How semantic processing affects recognition memory

Journal of Memory and Language 113 (2020) 104109

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How semantic processing affects recognition memory a,⁎

b

a

b,⁎

Michael S. Humphreys , Yanqi Ryan Li , Jennifer S. Burt , Shayne Loft a b

T

School of Psychology, The University of Queensland, Australia School of Psychological Science, The University of Western Australia, Australia

ARTICLE INFO

ABSTRACT

Keywords: Semantic processing Memory Recognition memory Prospective memory Lexical access

Memory researchers acknowledge the importance of semantic processing in recognition and recall, but there is a significant disconnect from the literature that addresses how to conceptualize words. We use the lexical literature to ask more analytic questions about the effects of semantic processing on memory. A prospective memory task requiring the initiation of a semantic search that was imposed during an ongoing task had an effect on the delayed recognition of words from the ongoing task, and this effect was similar whether the ongoing task was lexical decision (Experiment1) or naming (Experiment2). This finding indicates that the effect on memory of initiating a semantic search is in addition to the effect of lexical access. Further, although an associate-search prospective memory task and a multi-target prospective memory task both enhanced delayed recognition, the pattern of hits and false alarms was different. This finding indicates that prospective memory difficulty is not responsible for the enhancement on the delayed recognition test.

Introduction Instructions that direct attention to the phonemes or letters in a word typically produce poorer recognition and recall than instructions to think about a word’s meaning, how a word can be used, or how often a word occurs in the language. In an attempt to characterize the manipulations which produce better recognition and recall, Craik and Lockhart (1972) suggested that they involved “deeper” processing. This idea was criticized as being vague (Nelson, 1977). Craik and Tulving (1975) suggested that deeper processing could be equated with “semantic elaboration”. However, semantic elaboration often refers to manipulations that cause the participant to activate another word or concept and, at least sometimes, store the activated word or concept in memory (Humphreys & Chalmers, 2016). It is not clear that deciding how often a word occurs in the language involves elaboration in the Humphreys and Chalmers sense. As discussed below, the same point can be raised about initiating a search of a semantic network. The memory literature continues to acknowledge the importance of semantic processing in producing better recognition and recall. However, the use of the term semantic processing may simply reflect the fact that there is not a better scientific term to describe the type of manipulations that improve recognition and recall. To further complicate matters, articulating a studied word can also enhance recognition and recall (MacLeod, Gopie, Hourihan, Neary, & Ozubko, 2010). Prior work

indicates that the effects of semantic processing and articulation are potentially separable (Bodner, Taikh, & Fawcett, 2014; Fawcett, 2013; MacLeod et al., 2010). That is, semantic processing and articulation provide different sources of information which are not just combined in a single strength of evidence variable, but instead can be used separately and strategically in tests of episodic memory. The present paper draws on research in the reading and language production literatures which address how to conceptualize words and the relationships between the underlying orthographic, phonological and semantic codes (Burt & Humphreys, 1993; Levelt, Roelofs, & Meyer, 1999; Oppenheim, Dell, & Schwartz, 2010; Perfetti, 1992; Perfetti & Hart, 2002; Plaut, McClelland, Seidenberg, & Patterson, 1996). These literatures can not only provide better scientific terminology but also more informative questions about how semantic processing and articulation enhance recognition and recall. The language production literature differentiates between input and output representations. The input representations include semantic representations which can be directly activated by a picture or sentence, and phonological representations. The output representations are articulatory or pre-articulatory (output phonology). An abstract representation (lemma) sits in the middle of the system. The reading literature makes a similar analysis, except that it is also concerned with orthographic representations and a hypothesized role for a direct connection between orthography and phonology. In addition, there is less concern in the

⁎ Corresponding authors at: The University of Queensland, St Lucia, QLD 4000, Australia (M.S. Humphreys), School of Psychological Science, University of Western Australia, Crawley, WA 6009, Australia (S. Loft). E-mail addresses: [email protected] (M.S. Humphreys), [email protected] (S. Loft).

https://doi.org/10.1016/j.jml.2020.104109 Received 20 March 2019; Received in revised form 2 February 2020; Accepted 10 February 2020 0749-596X/ © 2020 Elsevier Inc. All rights reserved.

Journal of Memory and Language 113 (2020) 104109

M.S. Humphreys, et al.

reading than in the language production literature with separating semantics from the lemma, and typically the reading literature links semantics with orthography and phonology in a three-part lexical representation. Although greatly oversimplified, this conceptualisation is a useful starting point for asking questions about the role of semantic processing and articulation in producing a durable memory for recognition. Furthermore, some of the characteristics of the memory trace required to explain findings in the recognition memory literature resemble those of the lemma of the language production literature. A lemma-like central representation of a word is indicated by studies of list length effects and category length effects (the number of category exemplars presented in a list). List length effects in episodic recognition memory paradigms using words are now known to be quite small (Dennis & Humphreys, 2001; Dennis, Lee, & Kinnell, 2008; Kinnell & Dennis, 2011). Further, category length effects involving members of taxonomic categories are also quite small when either a forced-choice recognition test or an unequal variance signal detection model is used to assess performance (Cho & Neely, 2013; Maguire, Humphreys, Dennis, & Lee, 2010). These small list length and category length effects can be accommodated by the assumption that the words in these experiments had representations which were not very similar to the representations of the other words in the list.1 Because this low level of similarity applies to members of taxonomic categories (Cho & Neely, 2013; Maguire et al., 2010) it appears that the representations do not contain much semantic information (for an extended discussion of these issues see Humphreys & Chalmers, 2016). That is, the representations best equipped to explain recognition memory appear to be like the lemmas of the language production literature. The lexical representations proposed in the reading literature might also be a viable alternative if it is assumed that they contain only limited semantic information. While the lemmas of the language production and the lexical representations of the reading literatures can be used to access rich semantic information, this might not necessarily occur. That is, they could also be used on their own like category names or “labels” to access other lemmas or lexical representations (Humphreys & Hannah, unpublished manuscript). The formation of such word representations can be understood from a consideration of learning and development. Humphreys and Hannah propose a process by which a lemma-like amodal representation might be formed from the convergence of two sensory processing streams, such as occurs when a 2-year old child points to an object and an adult names the object. Humphreys and Hannah also discuss how memories can serve as more concrete (sensory/motor) representations, such as when low-verbal organisms (2-year old children, Akhtar & Tomasello, 1996) and non-verbal organisms (rats, Bae, Holmes, & Westbrook, 2015) associate a memory of an object or environment with an incoming stimulus. The behavior subsequently displayed by the organisms can be understood if the new association transfers to the original stimulus which provided the content for the original memory. Thus, extensions of accepted mnemonic processes can be used to create both sensory-motor and more amodal representations of words, removing some of the mystery around these constructs. In summary, investigating the impact of lexical and semantic tasks on recognition memory can be facilitated by separating the amodal representation of a word from its semantic links with other words, as well as from its links to sensory-motor representations, including its orthographic and phonological representations. In the current paper we use this framework to understand the enhancement in recognition memory performance produced by a) the addition of a prospective memory (PM) requirement involving the initiation of a semantic search

