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Forgetting motor programmes: Retrieval dynamics in procedural memory a
a
Tobias Tempel & Christian Frings a
Fachbereich I – Psychologie, University of Trier, Trier, Germany Published online: 14 Jan 2014.
To cite this article: Tobias Tempel & Christian Frings , Memory (2014): Forgetting motor programmes: Retrieval dynamics in procedural memory, Memory, DOI: 10.1080/09658211.2013.871293 To link to this article: http://dx.doi.org/10.1080/09658211.2013.871293
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Memory, 2014 http://dx.doi.org/10.1080/09658211.2013.871293
Forgetting motor programmes: Retrieval dynamics in procedural memory Tobias Tempel and Christian Frings
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Fachbereich I – Psychologie, University of Trier, Trier, Germany
(Received 17 July 2013; accepted 28 November 2013)
When motor sequences are stored in memory in a categorised manner, selective retrieval of some sequences can induce forgetting of the non-retrieved sequences. We show that such retrieval-induced forgetting (RIF) occurs not only in cued recall but also in a test assessing memory indirectly by providing novel test cues without involving recall of items. Participants learned several sequential finger movements (SFMs), each consisting of the movement of two fingers of either the left or the right hand. Subsequently, they performed retrieval practice on half of the sequences of one hand. A final task then required participants to enter letter dyads. A subset of these dyads corresponded to the previously learned sequences. RIF was present in the response times during the entering of the dyads. The finding of RIF in the slowed-down execution of motor programmes overlapping with initially trained motor sequences suggests that inhibition resolved interference between procedural representations of the acquired motor sequences of one hand during retrieval practice.
Keywords: Procedural memory; Motor control; Inhibition; Retrieval-induced forgetting.
The smooth execution of a trained body movement partially depends on its efficient retrieval from memory. Yet, interference between related movements can affect the retrieval. A sequence of key presses a piano player performs within the melody of one piece of music, for example, can be related to another sequence of a different piece of music. Activation of the wrong sequence would interfere with the playing of the current piece of music. We investigated the resolution of this kind of interference by examining retrieval-induced forgetting (RIF) of newly acquired motor sequences. RIF is typically analysed in the retrieval-practice paradigm (Anderson, Bjork, & Bjork, 1994; Levy & Anderson, 2002; Storm & Levy, 2012), which consists of three main phases. In the learning phase, participants study several sets of items in combination with a shared (category-)cue that
defines the specific set of items. In the subsequent retrieval-practice phase, participants are cued to recall half of the studied items from half of the sets. In the test phase, recall performance for all items is tested. The recall of practiced items (Rp+ items), unpracticed items from practiced sets (Rp− items) and unpracticed items from unpracticed sets (Nrp items) is compared. Rp+ items typically profit from retrieval practice and are better recalled than Nrp items. RIF manifests itself in significantly lower recall of Rp− items as compared to Nrp items. This phenomenon has been demonstrated for a variety of materials. Mostly, however, verbal items have been used in studies on RIF. Recently, we adapted the retrieval-practice paradigm to the use of sequential finger movements (SFM) as items (Tempel & Frings, 2013). Participants first learned 12 SFM, each consisting
Address correspondence to: Tobias Tempel, Fachbereich I – Psychologie, University of Trier, Trier 54286, Germany. Email: [email protected]
© 2014 Taylor & Francis
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of two consecutive key presses in response to a letter stimulus. Six items involved two fingers of the left hand, six involved two fingers of the right hand. After retrieval practice on three items of one hand, a final recall test assessed memory for all items. Rp− items were tested before Rp+ items in order to preclude any output interference by Rp+ items (cf. Anderson et al., 1994; Roediger & Schmidt, 1980). Rp− items were accordingly compared to the first three Nrp items tested (Nrp1), whereas Rp+ items were compared to the last three Nrp items tested (Nrp2). RIF occurred in significantly fewer recalled Rp− than Nrp1 items, as well as in significantly longer response times (RTs) to Rp− than to Nrp1 items. Thus, we were able to demonstrate for the first time that RIF also affects body movements (for a conceptual replication, see Reppa, Worth, Greville, & Saunders, 2013). This demonstration, however, did not allow distinguishing qualities of memory representations that had been affected by RIF. Motor sequences not only constitute a novel item pool allowing for a further demonstration of the robustness of RIF, but they also differ from other item materials by offering insight into the dynamics of procedural memory. Indeed, motor sequences involve declarative representations of the actions to be performed, for example, of fingers to be moved or buttons to be pressed, and these can be easily verbalised. However, it is an essential element of motor sequences that they also involve a representational format of the muscle commands for executing the corresponding movements. We here denominate this procedural representation as the motor programme. The distinction of declarative and procedural representations of motor sequences corresponds to models that postulate an anticipation of effects always accompanying the performance of an action (e.g., Hommel, Müsseler, Aschersleben, & Prinz, 2001). Whereas the anticipation of effect pertains to the declarative level, the actual execution relies on the motor programme. Evidence for the distinction is also provided by studies on the effects of sleep on the consolidation and transfer of stored motor sequences. Sleep enhances extrinsic transfer that requires access to declarative representations, for example, in a task that asks participants to perform an action with the right hand they had learned to execute with the left hand. In contrast, intrinsic transfer that involves a high degree of overlap in motor programmes is not enhanced by sleep (e.g., Cohen, Pascual-Leone, Press, & Robertson, 2005; Genzel et al., 2012; Witt, Margraf, Bieber,
Born, & Deuschl, 2010). Moreover, different brain regions are involved in the processing of declarative and procedural information. The hippocampus, for example, is essential for storing declarative but not procedural representations (e.g., Deweer et al., 1994). Support for the distinction between declarative and procedural representations of motor sequences has also come from studies with neurological samples (e.g., Helmuth, Mayr, & Daum, 2000; Pascual-Leone et al., 1993). Our study pertains to the question to what extent processes operating within procedural memory are similar to processes operating in declarative memory. The occurrence of RIF for motor sequences (Tempel & Frings, 2013) provided first evidence of parallel dynamics. Other evidence came from studies employing the retroactive interference paradigm. Wohldmann, Healy, and Bourne (2007) demonstrated that retroactive interference affects the retrieval of motor sequences (see also Wohldmann, Healy, & Bourne, 2008). Interference at retrieval in general depends on the organisation of memory. With regard to the organisation of procedural memory, research on the acquisition of generalised motor programmes has shown that motor programmes are often grouped together as classes of activities (Schmidt, 1975, 2003). A generalised motor programme is then abstracted from several motor programmes sharing prominent features, such as relative timing of movements. It can be regarded as a category within procedural memory. Effectors involved in movements can also act as such categories. Tempel and Frings (2013) found that selective retrieval of a subset of SFM of one hand (Rp + ) impaired recall accuracy for the non-retrieved SFM of that same hand (Rp − ). However, the RIF effect was more pronounced and more robust for the second dependent variable RT. The selective retrieval of Rp+ items slowed down the execution of Rp− compared to Nrp1 items. We take this slowing for first evidence that the motor programmes of Rp− items had been affected, and not only their declarative representations. It is necessary though to test this assumption further because the slowed execution might merely reflect a by-product of processes affecting declarative representations, but not operating in procedural memory at all. Therefore, we investigated whether RIF of motor sequences would occur in a memory test not relying on the recall of the previously encoded sequences, but the execution of corresponding movements in response to novel cues, thereby tapping the same motor programmes while
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circumventing the level of declarative representations. Participants had to type up letter dyads in this test. Some of these dyads required the execution of movements that corresponded to previously learned motor sequences. Thus, there was an overlap between test and learning in the motor programmes involved and the ease of executing corresponding movements is an index of memory. RIF is a consequence of selective retrieval, during which interference arises that is directly related to the occurrence and strength of RIF. Several studies have proven that the stronger Rp− items interfere with the retrieval of Rp+ items, the stronger RIF is (e.g., Anderson et al., 1994; Shivde & Anderson, 2001; Storm, Bjork, & Bjork, 2007), while it is still under debate in the current literature whether an inhibitory mechanism contributes to resolve this interference and thus causes RIF (cf. Raaijmakers & Jakab, 2013; Storm & Levy, 2012). Wohldmann, Healy, and Bourne (2008) showed that retroactive interference affected newly acquired motor sequences more strongly if the interfering sequences had to be executed as compared to a mere mental retrieval of those sequences. Apparently, the activation of motor programmes during movement execution intensified interference. This procedural kind of interference implies that dynamics underlying RIF of SFM probably also operate on a procedural level. Retrieval practice of SFM should produce interference between motor programmes that entails RIF of motor programmes. Assuming that the selective retrieval of Rp+ items affected motor programmes of Rp− items, we expected to find RIF of SFM present in an impaired execution of movements that corresponded to Rp− items. Learning and retrieval practice of our experiment closely followed the study of Tempel and Frings (2013). In the test phase, however, participants were placed in front of a different computer in a different cubicle. Their task was to type up letter dyads presented on the computer screen. Twelve letter dyads were presented that corresponded to the 12 SFM learned before. Sixteen filler dyads consisted of letters to be entered by fingers of both hands. We expected that the letter dyads corresponding to RP—movements would be typed more slowly than letter dyads corresponding to Nrp1 movements.
