AN INVESTIGATION OF THE COGNITIVE BASIS FOR THE SELECTIVITY OF AGE-RELATED MEMORY IMPAIRMENT

Older adults have been found to have a selective impairment in certain types of episodic memory, although other types of memory are generally preserved. The goal of this research is to determine whether the selective age-related memory deficit is best explained by an impairment  in perceptual processing, an impairment in the formation of associations between items and their contexts, or an impairment in controlled processing, which is presumed to be required for recollection. Three behavioral experiments were conducted which attempted to evaluate the relative merits of each of these three accounts of age-related memory impairment. To allow for a more meaningful comparison of the data from each experiment, the same participants completed all three behavioral experiments. In addition to the behavioral experiments, an event-related potential (ERP) experiment was conducted to provide further information regarding perceptual processing differences between older and younger adults. When relying solely on perceptual information, rather than semantic and perceptual information, older adults’ memory performance was especially poor for perceptually impoverished stimuli (words), but less so for perceptually rich stimuli (pictures). Unlike young adults, older adults did not benefit from repeated presentations of pair information, suggesting that older adults do not form associative links between to-be-remembered stimuli. However, older adults did not show a recollection-specific impairment as the controlled processing hypothesis would have predicted. Older adults were equivalently impaired for both recollection and familiarity measures, suggesting that controlled processing is not specifically impaired in older adults. ERPs for older adults had much more individual variability than for young adults and the differences in ERP waveforms between age groups were observed more consistently in word conditions than in picture conditions, which is consistent with the behavioral results. Additionally, older adult ERPs to pictures were most similar to young adults, in accordance with the behavioral results. The behavioral data support the hypothesis that there is a deficit in perceptual processing which may help explain age-related memory impairments. The ERP data, though limited, lends some support to this explanation as it reveals perceptual and semantic processing differences between young and older adults. An associative deficit may be an additional source of memory impairment.

1.0              INTRODUCTION 

Researchers frequently describe impairments in episodic memory that are associated with aging (e.g., Johnson, Hashtroudi & Lindsay, 1993), despite the preservation of other types of memory in older adults (e.g., Laver & Burke, 1993). Episodic memory can be roughly divided into two common types of subjective memory phenomena (Rugg & Yonelinas, 2003; Knowlton, 1998; Hintzman, et al., 1998; Hintzman & Curran, 1994; Yonelinas, 1994; Jacoby, 1991; Gardiner & Parkin, 1990; Humphreys, et al., 1989; Jacoby & Dallas, 1981, Mandler, 1980; Atkinson & Juola, 1974). Perhaps the more stereotypical of the two types is the recollective experience: one remembers having encountered an object, person, etc., and can specifically recall many of the particular details of that experience. These details might typically include the appearance of the object in question, the surrounding environment, the context of the experience in place and time, and perhaps even the thoughts or emotions being experienced during the encounter (Tulving, 1984). Another common memory experience is the experience of familiarity: one has a sense of knowing that something has been encountered before, but cannot recall the particular context in which the encounter took place. The familiarity-recollection division of episodic memory is a valuable framework for examining the age-related changes in episodic memory because the deficits repeatedly found in episodic memory among older adults can be conveniently described as a selective impairment of recollective memory (Light & Singh, 1987; Perfect, et al., 1995; Perfect & Dasgupta, 1997; Balota, etal., 2000; Clarys, etal., 2002). Recollection and familiarity, however, are often poorly defined terms in research of older adult memory and there is little explanation of the underlying cognitive processes. As a result, the cognitive basis of the selectivity in age-related memory impairment is not well understood.

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The goal of this research is to determine whether the cognitive underpinnings of the selective age-related memory deficit are best accounted for by an impairment in perceptual processing, an impairment in the formation of associations between items and their contexts, or an impairment in controlled processing. In pursuit of this goal, three behavioral experiments were conducted which attempted to capture each of the three hypothetical impairments listed above. To allow for a more meaningful comparison of the data from each experiment, the same participants completed all three behavioral experiments. In addition to the behavioral experiments, an event-related potential (ERP) experiment was conducted to provide further information regarding perceptual processing differences between older and younger adults. Each experiment is informed by a particular theory of age-related memory impairment. These three theories are described below.

1.1              THEORIES OF AGE-RELATED MEMORY IMPAIRMENT

1.1.1        Perceptual proccesing impairment

One way of characterizing the selective age deficit in memory is as a specific impairment of perceptual processing, whereas conceptual processing is preserved. According to this view, recollection and familiarity differ primarily in the use of perceptual information. Specifically, recollection depends on the use of perceptual information for the specific details of an item and familiarity depends on the use of conceptual information, such as semantic or relational features (Brainerd, et al., 1999; Brainerd, et al., 1995). In this framework, separate perceptual and conceptual representations are formed at the encoding stage of memory. The process of perceptual retrieval is an all-or-none process that corresponds to recollection. The process of conceptual retrieval is a graded process that corresponds to familiarity. Thus, according to this type of memory theory, familiarity and recollection are characterized in terms of the type of information they use.

