Elsevier

Brain Research

Volume 1250, 23 January 2009, Pages 190-201
Brain Research

Research Report
An event-related potential investigation of the processing of Remember/Forget cues and item encoding in item-method directed forgetting

https://doi.org/10.1016/j.brainres.2008.11.016Get rights and content

Abstract

This study examined the electrophysiological correlates of the processing of the Remember/Forget cues and the successful encoding of study items in item-method directed forgetting. Subjects engaged in an old/new recognition test and an item-method directed forgetting task. Event-related potentials (ERPs) time-locked to study items and Remember/Forget cues were compared according to the subsequent recognition performance. A reliable subsequent memory effect was elicited by the study items in the old/new recognition test. In contrast, the study items in the directed forgetting task did not yield reliable subsequent memory effects. Importantly, the Remember/Forget cues gave rise to ERPs that were predictive of the subsequent recognition performance to the study items preceding the cues. The subsequent memory effect elicited by the Remember cues was more sustained than that elicited by the Forget cues and showed distinct scalp distribution during the extended period. These results suggest that study items in the directed forgetting task are maintained in short-term memory with minimal further processing until the presentation of the Remember/Forget cues. In addition, the encoding mechanisms engaged by Remember cues and Forget cues are not entirely equivalent.

Introduction

Forgetting unwanted or irrelevant information is crucial for maintaining the functionality of memory. Intentional forgetting is often investigated with the directed forgetting paradigm, which instructs subjects to remember some study materials but to forget others (see Johnson, 1994, MacLeod, 1998, for reviews). In the item-method of directed forgetting, each study item is accompanied by a Remember cue or a Forget cue. These cues instruct subjects to remember or to forget on an item-by-item basis. A directed forgetting effect is obtained when items instructed to be forgotten (TBF) are less well remembered than items instructed to be remembered (TBR). It has been suggested that the item-method directed forgetting effect mainly results from the different processing of TBR and TBF items during encoding (e.g., Basden et al., 1993, Bjork, 1989; but see Ullsperger et al., 2000). In this study we recorded event-related potentials (ERPs) during the study phase of the item-method directed forgetting procedure to investigate the encoding processes related to the directed forgetting effect.

The differential rehearsal account for the directed forgetting effect proposes that TBR items received more rehearsal than TBF items (Bjork, 1970). Study items are initially maintained in short-term memory with rote rehearsal until the presentation of Remember/Forget cues. Rote rehearsal is terminated in response to a Forget cue, whereas elaborative rehearsal processes are allocated to the TBR items in response to a Remember cue. This view is supported by the finding that increasing the interval between study items and Remember/Forget cues has little effect on the recall of TBR and TBF items (Woodward and Bjork, 1971, Woodward et al., 1973). In addition, increasing the processing time of the Remember/Forget cues increases recollective experience for the recognition of TBR items but not TBF items (Gardiner et al., 1994). The differential rehearsal account, however, does not specify how TBF items are excluded from working memory (Taylor, 2005). The attentional inhibition account (Zacks et al., 1996) by contrast argues that following the presentation of the Forget cue, the TBF items become irrelevant information, subsequently inhibited actively and prevented from entering into working memory (Hasher and Zacks, 1988). This view is supported by the finding that older adults, who find it difficult to ignore TBF items, exhibited a smaller directed forgetting effect than young adults (Zacks et al., 1996). In addition, the instruction to forget was found to increase inhibition of return (Taylor, 2005); the way Forget cues discontinue memory encoding resembles the countermanding of a proponent response in a stop-signal paradigm (Hourihan and Taylor, 2006). However, there is also evidence suggesting that TBF items may not be actively inhibited, as TBR and TBF items elicited similar semantic priming effects (Marks and Dulaney, 2001).