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METHOD Participants Thirty-two psychology students at the University of Trier participated in the experiment. They received course credit for their participation.
Design Item type (Rp−, Nrp1, Nrp2, Rp + ) was manipulated within subjects.
Material The experiment was conducted using Dell Optiplex 755 PCs with Eizo FlexScan S1901 monitors and standard German QWERTZ keyboards. The software PXLab (Irtel, 2007) served for running the experiment. The items consisted of 12 twofinger movements. Six two-finger movements consisted of fingers of the left hand, the other six of fingers of the right hand. Participants learned these movements as responses to letters. The letters a to f were the stimuli for the left-hand movements, the letters u to z for the right-hand movements. The thumbs were excluded from the movements. For both hands, all two-finger movements started with one out of two fingers. Combining these starting fingers with all three remaining fingers resulted in the six items used for each hand. We counterbalanced if the starting fingers were the index fingers and the ring fingers or the middle fingers and the pinkies (see Appendix for all movements and stimuli). During the learning phase, a letter appeared at the centre of the computer screen together with an animation of the corresponding two-finger movement (cf. Figure 1). The fingers of the left hand were placed on the keys Q, W, E and R. The fingers of the right hand were placed on the keys U, I, O and P. Below the letter, a display of the two hands demonstrated which fingers should be moved by showing two consecutively flashing fingers (first finger was coloured yellow, and second finger was coloured blue, 200 ms per flash). After the display of the two hands disappeared, participants could perform the movement. If the performed sequence was incorrect, a feedback appeared, displaying: “Fehler!” (English: “Error!”).
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Figure 1. The upper section depicts a trial in the learning phase. It starts with a display of the letter stimulus together with a drawing of the two hands. After 400 ms, the first finger illuminates yellow for 200 ms and then the second finger illuminates blue for 200 ms. Subsequently, the hand display disappears, and the participant can enter the SFM just illustrated. The middle section depicts a trial in the retrieval-practice phase. A stimulus is given, and the participant is supposed to perform the corresponding SFM. The lower section depicts a trial in the final test phase. The participant enters a presented letter dyad, while his or her fingers are resting on the same eight keys as during learning and retrieval practice which are displayed below the letter dyad. The learning phase and the retrieval-practice phase took place in a cubicle containing a PC keyboard on which the response keys were marked by orange labels hiding the inscriptions (first cubicle). The final test phase took place in a different cubicle containing a PC keyboard without any marked keys (second cubicle). SFM = sequential finger movement.
Procedure The experiment consisted of three phases (learning, retrieval practice and indirect memory test). Instructions were given on the screen and summarised by an experimenter. After having read the instructions for the learning phase, the participant clicked an onscreen button in order to start with the learning phase. Participants had 10 seconds to place their fingers with exception of the thumbs on eight keys (Q, W, E, R, U, I, O and P) marked by labels hiding the inscription. Then the learning of the 12 items began. Participants had to consecutively press two keys in response to a displayed letter accompanied by an animation graphic
display showing which digits should be moved (cf. Figure 1, upper section). First, all 12 items appeared once in random order, whereupon an instruction screen informed the participant that the items just presented would appear again several times in the following. Eleven blocks each containing the 12 items in a random order were presented. In the retrieval-practice phase, participants had to retrieve three items of one hand. Counterbalancing of the retrieval-practiced items resulted in four retrieval-practice sets (abc, def, uvw and xyz). These four sets were counterbalanced between participants. The items were cued by their letter stimuli. A letter appeared on the screen and the participant entered the corresponding item while
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his or her fingers again rested on the marked keys (cf. Figure 1, middle section). Each of the three letters appeared five times. No feedback about the accuracy of the performed two-finger movement was given. The final test phase comprised an indirect memory test. The experimenter seated participants in a different cubicle in front of a PC with a keyboard without any marked keys. Their task consisted in entering letter dyads presented on the screen. The instructions emphasised speed as well as accuracy. The participants placed their fingers on the same keys as during learning and retrieval practice, so they would enter each letter with a different finger. During each trial of the test, a letter dyad appeared in the centre of the screen accompanied by a display of the keyboard at the bottom of the screen. This display contained only the inscriptions of the keys to be used (Q, W, E, R, U, I, O and P) and was intended to prevent participants from looking down on the keyboard keys (cf. Figure 1, lower section). Twelve dyads corresponded to the 12 SFM learned before because they required the same key presses, that is, the same motor sequences had to be executed. In addition, 16 dyads comprising key presses by fingers of both hands served as filler trials. The sequence of filler trials was the same for all participants. There were, however, different sequences of the experimental trials corresponding to previously learned SFM. The items of one hand were tested in succession, at which, Rp− items were tested before Rp+. Within the items of the non-retrieval-practiced hand the items were presented in one of two sequences thereby counterbalancing which items constituted Nrp1 and Nrp2 items. Also, it was counterbalanced which hand was tested first. The alternation of filler trials and experimental trials was constant over all participants. The test sequence started with two filler trials.
RESULTS Retrieval success in the retrieval-practice phase (M = 51%, SD = 34%) was similar to the level reported by Tempel and Frings (2013). Examining RIF, a t-test showed that RTs at entering letter dyads corresponding to Rp− items were significantly longer than RTs for letter dyads corresponding to Nrp1 items, t(31) = 2.54, p = .008,
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one-tailed, dz = 0.45. Rp+ enhancement did not occur with regard to RTs, that is, RTs for letter dyads corresponding to Rp+, and Nrp2 items did not differ significantly, t < 1.1 However, it was present in accuracy. Correct input of letter dyads corresponding to Rp+ items was significantly higher than correct input of letter dyads corresponding to Nrp2 items, t(31) = 1.76, p = .044, onetailed, dz = 0.31. Correct input of dyads corresponding to Rp− items and correct input of letter dyads corresponding to Nrp1 items did not differ significantly, t < 1 (see Figure 2). We additionally analysed RTs of only those trials in which the participants entered the dyad correctly. The results were almost identical to the results for all RTs combined. RTs for letter dyads corresponding to Rp− items were significantly longer than RTs for letter dyads corresponding to Nrp1 items, t(31) = 2.38, p = .012, one-tailed, dz = 0.43. RTs for letter dyads corresponding to Rp+ and Nrp2 items did not differ significantly, t < 1. Finally, we examined correlations of RIF and Rp+ enhancement. RIF was computed as the difference in RTs for letter dyads corresponding to Rp− items and Nrp1 items. For Rp+ enhancement, we computed two measures: the difference in RTs for letter dyads corresponding to Nrp2 and Rp+ items, as well as the difference in accuracy at entering letter dyads corresponding to Rp+ and Nrp2 items. There was no correlation between RIF and the RT measure of Rp+ enhancement (r = .002, p = .990), nor between RIF and the accuracy measure of Rp+ enhancement (r = .171, p = .349).