to an ongoing task involving lexical access (e.g., lexical decision), and b) the addition of articulation to a lexical access task (a naming ongoing task instead of a lexical decision task). In previous PM research, Loft and Humphreys (2012) had participants perform an ongoing lexical decision task, and in some blocks of trials some participants were also required to remember to make an alternative PM response to a PM target (instead of making the ongoing task response). The PM target was either a single studied word (singletarget PM task; e.g., bridge) or an exemplar from a category (category judgment PM task; e.g., any animal word). Following the completion of the ongoing task alone (control condition), or the ongoing task plus the PM task (the other conditions), there was a surprise final recognition test in which non-target words from the lexical decision task were intermixed with new words. The defining feature of PM tasks is that, unlike retrospective memory tasks, there are no requests from the experimenter directing participants when to engage in a memory search. As a result, PM tasks have a greater emphasis on the maintenance of the intention to remember, or the ability of the target to initiate that intent (Einstein & McDaniel, 2005). Remembering to respond to relatively infrequent PM task events can be difficult because not only must the participant remember a new episodic task; the PM task must compete for response selection with more routine ongoing task responses (Loft & Remington, 2013; Strickland, Loft, Remington, & Heathcote, 2018). Some PM tasks are harder than others, as reflected by reduced performance on the PM task and/or slowing down of responses to the ongoing task. The latter is referred to as the “cost” to the ongoing task (Marsh, Hicks, Cook, Hansen, & Pallos, 2003; Smith, 2003). According to standard ideas about reading and language production, lexical decision requires lexical access (Andrews, 1992) but it does not require the initiation of a search of a semantic network. That is, the relationship to any other word is not generally needed to decide on whether or not a string of letters is a word. Lexical decision also does not require semantic elaboration, if we define semantic elaboration as involving the activation of another word/concept and the storage of that word/concept in memory (Humphreys & Chalmers, 2016). The category judgment PM task also requires lexical access, but unlike lexical decision, it also requires searching for the relationship between the word being attended to and another word/concept. That is, it requires the access of a semantic network, and a limited search of that network, in order to reject a non-target. This initiation of a semantic search is termed “semantic search initiation” or just search initiation in the present paper. The limitation on the search is that participants presumably terminate an unsuccessful semantic search after a period of time because they are under time pressure to make lexical decisions. Given that the non-target search is limited, it probably does not result in semantic elaboration. That is, no other word or concept is likely to be activated during the search. This is consistent with Craik and Tulving (1975) findings that answering no to a semantic question had an impact on memory, but the impact was less than answering yes. Our proposal is that lexical access has an impact on recognition but that search initiation, as defined by our analysis of the category judgment PM task, has an additional impact. Semantic elaboration would have an even greater impact but we will not be investigating semantic elaboration in this paper. An important assumption which we are making is that having two tasks that require lexical access does not by itself improve recognition memory beyond that produced by a single task requiring lexical access. A single target PM task requires lexical access but does not require initiation of a semantic search. In line with this, in our previous work, the single-target PM task did not enhance final delayed recognition of non-target words beyond that produced by the lexical decision task alone (Loft & Humphreys, 2012). When the category judgment PM task is paired with a lexical decision task, we assume that participants first access the lexical representation of the presented word. Accessing the lexical representation is the necessary first step both for the process

1 For explanations as to why associates of a common cue (the DRM paradigm) produce much larger category length effects see Cho and Neely (2013) and Maguire et al. (2010). These explanations do not involve word similarity.

2

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which produces the decision about whether the letter string is a word and the semantic search which is required to determine that the letter string is a PM target. With respect to the non-target items we propose that there are two contributions to performance on the subsequent recognition tast. One comes from lexical access but lexical access is the same whether or not lexical access is followed only by a word-non-word decision, or whether it is followed by such a word-non-word decision and the initiation of a semantic search. It is the initiation of a semantic search for the category PM task which makes the non-target words more memorable than if the only requirement had been to make a lexical decision. There are several steps to be taken to support the hypothesis that semantic search initiation can enhance memory beyond that produced by lexical access alone. One of the most important is to show that other PM tasks that seem to share this search initiation process can also enhance recognition beyond lexical access alone. In the current two experiments we used the Loft and Humphreys (2012) method. We reasoned that instructing participants to remember to make a PM response if they were presented with any word that was meaningfully related with the word breakfast (e.g., morning, toast, etc), which we refer to as an associative PM task, would share the same need for search initiation as the category PM task used by Loft and Humphreys (2012), and thereby enhance memory on non-target words in the delayed recognition test. It is also necessary to rule out PM difficulty, as measured by PM performance and costs to the ongoing task, as an explanation for the enhanced performance on the delayed recognition task. The memory retrieval task required by the category judgment and associative PM tasks is more difficult than in the single-target PM task. At times task difficulty appears to improve memory performance (Bjork & Bjork, 2011; Bjork & Kroll, 2015). By contrast, task difficulty created by having participants perform a secondary task may reduce memory performance (Mulligan, 2008). We assessed the role of difficulty by including an additional PM task that was more difficult than the singletarget PM condition but was similar to it in the nature of the memory retrieval process required. Towards this end we chose a PM condition that required participants to make the PM response to any of eight previously studied unrelated words, which we refer to as a multipletarget PM task. The multi-target PM task is difficult, as evidenced by the finding that it produces a robust response time (RT) cost to non-PM target trials of ongoing tasks, and that these costs are greater than those that arise from single-target PM tasks (e.g., Hicks, Marsh, & Cook, 2005; Loft, Kearney, & Remington, 2008). Our final attempt to more adequately characterize the tasks we were using was to use a naming task in Experiment 2 instead of the lexical decision task used in Experiment 1 of the current study, and by Loft and Humphreys (2012). Naming tasks, like lexical decision, are generally agreed to involve lexical access (Andrews, 1992). However, reading a word out loud enhances recognition memory relative to reading the word silently (MacLeod et al., 2010), an effect known as the production effect. Although MacLeod et al. did not think that memory was enhanced by naming in a between subjects design, Fawcett (2013) published a meta-analysis and showed that the between subjects effect was significant. Bodner et al. (2014) assessed the effect of naming on recognition memory as a function of the design of the study list. When naming versus silent reading was manipulated either as a mixed-list or blocked design, the hit rates were higher after naming than after silent reading. However, in the between -subjects design the effect of naming was to primarily reduce the false alarm rate. The differences between mixed-list, blocked, and between-subject designs tells us that the production effect is not simply a strength effect. That is, the memory retrieval process does not just return a single strength of evidence result. Instead the information resulting from lexical access (lexical information) and information about whether or not a word was pronounced (articulatory/phonological information)

