Directed Forgetting Further Comparisons of the Item and List Methods

MEMORY,1996,4(6),633±653Directed Forgetting:Further Comparisons of the Itemand List MethodsBarbara H.Basden and David R.BasdenCalifornia State University,USAThree experiments contrasted the effects of directed forgetting instructions when given by item and given by list.In Experiment1,which involved free recall of a single-category list,directed forgetting was greater with the item method than with the list method when the study format was pictures or words whose referents were imaged(these encouraged item-specific processing),but not when the study format was words not imaged(this encouraged relational processing).In Experiment2, directed forgetting was observed with the item method but not with the list method in an indirect test of general knowledge.In Experiment3,``Recollect’’judgements showed directed forgetting with the item method but not with the list method.``Know’’judgements did not show directed forgetting with either method.These experiments show that the mechanisms underlying directed forgetting differ for the item and list methods.IN TR OD UCTIO NIn studies of directed forgetting,subjects are typically instructed to forget eitherthe first of two lists(the list method)or individual targets within the list(the item method).When the list method is used(e.g.Epstein,1970),the instruction to forget the first list is interpolated between the two successively presented lists. When the item method is used(e.g.Woodw ard,Bjork,&Jongew ard,1973),the instruction to remember or forget each individual target is given after each itemis presented.Bjork(1970,1972)proposed two mechanisms in directed forgetting:differential rehearsal of Remember and Forget items and segregation ofRemember and Forget items.He argued that different mechanisms mightunderlie these methods,with differential rehearsal occurring with the itemmethod and not with the list method.Subsequently,Bjork(1989)proposed Requests for reprints should be sent to Barbara H.Basden,Department of Psychology,CaliforniaState University,Fresno,CA93740-0011,USA.Email:barbb@.Portions of this research were presented at the34th annual meeting of the Psychonomic Societyand at the23rd annual Conference for Undergraduate Psychology Research at Santa Clara University.W e would like to thank Kim Maxwell,Scott Pennington,Diane Pugliese,Richard Torzynski,and John Williams for assistance in data collection.1996Psychology Press,an imprint of Erlbaum(UK)Taylor&Francis Ltd634BA SD EN AN D BA SD ENretrieval inhibition as an additional mechanism,but did not tie it to a specific method.We have argued(Basden et al.,1994;Basden,Basden,&Gargano, 1993)that different mechanisms are responsible for directed forgetting with the two methods,but we have proposed that retrieval inhibition underlies directed forgetting with the list method,and that differential processing of Remember and Forget targets underlies directed forgetting with the item method.In addition,we have assumed that relational(organisation)processing occurs to a greater extent with the list method than with the item method,and that item-specific processing occurs to a greater extent with the item method than with the list method.In a com prehensive review of the directed forgetting literature, Johnson(1994)drew a similar conclusion.She attributed greater recall of Remember than of Forget targets with the list method to segregation and selective search of each list of targets followed by inhibition of the to-be-forgotten list.With the item method,segregation and retrieval inhibition are not required because only the set of Remember targets is stored and searched.Three lines of evidence support the position that retrieval inhibition occurs with the list method and not with the item method.First,the item method typically yields greater directed forgetting than the list method on recall tests,a result that should be expected if Forget targets are more extensively processed with the list method than with the item method.Second,the item method yields directed forgetting on recognition tests,but the list method does not.If items are less well processed at storage(as we believe is the case with the item method), recognition memory should be affected.If a set of equally well-processed items is inhibited from retrieval(as we believe in the case of the list method),a test that de-emphasises retrieval should be unaffected.Third,the re-presentation of targets on a recognition test seems to effect a``release’’from inhibition on a subsequent recall test when the list method is used,but not when the item method is used1(e.g.Basden et al.,1993;Bjork,1989).Re-presentation of both Remember and Forget items would not be expected to eliminate a processing deficit for the Forget items,but might very well overcome retrieval inhibition.According to this distinction between relational and item-specific processing (Einstein&Hunt,1980;Hunt&Einstein,1981),procedures that focus the subject’s attention on the list as a whole(or at least on large sections of it) encourage the identification of relationships among the items,whereas procedures that focus the subject’s attention on individual items emphasise information that is item-specific.Thus,the list method of directed forgetting would encourage relational processing whereas the item method would encourage item-specific processing.This is not to say,of course,that either method limits the subject to only one type of processing.W e are merely 1Although Geiselman and Bagheri(1985)reported a release from inhibition with the item method,additional study of forget-cued targets was required to accomplish that release.Repetition may enhance processing rather than releasing items from retrieval inhibition.DIR ECTED F ORG ETTIN G635 suggesting that the mix of relational