1 The letter dyads partly overlapped with the letter stimuli used during learning and retrieval practice. Although counterbalancing of the retrieval practice sets and of the assignment of Nrp items to Nrp1 and Nrp2 precluded any confounding of RIF or Rp+ enhancement effects by item-specific influences, we were interested in how the results looked for only those letter dyads not including letters overlapping with stimuli from the previous phases. Seven letter dyads had to be excluded. As a consequence, data of 20 participants had to be excluded. Thereby, statistical power was considerably reduced. Yet, the basic pattern of results emerged again with longer RTs for Rp− (M = 1795 ms) than Nrp1 (M = 1554 ms) items, however, the highly diminished power prevented the RIF effect to reach a conventional significance level, t(11) = 1.31, p = .109, onetailed. RT for Rp+ and Nrp2 items did again not differ, t < 1.
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Percentage of correct input
100 80 60 96
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Response time in ms
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Figure 2. The upper section shows the percentages of correctly entered letter dyads in the test phase as a function of item type. The lower section shows mean response time (in milliseconds). Error bars depict standard error of the mean. Rp+ = retrieval practiced items; Rp− = unpracticed items of the retrieval practiced hand; Nrp1 = RIF baseline; Nrp2 = Rp+ enhancement baseline.
DISCUSSION We investigated the processes underlying RIF of motor sequences. Participants first learned SFM. Half of these pertained to the left hand, the other half to the right hand. Subsequently, participants performed retrieval practice on half of the items of one hand. Finally, participants entered letter dyads by pressing the respective keys of a standard PC keyboard, while their fingers were resting on the same keys as when entering the SFM during learning and retrieval practice. The input of letter dyads corresponding to Rp− items was significantly slower than the input of letter dyads corresponding to Nrp1 items. This slowing of movements is the first demonstration of RIF in procedural memory. It shows that retrieval practice of Rp+ items affected the motor programmes of Rp− items. These motor programmes were activated again in the final test without involving recall instructions or even providing any cues that could have been used for retrieval of the previously learned SFM.
Rp+ enhancement occurred only in accuracy but not RTs. We consider the order in the final test phase testing Rp− before Rp+ items to account for this pattern of results. The input of letter dyads corresponding to Rp+ items was probably impacted by the previous input of letter dyads corresponding to Rp− items. Nrp2 items were subject to the same potential interference by the previous execution of items of the same category, that is, the same hand (Nrp1). Hence, the testing order had the same impact on Rp+ and Nrp2 items but led only for Nrp2 items to a reduction in accuracy. Rp+ enhancement, then, emerged because the accuracy of the input of letter dyads corresponding to Rp+ items was less susceptible to output interference. In contrast, accuracy of the previously tested Rp− and Nrp1 items was nearly 100%, and RIF occurred in slower input of letter dyads corresponding to Rp− items. It is beyond the scope of the present investigation to distinguish the qualities of RTs and accuracy as measures of procedural memory. Future studies may explore whether RTs represent procedural memory more adequately because they directly reflect the ease of executing movements, whereas accuracy may equally represent access to declarative and procedural memory. Not asking for recall is an essential feature of implicit memory tests. These tests measure memory by requiring performances that match previously encoded items. Memory for learned items is indicated by the strength by which those items influence the answers in the task. For example, the task of category exemplar generation can serve as an implicit memory test if participants initially learned exemplars of that category. The more exemplars that had been presented before are spontaneously named in response to the category cue, the stronger the items obviously are activated in memory. Although retrieval attempts need to be precluded in order to qualify a specific task as truly implicit, in fact many implicit memory tests provide participants with information that can act as a retrieval cue, such as category names in category exemplar generation or even the complete items themselves, for example, in category exemplar verification (Perfect, Moulin, Conway, & Perry, 2002). In contrast, the test used in the present experiment did not provide such cues. Since participants might have noticed that several movements of entering the letter dyads overlapped with learned SFM, we hesitate to label this task as a novel kind of implicit memory test. Although it includes crucial features of implicit testing, it might be more appropriate to speak of an indirect
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memory test. However, even if participants noticed that some movements in the test matched SFM from the learning phase, this awareness would not have been of use for accomplishing the task at hand. The letter dyads corresponded with previously learned items only in the motor programmes involved. If participants would have tried to remember SFM, any recollection would not have been helpful in entering the dyads; it rather would have hurt performance because the letter dyads did not provide participants with any information that could have been used as a retrieval cue apart from the two-finger movement itself. Performing a specific two-finger movement might have reminded participants of the corresponding SFM learned before, but only in the course of or after its execution. Inhibitory as well as non-inhibitory explanations of RIF have been discussed in the literature. The inhibitory account (Anderson et al., 1994; Anderson & Spellman, 1995) assumes that during retrieval practice of one item all items of this set compete for conscious recollection. In order to resolve this competition, the Rp+ items are strengthened, while simultaneously the Rp− items are inhibited. In contrast, non-inhibitory explanations assume that RIF originates from changes in the strength of associations between items and cues or from blocking exerted by Rp+ items during the test (e.g., Williams & Zacks, 2001). Four key predictions distinguish the inhibitory account from non-inhibitory alternatives (Anderson, 2003). The inhibitory account posits that it is necessary to attempt to retrieve Rp+ items during retrieval-practice for RIF to occur (retrieval specificity). It further posits that the strength of the activation of Rp+ items during retrieval-practice does not influence the amount of resulting RIF (strength independence), whereas the strength of competition from Rp− items during retrievalpractice does (interference dependence). Finally, since inhibition lowers the activation of memory representations of Rp− items, RIF should also emerge in memory tests that do not provide information present at learning as retrieval cues (cue independence). The finding of RIF of motor sequences in a test with the novel test cues of letter dyads is in accord with the prediction of cue independence. It supports the inhibitory account because the final test phase assessed memory independently from previously studied cues. The inhibitory account can easily explain why the access to the motor programmes of Rp− items was reduced. The
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interference between motor programmes during retrieval practice was resolved by inhibiting the motor programmes of Rp− items. The occurrence of RIF in a test not relying on previously studied cues complements other studies that reported RIF in tests using cues to probe memory that were different to the cues used during learning and retrieval practice (Anderson & Bell, 2001; Anderson, Green, & McCulloch, 2000; Camp, Pecher, & Schmidt, 2005; Saunders & MacLeod, 2006; Shivde & Anderson, 2001). Although memory was probed by novel cues, non-inhibitory processes also might have contributed to the obtained RIF effects. The SFM were essentially linked to the hand involved in their execution. The input of letter dyads corresponding to previously encoded SFM in the final test thus, of course, also required the use of the same hand as during the learning of the SFM. Therefore, retrieval practice of Rp+ items might have strengthened their associations with the hand, subsequently blocking the execution of movements corresponding to Rp− items. However, RIF was independent of strengthening Rp+ items. There was no correlation of RIF with Rp+ enhancement in our experiment. Several studies reported the same finding (e.g., Hanslmayr, Staudigl, Aslan, & Bäuml, 2010; Hulbert, Shivde, & Anderson, 2012; Staudigl, Hanslmayr, & Bauml, 2010; Weller, Anderson, Gómez-Ariza, & Bajo, 2013). It has also been shown that manipulations strengthening Rp+ items by repeated study (e.g., Bauml, 2002; Ciranni & Shimamura, 1999; Staudigl et al., 2010) or non-competitive retrieval (Anderson, Bjork, & Bjork, 2000) do not induce forgetting of Rp− items. Moreover, Storm, Bjork, Bjork, and Nestojko (2006) found that RIF occurred even with an impossible retrieval task during the retrieval-practice phase, that is, they provided word stems as cues that did not correspond to any existing exemplars of categories used in the learning phase of the experiment (see also Storm & Nestojko, 2010). Hence, RIF even occurs in the absence of Rp+ strengthening. Taken together, the bulk of the evidence suggests that associative blocking cannot explain RIF. Still, it might be interesting for future studies to investigate whether the same findings can also be replicated with motor sequences. In particular, it is possible that practicing items by executing them without retrieving them from memory already produces a certain amount of interference with other motor sequences. Indirect evidence for this assumption comes from the study by Wohldmann
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et al. (2008) which found stronger retroactive interference by motor sequences that had to be executed as compared to mentally retrieved sequences. Accordingly, we assume that the execution of motor sequences may produce interference or increase interference in connection with retrieval of the executed sequences resulting in RIF, whereas the purely mental retrieval should also entail RIF, but perhaps to a lesser extent. The interference dependence of RIF of motor sequences deserves further investigation. Relatively little is known about retrieval dynamics in procedural memory. The transfer of the retrieval-practice paradigm to the realm of body movements offers new insight into processes that could not be investigated with verbal material. Retrieval of trained body movements gives rise to interference on a procedural level, impairing the execution of other trained body movements stored in memory linked by a common cue. Motion retrieval induces motion forgetting.