are at least partially separable. Further support for the separability of these two types of information comes from the MacLeod et al. (2010) finding that naming enhanced recognition even when the list items had been processed semantically. The separability of these two types of information is also a fundamental assumption of the present framework, which reflects assumptions in the language production and reading literatures. Because the lexical and articulatory information are assumed to be at least partially separable we expected to observe an enhancement of recognition memory due to semantic search initiation even when there was an enhancement due to naming. The general pattern of results in the Bodner et al. experiment on the production effect could be produced if participants in the betweensubjects design said yes when there was sufficient episodic lexical information and sufficient episodic articulatory information, and no when otherwise (Dodson & Schacter, 2001; Humphreys & Chalmers, 2016).2 That is, the reduction in the false alarm rate in the between subject condition of Bodner et al. can be explained by assuming that sometimes new words incorrectly appear to have lexical information, but can be rejected because they do not have enough articulatory information. In addition, the near equality of the hit rates in the articulation and no-articulation between-subject conditions suggests that there are relatively few instances when participants are unable to retrieve articulatory information if they have successfully retrieved lexical information. However, in the blocked and mixed list designs the Bodner et al. results can be explained if participants say yes when there was sufficient lexical information or sufficient articulatory information. The higher hit rates in these conditions suggest that participants will at times have articulatory information in the absence of lexical information. Loft and Humphreys (2012) found that a task requiring semantic search initiation (the category judgment PM task) increased the recognition task hit rate without increasing the false alarm rate. This result is clearly differentiable from the selective effect of word naming on false alarm rates observed by Bodner et al. in their between-subjects study of the production effect. These patterns of separate effects on the hit and false alarm rates allow the effects of semantic search initiation to be distinguished from the effects of the provision of articulatory information through naming, which will be critical for interpreting the current data. Based on the argument that an associative PM task shares the semantic search initiation requirement of the category judgment PM task, and that the lexical decision and naming tasks require lexical access but no semantic search initiation, we made the following predictions: Semantic search initiation performed in service of the associative PM task will increase accuracy on the delayed recognition task, compared to the single-target PM task and the control (no PM task) condition. Furthermore, this increase in recognition memory for the associative PM task conditions is expected to involve an increase in the hit rates, and have a similar effect size as the increase in recognition memory observed by Loft and Humphreys (2012) with their category judgment PM task. Based on the Loft and Humphreys finding we did not expect a difference between the single-target PM task and the control condition. Because of conflicting ideas about the effects of increased task difficulty on recognition memory we were unable to make a prediction about the effect of the multiple-target PM condition on recognition. In the crossexperiment comparison of the two ongoing tasks used in our experiments (lexical decision and naming), we predicted a production effect, manifested as a reduction in the false alarm rates in the delayed recognition test for the naming task, in all of the between subject

2

We need to emphasize that the lexical and articulatory information is episodic because the semantic information is always retrievable. Humphreys, Tehan, Baumann, & Loft, under revision) provide one way to conceptualize how “semantic” representations can be employed in episodic memory tasks. However, the way that this is done is not needed in the current paper. 3

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conditions, compared with the lexical decision task.3 However, we expected the difference between the associative PM condition and the control/single target conditions to be largely the same in Experiments 1 and 2.

condition (comparable to the associative PM condition of the current experiment) compared to a combined single-target PM/control condition. Therefore, given our sample size reported below we had a power of 0.83 in Experiment 1 to detect the recognition benefit for the associative PM condition compared to a combined single-target PM/control condition.

Experiment 1

Method

In Experiment 1 participants completed an ongoing lexical decision task that required them to decide if presented letter strings were words or non-words. Participants in all conditions were then assessed on their subsequent ability to recognise non-target words from the lexical decision task. They were asked to identify ‘old’ words that were previously presented in the lexical decision task amongst ‘new’ words that were never presented. The control condition had no PM task and was divided into two subsets; control-standard and control-multiple. The control-multiple condition studied the same eight words as the multiple-target PM condition, and were told they would be tested on their memory for these eight words after the lexical decision task. In contrast, the controlstandard condition did not study words prior to lexical decision. This allowed us to examine the effect of studying eight words prior to lexical decision making without a PM task. The single–target PM condition was the same as that used by Loft and Humphreys (2012). Participants were given one specific word and were told to make a PM response whenever that word was presented during lexical decision. In line with the PM literature, we expected to find that participants in the single-target PM condition would have better PM accuracy than the other two PM conditions, and no costs compared to the control condition (Einstein & McDaniel, 2005). We also expected that relative to the control condition there would be no improvement on the delayed recognition test for the single-target PM condition. Participants in the multiple-target PM condition studied eight unrelated words prior to completing the lexical decision task, and were instructed to make a PM response if presented with any of the eight words during lexical decision. We expected to replicate prior findings of costs for the multiple-target PM condition compared to the control condition (Hicks et al., 2005). In order to examine if there was a benefit to delayed recognition, we compared delayed recognition for the multiple-target PM condition compared to the single-target PM condition/ control condition. Participants in the associative PM condition were instructed to make a PM response if presented words during lexical decision that were ‘meaningfully related or strongly associated’ with the word breakfast. We expected to find costs for the associative PM condition compared to the control condition, and improved delayed recognition for the associative condition compared to single-target/control condition. To increase the power of Experiment 1 to detect a delayed recognition effect we combined the single-target PM and control conditions for the delayed recognition analyses on the basis that Loft and Humphreys (2012) reported that a single-target PM task did not improve delayed recognition compared to a control condition. We confirm this in the current study with a contrast comparing delayed recognition for the single-target PM condition compared to the control condition. The Loft and Humphreys (2012) data indicated a medium sized delayed recognition effect (Cohen’s d = 0.47) for the category PM (“non-focal”)