and item-specific information is influenced by the method of directed forgetting.Relational processing should facilitate list-method directed forgetting because in this case suppression of an entire,already-processed list must occur.Item-specific processing should facilitate item-method directed forgetting because in this case individual targets must be forgotten at the time they are undergoing processing.If the item method encourages item-specific processing and the list method encourages relational processing,and if directed forgetting results from a processing deficit with the item method and from retrieval inhibition with the list method,then factors that enhance item-specific processing should increase the magnitude of directed forgetting with the item method,and factors that enhance relational processing should increase directed forgetting with the list method.In Experiment1,we manipulated the study format as a means of encouraging either relationa l or item-specific processing.Our expectation was that the relative magnitude of directed forgetting with the two methods would vary with study format.EX PER IM ENT1In this experiment one group of subjects attempted to memorise a set of animal pictures and two other groups of subjects attempted to memorise a list of names for those pictures.The subjects in one of the two latter groups were given simple learning instructions and those in the other group were told to form a mental image of the referent of each target.A few prior studies have employed images or pictures in the context of directed forgetting(Bray,Justice,&Zahm,1983; Bugelski,1970).Unfortunately,no firm conclusions could be drawn from these previous studies.According to Hunt and his colleagues,item-specific processing is encouraged either by forming images of the targets(Hunt&Marschark,1989)or by studying pictures corresponding to the targets(Hunt&McDaniel,1993).Hunt and McDaniel have also argued that simple presentation of a categorised list for learning encourages relationa l processing.As mentioned earlier,item-m ethod directed forgetting is usually greater than list-method directed forgetting. According to our analysis,this difference in the magnitude of directed forgetting should be greater when subjects study pictures or study words with imagery instructions that when they study words alone,particularly when the words belong to a single category.One interpretation of directed forgetting is that contextual information about Forget targets is inaccessible on recall tests.Geiselman,Bjork,and Fishman (1983)used the list method,asking subjects to write their recall in separate columns corresponding to the two lists they had studied.Control subjects remembered list membership of Forget targets better than did directed forgetting subjects.Geiselman et al.suggested that loss of contextual information underlies636BA SD EN AN D BA SD ENretrieval inhibition.Unfortunately,a potential source of confoundin g is present if subjects base their judgem ents of list membership on item strength.If this were the case,judgements of list membership might not reflect context information alone.A more direct measure of memory for context information is to have subjects indicate the approxim ate serial position of previously recalled targets.Tzeng,Lee,and Wetzel(1979)introduced this technique.With the item method they found that serial position information was remembered better for Remember than for Forget targets.No control subjects were tested,so no absolute assessments were possible.The results of Tzeng et al.are equally consistent with the idea that Forget items are less extensively processed with the item method.If Remember and Forget targets are equally well processed with the list method,then accuracy of serial position information should be equivalent for the Forget and Remember items with this method.However,if Geiselman et al.are correct and context memory is reduced by directed forgetting instructions,then memory for serial position of Forget targets should be affected with both the item and the list methods.In this experiment we asked our subjects to indicate approximate serial positions for the items they recalled.To determ ine the influence of directed forgetting instructions on absolute memory for contextual information,we included control subjects who did not receive directed forgetting instructions.If contextual information is lost during directed forgetting,then memory for serial position should be less accurate for Forget targets in the experimental conditions than in the control conditions.Although control subjects were included to permit measurement of absolute loss of contextual information,their inclusion also permitted us to compare the absolute effects of directed forgetting instructions on Remember and Forget targets for each of the two methods.Past research has shown that directed forgetting instructions yield not only lower recall of Forget targets,but also greater recall of Remember targets(see Bjork,1972).M ethodSubjects.We tested194students enrolled in introductory psychology classes at California State University,Fresno.Their participation was in partial fulfilment of course requirements.Approximately22subjects were tested in each of the nine treatment conditions.Materials and Apparatus.We selected24pictures of animals from the Snodgrass and Vanderwart(1980)norms.All pictures showed high levels of name agreement(M=89%)according to those norm s.A set of35mm slides was made for the pictures and another set was made for the names.The slides were presented using a Kodak slide projector paced by a Hunter timer.Each targetDIR ECTED F ORG ETTIN G637 was designated Forget and Remember equally often across groups.Order was varied across groups to ensure that particular targets did not consistently occupy favourable serial