A perceptual/conceptual processing model can account for the selectivity of the age-related memory deficit by proposing that perceptual memory processing is specifically impaired in older adults (Koutstaal et al., 2001; Koutstaal, et al., 1999; Koutstaal & Schacter, 1997). Thus the tendency for older adults to rely on familiarity is the result of preserved conceptual-based processing. A perceptual-processing deficit impairs the ability to distinguish between items studied in different contexts.

1.1.2        Associative encoding impairment

Some theories of age-related memory impairment argue that older adults are impaired in memory for context but not for item (Naveh-Benjamin, 2000; Glisky, et al., 2001; Smith et al., 1998; Naveh-Benjamin & Craik, 1995; Park et al., 1990; McIntyre & Craik, 1987). Some research in young adults has supported the idea that recollection is characterized by memory for the context in which an item was first experienced (Perfect, et al., 1996; Johnson, 1997; Johnson, et al., 1993). However, results have been mixed regarding the ability of older adults to utilize context. In fact, the problem for older adults may not be with processing context per se but in binding an item to its context. Several studies highlight a context-item binding difficulty for older adults (Chalfonte & Johnson, 1996; Mitchell, et al., 2000; Naveh-Benjamin, 2000). Interestingly,

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Naveh-Benjamin’s associative encoding hypothesis (AEH) for older adults is quite similar to a model of healthy episodic memory, the ICE model (item-context-ensemble; Murnane, et al., 1999), although both were developed independently. ICE makes the claim that accurate recollection depends not only on memory for item and context information individually, but, crucially, on the integration of these two types of information into unique memory representation called an ensemble (Murnane, et al., 1999). The ensemble enables the individual to  have accurate memory for an item embedded within a specific context, rather than mere familiarity with both the item and context but not their relationship. The distinction between recollection and familiarity is defined at the encoding stage, based on whether an ensemble is formed that will enable future recollection. Formation of an ensemble requires the creation of associative features based on conjunctive information about item and context derived through elaborate processing.

The associative encoding model explains age-related deficits in memory as a specific impairment in the memory for components (items and context) of an episode and the relationship of the components to each other (Naveh-Benjamin, 2004). This explanation is the same as the ICE model explanation. It is the failure to properly associate the item and context at encoding, rather than a deficit in the processing of either item or context information individually, that is difficult for older adults. If associative links are not properly formed between items and their contexts at the encoding stage, the circumstantial details related to items cannot be effectively used in determining whether a cue matches an item in memory. For example, impaired ensemble formation would decrease the ability to discriminate between study lists. The process- dissociation procedure (Jacoby, 1991), explains inability to discriminate between study lists as a failure of recollection to oppose familiarity but impaired ensemble formation could explain it due to difficulty remembering in which experimental context an item was originally embedded. If normal memory processes involve the encoding of associative features between items and context, then it should be expected that associative features should be encoded when the context is actually another item in a pair.

1.1.3        Controlled processing impairment

Another common characterization of the selective age deficit in memory is as a specific impairment of controlled processing. According to such an account, the distinction between recollection and familiarity can primarily be defined by differences in attentional resources required to carry out the component processes. Specifically, recollection is supported by controlled processes and familiarity is supported by automatic processes (see Yonelinas, 2002, for review). The cognitive processes underlying both recollection and familiarity may operate on the same informational content from the environment, including perceptual and conceptual features of external stimuli and memory traces. Controlled processes are assumed to require attentional resources and occur at a relatively slow rate. Automatic processes are assumed to occur at a relatively fast rate, without the use of attentional resources.

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The selectivity of the age-related deficit in memory can be accounted for, in this theoretical framework, as a specific impairment of controlled processing. If controlled  processing is damaged, then the necessary cognitive operations underlying recollective memory will not effectively be carried out. Processes underlying familiarity are thought to be spared in old age because they can be executed without the need for controlled processing.