Participants Two hundred and thirty-one undergraduates participated in return for course credit, and were randomly assigned to condition. There were 57 participants in the control condition (28 in standard, 29 in multiple), and 58 participants in each of the three PM conditions. All participants in Experiments 1 and 2 were self-reported native English speakers (spoke English as their first language as children). Materials Three hundred and eighty-four medium frequency words (occurring 20–50 times per million, length 4–8 letters) were randomly selected from the Sydney Morning Herald Word Database (SMHWD; Dennis, 1995). The 384 words were equally divided into two lists (A, B) of 192 words each. In each list, 100 words were changed to non-words by replacing the vowels within them with random vowels (e.g. chemist to chamust). Lists A and B contained 92 word and 100 non-words each. For every participant, stimuli for the lexical decision task were selected from one of the two lists (e.g., List A), and stimuli for the delayed recognition task were selected from the other list (e.g., List B), with list assignment counterbalanced across participants. For the lexical decision task, the presentation of words and nonwords within each list was random, except that PM targets were presented in a random position between trials 5 and 25, 26 and 50, 51 and 75, 76 and 100, 101 and 125, 126 and 150, 151 and 175, and 176 and 200. The single-target condition was presented with one word eight times that was selected from the list that was not being used for lexical decision for that particular participant. The associative PM condition targets were selected on the basis that they were meaningfully related to the word breakfast (Nelson, McEvoy, & Schreiber, 2004); lunch, dinner, eggs, food, cereal, meal, morning, juice. Each associate was randomly selected (without replacement) to be presented during the lexical decision task. For the multiple-target PM condition, eight words selected from the alternate list served as targets, randomly presented (without replacement). There were two control conditions; controlstandard and control-multiple. The former was presented with the same targets during the lexical decision task as the multiple-target PM condition, but the targets held no significance because they had not been studied. The control-multiple condition was presented with eight words from the alternative list (words that they had not studied). The delayed recognition task presented 80 of the old words previously presented in the lexical decision task and 40 randomly selected new words from the alternative list. Old words were excluded from the delayed recognition task if they were presented on the first two trials of the lexical decision task, were targets, or were presented in one of the two trials following targets. The recognition task consisted of four blocks of 30 words (20 old and 10 new). In order to approximately equate the average retention interval across items, the first 20 valid words presented in the lexical decision task were presented in the first recognition block, the next 20 lexical decision valid words were presented in the second block, and so on for the third and fourth blocks. The assignment of new words to the recognition task blocks was random, as was the presentation order of new and old words within each block. A target recognition task containing 16 items (eight old and eight new items) was completed by participants in the control-multiple,

3 Michaelian (2016) has argued for the need to be able to distinguish between recall and imagination. In any memory theory which assumes that representations of sensory events are retrieved, and not the raw sensory experience (Humphreys, Tehan, Baumann, & Loft, under review), it is also necessary to distinguish whether the representation was retrieved due to its episodic relevance or due to its strength in long-term or semantic memory. Our assumption is that that this ability to differentiate between these two types of memories is based at least in part on intent and the recruitment of cues.

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Table 1 Prospective memory accuracy (PM accuracy), lexical decision response time (LD RT), and hit rate, false alarm rate, and discrimination (d’) on the delayed recognition task as a function of condition in Experiment 1. 95% between-subject confidence intervals are presented in parentheses. LD/PM Task

Delayed Recognition Task

PM accuracy

LD RT

Hit

Control

–

Single-target PM

0.74 [0.69, 0.79] 0.51 [0.44, 0.58] 0.47 [0.40, 0.53]

617 [589, 646 [616, 774 [734, 716 [685,

0.69 [0.65, 0.70 [0.67, 0.68 [0.65, 0.74 [0.70,

Multiple-target PM Associative PM

645] 675] 814] 748]

0.72] 0.74] 0.71] 0.77]

Target Recognition Task

False Alarm

d’

0.28 [0.24, 0.29 [0.25, 0.23 [0.20, 0.26 [0.23,

1.17 [1.05, 1.16 [1.03, 1.29 [1.18, 1.37 [1.24,

0.32] 0.33] 0.27] 0.30]

HIT-FA Rate 1.29] 1.30] 1.42] 1.50]

0.91* [0.86, 0.92] – 0.84 [0.79, 0.89] 0.87 [0.83, 0.90]

Note. * Only the control-multiple condition performed the target recognition task.

Results and discussion

multiple-target PM and associative PM conditions. The purpose was to check that targets could be identified under single-task conditions. For the multiple-target PM condition, old items were the PM targets. For the associative PM condition, old items were the eight associates of breakfast. For the control-multiple PM condition the eight old words were the words participants memorised prior to the lexical decision task. New items were words randomly selected from the alternate list. The presentation of old and new items was random.

PM performance, RT to the lexical decision task, and hit rates, false alarm rates, and discrimination (d′) for the delayed recognition task are presented in Table 1. There was no difference between the controlstandard and control-multiple conditions on dependent measures (lexical decision accuracy, lexical decision RT, or delayed recognition, smallest p = .13). Thus, studying eight words prior to the lexical decision task with the expectation of a delayed recognition test had no effect on performance compared to the standard control condition.