positions across methods.Subjects responded by writing their recall on lined pages included in their response booklets.Design.A322mixed factorial design was employed with study format(pictures,words with imagery instructions,or words without imagery instructions)and method(list or item)as between-subjects factors and instruction(Remember or Forget)as a within-subject factor.Three outside control groups were also tested,one with each of the three study formats. Subjects in these groups were not given directed forgetting instructions.Procedure.Groups of up to six subjects at a time were assigned to testing conditions in accordance with a block-random isation schedule.Subjects were given instructions appropriate to their study format prior to target presentation. For the image study format,subjects were instructed to form an image of each word as it was presented to them.For the picture and word study formats, subjects were simply instructed to do their best to recall all targets.A blank screen or a spot of light of1.1second duration followed each target for all subjects.Subjects tested with the item method were given the following additional instructions:After each item has been on the screen for a few seconds,it will be followed by a blank screen or a spot of light.A blank screen means you are to forget that item buta spot of light means you are to remember that item.Subjects tested by the list method were not told to differentiate among items and were told to ignore the presence or absence of lights.After subjects had read the initial instructions,they were shown the words or pictures individually at a three-second rate.After the first12targets had been presented,subjects tested by the item method were told to rest for a few seconds. Subjects tested by the list method were given directed forgetting instructions for the first list.Thus,the time interval between list halves was equivalent for the two methods.Then the remaining12targets were presented.Target presentation was immediately followed by a distractor task intended to purge short-term memory.Subjects completed simple arithmetic problems in their response booklets for30seconds;then they were instructed to write as many of the targets they had studied as they could remember,including both the targets they were told to remem ber and those they were told to forget.They were given three minutes for this free recall test.Subjects were then instructed to indicate the approxim ate serial position of each word they had recalled.This was done by asking them to write a``1’’next to a word if it occurred among the first four targets,a``2’’if it occurred among the second four targets,and so onthrough to ``6’’if it occurred among the last four targets (cf Tzeng et al.,1979).After the experim ent was over,the subjects were told the purpose of the forget instruction and were asked not to discuss the experiment with other potential subjects.R esultsThe dependent variable in free recall was the proportion of Remember or Forget targets recalled.For control subjects,targets that occupied the same serial positions as actual Remember and Forget targets in the experimental conditions were designated nominal Remember and Forget targets.Thus,determination of nominal Remember and Forget targets for individual control subjects depended on whether the comparison was with list method or item method experimental subjects.Mean recall proportions for each of the conditions are shown in Table 1.A mixed three-factor analysis of variance was performed with method and study format as between-subjects factors and instruction as a repeated measure.The three-factor interaction was significant,F (2,127)=3.53,MSe =0.036.Subsequent analysis revealed that the simple interaction between method and instruction was significant for pictures,F (1,42)=4.21,MSe =0.032;and for words with images,F (1,45)=14.89,MSe =0.027,but was not significant for words without images,F <1.Thus,the magnitude of directed forgetting differed as a function of method when pictures or words with images were studied,but not when words were studied.These results,with directed forgetting expressed as difference scores between the mean proportion of Remember and Forget targets recalled,are shown in Fig.1.With the item method,the magnitude of directed forgetting was statistically significant for all three study form ats:for pictures,F (1,21)=58.33,TA BL E 1M e an Proportions of Rem e m ber,F orget a nd Control Targ ets Produced duringFree Rec all638BA SD EN AN D BA SD ENMSe =0.037,for words with images,F (1,22)=95.86,MSe =0.022,and for words without images,F (1,19)=15.62,MSe =0.043.With the list method,the magnitude of directed forgetting was also statistically significant for all three study formats:for pictures,F (1,21)=12.47,MSe =0.038,for words with images,F (1,23)=11.12,MSe =0.031,and for words without images,F (1,21)=20.45,MSe =0.048.As mentioned earlier,we compared the list method and item method directed forgetting subjects with the same control subjects.This necessitated separate three-factor analyses of variance for each method,with study format and group (experimental vs.control)as between-subjects factors and instruction as a repeated measures factor.For the item method analysis,the effect of study format was significant,F (2,120)=7.77,MSe =0.035.Images were recalled better than pictures or words.The interaction between instruction and group was significant,F (1,120)=65.21.Tests of simple effects confirmed that recall of Remember targets was greater for experimental than for control subjects,F (1,120)=13.04,MSe =0.158;but recall of Forget targets was poo rer for experimental than for control subjects,F (1,120)=46.06,MSe =0.192.2ForFIG.1.Magnitude of directed forgetting as a function of study format and instruction.2The triple interaction narrowly