1.2 SUMMARY 

Older adults experience a deficit in the type of memory referred to as recollection which requires remembering details of a past experience, such as perceptual features or the context in which the experience took place. The perceptual processing impairment theory posits that older adults  have difficulty extracting and/or manipulating perceptual features when processing information. The associative encoding impairment posits that older adults cannot bind information about contexts and the items in the context. The controlled processing impairment posits that older adults have difficulty allocating attention to details of an experience. Since the goal of this study is to determine the best characterization of the age-related memory impairment, the three theories, perceptual processing impairment, associative encoding impairment, and controlled processing impairment, are necessarily framed as competitors. However, it is possible that the explanations are not mutually exclusive, as there may be more than one cognitive impairment in older adults that contributes to age-related memory impairment. Perceptual processing deficits could be the source of the associative encoding impairment and associative encoding could be a type of controlled process. Based on the data reported below I will argue that the age-related memory deficit is best accounted for by a perceptual processing impairment but that associative encoding may also play a role when context-item relationships are specifically tested. The data do not support the controlled processing impairment as an explanation of age-related memory deficits.

2.0              EXPERIMENT 1 

2.1              RATIONALE 

Two competing hypotheses for the selectivity of the age deficit are that it results from an impairment of representations for perceptual details, and that it results from an impairment of controlled processing. Experiment 1 tested both of these hypotheses simultaneously.

If the encoding of perceptual details is specifically impaired in older adults, then older adults should exhibit preferential processing of semantic information as opposed to perceptual information. Three previous studies have specifically tested the encoding of perceptual versus conceptual information in older adults. One study found that older adults had more false alarms for concrete pictures, than for abstract pictures (Koutstaal, et al., 2003). Concrete pictures were picture representations of objects in the world. Abstract pictures were line drawings that were  not representative of any object or concept in the world. The concrete pictures carried more semantic (conceptual) information than the abstract pictures, which lacked semantic information since they did not correspond to any object or concept. The fact that older adults had more false alarms to concrete pictures than to abstract pictures can be interpreted as a tendency for older adults to disregard perceptual information by relying on semantic information when it is available, as in the case of concrete pictures. However, a different study using words and nonwords, which should share the same semantic/non-semantic distinction that concrete and abstract pictures have, did not find more false alarms for words than for nonwords for older adults. Memory for words versus nonwords also was not significantly different between young and older adults (Perfect & Dasgupta, 1997), indicating that older people did not have a greater reliance on semantic information as a perceptual/conceptual distinction theory would predict. Finally, older adults have been shown to use perceptual details to the same extent as younger adults on a “meaning recognition” task (Koutstaal, 2003).

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Thus, there are conflicting results in the literature regarding older adults’ ability to use perceptual information in episodic memory tasks. Experiment 1 further examined this question by manipulating perceptual details in a task that held semantic information constant. The experiment used stimuli consisting of words and pictures that represented concrete objects. The pictures had distinctive perceptual features, whereas the perceptual features of the words (i.e., letters) were relatively generic. In a recognition memory task, participants were forced to use recollective memory processes by the presence on the test list of “lure” items that represented the same semantic content as items on the study list, but with different perceptual features (e.g., a picture of a bowl on the study list, and the word “BOWL” on the test list). This technique assumes that the picture of an object and the word referent for an object activate the same concept in the semantic network (Carr, et al., 1982).

Participants were instructed to identify a stimulus as “old” only if they saw the exact stimulus on the study list. If older adults are specifically impaired in their processing of perceptual information, then their performance should be especially bad for items that have generic perceptual features (i.e. words) because older adults are unable to make the fine-grained distinctions necessary to correctly identify words as “old” or “new.” Memory for items with  very distinctive perceptual features (i.e., pictures) should be relatively preserved for older adults, since the damage to perceptual processing would less effectively wipe out discriminability of those items. If, on the other hand, information content is orthogonal to the age-related memory deficit, then older adults should be equally impaired on memory for words and pictures relative to younger adults.

2.2              METHODS 

2.2.1        Participants 

A specific effort was made to improve on previous studies by recruiting older adults who were representative of the general aged population. Sixty-one older adults, 41 females and 20 males (mean age = 82.2 years, range = 61-96; mean education = 13.8 years, range = 9-20 years), were recruited from the Pittsburgh region, including retirement communities and churches. The older adults received $7.00 compensation for participation.

Ninety young adults, 54 females and 36 males (mean age = 21.2 years, range = 18-39 years; mean education = 14.3 years, range = 12-23 years), were recruited from the University of Pittsburgh community and Introductory Psychology courses. The young adults received either

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A core group of 34 young people and 37 old people participated in three experiments: Experiments 1, 2, and 3. An additional 56 young people and 24 older adults also participated in Experiments 2 and 3 (total each for Exps. 2 & 3 = 90 young & 61 older). Experiment order was randomly assigned to avoid order effects.

All participants were native English speakers, right-handed, and had no history of major medical, neurological, or psychiatric disorders. After the explanation of procedures and prior to

testing, all participants provided written informed consent to participate using consent forms approved by the Institutional Review Board of the University of Pittsburgh.