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The role of awareness. Psychonomic Bulletin & Review, 12, 490–494. doi:10.3758/BF03193793 Ciranni, M. A., & Shimamura, A. P. (1999). Retrievalinduced forgetting in episodic memory. Journal of Experimental Psychology: Learning, Memory, and Cognition, 25, 1403–1414. doi:10.1037/0278-7393.25. 6.1403 Cohen, D. A., Pascual-Leone, A., Press, D. Z., & Robertson, E. M. (2005). Off-line learning of motor skill memory: A double dissociation of goal and movement. Proceedings of the National Academy of Sciences, 102, 18237–18241. doi:10.1073/pnas.05060 72102 Deweer, B., Ergis, A. M., Fossati, P., Pillon, B., Boller, F., Agid, Y., & Dubois, B. (1994). Explicit memory, procedural learning and lexical priming in Alzheimer’s disease. Cortex, 30(1), 113–126. doi:10.1016/ S0010-9452(13)80327-9 Genzel, L., Quack, A., Jäger, E., Konrad, B., Steiger, A., & Dresler, M. (2012). Complex motor sequence skills profit from sleep. Neuropsychobiology, 66, 237–243. doi:10.1159/000341878 Hanslmayr, S., Staudigl, T., Aslan, A., & Bäuml, K.-H. (2010). Theta oscillations predict the detrimental effects of memory retrieval. Cognitive, Affective, & Behavioral Neuroscience, 10, 329–338. doi:10.3758/ CABN.10.3.329 Helmuth, L. L., Mayr, U., & Daum, I. (2000). Sequence learning in Parkinson’s disease: A comparison of spatial-attention and number-response sequences. Neuropsychologia, 38, 1443–1451. doi:10.1016/S00283932(00)00059-2 Hommel, B., Müsseler, J., Aschersleben, G., & Prinz, W. (2001). The theory of event coding (TEC): A framework for perception and action planning. Behavioral and Brain Sciences, 24, 849–878. doi:10.1017/ S0140525X01000103 Hulbert, J. C., Shivde, G., & Anderson, M. C. (2012). Evidence against associative blocking as a cause of cue-independent retrieval-induced forgetting. Experimental Psychology, 59(1), 11–21. doi:10.1027/16183169/a000120 Irtel, H. (2007). PXLab: The Psychological Experiments Laboratory [Version 2.1.11]. Mannheim: University of Mannheim. Retrieved from http://www.pxlab.de Levy, B., & Anderson, M. C. (2002). Inhibitory processes and the control of memory retrieval. Trends in Cognitive Sciences, 6, 299–305. doi:10.1016/S13646613(02)01923-X Pascual-Leone, A., Grafman, J., Clark, K., Stewart, M., Massaquoi, S., Lou, J.-S., & Hallett, M. (1993). Procedural learning in Parkinson’s disease and cerebellar degeneration. Annals of Neurology, 34, 594– 602. doi:10.1002/ana.410340414 Perfect, T. J., Moulin, C. J. A., Conway, M. A., & Perry, E. (2002). Assessing the inhibitory account of retrieval-induced forgetting with implicit memory tests. Journal of Experimental Psychology: Learning, Memory, and Cognition, 28, 1111–1119. doi:10.1037/02787393.28.6.1111 Raaijmakers, J. G. W., & Jakab, E. (2013). Rethinking inhibition theory: On the problematic status of inhibition theory for forgetting. Journal of Memory
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and Language, 68(2), 98–122. doi:10.1016/j.jml.2012. 10.002 Reppa, I., Worth, E. R., Greville, W. J., & Saunders, J. (2013). The representation of response effector and response location in episodic memory for newly acquired actions: Evidence from retrieval-induced forgetting. Acta Psychologica, 143, 210–217. doi:10.1016/j.actpsy.2013.03.007 Roediger, H. L., & Schmidt, S. R. (1980). Output interference in the recall of categorized and paired associate lists. Journal of Experimental Psychology: Human Learning and Memory, 6(1), 91–105. doi:10.1037/0278-7393.6.1.91 Saunders, J., & MacLeod, M. D. (2006). Can inhibition resolve retrieval competition through the control of spreading activation? Memory & Cognition, 34, 307– 322. doi:10.3758/BF03193409 Schmidt, R. A. (1975). A schema theory of discrete motor skill learning. Psychological Review, 82, 225– 260. 10.1037/h0076770 Schmidt, R. A. (2003). Motor schema theory after 27 years: Reflections and implications for a new theory. Research Quarterly for Exercise and Sport, 74, 366–375. Shivde, G., & Anderson, M. C. (2001). The role of inhibition in meaning selection: Insights from retrieval-induced forgetting. In D. Gorfein (Ed.), On the consequences of meaning selection: Perspectives on resolving lexical ambiguity (pp. 175–190). Washington, DC: American Psychological Association. Staudigl, T., Hanslmayr, S., & Bauml, K.-H. (2010). Theta oscillations reflect the dynamics of interference in episodic memory retrieval. Journal of Neuroscience, 30, 11356–11362. doi:10.1523/JNEUROSCI.0637-10.2010 Storm, B. C., Bjork, E. L., & Bjork, R. A. (2007). When intended remembering leads to unintended forgetting. The Quarterly Journal of Experimental Psychology, 60, 909–915. doi:10.1080/17470210701288706 Storm, B. C., Bjork, E. L., Bjork, R. A., & Nestojko, J. F. (2006). Is retrieval success a necessary condition for
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retrieval-induced forgetting? Psychonomic Bulletin & Review, 13, 1023–1027. doi:10.3758/BF03213919 Storm, B. C., & Levy, B. J. (2012). A progress report on the inhibitory account of retrieval-induced forgetting. Memory & Cognition, 40, 827–843. doi:10.3758/ s13421-012-0211-7 Storm, B. C., & Nestojko, J. F. (2010). Successful inhibition, unsuccessful retrieval: Manipulating time and success during retrieval practice. Memory, 18(2), 99–114. doi:10.1080/09658210903107853 Tempel, T., & Frings, C. (2013). Resolving interference between body movements: Retrieval-induced forgetting of motor sequences. Journal of Experimental Psychology: Learning, Memory, and Cognition, 39, 1152–1161. doi:10.1037/a0030336 Weller, P., Anderson, M. C., Gómez-Ariza, C. J., & Bajo, T. (2013). On the status of cue independence as a criterion for memory inhibition: Evidence against the covert blocking hypothesis. Journal of Experimental Psychology: Learning, Memory, and Cognition, 39, 1232–1245. doi:10.1037/a0030335 Williams, C. C., & Zacks, R. T. (2001). Is retrieval-induced forgetting an inhibitory process? The American Journal of Psychology, 114, 329–354. doi:10.2307/1423685 Witt, K., Margraf, N., Bieber, C., Born, J., & Deuschl, G. (2010). Sleep consolidates the effector-independent representation of a motor skill. Neuroscience, 171, 227–234. doi:10.1016/j.neuroscience.2010.07.062 Wohldmann, E. L., Healy, A. F., & Bourne, Jr., L. E. (2007). Pushing the limits of imagination: Mental practice for learning sequences. Journal of Experimental Psychology: Learning, Memory, and Cognition, 33, 254–261. doi:10.1037/0278-7393.33. 1.254 Wohldmann, E. L., Healy, A. F., & Bourne, Jr., L. E. (2008). A mental practice superiority effect: Less retroactive interference and more transfer than physical practice. Journal of Experimental Psychology: Learning, Memory, and Cognition, 34, 823–833. doi:10.1037/0278-7393.34.4.823
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APPENDIX Items
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Set A
Set B
Hand
Stimulus
First finger
Second finger
Left Left Left Left Left Left Right Right Right Right Right Right
a b c d e f u v w x y z
Index finger Index finger Index finger Ring finger Ring finger Ring finger Ring finger Ring finger Ring finger Index finger Index finger Index finger
Pinkie Ring finger Middle finger Middle finger Index finger Pinkie Middle finger Index finger Pinkie Pinkie Ring finger Middle finger
First finger Middle Middle Middle Pinkie Pinkie Pinkie Pinkie Pinkie Pinkie Middle Middle Middle
finger finger finger