Procedure

Prospective memory

For lexical decision, participants decided whether letter strings were words or non-words, and responded quickly and accurately by pressing “f” (word) or “j” (non-word). The first display was a fixation point “+” displayed in white on a black background for 500 ms. The fixation point was replaced by a blank screen for 250 ms, followed by the presentation of the letter string, which remained on the screen until the participant response. Participants in the PM conditions were instructed to press the “9” key instead of the “f” (word) key when presented with target words during the lexical decision task. Participants in the single-target PM condition were instructed to make the PM response whenever their specific target word was presented. Participants in the associative PM condition were instructed to make the PM response whenever words ‘meaningfully related or strongly associated’ with the word breakfast were presented. Participants in the multiple-target PM condition were given three minutes to study a list of eight PM targets, and were instructed to make the PM response whenever one of the eight words was presented. Participants in the control-multiple condition also studied the same eight words prior to lexical decision, and were informed that they would be tested on their memory for those eight words later after completion of the lexical decision task. All participants completed a 3min distractor puzzle before beginning lexical decision. Following lexical decisions, participants completed a second 3-min distractor puzzle before the delayed recognition task. On the delayed recognition task, participants were presented with a 500-ms blank screen, followed by a single word. Participants pressed “o” if they believed that the word had been presented in the lexical decision task and “n” if they believed that the word had not appeared in the lexical decision task. For the target recognition task, participants were presented with a 500-ms blank screen, followed by a single word. The associative PM condition were instructed to press the “o” key if presented words that were meaningfully related or strongly associated to the word breakfast, or the ‘n’ key if not. The multiple-target PM condition were asked to identify the eight PM target words (“o” key) presented amongst new words (“n” key). Participants in the control-multiple condition were asked to recognise the eight words they were asked to remember prior to the lexical decision task (“o” key) presented amongst new words (“n” key).

PM responses were scored as correct if participants pressed the “9” key on the target trial. PM false alarms were rare, with participants making PM false alarms to 0.3% of non-target words, and were not further analysed. As predicted, PM accuracy for participants in the single-target PM condition was higher than for the multiple-target PM condition, t(114) = 5.44, p < .001, d = 1.0, and the associative PM condition, t(114) = 6.86, p < .001, d = 1.27. Ongoing lexical decision Lexical decision accuracy was near ceiling (M = 0.96, 95% CI, [0.959, 0.967]). There was no difference in lexical decision accuracy between the control condition and either the single-target or multipletarget PM conditions (ts < 1). However, lexical decision accuracy was higher for the associative PM condition [(M = 0.97, [0.963, 0.974)] compared to the control condition [(M = 0.96, [0.948, 0.966)], t (113) = 2.30, p = .02, d = 0.42. For RTs, we excluded the first two trials, target trials, PM false alarms, and the two trials following targets and following false alarms. Only word trials were included, and we excluded incorrect lexical decisions and RTs that were greater than 3 SDs from a participant’s grand mean. As expected, there was no difference in RT between participants in the single-target PM and control conditions, t(113) = 1.43, p = .16, d = 0.28. Participants in the associative PM condition made slower lexical decisions than controls, t(113) = 4.75, p < .001, d = 0.86. Participants in the multiple-target PM condition also made slower lexical decisions than controls, t(113) = 6.46, p < .001, d = 1.21. Delayed recognition task The parameter d′ was used as the measure of discrimination. Old words were excluded from the delayed recognition analyses if they had been previously incorrectly responded to during the lexical decision task. Although there was a trend, participants in the multiple-target PM condition did not discriminate old from new words at delayed recognition better than the single-target PM/control conditions, t 5

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(171) = 1.68, p = .09, d = 0.27. However, participants in the associative PM condition had better delayed recognition than the singletarget PM/control conditions, t(171) = 2.64, p = .01, d = 0.42. This finding conceptually replicates the Loft and Humphreys (2012) category PM task delayed recognition effect and supports the hypothesis that both the category PM and the associative PM task share lexical access with the lexical decision task but differ from that task in the requirement for semantic search initiation. As expected, there were no differences in discrimination between participants in the single-target PM and control condition, t < 1. We also conducted ANCOVAs, with correct lexical decision RT used as a covariate to control for differences in encoding time, and found that the pattern of delayed recognition effects remained the same (multi-target vs. single-target/control, F(1, 170) = 3.80, p = .05; associative vs. single-target/control, F(1, 170) = 6.21, p = .01). Futhermore, there was no difference in lexical decision RT for words subsequently correctly recognized on the delayed recognition task as compared with those not correctly recognized. This was confirmed in the multiple-target PM condition, t < 1, the associative PM condition, t (57) = 1.43, p = .16, and the single-target PM condition, t < 1. Taken together, these follow up analyses indicate the improved delayed recognition of non-targets is not an epiphenomenon of prolonged encoding (study) time during lexical decision (Bjork, 1994). For participants in both the multiple-target PM condition (r = .33, p = .01) and the associative PM condition (r = .31, p = .02), discrimination on the delayed recognition test was positively correlated with PM accuracy, suggesting a link between the processing of nontargets during lexical decision and the probability of PM retrieval. This finding is consistent with the idea that lexical access plus semantic search initiation support PM accuracy as well as the delayed recognition of the non-target items.

lexical decision tasks would be obtained if the associative PM manipulation produces similar effect sizes in the recognition tasks of Experiment 2 and Experiment 1. This finding would also support our proposal that lexical access and semantic search initiation are separable components of what we mean by semantic processing. If we also obtain a similar effect size for the multiple-target PM task on recognition in Experiment 2 as we obtained in Experiment 1 it is likely that a combined analysis would show that the difference between the multipletarget PM condition and single-target PM/control condition is significant. A significant effect would support the idea that PM task difficulty was responsible for the enhancement of performance in the multiple-target PM condition. However, before coming to this conclusion we will also look at the recognition task hit and false alarm rates in an effort to determine whether the increase in recognition in the multiple-target PM condition is produced by the same process which increases recognition in the category judgment and associative PM tasks. Experiment 2 contained the same conditions that were used in Experiment 1. However, a naming task was used as the ongoing task instead of the lexical decision task used in Experiment 1 and by Loft and Humphreys (2012). Our sample size in Experiment 2 provided a power of 0.75 to detect the medium–sized (d = 0.42) recognition benefit for the associative PM condition compared to a combined single-target PM/ control condition observed in Experiment 1. However, this sample size only provided a power of .40 to detect the small-sized (d = .27) recognition benefit for the multiple-target PM condition compared to a combined single-target PM/control condition observed in Experiment 1. Method Participants

Target recognition task

Two-hundred and forty-four undergraduates participated in return for course credit, and were randomly assigned to condition. There were 63 participants in the control condition (32 in standard, 21 in multiple), 63 participants in the single-target PM condition, 58 participants in the associative PM condition, and 60 in the multiple-target PM condition.

Performance on the target recognition task was analyzed by calculating a hit minus false alarm rate. There was no difference in target recognition task between the control-multiple and multiple-target PM groups, t(85) = 1.76, p = .08, d = 0.43. Target recognition was high for the associative PM condition, confirming that participants could adequately identify words associates of the word breakfast.