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2.2.2        Stimuli

 

 

Stimuli consisted of 95 words presented in black uppercase lettering against a white screen and 95 objects presented as black line drawings against a white screen (pictures; Snodgrass & Vanderwert, 1980). A pilot study with both older and young adults was conducted in order to determine the word referent of each member of the picture corpus. Pictures that produced multiple word referent variants (e.g., sofa, couch, davenport, loveseat, settee) were excluded from Experiment 1.

2.2.3        Design

 

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Thirty-seven of the word stimuli and 37 of the picture stimuli were presented in random order, alternating word/picture for each participant during the study session. For the test session, 57 words and 57 pictures alternated (114 stimuli total, at test). The randomly ordered test list containing 19 items in each of the following conditions: word targets, picture targets, word  lures, pictures lures, word distractors and picture distractors (See Table 2 in Appendix A).

2.2.4        Procedure

 

 

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During the study session, participants were presented with a sequence of single pictures and words on the computer screen. Stimuli were presented until the participant responded or for a maximum of 5000 ms. After participants responded to each stimulus, another stimulus would

appear. During the study session, participants were instructed to make a decision about the stimuli presented (e.g., “pleasant or unpleasant”). Making a judgment about the pleasantness of an item requires consideration of semantic properties and has repeatedly been shown to increase encoding and attention to the study stimuli (Hyde & Jenkins, 1969; Craik & Lockhart, 1972; Hyde & Jenkins, 1973). It was assumed that the pleasantness ratings would not result in any differences in emotional processing between age groups.

Participants were informed that they would be asked about the stimuli later in the experiment. Participants proceeded immediately from the study session to the test session instructions in which participants were instructed to make an “old/new” decision task. They  were told that a “yes” response was to be given only if there was an exact physical match to previously seen study items. Test items that matched study items only in semantic information but not perceptual information (i.e., not identical physical matches) were to be considered “new” and served as lures. Test items that did not match the items at study semantically or perceptually were to be considered “new” and served as distractors. Trial sequence for study and test sessions are in Table 2 of Appendix A. After the participant pressed the space bar a new stimulus (word or picture) appeared, which remained until the participant made a response, or for a maximum of 3000 ms.

The experiment took place in true-to-life settings in retirement homes, apartments, and campus classrooms or offices. Lab settings were purposely avoided when testing the young subjects because the older adults were not tested in lab settings. The testing environment was always an isolated room with closed doors to decrease distraction. Each participant viewed the trials on a laptop computer screen in the testing room, while the experimenter was present in the room to ensure that participants did not progress to the next section of the experiment before they

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were required to do so. The experimenter was present in the room because in pilot studies, both young and older adults often failed to obey the instruction screen that stated, “STOP! ALERT EXPERIMENTER,” despite repeated verbal instruction prior to the start of the experiment.

2.2.5        Analytic technique

 

 

Standard signal detection measures of hits (“yes” responses to targets) and false alarms (“yes” responses to lures and/or distractors) were used in the analyses of data for this experiment (MacMillan & Creelman, 1991; Green & Swets, 1966). For some analyses the difference between hits and false alarms was used as a measure of discrimination between old and new items.

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2.3              RESULTS

 

 

Reaction times were displayed as box plots and subjects who consistently had reaction times (across multiple conditions) that were outliers were excluded. An outlier was defined as a reaction time that was more than 1.5 times the box length (interquartile range) away from the bottom or top edge of the box. Older adults had slower reaction times than young adults overall (t(59)= -6.02, p<.001, Cohen’s d=1.57). Mean RT for young adults was 1191 ms and for older adults was 1729 ms. For some conditions the older adults did not have enough correct responses (i.e., word lures) and for some conditions the young adults did not have enough incorrect responses (i.e., picture targets). Therefore, for each subject the median reaction times for each condition were averaged for all response types for which there were more than three responses.

It was expected that older adults’ accuracy would be worse overall than the young adults’ accuracy and that the older adults would benefit from the additional perceptual details available in the picture condition (over the word condition) and would do so to a greater extent than young adults. This was expected because according to the perceptual impairment hypothesis, older adults are not able to process perceptual cues as well as younger adults. Thus, an excess of unique perceptual cues in the picture condition as compared to the word condition should help the older adults and it should help them more than it should help the younger adults who are not impaired at perceptual processing. Finally, older adults should have a greater increase in false alarms for the lure condition than the distractor condition because the lures require more reliance on perceptual information (i.e., the lures have the same degree of semantic familiarity as the targets so semantic familiarity cannot distinguish lures from targets).

