiveness. They found that repressors actually did recall less of the unpleasant to-be-forgotten words than the controls. However, when the experimental stimuli were not processed in relation to the self, repressors and control participants did not differ in their memory performances (McNally et al., 2004; Myers &

Derakshan, 2004).

Concerning dissociative tendencies, DePrince & Freyd (2001) investigated directed forgetting within a student population using the item method paradigm. The participants were divided into groups of high and low dissociators according to dissociation questionnaire scores. Item method directed forgetting of neutral, positive, and trauma-related words under different conditions of cognitive load (selective attention, moderately difficult divided attention condition, and highly difficult divided attention condition) was in the focus of this study. In the moderately difficult condition of divided attention, impaired recall of trauma-related and increased retrieval of neutral to-be-remembered words was found for high compared to low dissociators. In a second study, DePrince and

Freyd (2004) used the list method design to explore directed forgetting for different dissociation levels under different conditions of cognitive load. Again, high dissociators showed impaired recall of trauma-related to-be-remembered items and enhanced recall of neutral to-be-remembered items compared to low dissociators when words were presented under divided-attention conditions. Devilly and colleagues (2007) tried to replicate the findings of the two DePrince & Freyd studies (2001; 2004). Although, Devilly et al.

(2007) did not find that subjects with high scores of dissociation showed impaired recall of trauma-related to-be-remembered words compared to neutral to-be-remembered words, DePrince, Freyd, & Malle (2007) argued that the results actually were a replication but were underpowered and therefore did not reach significance. In a related study (experiment 1, Elzinga, de Beurs, Sergeant, van Dyck, & Phaf, 2000), a high and a low dissociative group of students were tested for directed forgetting using neutral words within an item method paradigm. Here, directed forgetting occurred for both dissociative groups. In a following experiment (experiment 2, Elzinga et al., 2000) an additional group of patients with a dissociative identity disorder were included and tested for directed forgetting of neutral and emotional (sexual-related, anxiety-related) words. Directed forgetting appeared to be related to the level of dissociative style. The low dissociative group showed the strongest directed forgetting effect, next the high dissociative group, and least the clinical group. For dissociative patients the forget instruction increased the recall performance, especially for the sexual-related words. The authors interpreted these results in terms of a construction hypothesis that proposed enhanced skills in construction of experience in people with dissociative style.

Delaney & Sahakyan (2007) investigated the influences of individual working memory capacity on directed forgetting. They assumed stronger directed forgetting effects in people with a high memory span. This idea was based on data showing (1) that high-span people are less vulnerable to interference and distraction by irrelevant material (Engle, Tuholski, Laughlin, & Conway, 1999), suggesting enhanced remembering of to-be-remembered items, and (2) that high-span people control their memory more effectively (Brewin & Beaton, 2002), suggesting reduced remembering of to-be-forgotten items.

Delaney and Sahakyan (2007) found that list method directed forgetting was related to working memory capacity measured by both a verbal and a non-verbal task. High-span subjects showed decreased recall of list 1 in the forget condition while low-span subjects did not. Based on a context change control condition, which also showed enhanced forgetting in the high-span group, the authors suggested that the effective forgetting in

high-span subjects in list method directed forgetting might be more context dependent than that of low-span people.

To sum up, there are some personality related characteristics that appear to modulate directed forgetting, such as social desirability or empathy (Geiselman & Panting, 1985).

Also, a repressive coping style influences directed forgetting as reduced recall of unpleasant to-be-forgotten words occurred, but only when stimuli were processed in relation to the self (Myers et al., 1998). For dissociative tendencies, the extent of directed forgetting seems to vary with the dissociative style; subject with low dissociative style produce the strongest directed forgetting effect, participants with high dissociative style generating a medium effect, and clinical patients yielding no effect (Elzinga et al., 2000).