Materials

Experiment 2

Two hundred and ninety-six medium frequency words (occurring 20–50 times per million, length 4–8 letters) were randomly selected from the SMHWD (Dennis, 1995). For each participant, one hundred and ninety-two words were randomly selected to be presented for naming. The remaining details about the selection of words and targets were the same as in Experiment 1. The delayed recognition task presented 160 of the old words previously presented in the naming task and 80 randomly selected new words from the master list. The delayed recognition task consisted of eight blocks of 30 words (20 old and 10 new). In order to approximately equate the average retention interval across items, the first 20 valid words presented in the naming task were presented in the first recognition block, the next 20 naming task valid words were presented in the second block, and so on for the third and fourth blocks. The assignment of new words to the delayed recognition task blocks was random, as was the presentation order of new and old words within each block. A target recognition task containing 16 items (eight old and eight new words) was completed by the control-multiple, multiple-target PM and associative PM conditions. For the multiple-target PM condition, old items were the eight PM targets. For the associative PM condition, old items were the eight associates of breakfast. For the control-multiple condition the old items were the eight words studied prior to the naming task. New items were words which were randomly selected from the master list. The presentation of old and new items was random.

In Experiment 1 we found a small (but insignificant) delayed recognition benefit for the multiple-target PM condition compared to the single-target PM/control condition (d = 0.27) and a medium (significant) effect produced by the associative PM task (d = 0.42). Loft and Humphreys (2012) also observed a medium sized delayed recognition effect (d = 0.47) produced by their category PM task. The medium effect size for the semantically related targets (category and associative PM) can be understood in terms of three stages of semantic processing, namely, accessing a lexical representation, semantic search initiation, and semantic elaboration. The associative PM task, like the category PM task used by Loft and Humphreys (2012), presumably involves semantic search initiation and lexical access but not semantic elaboration, whereas the lexical decision task and the single-target PM and multiple-target PM conditions presumably involve lexical access but not semantic search initiation or elaboration. In order to provide further support for the partition of semantic processing into three components we wanted to pair our associative PM task with another task involving lexical access. We chose a naming task because in the reading literature it is frequently compared to lexical decision in order to determine whether the observed effects of manipulations are lexical in nature, based on an assumption that lexical decision and naming are highly similar with respect to lexical access. Evidence for the similarity of the lexical components of the naming and 6

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Target recognition task There was no difference on the target recognition task between the control-multiple condition and the multiple-target PM condition, t (89) = 1.12, p = .27, d = 0.25. Performance on the target recognition task was again high for the associative PM condition. Meta-analysis

Fig. 1. Difference scores for discrimination on the delayed recognition test between the category/associate conditions and the focal single-target PM/ control conditions in Loft and Humphreys (2012; first line, with circle; category PM task), the current Experiment 1 (second line, with circle; associative PM) task and Experiment 2 (third line, with circle; associative PM task). The fourth line with the square represents the meta-analysis data point. The 95% confidence intervals for each mean paired difference are presented.

To establish the robustness of the findings published to date concerning the effect of PM on delayed recognition we conducted a metaanalysis across the Loft and Humphreys (2012) and current experiments using the procedures recommended by Cumming (2012). The metaanalysis was first conducted on the difference scores between each of the PM conditions that involve semantic search initiation, and the single-target PM/control conditions, for discrimination on the delayed recognition test. The semantic search initiation PM conditions included the category PM condition from the Loft and Humphreys experiment and the two associative PM conditions from the current experiments. The experiments were weighted according to the inverse of the variance of their effect sizes (a study with a smaller confidence interval would have larger meta-analytic weight). We applied the more conservative random effect model to account for the heterogeneity of the three experiments as well as for the variance in the individual effect sizes. The forest plots showing mean effect sizes and 95% CIs (if a CI captures zero, then we cannot say the effect differs significantly from zero) are presented in Fig. 1. It is clear from Fig. 1 that the category and associative PM conditions have similar medium sized delayed recognition effects when compared to the single-target/control conditions. The overlap in the confidence intervals also indicates that the improvements in recognition observed across the category and associative PM conditions do not significantly differ. We then applied the meta-analytic procedure to the delayed recognition difference scores between the multiple-target PM conditions and the single-target PM/control conditions in Experiment 1 and 2 (Fig. 2). The multiple-target PM condition produced nearly the same small increase in recognition accuracy in both experiments. Because neither effect was significant they need to be interpreted with caution. Nonetheless, when the data from the Experiment 1 and 2 are combined the delayed recognition advantage for the multiple-target PM condition is reliably different from zero, albeit with a consistently small effect size. We suspect that the nature of PM target identification is at times different for the multiple-target PM task compared to the single-target PM task. However, before interpreting this difference as support for an effect of PM difficulty on recognition performance, we will first examine the pattern of results on the recognition task hit and false alarm rates. We conducted a 3 Condition (single-target PM/control, associative PM, multi-target PM) X 2 Experiment (Experiment 1, Experiment

Procedure For naming, participants were instructed to read each word presented aloud into their microphone. The first display was a fixation point “+” displayed in white on a black background for 500 ms. The fixation point was replaced by the word which remained on the screen for 1500 ms, followed by a message that read “please press the spacebar to continue”. After the participant pressed the spacebar the next fixation cross and word were presented. In the PM conditions if a target was detected participants were instructed to press the “9” key. The instructions given to each PM and control condition, were identical to Experiment 1, other than the fact the ongoing task was referred to as the pronunciation task. All participants completed a 3min distractor puzzle before beginning word pronunciation. Following pronunciation, participants completed a second 3-min distractor puzzle before performing the delayed recognition task, and then the target recognition task. Results and discussion Word naming responses were examined and indicated that all participants followed the naming task instructions (participants named the vast majority of presented words). Prospective memory As expected, PM accuracy for participants in the single-target PM condition was higher than for the multiple-target PM condition, t (121) = 6.53, p < .001, d = 1.18, and associative PM condition, t (119) = 8.28, p < .001, d = 1.50. PM false alarms were rare, with participants making PM false alarms to 0.7% of non-targets, and they were not further analysed. Delayed recognition task Participants in the multiple-target PM condition did not discriminate old from new words on the delayed recognition task better than participants in the single-target PM/control conditions, t(184) = 1.76, p = .07, d = 0.28, but the effect was in the same positive direction as Experiment 1 (an almost identical small effect size). Delayed recognition for participants in the associative PM condition was better than for participants in the single-target PM/control conditions, t(182) = 2.64, p = .01, d = 0.41 (an almost identical small-medium size as that obtained in Experiment 1). There were no differences in discrimination between participants in the single-target PM and the control condition, t < 1. Discrimination on the delayed recognition test was not significantly correlated with PM accuracy for either participants in the multipletarget PM condition (r = .18, p = .16) or the associative PM condition (r = .15, p = .26), but the correlations were both in the same positive direction as found in Experiment 1.