finger finger finger
Second finger Index finger Pinkie Ring finger Ring finger Middle finger Index finger Ring finger Middle finger Index finger Index finger Pinkie Ring finger
Memory Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/pmem20
Forgetting motor programmes: Retrieval dynamics in procedural memory a
a
Tobias Tempel & Christian Frings a
Fachbereich I – Psychologie, University of Trier, Trier, Germany Published online: 14 Jan 2014.
To cite this article: Tobias Tempel & Christian Frings , Memory (2014): Forgetting motor programmes: Retrieval dynamics in procedural memory, Memory, DOI: 10.1080/09658211.2013.871293 To link to this article: http://dx.doi.org/10.1080/09658211.2013.871293
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Memory, 2014 http://dx.doi.org/10.1080/09658211.2013.871293
Forgetting motor programmes: Retrieval dynamics in procedural memory Tobias Tempel and Christian Frings
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Fachbereich I – Psychologie, University of Trier, Trier, Germany
(Received 17 July 2013; accepted 28 November 2013)
When motor sequences are stored in memory in a categorised manner, selective retrieval of some sequences can induce forgetting of the non-retrieved sequences. We show that such retrieval-induced forgetting (RIF) occurs not only in cued recall but also in a test assessing memory indirectly by providing novel test cues without involving recall of items. Participants learned several sequential finger movements (SFMs), each consisting of the movement of two fingers of either the left or the right hand. Subsequently, they performed retrieval practice on half of the sequences of one hand. A final task then required participants to enter letter dyads. A subset of these dyads corresponded to the previously learned sequences. RIF was present in the response times during the entering of the dyads. The finding of RIF in the slowed-down execution of motor programmes overlapping with initially trained motor sequences suggests that inhibition resolved interference between procedural representations of the acquired motor sequences of one hand during retrieval practice.
Keywords: Procedural memory; Motor control; Inhibition; Retrieval-induced forgetting.
The smooth execution of a trained body movement partially depends on its efficient retrieval from memory. Yet, interference between related movements can affect the retrieval. A sequence of key presses a piano player performs within the melody of one piece of music, for example, can be related to another sequence of a different piece of music. Activation of the wrong sequence would interfere with the playing of the current piece of music. We investigated the resolution of this kind of interference by examining retrieval-induced forgetting (RIF) of newly acquired motor sequences. RIF is typically analysed in the retrieval-practice paradigm (Anderson, Bjork, & Bjork, 1994; Levy & Anderson, 2002; Storm & Levy, 2012), which consists of three main phases. In the learning phase, participants study several sets of items in combination with a shared (category-)cue that
defines the specific set of items. In the subsequent retrieval-practice phase, participants are cued to recall half of the studied items from half of the sets. In the test phase, recall performance for all items is tested. The recall of practiced items (Rp+ items), unpracticed items from practiced sets (Rp− items) and unpracticed items from unpracticed sets (Nrp items) is compared. Rp+ items typically profit from retrieval practice and are better recalled than Nrp items. RIF manifests itself in significantly lower recall of Rp− items as compared to Nrp items. This phenomenon has been demonstrated for a variety of materials. Mostly, however, verbal items have been used in studies on RIF. Recently, we adapted the retrieval-practice paradigm to the use of sequential finger movements (SFM) as items (Tempel & Frings, 2013). Participants first learned 12 SFM, each consisting
Address correspondence to: Tobias Tempel, Fachbereich I – Psychologie, University of Trier, Trier 54286, Germany. Email: [email protected]
© 2014 Taylor & Francis
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of two consecutive key presses in response to a letter stimulus. Six items involved two fingers of the left hand, six involved two fingers of the right hand. After retrieval practice on three items of one hand, a final recall test assessed memory for all items. Rp− items were tested before Rp+ items in order to preclude any output interference by Rp+ items (cf. Anderson et al., 1994; Roediger & Schmidt, 1980). Rp− items were accordingly compared to the first three Nrp items tested (Nrp1), whereas Rp+ items were compared to the last three Nrp items tested (Nrp2). RIF occurred in significantly fewer recalled Rp− than Nrp1 items, as well as in significantly longer response times (RTs) to Rp− than to Nrp1 items. Thus, we were able to demonstrate for the first time that RIF also affects body movements (for a conceptual replication, see Reppa, Worth, Greville, & Saunders, 2013). This demonstration, however, did not allow distinguishing qualities of memory representations that had been affected by RIF. Motor sequences not only constitute a novel item pool allowing for a further demonstration of the robustness of RIF, but they also differ from other item materials by offering insight into the dynamics of procedural memory. Indeed, motor sequences involve declarative representations of the actions to be performed, for example, of fingers to be moved or buttons to be pressed, and these can be easily verbalised. However, it is an essential element of motor sequences that they also involve a representational format of the muscle commands for executing the corresponding movements. We here denominate this procedural representation as the motor programme. The distinction of declarative and procedural representations of motor sequences corresponds to models that postulate an anticipation of effects always accompanying the performance of an action (e.g., Hommel, Müsseler, Aschersleben, & Prinz, 2001). Whereas the anticipation of effect pertains to the declarative level, the actual execution relies on the motor programme. Evidence for the distinction is also provided by studies on the effects of sleep on the consolidation and transfer of stored motor sequences. Sleep enhances extrinsic transfer that requires access to declarative representations, for example, in a task that asks participants to perform an action with the right hand they had learned to execute with the left hand. In contrast, intrinsic transfer that involves a high degree of overlap in motor programmes is not enhanced by sleep (e.g., Cohen, Pascual-Leone, Press, & Robertson, 2005; Genzel et al., 2012; Witt, Margraf, Bieber,