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A 2 (condition) X 2 (stimulus format) X 2 (age group) split-plot univariate analysis of variance (ANOVA) was performed on the old/new discrimination data (hits minus false alarms) for the young (n=29) and older adults (n=32), with condition and stimulus format as within- subjects factors and age-group as a between subjects factor. This was conducted across the two false alarm conditions, lures and distractors, and the two stimulus forms, pictures and words, and across the two age groups, young and old.¹ As expected, young adults had better old/new discrimination than older adults (main effect of age) (F(1,59)=71.02, p <.001, η²=.546). Also as expected, older adults benefited from the additional perceptual cues available from pictures more than young adults did (age X form interaction) (F(1,59)=27.45, p<.001, η²=.318). As predicted, older adults had a greater difference in false alarms between lures and distractors than young adults did (age X condition interaction) (F(1,59)=19.31, p<.001, η²=.247. Lastly, there was an

1 All effects and interactions were significant (between age groups and all within-subjects effects and interactions)

p<.001.

age group X form X condition interaction (F(1,59)=11.19, p=.001, η²=.159. The extent to which older adults had a greater benefit of pictures than young adults was seen more in the comparison of targets to lures than in the comparison of targets to distractors. This is illustrated in Figure 1. Unlike distractors, lures lacked novel semantic information that older adults could use and this affected their responses to words more than to pictures. The nature of this interaction can be viewed in Figure 2.

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Figure 2 shows false alarms for lures relative to distractors – the distractor false alarms provide a baseline for false alarms in general, and allow for comparison across conditions and age groups. Remember that use of the perceptual details is essential for identifying an item as a lure since the lures share conceptual details with the targets but they do not share perceptual details. The lure conditions tested whether participants could use perceptual details to reject items that were semantically identical to studied items. If perceptual processing (encoding or retrieval) is impaired, then older adults should have more difficulty rejecting word lures than picture lures because words have less distinctive perceptual characteristics than pictures. The increased false alarm rate for lures over and above distractors indicates the extent to which participants failed to use perceptual details to correctly reject items. That is, how much does having only new perceptual details impair identification of a lure more than having new perceptual and new conceptual details (distractor condition).

Younger adults had about the same increase in false alarms for lures regardless of the physical format of the lure. Older adults, on the other hand, made many more false alarms to word lures than to picture lures (relative to the distractors).

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Words Pictures

Stimulus Type

Figure 1. Old/new discrimination for young and older adults. Error bars represent standard error of

the mean.

 

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Words Pictures

Stimulus Type

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Figure 2. False alarms for words and pictures for young and older adults. Error bars represent

standard error of the mean.

2.4              DISCUSSION

 

 

According to the perceptual impairment hypothesis, recollection critically depends on the encoding and retrieval of unique perceptual characteristics of the original episode in order to allow for reconstruction of the episode later. Recollection and familiarity might depend on both perceptual and conceptual information, but familiarity would not necessary fail for lack of perceptual details while recollection would. If older adults are impaired in processing of perceptual details, then in a task where the use of perceptual information is necessary to make memory judgments, the older adults’ memory impairment (relative to young) should be less severe for perceptually distinctive items and more severe for perceptually generic items. Word memory should be more impaired than picture memory because perceptual deficit will hurt visual distinctiveness for words more than for pictures, which have many more distinctive perceptual features. If the perceptual distinctiveness of stimuli is manipulated while keeping semantic/conceptual information constant, we should be able to observe any differences in performance due to impaired processing of surface/perceptual features. Experiment 1 found that older adults were impaired by the absence of unique perceptual details much more than young adults. This lends supports to the hypothesis that older adults are processing perceptual details less effectively than young adults, especially when perceptual details are sparse as is the case with words.

3.0              EXPERIMENT 2

 

 

 

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3.1              RATIONALE

 

 

Experiment 2 will test whether a problem with ensemble encoding causes age-related memory deficits. The ICE (item-context-ensemble) model explains age related deficits as an impairment of ensemble formation at encoding, or the ability to encode features of the study event that represent integrative information about item and context. The results of studies that manipulate encoding strategies are consistent with ICE because these experiments improved older adult performance by providing more time or encouragement for them to elaborate on the relationships between item and context information during the study sessions. If ensemble encoding is specifically impaired in older adults, then memory should be affected by manipulations of the relationship between item and context information. Only one study has been done that specifically tests this prediction of the ICE model in older adults (Bayen, et al., 2000). That  study found that young adults, and not older adults, performed better during recognition tasks in which study items were embedded in rich visual contexts, such as full visual scenes, than when they were in simple visual contexts. Older adults presumably did not show this benefit because they did not use the extra context information in ensemble formation (whereas the young adults did). Larger differences between older and young adults have also been found in a cued-recall task when the item and the context were unrelated than when they were related, possibly because it is harder to make an ensemble when the context and item are unrelated (Park, etal., 1990;

Smith,  etal., 1998). Neither of these findings is readily explained by a specific deficit in controlled versus automatic processing or perceptual versus conceptual processing.