missed significance (P =0.07).The magnitude of the difference between Forget and control items was greater with the picture and image formats than with the word format.These results are consistent with our argument that subjects perform only superficial processing of Forget targets with the item method.DIR ECTED F ORG ETTIN G 639640BA SD EN AN D BA SD ENthe list method analysis,the interaction between group type and instruction was again significant,F(1,123)=27.87.As in the analysis of the item method,recall of Remember targets was greater for experimental than for control subjects,F(1, 123)=8.03,M Se=0.201;but recall of Forget targets was poorer for experimental than for control subjects,F(1,123)=17.75,MSe=0.017.An analysis conducted on the proportion of correct serial position placements for the item method yielded a significant main effect for instruction,F(1, 60)=5.64,MSe=0.054.The proportion of correct placements was0.50for Remember targets and0.40for Forget targets.A similar analysis for the list method yielded no significant effects,the mean proportion of correct placements was0.42for Remember targets and0.48for Forget targets.An analysis was conducted on the proportion of correct serial position placements of Forget items contrasting directed forgetting subjects with controls.Subjects placed Forget targets equally accurately in the experimental and control conditions,F s<1.This held true for both the item and list methods.D iscussionW e have hypothesised that study formats encouraging item-specific processing would increase directed forgetting more with the item method than with the list method.This hypothe sis was confirmed.The difference in magnitude of directed forgetting with the item and list methods was greater when subjects studied pictures or words for which they formed images than when they simply studied words.Directed forgetting was actually equivalent for the two methods when subjects studied words without forming images.These results are consistent with our distinction between item and list methods,i.e.that relational processing underlies directed forgetting with the list method,but that item-specific processing underlies directed forgetting with the item method.The present results are not consistent with those of Bugelski(1970),who reported an absence of directed forgetting with the item method when subjects were asked to form images of the targets they studied.His report is quite sketchy with regard to procedures,but we assume that they differed from our own in som e important way.Our results are consistent with those of Bray and his colleagues,e.g.Bray et al.(1983).These investigators reported robust directed forgetting when subjects studied pictures.Bugelski had argued,on the basis of his failure to find directed forgetting, that subjects could not inhibit targets for which they had formed images.On the basis of our own results we would argue that subjects did not carry out extensive processing of Forget targets even when they were presented in the picture and image study formats.This interpretation is supported by our finding that control subjects recalled those same targets better than did the experimental subjects.Based on the directed forgetting literature,we had expected the directed forgetting instruction to both reduce recall of Forget items and increase recall ofDIR ECTED F ORG ETTIN G641 Remember items.In the present study this occurred with both the list and item methods.Recall was poorer for Forget targets and better for Remember targets as compared with controls.Bjork(1970)has argued that Remember targets are subject to less interference in the experimental conditions.This argum ent could be applied to either method of directed forgetting.If differential processing underlies item-method forgetting,then serial position information should be better for Remember than for Forget items with this method.If differential processing is not responsible for list-method directed forgetting,then serial position information should be the same for Remember and Forget items with this method.As predicted,memory for serial position information was better for Remember than for Forget items with the item method,but not with the list method.These results support our position.To test the hypothesis expressed by Geiselman et al.(1983)that directed forgetting occurs when subjects lose access to contextual information,we com pared accuracy of serial position information for Forget targets in the experimental and control conditions.Although Geiselman et al.reported that memory for list membership of Forget items was greater for control than for experimental subjects,we found no corresponding difference in the accuracy of memory for serial position.Furthermore,our results were quite similar with the list and item methods.Thus,our results do not support the hypothesis that directed forgetting results from loss of contextual information.Of course,a quite different picture might emerge if recollection for serial position of all items had been assessed.Thus,results of Experiment1were consistent with the hypothesis that retrieval inhibition and relational processing underlie directed forgetting with the list method,but that differential item-specific processing underlies directed forgetting with the item method.In Experiment2,we compared the influence of the list-and item-m ethod directed forgetting on performance in an implicit memory test.Current research and reviews(e.g.Brown&Mitchell,1994; Thapar&Greene,1994)indicate that levels of processing manipulations may influence priming on implicit tests.If,as we suggest,Remember targets are more extensively processed than Forget targets with the item method,then item-method directed forgetting may occur on implicit tests but list-method directed forgetting should not.EX PER IM ENT2Directed