Born, & Deuschl, 2010). Moreover, different brain regions are involved in the processing of declarative and procedural information. The hippocampus, for example, is essential for storing declarative but not procedural representations (e.g., Deweer et al., 1994). Support for the distinction between declarative and procedural representations of motor sequences has also come from studies with neurological samples (e.g., Helmuth, Mayr, & Daum, 2000; Pascual-Leone et al., 1993). Our study pertains to the question to what extent processes operating within procedural memory are similar to processes operating in declarative memory. The occurrence of RIF for motor sequences (Tempel & Frings, 2013) provided first evidence of parallel dynamics. Other evidence came from studies employing the retroactive interference paradigm. Wohldmann, Healy, and Bourne (2007) demonstrated that retroactive interference affects the retrieval of motor sequences (see also Wohldmann, Healy, & Bourne, 2008). Interference at retrieval in general depends on the organisation of memory. With regard to the organisation of procedural memory, research on the acquisition of generalised motor programmes has shown that motor programmes are often grouped together as classes of activities (Schmidt, 1975, 2003). A generalised motor programme is then abstracted from several motor programmes sharing prominent features, such as relative timing of movements. It can be regarded as a category within procedural memory. Effectors involved in movements can also act as such categories. Tempel and Frings (2013) found that selective retrieval of a subset of SFM of one hand (Rp + ) impaired recall accuracy for the non-retrieved SFM of that same hand (Rp − ). However, the RIF effect was more pronounced and more robust for the second dependent variable RT. The selective retrieval of Rp+ items slowed down the execution of Rp− compared to Nrp1 items. We take this slowing for first evidence that the motor programmes of Rp− items had been affected, and not only their declarative representations. It is necessary though to test this assumption further because the slowed execution might merely reflect a by-product of processes affecting declarative representations, but not operating in procedural memory at all. Therefore, we investigated whether RIF of motor sequences would occur in a memory test not relying on the recall of the previously encoded sequences, but the execution of corresponding movements in response to novel cues, thereby tapping the same motor programmes while
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circumventing the level of declarative representations. Participants had to type up letter dyads in this test. Some of these dyads required the execution of movements that corresponded to previously learned motor sequences. Thus, there was an overlap between test and learning in the motor programmes involved and the ease of executing corresponding movements is an index of memory. RIF is a consequence of selective retrieval, during which interference arises that is directly related to the occurrence and strength of RIF. Several studies have proven that the stronger Rp− items interfere with the retrieval of Rp+ items, the stronger RIF is (e.g., Anderson et al., 1994; Shivde & Anderson, 2001; Storm, Bjork, & Bjork, 2007), while it is still under debate in the current literature whether an inhibitory mechanism contributes to resolve this interference and thus causes RIF (cf. Raaijmakers & Jakab, 2013; Storm & Levy, 2012). Wohldmann, Healy, and Bourne (2008) showed that retroactive interference affected newly acquired motor sequences more strongly if the interfering sequences had to be executed as compared to a mere mental retrieval of those sequences. Apparently, the activation of motor programmes during movement execution intensified interference. This procedural kind of interference implies that dynamics underlying RIF of SFM probably also operate on a procedural level. Retrieval practice of SFM should produce interference between motor programmes that entails RIF of motor programmes. Assuming that the selective retrieval of Rp+ items affected motor programmes of Rp− items, we expected to find RIF of SFM present in an impaired execution of movements that corresponded to Rp− items. Learning and retrieval practice of our experiment closely followed the study of Tempel and Frings (2013). In the test phase, however, participants were placed in front of a different computer in a different cubicle. Their task was to type up letter dyads presented on the computer screen. Twelve letter dyads were presented that corresponded to the 12 SFM learned before. Sixteen filler dyads consisted of letters to be entered by fingers of both hands. We expected that the letter dyads corresponding to RP—movements would be typed more slowly than letter dyads corresponding to Nrp1 movements.
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METHOD Participants Thirty-two psychology students at the University of Trier participated in the experiment. They received course credit for their participation.
Design Item type (Rp−, Nrp1, Nrp2, Rp + ) was manipulated within subjects.
Material The experiment was conducted using Dell Optiplex 755 PCs with Eizo FlexScan S1901 monitors and standard German QWERTZ keyboards. The software PXLab (Irtel, 2007) served for running the experiment. The items consisted of 12 twofinger movements. Six two-finger movements consisted of fingers of the left hand, the other six of fingers of the right hand. Participants learned these movements as responses to letters. The letters a to f were the stimuli for the left-hand movements, the letters u to z for the right-hand movements. The thumbs were excluded from the movements. For both hands, all two-finger movements started with one out of two fingers. Combining these starting fingers with all three remaining fingers resulted in the six items used for each hand. We counterbalanced if the starting fingers were the index fingers and the ring fingers or the middle fingers and the pinkies (see Appendix for all movements and stimuli). During the learning phase, a letter appeared at the centre of the computer screen together with an animation of the corresponding two-finger movement (cf. Figure 1). The fingers of the left hand were placed on the keys Q, W, E and R. The fingers of the right hand were placed on the keys U, I, O and P. Below the letter, a display of the two hands demonstrated which fingers should be moved by showing two consecutively flashing fingers (first finger was coloured yellow, and second finger was coloured blue, 200 ms per flash). After the display of the two hands disappeared, participants could perform the movement. If the performed sequence was incorrect, a feedback appeared, displaying: “Fehler!” (English: “Error!”).
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Figure 1. The upper section depicts a trial in the learning phase. It starts with a display of the letter stimulus together with a drawing of the two hands. After 400 ms, the first finger illuminates yellow for 200 ms and then the second finger illuminates blue for 200 ms. Subsequently, the hand display disappears, and the participant can enter the SFM just illustrated. The middle section depicts a trial in the retrieval-practice phase. A stimulus is given, and the participant is supposed to perform the corresponding SFM. The lower section depicts a trial in the final test phase. The participant enters a presented letter dyad, while his or her fingers are resting on the same eight keys as during learning and retrieval practice which are displayed below the letter dyad. The learning phase and the retrieval-practice phase took place in a cubicle containing a PC keyboard on which the response keys were marked by orange labels hiding the inscriptions (first cubicle). The final test phase took place in a different cubicle containing a PC keyboard without any marked keys (second cubicle). SFM = sequential finger movement.