Recent studies (Criss & Shiffrin, 2005) have suggested that the formation of memory traces that use ensemble information occurs in paired-associate memory as well as item-context memory. That is, individuals encode integrative information about both items in a pair in a manner similar to the encoding of integrative information about an item and its surrounding context. If a deficit in forming integrative associations between item and context is to blame in older adults’ impaired recollection, then this deficit in forming associations should also be seen in paired-associate memory.

3.2              METHODS

 

 

3.2.1        Participants

 

 

Sixty-one older adults and 90 young adults participated in Experiment 2.  All of these people  also participated in Experiment 3. Of the 61 older adults and 90 young adults who participated  in Experiments 2 and 3, 37 of the older adults and 34 of the young adults were the same people who participated in Experiment 1. Experiment order was randomly assigned to avoid order effects.

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3.2.2        Stimuli

 

 

The study used standardized black and white photographs of faces (see Criss & Shiffrin, 2005, for standardization details) and abstract words (Ex: incident) of varying environmental frequency

(M=18.59, range=1-245, SD=24.32; Kucera & Francis, 1967) and low imageability (M=341.69, range=129-400, SD=43.13; Colthart, 1981). The set of words did not include any words that might describe a face, a person, or a characteristic of either.

3.2.3        Design

 

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The design of the study and test lists are illustrated in Table 3 in Appendix A. The conditions differ in the repetition both of individual items and pairs of items. Test pairs in the List 2 condition were composed of items that were seen in pairs on the second study list only. Test pairs in the Lists 1 & 2 Re-arranged condition consisted of items that were seen in pairs on both study lists, but whose pairings changed from one list to the other list. Test pairs in the Lists 1 &

2. Exact condition consisted of items that were seen on both study lists, in the same pair combination on each of the study lists. The other conditions (List 1 Exact and List 1&2 Re- arranged) were used as controls.

3.2.4        Procedure

 

 

The location and computer equipment were the same for this experiment as for Experiment 1. Participants received two study lists. The first study list contained 52 pairs of items and the second contained 60 pairs. On each trial of each list, participants performed an incidental task that involved rating each pair on the following question: “Are these items pleasant or unpleasant?” Items were presented until the participant responds or for a maximum of 5000 ms. Each study trial were separated by a 500 ms inter-stimulus interval (ISI). At the end of the first list, participants were reminded that they have just seen the first of two study lists. Participants were given a three minute break during which they completed a number search task and then

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advanced to the second study list, which was presented in the same manner as the first study list. Following the final study list, participants engaged in a 1 minute math task before being informed that they would take an unexpected memory test. Prior to the presentation of this 72 trial test list, participants were given examples of all the possible types of targets and lures and instructed to respond “yes” only if they have seen intact pairs from List 2 during the study session and to respond “no” to all other pairs.

3.2.5        Analytic technique

 

 

Standard signal detection measures of hits (“yes” responses to targets) and false alarms (“yes” responses to lures and/or distractors) were used in the analyses of data for this experiment (MacMillan & Creelman, 1991; Green & Swets, 1966). For some analyses the difference between hits and false alarms was used as a measure of discrimination between old and new items.

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3.3              RESULTS

 

 

The same exclusion procedure for outliers used in Experiment 1 was used in Experiment 2.  Older adults had slower reaction times than young adults for both correct (t(132)= -5.81, p<.001, Cohen’s d=1.05) and incorrect responses (t(132)= -2.90, p=.004, Cohen’s d=.52). Correct response mean RT for older adults was 2192 ms and mean RT for correct responses for young adults was 1730 ms. Mean RT for incorrect responses for older adults was 2165 ms and for young adults was 1922 ms.

A 4 (condition) by 2 (age-group) split-plot univariate analysis of variance (ANOVA) was performed for the young (n=84) and older adults (n=50), with condition as a within-subjects factor and age-group as a between subjects factor. For each of the four conditions, a measure of old/new discrimination was calculated by subtracting false alarms from hits. Figure 3 shows hits minus false alarms (i.e., old/new discrimination) in three conditions. In “Lists 1 & 2 Exact,”- a test pair was studied twice. In “Lists 1 & 2 Rearranged,” twice-studied items were studied only once in pair form (on the 2^nd list) and the individual items appeared once (on the 1^st list paired with other items). In “List 2 Only,”  the items/pair were studied once (only on List 2, only in  pair form). There was a small main effect of condition, F(2.97, 392.52)=6.39, p<.001, η²=.046, and a very small condition by age group interaction, F(2.97, 392.52)=4.37, p=.005, η²=.032, using the conservative Greenhouse-Geisser correction due to violation of the sphericity assumption (that the variance of the difference scores in a within-subjects design are equal across all the groups). There was also a main effect of age group, F(1,132)=45.06, p<.001, η²=.254.

