be interpreted as a lack of rehearsal effectiveness (R items remain low) or inhibitory power (F items are too high) in PTSD. However, when separating hits from false alarms, it becomes clear that in study I (as in study II and III) most of the overall effect is based on divergent false alarm patterns whereas there is not much of a difference in hits. Together with the findings from study IV, this feeds the assumption that a third process - I called this ‘alert(ing)’ throughout the text - apart from inhibition and re-hearsal plays a central role in item-method directed forgetting. With regards to trau-matic diseases, it might therefore be of special importance to keep the alert(ing) low in order to prevent an excessive rebound.
4.3 A speculative model of item-method directed forgetting
The present dissertation was designed to investigate stress effects on directed forgetting and mechanisms that modulate them. While traumatic stress indeed disrupted item-method directed forgetting, experimental stress did not. Stimulus arousal showed up as correlate of the effect. Further preliminary evidence that supports this interpretation comes from a study of item-method directed forgetting in former drug addicts with and without PTSD (Zwissler et al., in prep.), where we found intact directed forgetting of stimuli rated as non-relevant in traumatized individuals. Hyperaroused reactions to
‘trauma-relevant’ stimuli have also been demonstrated in individuals suffering from PTSD (Liberzon et al., 1999). The results of both the present and previous studies are consistent with a neuroanatomic model of PTSD that posits the medial prefrontal cor-tex’s failure to inhibit a hyperresponsive amygdala (e.g., Bremner et al 1999b; Rauch et al 1998, 2000). Both in study I and study II, the directed forgetting effect was mostly due to higher false alarm rates for R lures, while hit rates did not greatly differ. To-gether with the findings from study IV, it seems as though not only impaired selective rehearsal or inhibitory processes contribute to the reduced effect, as this would have affected hits as well. Because of the observed variations in false alarms, I come to the present conclusion that this aspect deserves more attention. I do not wish to become too
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speculative in the end, but I have developed a model that might be able to pretty well incorporate some of the central findings of this dissertation (Fig. 15). It is rather sche-matic and since I worked with behavioral data, I wish to primarily stay on this level.
The following variables are central to the model: processing ‘intensity’ refers to basic perceptual and attentional processes. It is assumed that at its appearance (onset), each stimulus receives identical processing (since no cue has yet been presented). At cue on-set, the perceiver needs a certain amount of time to grasp which cue had been given.
During this phase, the preceding stimulus is held online and is therefore more intensely processed. When the cues have been differentiated, the classical item-method directed forgtting processes take place: R items are further rehearsed and therefore keep on ris-ing (this is sometimes, mostly in list-method designs but MacLeod (1998) also applies it to the item-method, called the ‘benefit’ of directed forgetting). F items, in contrast, are weakended and pushed out of attention by active inhibition (so-called ‘costs’ of directed forgetting). This is the pattern that we found in the studies I, II, III, and IV. Items that do not receive any attention (i.e., cue) remain at a low level (study IV). These basic processes are reflected in the hit rates and a directed forgetting effect at test. Cued items alert the individual to the need for processing the instruction and, possibly, R items might even have a slightly higher alerting potential than F items (see Fig. 15, left side).
Divergent patterns can be found in the false alarm rates. In neutral/non-relevant mate-rial, alert and alerting is relatively low and due to instructions; false alarms then more or less mirror the respective hit pattern (studies I, II, IV). If an item is processed better, it is also more easily distinguishable from a similar distractor. As a consequence, correct recognition of the learning stimuli is inversely proportional to false recognition of their lures (see upper panel of Fig. 15). In emotional/self-relevant stimuli, false alarm pat-terns are reversed. The basic alert(ing) is potentiated by emotional arousal and leads to a special way of processing the respective stimulus in which the person strongly focuses on its central elements. Peripheral details, however, are more or less blanked out (for empirical support, see, for example, Heuer & Reisberg, 1990, or Christianson & Loftus, 1987). This distortion may be directly proportional to the amount of associated alert(ing). The advantage or more intense initial processing of R items is thus being turned into its opposite (see lower panel of Fig. 15). The false alarm bars are left so vague in the illstration of the model to indicate that in the data we collected there is much variation on this side of the effect. In this respect, I even make a prediction about
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a previously fully untested condition. As can be seen at the very right of the lower panel of Fig. 15, when following my assumptions, lures of emotional U stimuli should actu-ally yield the lowest false alarm rate. This is a concrete hypothesis derived from the model that remains to be tested. Also, the bars are not scaled: the depictions are in-tended to be purely symbolic.
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Figure 15. A speculative model of item-method directed forgetting. The upper panel illustrates the 'no alert(ing)' situation (e.g., low-arousing stimuli), the lower panel the 'alert(ing)' (e.g., highly arousing stim-uli, trauma history) situation.
I did not include a possible fourth condition in the illustration. Our U condition in study IV might be understood as a baseline of item-method directed forgetting. There are at least two other studies that have already incorporated ‘baseline’ measurements (Muther, 1965; Sahakyan & Foster, 2009). Those studies, however, clearly differ from ours as they chose a ‘remember all’ (R all) condition as the baseline. Upon testing, these items had a lower recognition rate than R items but a higher one than F items. In my opinion, this finding is also much in line with this model. At first, R all items are processed like ordinary R items but in the end, they do not gain the benefits that R items receive in