APA Style Psychology Essay
Retrieval Inhibition in Directed Forgetting Following Severe Closed-Head Injury
Maureen Schmitter-Edgecombe Washington State University
William Marks The University of Memphis
Matthew J. Wright Washington State University
Matthew Ventura The University of Memphis
A variant of the list method directed forgetting procedure was used to examine the role of inhibition in memory performance following severe closed-head injury (CHI). Twenty-four participants with severe CHI and 24 controls studied picture and word stimuli in both forget and remember conditions. Memory testing for the to-be-forgotten and to-be-remembered items consisted of a free-recall test followed by a source-monitoring task. Despite poorer recall performance, the participants with CHI exhibited a directed forgetting effect similar to that in controls. Item recognition scores indicated that the inhibited items were not forgotten but rather were items whose accessibility had been lowered. These findings suggest that residual memory deficits in patients with severe CHI are unlikely to reflect inefficient retrieval inhibition.
In many types of everyday settings individuals are cued to set aside, get rid of, suppress, or inhibit, either permanently or tem- porarily, something that resides in memory (E. L. Bjork, Bjork, & Anderson, 1998). For example, we have all probably been told something such as the following: “Forget what I said earlier. I gave you the wrong information. Here is the correct meeting time.” In other words, although forgetting is most often viewed as having negative effects, to function efficiently in our everyday environ- ment, we frequently need to forget or inhibit previous information. Within the traumatic brain injury literature, few studies have investigated the influences of inhibitory mechanisms on the cog- nitive performances of patients with severe closed-head injury (CHI; e.g., Simpson & Schmitter-Edgecombe, 2000; Veltman, Brouwer, van Zomeren, & van Wolffelaar, 1996). This is an important area of research because being able to suppress irrele- vant information can be as important to attaining performance goals as being able to remember task-relevant information. In the present study, we used a directed forgetting task to examine the role of inhibition in memory performance following severe CHI.
Directed forgetting tasks have emerged as the primary way to investigate “intentional forgetting” in the laboratory (MacLeod, 1999). There are two basic directed forgetting paradigms: the item method and the list method (Basden, Basden, & Gargano, 1993).
In the item method, each item in a list is presented for a period of study and designated as a word that is either “to be forgotten” or “to be remembered.” In the list method, participants are presented with a list of items to be remembered. After the first half of the list is presented (List 1), participants are told that all previously presented items should be forgotten and that only the subsequently presented items (List 2) should be remembered for a later recall test. In both the item and the list method paradigms, recall of both to-be-forgotten and to-be-remembered items is tested. The typical result for both paradigms is that recall of the to-be-forgotten material is poorer than recall of the to-be-remembered items (e.g., Basden et al., 1993; MacLeod, 1999; Whetstone, Cross, & Whet- stone, 1996).
Although there are many similarities between the effects ob- tained with the item and list method directed forgetting procedures, one notable difference relates to recognition memory. That is, poorer recognition of to-be-forgotten than to-be-remembered ma- terial has consistently been found for the item method, but not for the list method (e.g., Basden et al., 1993; R. A. Bjork & Geisel- man, 1978; Geiselman & Bagheri, 1985; Geiselman, Bjork, & Fishman, 1983; MacLeod, 1999). As a means of explaining this difference, it has been hypothesized that the item method fosters selective rehearsal during encoding, so that only the to-be-remem- bered items are elaborately processed, and this would be evident on any retention test (Golding, Roper, & Hauselt, 1996; Johnson, 1994; MacLeod, 1999). In contrast, in the list method, the to-be- forgotten items are learned normally and at retrieval a repression- type process (i.e., retrieval inhibition) is thought to prevent them from being recovered in long-term memory (see Basden et al., 1993; R. A. Bjork, 1989; Wilson & Kipp, 1998). Because retrieval inhibition only lowers the accessibility of normally acquired items, reexposure of the actual list items during recognition testing ap- pears to release the retrieval inhibition (E. L. Bjork & Bjork, 1996; E. L. Bjork et al., 1998; Harnishfeger & Pope, 1996; for additional evidence supporting retrieval inhibition in list method directed forgetting, see Basden et al., 1993; R. A. Bjork, 1989; Geiselman et al., 1983; MacLeod, 1999; Whetstone et al., 1996).
Maureen Schmitter-Edgecombe and Matthew J. Wright, Department of Psychology, Washington State University; William Marks and Matthew Ventura, Department of Psychology, The University of Memphis.
William Marks passed away on July 11, 2003. This research was supported in part by National Institutes of Health
Grant RO3 HD35838 to Maureen Schmitter-Edgecombe. We thank Leigh Beglinger and Amy Simpson for their support in coordinating data collec- tion. We also thank the members of the Head Injury Research Team for their help in collecting and scoring the data.