Fig. 2. Difference scores for discrimination on the delayed recognition test between the multiple-target PM condition and single-target PM/control conditions in Experiments 1 (first line, with circle) and Experiment 2 (second line, with circle). The third line with the square represents the meta-analysis data point. The 95% confidence intervals for each mean paired difference are presented. 7

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Table 2 Prospective memory accuracy (PM accuracy), and hit rate, false alarm rate, and discrimination (d’) on the delayed recognition task as a function of condition in Experiment 2. 95% between-subject confidence intervals are presented in parentheses. PM Task

Delayed Recognition Task

PM Accuracy

Hit

Control

–

Single-target PM

0.97 [0.94, 1.00] 0.74 [0.68, 0.81] 0.65 [0.58, 0.72]

0.68 [0.65, 0.67 [0.63, 0.68 [0.64, 0.73 [0.69,

Multiple-target PM Associative PM

0.71] 0.71] 0.72] 0.77]

Target Recognition Task False Alarm

d’

0.17 [0.14, 0.18 [0.15, 0.14 [0.12, 0.17 [0.14,

1.54 [1.41, 1.52 [1.38, 1.68 [1.55, 1.77 [1.61,

0.20] 0.21] 0.17] 0.20]

HIT-FA Rate 1.68] 1.66] 1.80] 1.93]

0.95* [0.93, 0.97] – 0.93 [0.90, 0.96] 0.91 [0.89, 0.93]

Note. * Only the control-multiple condition performed the target recognition task.

2) X Type (Hit, Correct Rejection) mixed ANOVA, with condition and experiment as between-subject factors, and type as the within-subject factor. Main effects of type, F(1, 469) = 69.85, p < .001, ηp2 = .13, condition, F(2, 469) = 7.37, p < .001, ηp2 = .03, and experiment, F(1, 469) = 38.83, p < .001, ηp2 = .08, were qualified by interactions between experiment and type, F(1, 469) = 24.72, p < .001, ηp2 = .05, and between condition and type, F(2, 469) = 4.23, p = .02, ηp2 = .02. The two way interaction between condition and experiment, and the three way interaction, were not significant (Fs < 1). The significant interaction between experiment and type confirms that the hit and correct rejection (and hence false alarm) rates differed between Experiment 1 where participants made lexical decisions as the ongoing task, and in Experiment 2 where they named words (see Tables 1 and 2). As indicated in the Introduction, we expected the articulatory information provided by the naming task to exert its effect primarily on false alarm rates. Follow up t tests indicated that correct rejection rates were significantly higher (false alarms lower) in the naming experiment (Experiment 2) compared to the lexical decision experiment (Experiment 1), t(473) = 11.49, p < .001, d = 0.77, whereas there was no difference in hit rates as a function of experiment (t < 1). The significant interaction between condition and type is indicative of a differential effect of the multi-target PM and semantic search initiation (associative) PM tasks on the pattern of hits and false alarm rates. Follow up t tests indicated that hit rates in the associative PM conditions were higher than the single target PM/control conditions, t (355) = 3.25, p = .001, d = 0.37, but there was no corresponding difference in correct rejection (false alarm) rates (t < 1). In contrast the hit rates in the multi-target PM conditions were not statistically different than in the single-target PM/control conditions (t < 1), but the correct rejection rates in the multi-target PM conditions were higher (false alarms lower) compared to the single-target PM/control conditions, t(357) = 2.56, p = .01, d = 0.30. Thus, the effect of increasing the number of PM targets was on the false alarm rate, in contrast to the effect of associative PM tasks requiring semantic search initiation, which affected the hit rates. The Loft and Humphreys (2012) data also indicated that the improvement in delayed recognition for their category PM condition compared to single-target PM/control condition was driven by shifts in the hit rate, and not the false alarm rate. This differential pattern of hit and false alarm effects due to the semantic search initiation PM tasks and the multi-target PM tasks indicates that the effect of semantic search initiation on final delayed recognition is not the result of PM task difficulty. General discussion

ongoing lexical decision task, increased delayed recognition beyond that produced by the lexical decision task on its own. These findings also support the hypothesis that lexical access and semantic search initiation have separate effects on recognition memory. The primary contribution of the current two experiments, taken together with the findings of Loft and Humphreys (2012), is first, the consistency of the effects of the two different semantic search initiation tasks on recognition memory (associative and category judgment PM), and second, the consistency of the semantic initiation effect on recognition memory produced by the associative PM task over the two different ongoing tasks of lexical decision and naming. These results provide the first steps of a systematic cross-task empirical analysis of semantic effects on memory. A problem in the memory literature has been the lack of an adequate language for describing or hypothesizing about semantic effects on memory. The reading literature has had a different problem. The belief in the reading literature that the lexicon contains semantics is justified by the fact that it is meaning that distinguishes a letter string which makes up a word and a letter string which does not.4 However, this literature is largely unconcerned with the nature of meaning and how much meaning would be required to distinguish word from non-word letter strings. The reading literature also has little to say about whether or not some aspects of meaning require an additional memory retrieval operation beyond that required to access an abstract lexical representation. These additional aspects of meaning might involve embodied knowledge, or the retrieval of other words. Our review of the literature also established the possibility that the effects of naming are separable from the effects of semantic search initiation. This possibility was largely based on the Bodner et al. (2014) study which showed that in a between-subjects design, the effect of naming was largely to reduce the false alarm rate. In contrast, in Loft and Humphreys (2012) the effect of semantic search initiation was largely on the hit rate. The pattern of hit and false alarm rates on the recognition memory tests in the present two experiments support the separation of the effects on recognition due to semantic search initiation and naming. With respect to naming, there was a significant decrease in the false alarm rates from Experiment 1 (lexical decision) to Experiment 2 (naming), and no significant changes in the hit rate. With respect to semantic search initiation, adding the associative PM task to lexical access produced a modest but significant increase in the hit rate, and a non-significant change in the false alarm rate. Also, as predicted, the recognition effect size due to adding semantic search initiation to lexical access was similar across the category judgment PM task (d = .47 in Loft & Humphreys) and the associative PM task, with the

In Experiments 1 and 2 we showed that an associative PM task increased delayed recognition accuracy on nontarget items from an ongoing task (lexical decision and naming respectively), relative to singletarget PM/control tasks. These results extend the finding of Loft and Humphreys (2012) that a category judgment PM task, paired with an

4 The existence of a representation also distinguishes letter strings which have and have not been previously encountered. Thus, it is possible that finding a representation or converging to a stable state (Chappell & Humphreys, 1994) could distinguish the two types of strings.