The main effect of condition was driven by the young adults. In the paired sample t-tests the old/new discrimination differed between conditions (p<.01) for all comparisons except the comparison of conditions “Lists 1&2 Rearranged” and “List 2 Only”. Older adults did not have any condition effects which is the source of the condition by age group interaction. The nature  of the interaction can be seen in Figure 3. Young adults’ old/new discrimination was significantly improved in the Lists 1&2 Exact condition relative to the Lists 1&2 Rearranged and the List 2 Only conditions, whereas the older adults’ old/new discrimination did not differ across conditions and was overall worse than young adults. The improved performance of the young adults in the Lists 1&2 Exact condition represents a specific benefit of pair repetition. The lack

of benefit of pair repetition for the older adults suggests that they did not use associative information about pairs in their memory decisions.

Because some of the subjects in Experiment 2 did not participate in Experiment 1, a second analysis was performed excluding the people who did not participate in Experiment 1.  Of the people who participated in Experiment 2, there were 32 young and 32 older adults who participated in Experiment 1. There was a main effect of condition (F(2,124)=3.35, p=.038, η²=.051, but the condition by age group interaction was marginally significant (F(2,124)=2.98, p=.054, η²=.046. There was also a main effect of age group (F(1,62)=20.17, p<.001, η²=.245. Note that this effect size for age group in this analysis of only the subjects who participated in both Experiment 2 and Experiment 1 is equivalent to that in the larger group of all subjects who participated in Experiment 2 (η²=.254).

For this additional analysis, older adults had slower reaction times than young adults for both correct (t(62)= -4.97, p<.001, Cohen’s d=1.26) and incorrect responses (t(62)= -2.32, p=.024, Cohen’s d=.59). Correct response mean RT for older adults was 2354 ms and mean RT for correct responses for young adults was 1803 ms. Mean RT for incorrect responses for older adults was 2281 ms and for young adults was 1988 ms. Figure 3 shows the results for the more inclusive analysis, not for the second analysis detailed above.

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Lists 1 & 2 Exact Lists 1 & 2 Rearr List 2 Only

Condition

Figure 3. Old/new discrimination across three conditions for young and older adults. Error bars represent standard error of the mean.

 

 

 

 

3.4              DISCUSSION

 

 

According to the associative encoding theory of impairment, older adults are specifically impaired in the ability to form links between items and their contexts. Associative encoding might be critical to recollective-type memory because it enables the reconstruction of other information surrounding the item in the original episode, possibly in the form of extra features in the memory trace. Experiment 2 used pairs of words and faces to evaluate associative encoding. A recent study (Criss & Shiffrin, 2005) found that young people do use associative information in memory for pairs (not just individual item information), so if the age-related memory impairment is due to an inability to encode associative information between items and their

contexts, then this impairment should also be seen in the encoding of associations between multiple items (e.g., paired-associate memory). The young people benefited from repetition of pairs, over and above any benefit of item repetition, but older adults showed no such benefit. In addition, older adults were worse overall at pair memory. Both findings indicate a deficit for associative encoding.

4.0              EXPERIMENT 3

 

 

 

4.1              RATIONALE

 

 

Experiment 3 attempted to replicate the alleged controlled processing deficit in older adults using a traditional process-dissociation paradigm. The purpose of Experiment 3 is for use as a baseline for the other two experiments since the process-dissociation framework has been so frequently used and the controlled processing deficit is the most common explanation for older adult memory impairment.

The controlled process thought to contribute primarily to recollection consists of an active search through memory traces of previously studied items for comparison to each test item (as opposed to an automatic evaluation of the global familiarity of each test item; Yonelinas, 2002). Typically in experiments that use the process-dissociation procedure it has been found that older adults’ performance is based less on recollection than young adults’ performance, but that both groups rely equally on familiarity (Dywan & Jacoby, 1990; Jennings & Jacoby, 1997; Titov & Knight, 1997).