forgetting on implicit tests has sometimes been observed with the item method,but has never been observed with the list method(e.g.Basden et al., 1993;MacLeod,1989;Paller,1990).W e suggest that this difference occurs because implicit tests typically involve item-by-item cueing and thus are more sensitive to the effects of differential processing than to the effects of retrieval inhibition.To our know ledge,even explicit tests that provide item-by-item cues642BA SD EN AN D BA SD EN(e.g.word fragm ent cued recall,stem-cued recall,recognition,and word association)do not produce list-method directed forgetting(see Basden et al., 1993).List-method directed forgetting instructions appear to act on the list as a whole rather than on individual items.In previous experiments that obtained item-method directed forgetting on implicit tests(e.g.MacLeod,1989),perceptual tests such as word fragment completion were used.Such tests are typically less sensitive to differential processing(see Roediger&McDermott,1993)than are conceptual tests(tests relying on meaning).Thus,demonstrations of item-method directed forgetting should be easier to obtain on implicit conceptual tests.In research reported earlier we failed to observe item-method directed forgetting with an implicit word association test(Basden et al.,1993,Experiments1&2).However,this failure may have resulted from a floor effect,as priming was not statistically significant with the conceptual test we used.The present experiment represents another attempt to obtain item-method directed forgetting with an implicit conceptual test.The list method was included for purposes of com parison.After studying a list of low-frequency words with either item-or list-method directed forgetting instructions,the subjects were given an implicit test of general know ledge.Definitions of targets and distractors were provided at the time of the test,and subjects were instructed to respond to each of them with the first word that came to mind.Low-frequency words were used because such materials typically yield higher levels of priming than do high-frequency words (Roediger&McDermott,1993).As this test,like other implicit tests,includes item-by-item cueing,it should be sensitive to differential processing of Remember and Forget items of the sort we believe the item method encourages. Therefore,we expected directed forgetting with the item method but not with the list method.After com pleting the implicit general know ledge test,subjects were asked to free recall the Remember and Forget targets.We expected directed forgetting with the list method as well as with the item method on this test,because free recall is sensitive to the retrieval inhibition we believe occurs with the list method.We expected greater directed forgetting with the item method than with the list method as in our previous research.M ethodSubjects.We initially tested68subjects and later added69more subjects. W e also tested28similar subjects in a pilot study used to assess the materials. All were of the same description as in Experim ent1.Materials and Apparatus.The materials comprised192low-frequency, multisyllabic words(Tulving,Schacter,&Stark,1982).Definitions were developed for each of these words by consulting W ebster’s New CollegiateDIR ECTED F ORG ETTIN G643 Dictionary.The materials were then piloted to confirm that prospective subjects could match the words with their definitions.These definitions were used to prepare a test of general know ledge.All materials were presented using a microcomputer.The subjects typed their responses at the computer keyboard.Design.We employed a mixed two-factor design with method(item or list) as a between-subjects factor and instruction(Forget or Remember)as a within-subject factor.The dependent measure was the number of experimenter-designated terms produced on the test of general know ledge and on the subsequent free recall test.Procedure.Subjects were assigned to the method of directed forgetting in accordance with a block-random isation schedule.After entering the condition code at the com puter keyboard,the experimenter left the test cubicle;the remainder of the procedure was automatically administered.The programme randomly selected a study list of48targets and48distractors from the corpus of 192words.The48list members were randomly separated into24Remember and24Forget targets.Individual random presentation and testing orders were also program-generated.Prior to list presentation all subjects were informed that their ability to remem ber list members would be tested later.Subjects tested with the item method were also given the following instructions:After each word has been on the screen for a few seconds,a brief signal will tell you whether to REM EMBER it or FORGET it.If the signal is REMEMBER you should be prepared to recall the word later,but if the signal is FORGET you can forget the word.After reading these initial instructions,all subjects were shown the targets individually at a six-second rate.For subjects tested with the item method, ``REMEM BER’’or``FORGET’’joined each item during its final three seconds of exposure.After the first24targets had been presented,subjects tested with the item method were told to rest for a few seconds and subjects tested with the list method were given the following directed forgetting instructions:The list you have just studied was only for practice.You can forget it now.The list you will see next is the one we want you to remember,so forget the practice list and concentrate on this new list.Then the remaining list of24targets was presented.After list presentation,all subjects were given a distractor task in which a list of24products,services,or activities appeared on the monitor screen simultaneously.The subject was instructed to type the name of a state he/she。