Procedure The experiment consisted of three phases (learning, retrieval practice and indirect memory test). Instructions were given on the screen and summarised by an experimenter. After having read the instructions for the learning phase, the participant clicked an onscreen button in order to start with the learning phase. Participants had 10 seconds to place their fingers with exception of the thumbs on eight keys (Q, W, E, R, U, I, O and P) marked by labels hiding the inscription. Then the learning of the 12 items began. Participants had to consecutively press two keys in response to a displayed letter accompanied by an animation graphic
display showing which digits should be moved (cf. Figure 1, upper section). First, all 12 items appeared once in random order, whereupon an instruction screen informed the participant that the items just presented would appear again several times in the following. Eleven blocks each containing the 12 items in a random order were presented. In the retrieval-practice phase, participants had to retrieve three items of one hand. Counterbalancing of the retrieval-practiced items resulted in four retrieval-practice sets (abc, def, uvw and xyz). These four sets were counterbalanced between participants. The items were cued by their letter stimuli. A letter appeared on the screen and the participant entered the corresponding item while
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his or her fingers again rested on the marked keys (cf. Figure 1, middle section). Each of the three letters appeared five times. No feedback about the accuracy of the performed two-finger movement was given. The final test phase comprised an indirect memory test. The experimenter seated participants in a different cubicle in front of a PC with a keyboard without any marked keys. Their task consisted in entering letter dyads presented on the screen. The instructions emphasised speed as well as accuracy. The participants placed their fingers on the same keys as during learning and retrieval practice, so they would enter each letter with a different finger. During each trial of the test, a letter dyad appeared in the centre of the screen accompanied by a display of the keyboard at the bottom of the screen. This display contained only the inscriptions of the keys to be used (Q, W, E, R, U, I, O and P) and was intended to prevent participants from looking down on the keyboard keys (cf. Figure 1, lower section). Twelve dyads corresponded to the 12 SFM learned before because they required the same key presses, that is, the same motor sequences had to be executed. In addition, 16 dyads comprising key presses by fingers of both hands served as filler trials. The sequence of filler trials was the same for all participants. There were, however, different sequences of the experimental trials corresponding to previously learned SFM. The items of one hand were tested in succession, at which, Rp− items were tested before Rp+. Within the items of the non-retrieval-practiced hand the items were presented in one of two sequences thereby counterbalancing which items constituted Nrp1 and Nrp2 items. Also, it was counterbalanced which hand was tested first. The alternation of filler trials and experimental trials was constant over all participants. The test sequence started with two filler trials.
RESULTS Retrieval success in the retrieval-practice phase (M = 51%, SD = 34%) was similar to the level reported by Tempel and Frings (2013). Examining RIF, a t-test showed that RTs at entering letter dyads corresponding to Rp− items were significantly longer than RTs for letter dyads corresponding to Nrp1 items, t(31) = 2.54, p = .008,
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one-tailed, dz = 0.45. Rp+ enhancement did not occur with regard to RTs, that is, RTs for letter dyads corresponding to Rp+, and Nrp2 items did not differ significantly, t < 1.1 However, it was present in accuracy. Correct input of letter dyads corresponding to Rp+ items was significantly higher than correct input of letter dyads corresponding to Nrp2 items, t(31) = 1.76, p = .044, onetailed, dz = 0.31. Correct input of dyads corresponding to Rp− items and correct input of letter dyads corresponding to Nrp1 items did not differ significantly, t < 1 (see Figure 2). We additionally analysed RTs of only those trials in which the participants entered the dyad correctly. The results were almost identical to the results for all RTs combined. RTs for letter dyads corresponding to Rp− items were significantly longer than RTs for letter dyads corresponding to Nrp1 items, t(31) = 2.38, p = .012, one-tailed, dz = 0.43. RTs for letter dyads corresponding to Rp+ and Nrp2 items did not differ significantly, t < 1. Finally, we examined correlations of RIF and Rp+ enhancement. RIF was computed as the difference in RTs for letter dyads corresponding to Rp− items and Nrp1 items. For Rp+ enhancement, we computed two measures: the difference in RTs for letter dyads corresponding to Nrp2 and Rp+ items, as well as the difference in accuracy at entering letter dyads corresponding to Rp+ and Nrp2 items. There was no correlation between RIF and the RT measure of Rp+ enhancement (r = .002, p = .990), nor between RIF and the accuracy measure of Rp+ enhancement (r = .171, p = .349).
1 The letter dyads partly overlapped with the letter stimuli used during learning and retrieval practice. Although counterbalancing of the retrieval practice sets and of the assignment of Nrp items to Nrp1 and Nrp2 precluded any confounding of RIF or Rp+ enhancement effects by item-specific influences, we were interested in how the results looked for only those letter dyads not including letters overlapping with stimuli from the previous phases. Seven letter dyads had to be excluded. As a consequence, data of 20 participants had to be excluded. Thereby, statistical power was considerably reduced. Yet, the basic pattern of results emerged again with longer RTs for Rp− (M = 1795 ms) than Nrp1 (M = 1554 ms) items, however, the highly diminished power prevented the RIF effect to reach a conventional significance level, t(11) = 1.31, p = .109, onetailed. RT for Rp+ and Nrp2 items did again not differ, t < 1.
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Percentage of correct input
100 80 60 96
95
Rp–
Nrp1
40
83
92
20 0 Nrp2
Rp+
Response time in ms
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2000
1000
1802
1617
1616
1565
0 Rp–
Nrp1
Nrp2
Rp+
Figure 2. The upper section shows the percentages of correctly entered letter dyads in the test phase as a function of item type. The lower section shows mean response time (in milliseconds). Error bars depict standard error of the mean. Rp+ = retrieval practiced items; Rp− = unpracticed items of the retrieval practiced hand; Nrp1 = RIF baseline; Nrp2 = Rp+ enhancement baseline.
DISCUSSION We investigated the processes underlying RIF of motor sequences. Participants first learned SFM. Half of these pertained to the left hand, the other half to the right hand. Subsequently, participants performed retrieval practice on half of the items of one hand. Finally, participants entered letter dyads by pressing the respective keys of a standard PC keyboard, while their fingers were resting on the same keys as when entering the SFM during learning and retrieval practice. The input of letter dyads corresponding to Rp− items was significantly slower than the input of letter dyads corresponding to Nrp1 items. This slowing of movements is the first demonstration of RIF in procedural memory. It shows that retrieval practice of Rp+ items affected the motor programmes of Rp− items. These motor programmes were activated again in the final test without involving recall instructions or even providing any cues that could have been used for retrieval of the previously learned SFM.