The question of whether TBF items are actively suppressed or passively decayed relates to how well the TBF items are initially encoded and how effective the forget instruction is, both are important factors for the success of intentional forgetting (Johnson, 1994). A relevant issue of exploration is whether successfully remembered TBR and TBF items are encoded in different ways. Brain activities elicited by study items and Remember/Forget cues may shed light on these questions. Specifically, if Remember cues and Forget cues engage different processes, different brain activities should be observed. Moreover, the investigation of how brain activities elicited by study items and Remember/Forget cues relate to the subsequent memory performance, the so-called subsequent memory effect (Paller et al., 1987, Rugg, 1995), should reveal whether the successful encoding of TBR and TBF items involves different mechanisms. Paller (1990) used word colors as Remember/Forget cues and found that the ERPs elicited by TBR items demonstrated greater initial positivity and subsequent negativity than TBF items. A similar finding was reported by Paz-Caballero and Menor (1999), who presented Remember/Forget cues after the offset of study items. These findings are consistent with the view that different processes are elicited by Remember and Forget cues. Paller (1990) also reported indistinguishable ERP subsequent memory effects for TBR and TBF items, suggesting similar mechanisms underlying the successful encoding of TBR and TBF items. However, the simultaneous presentation of study items and Remember/Forget cues (i.e., item colors) in Paller's study made it difficult to differentiate between the encoding processes elicited by study items and those modulated by the Remember/Forget instructions. Paz-Caballero, Menor, and Jiménez (2004) reported that subjects who exhibited a large directed forgetting effect and those who demonstrated a smaller effect exhibited distinct patterns of ERP differences between Remember and Forget cues. However, Paz-Caballero et al. (2004) did not compare the subsequent memory effects associated with the Remember and Forget cues. It is therefore not clear whether the encoding processes elicited by the Remember and Forget cues are different.

To elucidate the nature of the directed forgetting effect, the subjects of the present work engaged in an old/new recognition test and two sessions of item-method directed forgetting task. ERPs were recorded in the study phase of both tasks. We attempted to test the following hypotheses: (1) if study items in the directed forgetting task are initially maintained with rote rehearsal, the subsequent memory effect elicited by the study items in the old/new recognition test should not be elicited by the study items in the directed forgetting task. In contrast, the ERPs elicited by the Remember/Forget cues should vary according to whether the study items immediately preceding the cues are subsequently recognized. (2) If the encoding of TBR and TBF items is of qualitatively difference, the subsequent memory effect elicited by the Remember cues and Forget cues should differ, as different patterns of subsequent memory effects have been observed in deep and shallow encoding tasks. (Otten and Rugg, 2001).

Section snippets

Results

Repeated measures ANOVA was used to analyze the behavioral and ERP data. The Greenhouse–Geisser correction for non-sphericity was applied when necessary.

Discussion

A directed forgetting effect was revealed in the behavioral data: the hit rate for TBR items was higher than that for TBF items. Additionally the hit rate in the old/new recognition test was lower than the recognition rate for TBR items in the directed forgetting task, but higher than that for TBF items. Differences in recognition performance may result from interference caused by an increased number of items to be remembered in the old/new recognition test comparative to the directed

Concluding remarks

We have demonstrated that Remember/Forget cues elicited a reliable subsequent memory effect in the item-method directed forgetting task, and that their preceding study items comparatively elicited no such effect. This result indicates that study items are maintained in short-term memory with rote rehearsal until the presence of the Remember/Forget cues. The subsequent memory effect elicited by the Remember/Forget cues differed from the effect elicited by the study items in old/new recognition,

Participants

A total of 27 undergraduate students from National Central University were recruited. All these participants were right-handed native Mandarin Chinese speakers with normal or corrected-to-normal vision. They were paid at the rate of 250 New Taiwan Dollars per hour.

Materials

Stimuli consisted of 600 Chinese two-character nouns. These 600 words were divided into three experimental lists of 200 words, which were then assigned to one session of old/new recognition test and two sessions of directed forgetting

Acknowledgments

This research was supported by grants from National Science Council, Taiwan to Shih-kuen Cheng (NSC 96-2413-H-008-002) and Daisy L. Hung (NSC 95-2413-H-010-001).