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latter effect similar over the current two ongoing tasks (at d = .42 for lexical decision and d = .41 for naming). We have already noted that the naming results in between subject designs can be explained if the participants are saying yes if they have both lexical information and articulatory information and no otherwise. If we accept this hypothesis, the very small effect of naming on recognition hit rates tells us that there are relatively few occasions where with an old word there was lexical information but no articulatory information. This assumes that the availability of lexical information was the same in the naming and silent reading conditions. We had also noted that the naming results in mixed and blocked designs could be explained if the participants were saying yes if they could retrieve either useable lexical information or usable articulatory information. The significant increase in the hit rate due to naming in this design (Bodner et al., 2014) tells us that participants frequently have usable articulatory information when they do not have usable lexical information. This also assumes that the availability of lexical information was the same in the naming and silent reading conditions. When these obsevations are taken together it suggests an asymmetry in the ability to access lexical and articulatory information. This pattern follows from ideas about associative interference and the relative similarity of articulatory and lexical information (Humphreys Tehan, Baumann, & Loft, under revision). There are 44 phonemes in the English language and several of them are acoustically confusable (Conrad, 1964). Thus, the episodic retrieval of lexical information about a word, given articulatory information about that word, will be difficult because the articulatory information about the other words in the list will interfere. However, we have noted that the list length and taxonomic category length effects in the recognition memory literature are small, suggesting that the lexical representations of the words used in prior experiments are not very similar to each other. If this is the case we would expect very little interference when using a lexical representation to episodically cue the articulatory information. We included the multi-target PM condition to see if PM task difficulty could explain the enhancement in delayed recognition resulting from the category PM task used by Loft and Humphreys (2012). When d’ in the multi-target PM condition was compared to d’ in the singletarget PM/control condition the difference was not significant in either experiment. However, the difference was significant in our meta-analysis. The significant effect in the meta-analysis could indicate that PM difficulty was responsible for the enhancement in delayed recognition for the category and associative PM conditions, and not semantic search initiation. However, when we examined the recognition hit and false alarm rates separately, the false alarm rate difference between the multi-target PM condition and single-target PM/control condition was significant while the hit rate did not significantly change. This is different from the pattern which we have attributed to semantic search initiation. When a category judgment PM task was paired with a lexical decision task, or an associative PM task is paired with either a lexical decision or a naming task, there was a significant increase in the hit rate and no significant change in the false alarm rate. It is possible, but by no means certain, that the small effects on delayed recognition produced by the multi-target PM task are caused by task difficulty. What we can conclude with more certainty is that the multi-target PM effect on recognition is differentiable from the effect of semantic search initiation on recognition. We believe that it is critical to ground theories and computational models of PM in the converging evidence provided by applying theories, methods, and data analytic techniques from the wider memory literature, and the current paper contributes to understanding PM in this regard (also see Loft, Humphreys, & Whitney, 2008). The PM literature refers to individuals “monitoring” the ongoing task for targets (e.g., Einstein & McDaniel, 2005), “checking” for targets (Guynn, 2003), or in computational models “accumulating evidence” for the PM task response (Strickland et al., 2018). But what does it actually mean, qualitatively, for individuals to “monitor” or “accumulate evidence” for

a PM task response (what is the content of the PM evidence being accumulated)? The results from Loft and Humphreys (2012), along with the current experiments, indicate a role of semantic search initiation for deciding whether an ongoing task item is an associative or category PM target. Conclusions In the memory literature semantic processing is said to improve recognition and recall, but researchers do not have scientific terminology to propose more detailed questions about semantic processing. The language production and reading literatures have terminology for the component representations which make up words, but have not applied that terminology to the question of how semantic processing enhances memory. Our extensions to the Loft and Humphreys (2012) and the Bodner et al. (2014) findings establish that we can use the terminology of the language production and reading literatures to propose questions about how semantic processing and naming affect memory. These extensions have also validated our novel methodology of pairing a PM manipulation with an ongoing task to answer questions about how semantic processing and naming affect recognition memory. Although our specific findings are foreshadowed by the findings of Loft and Humphreys (2012) and Bodner et al. (2014), the combined set of findings now provides a firm foundation to characterize semantic processing and naming. We have presented evidence that lexical access enhances delayed recognition and the initiation of a semantic search provides an additional benefit. Further support that the effect of semantic search initiation is the critical psychological process could come from the use of a PM task that has an indefinite number of possible targets but which does not involve semantics, such as identifying words which start with the letter s.5 The added benefits due to semantic search initiation are not the result of PM task difficulty. However, future research needs to more firmly establish that lexical access also enhances delayed recognition. Support for this proposal comes from research comparing orthographic or phonological processing instructions with semantic processing instructions. A possible problem is that with orthographic and phonological processing instructions participants process only part of a letter string. Other support comes from Chalmers and Humphreys (1990) demonstration that training participants on the meaning of very low frequency words improved recognition more than just familiarizing them with the words. More direct evidence might be obtained by inducing participants to name words without accessing the lexicon. The current findings have also firmly established that the effects of naming (articulatory information) are largely independent of the effects of semantic processing (lexical information) so that participants have some discretion about when and how to use articulatory information. It also seems likely that the probability of the retrieval of articulatory information given lexical information is higher than the probability of retrieval of lexical information given articulatory information. This inference follows from facts about associative interference and the relative independence of articulatory and lexical information. The independence of the articulatory and lexical information, and the inference about probabilities of retrieving one source of information from the other, have implications for investigations of episodic memories of words. Funding This research was supported by Discovery Grant DP12010311 from the Australian Research Council awarded to Loft. 5

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We would like to thank an anomynous reviewer for making this suggestion.

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CRediT authorship contribution statement

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