Rp+ enhancement occurred only in accuracy but not RTs. We consider the order in the final test phase testing Rp− before Rp+ items to account for this pattern of results. The input of letter dyads corresponding to Rp+ items was probably impacted by the previous input of letter dyads corresponding to Rp− items. Nrp2 items were subject to the same potential interference by the previous execution of items of the same category, that is, the same hand (Nrp1). Hence, the testing order had the same impact on Rp+ and Nrp2 items but led only for Nrp2 items to a reduction in accuracy. Rp+ enhancement, then, emerged because the accuracy of the input of letter dyads corresponding to Rp+ items was less susceptible to output interference. In contrast, accuracy of the previously tested Rp− and Nrp1 items was nearly 100%, and RIF occurred in slower input of letter dyads corresponding to Rp− items. It is beyond the scope of the present investigation to distinguish the qualities of RTs and accuracy as measures of procedural memory. Future studies may explore whether RTs represent procedural memory more adequately because they directly reflect the ease of executing movements, whereas accuracy may equally represent access to declarative and procedural memory. Not asking for recall is an essential feature of implicit memory tests. These tests measure memory by requiring performances that match previously encoded items. Memory for learned items is indicated by the strength by which those items influence the answers in the task. For example, the task of category exemplar generation can serve as an implicit memory test if participants initially learned exemplars of that category. The more exemplars that had been presented before are spontaneously named in response to the category cue, the stronger the items obviously are activated in memory. Although retrieval attempts need to be precluded in order to qualify a specific task as truly implicit, in fact many implicit memory tests provide participants with information that can act as a retrieval cue, such as category names in category exemplar generation or even the complete items themselves, for example, in category exemplar verification (Perfect, Moulin, Conway, & Perry, 2002). In contrast, the test used in the present experiment did not provide such cues. Since participants might have noticed that several movements of entering the letter dyads overlapped with learned SFM, we hesitate to label this task as a novel kind of implicit memory test. Although it includes crucial features of implicit testing, it might be more appropriate to speak of an indirect
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memory test. However, even if participants noticed that some movements in the test matched SFM from the learning phase, this awareness would not have been of use for accomplishing the task at hand. The letter dyads corresponded with previously learned items only in the motor programmes involved. If participants would have tried to remember SFM, any recollection would not have been helpful in entering the dyads; it rather would have hurt performance because the letter dyads did not provide participants with any information that could have been used as a retrieval cue apart from the two-finger movement itself. Performing a specific two-finger movement might have reminded participants of the corresponding SFM learned before, but only in the course of or after its execution. Inhibitory as well as non-inhibitory explanations of RIF have been discussed in the literature. The inhibitory account (Anderson et al., 1994; Anderson & Spellman, 1995) assumes that during retrieval practice of one item all items of this set compete for conscious recollection. In order to resolve this competition, the Rp+ items are strengthened, while simultaneously the Rp− items are inhibited. In contrast, non-inhibitory explanations assume that RIF originates from changes in the strength of associations between items and cues or from blocking exerted by Rp+ items during the test (e.g., Williams & Zacks, 2001). Four key predictions distinguish the inhibitory account from non-inhibitory alternatives (Anderson, 2003). The inhibitory account posits that it is necessary to attempt to retrieve Rp+ items during retrieval-practice for RIF to occur (retrieval specificity). It further posits that the strength of the activation of Rp+ items during retrieval-practice does not influence the amount of resulting RIF (strength independence), whereas the strength of competition from Rp− items during retrievalpractice does (interference dependence). Finally, since inhibition lowers the activation of memory representations of Rp− items, RIF should also emerge in memory tests that do not provide information present at learning as retrieval cues (cue independence). The finding of RIF of motor sequences in a test with the novel test cues of letter dyads is in accord with the prediction of cue independence. It supports the inhibitory account because the final test phase assessed memory independently from previously studied cues. The inhibitory account can easily explain why the access to the motor programmes of Rp− items was reduced. The
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interference between motor programmes during retrieval practice was resolved by inhibiting the motor programmes of Rp− items. The occurrence of RIF in a test not relying on previously studied cues complements other studies that reported RIF in tests using cues to probe memory that were different to the cues used during learning and retrieval practice (Anderson & Bell, 2001; Anderson, Green, & McCulloch, 2000; Camp, Pecher, & Schmidt, 2005; Saunders & MacLeod, 2006; Shivde & Anderson, 2001). Although memory was probed by novel cues, non-inhibitory processes also might have contributed to the obtained RIF effects. The SFM were essentially linked to the hand involved in their execution. The input of letter dyads corresponding to previously encoded SFM in the final test thus, of course, also required the use of the same hand as during the learning of the SFM. Therefore, retrieval practice of Rp+ items might have strengthened their associations with the hand, subsequently blocking the execution of movements corresponding to Rp− items. However, RIF was independent of strengthening Rp+ items. There was no correlation of RIF with Rp+ enhancement in our experiment. Several studies reported the same finding (e.g., Hanslmayr, Staudigl, Aslan, & Bäuml, 2010; Hulbert, Shivde, & Anderson, 2012; Staudigl, Hanslmayr, & Bauml, 2010; Weller, Anderson, Gómez-Ariza, & Bajo, 2013). It has also been shown that manipulations strengthening Rp+ items by repeated study (e.g., Bauml, 2002; Ciranni & Shimamura, 1999; Staudigl et al., 2010) or non-competitive retrieval (Anderson, Bjork, & Bjork, 2000) do not induce forgetting of Rp− items. Moreover, Storm, Bjork, Bjork, and Nestojko (2006) found that RIF occurred even with an impossible retrieval task during the retrieval-practice phase, that is, they provided word stems as cues that did not correspond to any existing exemplars of categories used in the learning phase of the experiment (see also Storm & Nestojko, 2010). Hence, RIF even occurs in the absence of Rp+ strengthening. Taken together, the bulk of the evidence suggests that associative blocking cannot explain RIF. Still, it might be interesting for future studies to investigate whether the same findings can also be replicated with motor sequences. In particular, it is possible that practicing items by executing them without retrieving them from memory already produces a certain amount of interference with other motor sequences. Indirect evidence for this assumption comes from the study by Wohldmann
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et al. (2008) which found stronger retroactive interference by motor sequences that had to be executed as compared to mentally retrieved sequences. Accordingly, we assume that the execution of motor sequences may produce interference or increase interference in connection with retrieval of the executed sequences resulting in RIF, whereas the purely mental retrieval should also entail RIF, but perhaps to a lesser extent. The interference dependence of RIF of motor sequences deserves further investigation. Relatively little is known about retrieval dynamics in procedural memory. The transfer of the retrieval-practice paradigm to the realm of body movements offers new insight into processes that could not be investigated with verbal material. Retrieval of trained body movements gives rise to interference on a procedural level, impairing the execution of other trained body movements stored in memory linked by a common cue. Motion retrieval induces motion forgetting.
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retrieval-induced forgetting? Psychonomic Bulletin & Review, 13, 1023–1027. doi:10.3758/BF03213919 Storm, B. C., & Levy, B. J. (2012). A progress report on the inhibitory account of retrieval-induced forgetting. Memory & Cognition, 40, 827–843. doi:10.3758/ s13421-012-0211-7 Storm, B. C., & Nestojko, J. F. (2010). Successful inhibition, unsuccessful retrieval: Manipulating time and success during retrieval practice. Memory, 18(2), 99–114. doi:10.1080/09658210903107853 Tempel, T., & Frings, C. (2013). Resolving interference between body movements: Retrieval-induced forgetting of motor sequences. Journal of Experimental Psychology: Learning, Memory, and Cognition, 39, 1152–1161. doi:10.1037/a0030336 Weller, P., Anderson, M. C., Gómez-Ariza, C. J., & Bajo, T. (2013). On the status of cue independence as a criterion for memory inhibition: Evidence against the covert blocking hypothesis. Journal of Experimental Psychology: Learning, Memory, and Cognition, 39, 1232–1245. doi:10.1037/a0030335 Williams, C. C., & Zacks, R. T. (2001). Is retrieval-induced forgetting an inhibitory process? The American Journal of Psychology, 114, 329–354. doi:10.2307/1423685 Witt, K., Margraf, N., Bieber, C., Born, J., & Deuschl, G. (2010). Sleep consolidates the effector-independent representation of a motor skill. Neuroscience, 171, 227–234. doi:10.1016/j.neuroscience.2010.07.062 Wohldmann, E. L., Healy, A. F., & Bourne, Jr., L. E. (2007). Pushing the limits of imagination: Mental practice for learning sequences. Journal of Experimental Psychology: Learning, Memory, and Cognition, 33, 254–261. doi:10.1037/0278-7393.33. 1.254 Wohldmann, E. L., Healy, A. F., & Bourne, Jr., L. E. (2008). A mental practice superiority effect: Less retroactive interference and more transfer than physical practice. Journal of Experimental Psychology: Learning, Memory, and Cognition, 34, 823–833. doi:10.1037/0278-7393.34.4.823
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APPENDIX Items
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Set A
Set B
Hand
Stimulus
First finger
Second finger
Left Left Left Left Left Left Right Right Right Right Right Right
a b c d e f u v w x y z
Index finger Index finger Index finger Ring finger Ring finger Ring finger Ring finger Ring finger Ring finger Index finger Index finger Index finger
Pinkie Ring finger Middle finger Middle finger Index finger Pinkie Middle finger Index finger Pinkie Pinkie Ring finger Middle finger
First finger Middle Middle Middle Pinkie Pinkie Pinkie Pinkie Pinkie Pinkie Middle Middle Middle
finger finger finger
finger finger finger
Second finger Index finger Pinkie Ring finger Ring finger Middle finger Index finger Ring finger Middle finger Index finger Index finger Pinkie Ring finger