Correspondence concerning this article should be addressed to Maureen Schmitter-Edgecombe, Department of Psychology, Washington State Uni- versity, P.O. Box 644820, Pullman, WA 99164-4820. E-mail: schmitter-e @wsu.edu
Neuropsychology Copyright 2004 by the American Psychological Association, Inc. 2004, Vol. 18, No. 1, 104 –114 0894-4105/04/$12.00 DOI: 10.1037/0894-4105.18.1.104
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Given our interest in investigating inhibitory mechanisms in memory performance in a population with severe CHI, we used a variant of the list method directed forgetting procedure in this study.1 Inhibition has been conceptualized in the literature as a basic cognitive suppression mechanism that keeps task-irrelevant information from entering and interfering with the processing of pertinent information (R. A. Bjork, 1989). Within the domain of memory, inhibitory mechanisms are thought to play an important role in the gating of irrelevant information from active work space during memory processing (e.g., R. A. Bjork, 1989; Zacks, Rad- vansky, & Hasher, 1996). Thus, inefficient inhibition could impede memory by taking up space and by consuming processing re- sources that could be used to help process and retrieve additional relevant information (Bjorklund & Harnishfeger, 1990).
Although deficits in explicit memory processes have been well documented in the severe CHI literature (e.g., Brooks, 1972, 1975; Levin, 1989; Paniak, Shore, & Rourke, 1989), no study to date has directly evaluated the role of inhibitory mechanisms in memory performance in the CHI population. The few studies that have investigated inhibitory processes following severe CHI have fo- cused on inhibition in situations in which an item is automatically activated but must be inhibited for successful task performance (e.g., negative priming and selective attention paradigms). The results of these studies currently present an inconsistent picture, with some studies suggesting deficient (e.g., Stuss et al., 1989; Vakil, Weisz, Jedwab, Groswasser, & Aberbuch, 1995; Van Zomeren, 1981) and others intact (e.g., Simpson & Schmitter- Edgecombe, 2000; Schmitter-Edgecombe & Kibby, 1998; Velt- man et al., 1996) inhibitory mechanisms in the population with CHI. In terms of inhibitory mechanisms in memory functioning, it has been postulated that participants with CHI may have greater difficulty than controls in screening out irrelevant information during memory testing (Levin & Goldstein, 1986). This hypothesis derives largely from research that has documented frequent intru- sion errors by participants with CHI on verbal memory tasks (e.g., Brooks, 1975; Crosson, Novack, Trenerry, & Craig, 1988; Levin & Goldstein, 1986). Extrapolating from this hypothesis, one might expect to see deficient retrieval inhibition in memory performance in patients with severe CHI.
In this study, participants with CHI and control participants studied stimulus items in both “forget” and “remember” condi- tions. During the study phase of each condition, participants were presented with two lists of items: List 1 and List 2. Within each list, items were presented as either a picture or a word. Following presentation of List 1 in the forget condition, but not the remember condition, participants were told to forget the previously presented items and to concentrate on learning the List 2 items. In both conditions, subsequent memory testing consisted of a free-recall test followed by a source-monitoring task (picture, word, or new), which provided measures of both item recognition and source discrimination.
Consistent with retrieval inhibition, we expected that the control participants would exhibit poorer free recall for List 1 items compared with List 2 items in the forget condition. Furthermore, directed forgetting was not expected to be evident in the item recognition measure, indicating that List 1 items were available in memory but were temporarily inaccessible. For the population with CHI, we hypothesized that if inhibitory mechanisms are
deficient, then the participants with CHI should be less successful than controls in complying with the forget instructions. In contrast, if inhibitory mechanisms are intact 1 year after severe CHI, then the participants with CHI should show directed forgetting in free recall as well as release from inhibition in item recognition. Fur- thermore, we expected that the participants with CHI would recall a smaller proportion of studied items than controls.
In terms of source discrimination, it currently remains unclear as to whether some of the contextual features associated with forget items continue to be inhibited when there is release of inhibition (see Basden & Basden, 1996; Geiselman et al., 1983). Therefore, this study was designed to provide additional information concern- ing discrimination of source information in list method directed forgetting in both a neurologically intact population and a popu- lation with impairment (i.e., Is contextual information inhibited or equally available for forget items that are retrieved?). The few previous studies that have investigated source memory in the CHI literature have consistently demonstrated impaired memory for source following CHI when tested using direct, as opposed to indirect, testing methods (Dywan, Segalowitz, Henderson, & Ja- coby, 1993; Vakil, Golan, Grunbaum, Groswasser, & Aberbuch, 1996; Vakil, Openheim, Falck, Aberbuch, & Groswasser, 1997).