Age-related differences

Relatively well investigated are age-related differences in directed forgetting. Several researchers were interested in the developmental improvements in memory performance of children and how these interacted with directed forgetting (Harnishfeger & Pope, 1996;

Lehman, McKinley-Pace, Leonard, Thompson, & Johns, 2001; Lehman, Morath, Franklin,

& Elbaz, 1998; Lehman, Srokowski, Hall, Renkey, & Cruz, 2003; Wilson & Kipp, 1998;

Wilson, Kipp, & Daniels, 2003). Typical findings showed that children produced smaller directed forgetting than adults did (Harnishfeger & Pope, 1996; Lehman et al., 2001;

Lehman et al., 1998; Lehman et al., 2003). For their list method study, Harnishfeger &

Pope (1996) interpreted these findings as resulting from inefficient inhibition processes in children. The inhibitory mechanisms are thought to improve during development as comparisons of the memory performance across different grade levels suggested: While first graders showed little inhibition processes, the memory pattern of fifth graders showed more similarities with the patterns of efficient inhibition college students show in their memory performance. Thus, in young children the inhibitory processes are not fully developed resulting in to-be-forgotten or task-irrelevant information leaking into working memory. In adults the inhibition mechanisms become more effective and enable more efficient cognitive processing leading to better retrieval inhibition in directed forgetting (Harnishfeger & Bjorklund, 1994). Lehman and co-workers (2003) used the item method and interpreted their reduced directed forgetting in children also as stemming from inefficient inhibition. However, in contrast to retrieval inhibition, they located the inhibitory mechanisms mainly in early processes which is consistent with the attentional inhibition hypothesis of Zacks and colleagues (1996). An additional explanation for the reduced directed forgetting in children was suggested by Lehman and colleagues (2001;

1998) who suggested that the encoding of the cue information whether an item should be remembered or could be forgotten is poorer in children. They also assumed that the major developmental change occurred in adolescence as second, fourth, and sixth graders differed remarkably from college students (Lehman et al., 1998).

Several other studies investigated whether and how directed forgetting differed between younger and older adults and ambiguous results were obtained. One line of evidence supported the view of reduced inhibitory efficiency in older people as proposed for example by Hasher & Zacks (1988). A framework of inhibitory mechanisms is assumed which makes sure that relevant information can enter the working memory while irrelevant information is kept outside. For elderly subjects this inhibition processes are thought to become less efficient resulting in more irrelevant information entering the working memory. Originally, this hypothesis accounted for deficits in working memory but since then the concept has been applied to various other cognitive domains. For example, age-related impairments were found in response inhibition in Stroop tasks (McCabe, Robertson, & Smith, 2005), in modified Stroop tasks (Troyer, Leach, & Strauss, 2006), in antisaccade tasks (Butler & Zacks, 2006), and also in the fan effect paradigm (Radvansky, Zacks, & Hasher, 2005). Concerning the directed forgetting effect, Earles &

Kersten (2002) as well as Dulaney, Marks, & Link (2004) found that younger adults produced stronger directed forgetting effects for verbal material in an item method paradigm than older subjects did. Accordingly, when asked to recall to-be-remembered items, older adults showed more intrusions of to-be-forgotten stimuli than younger subjects during immediate recall (experiment 1, Zacks et al., 1996). Sego and colleagues (2006) as well as Salthouse, Siedlecki, & Krüger (2006) found that no age-related differences occurred for recall of to-be-forgotten items while older subjects retrieved less to-be-remembered stimuli resulting in smaller directed forgetting effects. When tested with a modified list method, older subjects did not intrude more to-be-forgotten items than younger adults during immediate recall but did so in the delayed recall test (experiment 2, Zacks et al., 1996) and they also took longer to reject to-be-forgotten stimuli during an immediate recognition task (experiment 3, Zacks et al., 1996). Andrés and co-workers (2004) also found less directed forgetting in elderly adults compared to younger ones in a modified directed forgetting paradigm: Two trigrams were presented to the subjects consecutively with the second one being cued to-be-forgotten. In the following recall phase only the first trigram had to be retrieved. Older subjects were less able to inhibit the second trigram compared to younger ones. On the other hand, there are some studies that

did find equivalent directed forgetting effects for older and younger individuals using the item method (Gamboz & Russo, 2002) and list method directed forgetting (experiment 2, Sego et al., 2006; Zellner & Bäuml, 2006).

To sum up, there is evidence for inefficient inhibitory mechanisms in both children and elderly people while young adults seem to have the most effective inhibition processes.

However, some studies suggest equivalent directed forgetting in younger and older adults.