References (37)

  • PolichJ.

    Updating P300: an integrative theory of P3a and P3b

    Clin. Neurophysiol.

    (2007)
  • RuggM.D. et al.

    Event-related potentials and memory

    Trends Cogn. Sci.

    (2007)
  • SonntagP. et al.

    Impaired strategic regulation of contents of conscious awareness in schizophrenia

    Conscious. Cogn.

    (2003)
  • WoodwardA.E. et al.

    Recall and recognition as a function of primary rehearsal

    J. Verbal Learn. Verbal Behav.

    (1973)
  • AzizianA. et al.

    Evidence for attentional gradient in the serial position memory curve from ERPs

    J. Cogn. Neurosci.

    (2007)
  • BasdenB.H. et al.

    Directed forgetting in implicit and explicit memory tests: a comparison of methods

    J. Exp. Psychol. Learn. Mem. Cogn.

    (1993)
  • BjorkR.A.

    Retrieval inhibition as an adaptive mechanism in human memory

  • FabianiM. et al.

    Encoding processes and memory organization: a model of the von Restorff effect

    J. Exp. Psychol. Learn. Mem. Cogn.

    (1995)
  • Cited by (46)

    • A functional near-infrared spectroscopy investigation of item-method directed forgetting

      2022, Neuroscience Research
      Citation Excerpt :

      There are some limitations of ERP and fMRI techniques in investigating intentional forgetting. For the ERP technique, previous DF studies have mainly focused on the cue-evoked ERPs within a 1 s time window [e.g., P2, N2, P3, early frontal potentials (200–300 ms), and late central-parietal potentials (400–600 ms)] (Gao et al., 2016a; Hsieh et al., 2009; Ullsperger et al., 2000; van Hooff and Ford, 2011; Yang et al., 2012), but the neural activity after the 1 s post-cue-onset has not been well investigated. For the fMRI studies, although the brain activation associated with the cues has been investigated in a relatively long time window (about 3–9 s, e.g., Bastin et al., 2012; Nowicka et al., 2011; Rizio and Dennis, 2013; Wylie et al., 2008; Yang et al., 2016), the brain activation of two stages (inhibition control and involuntarily encoding) during intentional forgetting could not be distinguished.

    • Separable neural mechanisms support intentional forgetting and thought substitution

      2021, Cortex
      Citation Excerpt :

      An early, sustained central ERP response differentiated cue conditions, and was predictive of accuracy for Remember cues. This finding of greater amplitude ERPs for Remember versus Forget cues confirmed our hypothesis and replicated similar work examining ERPs to memory cues (Gallant & Dyson, 2016; Hsieh, Hung, Tzeng, Lee, & Cheng, 2009; Paz-Caballero et al., 2004; Van Hooff & Ford, 2011). The posterior scalp distribution of the effect was similar to that of a P300 component (Polich & Kok, 1995), though with an earlier onset than is usually observed, potentially suggesting a P2 component difference as well (Luck & Hillyard, 1994).

    • Motivated forgetting increases the recall time of learnt items: Behavioral and event related potential evidence

      2020, Brain Research
      Citation Excerpt :

      It is demonstrated that larger N2 components are evoked by No-Think cues compared to Think cues (Yang, 2012), suggesting that it is related to cognitive control and inhibitory activity during memory suppression (Anderson, 2004; Bergström et al., 2009; Mecklinger et al., 2009; Wessel and Merckelbach, 2006). In some MF studies, the N2 component was also referred to as “the frontal positivity”, since this negative component had positive amplitude (Cheng et al., 2012; Hsieh et al., 2009; Brandt et al., 2013). The final component is a late parietal positivity (LPP), which is a slow potential that emerges later than 400 ms post-stimulus.

    View all citing articles on Scopus
    View full text