The experiment used a process-dissociation procedure in order to identify the separate contributions of the putative controlled and automatic processing mechanisms. If both types of mechanisms occur in normal memory function, then they should both contribute in a recognition memory task. The process-dissociation procedure enables the researcher to estimate the contributions of each by using two different memory tests that tap the processes in different

ways. A standard process-dissociation paradigm is to present two study lists to participants, one after another. During an inclusion test, participants are instructed to respond “yes” to any previously studied item, regardless of which study list it was on. In this case the controlled and automatic processes collaborate to produce a successful retrieval. During an exclusion test, participants are instructed to respond “yes” only to items from one of the study lists. In order to successfully complete the task, participants are required to reject familiar, recently studied items that did not appear on the target list. As a result, the automatic and controlled processes oppose one another and an index of recollection can be calculated by comparing data from the inclusion and exclusion tasks.

4.2              METHODS

 

 

4.2.1        Participants

 

 

Sixty-one older adults and 90 young adults participated in Experiment 3.  All of these people  also participated in Experiment 2. Of the 61 older adults and 90 young adults who participated  in Experiments 2 and 3, 37 of the older adults and 34 of the young adults were the same people who participated in Experiment 1. Experiment order was randomly assigned to avoid order effects.

4.2.2        Stimuli

 

 

The study used the same database of abstract words detailed in Experiment 2, but none of the words were duplicates of those used in Experiment 2.

4.2.3        Design

 

 

Ninety-six abstract words were divided into four lists of 24 words. Two of the lists were randomly chosen to be study lists and the items on the other two lists were used as distractors during the test tasks. Every word on the two lists presented at study was a target word. All the target words were presented at test, but half were presented in the inclusion task and the other half in the exclusion task. The inclusion and exclusion tasks contained distractor words: thus, both the inclusion and exclusion tests consisted of 24 studied words (12 targets from each study list) and 24 new words (distractors).

4.2.4        Procedure

 

 

The location and computer equipment were the same for this experiment as for Experiments 1 &

2. Participants received two study lists and they were asked to complete an incidental encoding task that involves a pleasantness rating. Items were presented until the participants responded or for a maximum of 5000 ms, with a 500 ms inter-stimulus interval (ISI). At the end of the first list, participants were reminded that they had just seen the first of two study lists. Participants were given a three minute break during which they completed a number search task and then advanced to the second study list, which were presented in the same manner as the first study  list. Following the final study list, participants engaged in a 1 minute math task before being informed that they were taking an unexpected memory test. The participant received either an inclusion or an exclusion memory test. Before taking the test, participants were given verbal instructions and were also able to read them on the computer screen. In the inclusion test, participants were asked to respond “yes” if they have seen the word during the study session and

“no” if the word is new. The exclusion task instructions were identical except that participants were asked to respond “yes” only to words from a specific study list rather than all words from the study session and to respond “no” if a word is from the non-specified list or is a new word. Presentation of the study lists, and assignment of study lists to inclusion or exclusion task were counterbalanced.

4.2.5        Analytic technique

 

 

“Yes” responses to old items (List 1) in the exclusion task are false alarms and are assumed to result from dependence of only familiarity, not recollection (F only, no R) because using recollection would result in a correct rejection, whereas “yes” responses to List 1 items in the inclusion task are correct responses and are assumed to result from the contribution of either recollection or familiarity or both ((F+R)-(F*R)). The probability of R can be obtained by subtracting the probability of F only (exclusion “yes” responses) from the total probability of F or R (inclusion “yes” responses). Once the probability of R is derived, it can be used to calculate the value for F. “Yes” responses to List 1 items in the exclusion task reflect F only without R, thus false alarms = F-F*R. Solving the equation for F results in FA/(1-R) and R is already  known from the previous calculation.

4.3              RESULTS

 

 

The same exclusion procedure for outliers used in Experiment 1 was used in Experiment 2.  Older adults had significantly slower reaction times for correct responses than young adults

(t(129)= -8.15, p<.001, Cohen’s d=1.48). Correct response mean RT for older adults was 1316 ms and mean RT for correct responses for young adults was 996 ms.

Jacoby’s process-dissociation procedure (1991) was used to create values of R (recollection) and F (familiarity) for each subject. The parameter for R was computed by subtracting proportion of “yes” responses to List 1 items in the exclusion task from proportion of “yes” responses to items in the inclusion task. The parameter F was computed by dividing the proportion of “yes” responses in the exclusion task by 1-R. This was done for each subject. In Figure 4, recollection (R) and familiarity (F) parameters were derived by comparing the  inclusion and exclusion tasks. There was a main effect of age; young people had significantly higher values on both recollection and familiarity than older adults. There was also a main effect of memory type, the familiarity parameter value was greater than the recollection parameter value for both groups. Surprisingly, however, the expected interaction of age and memory type was not seen. A 2 (memory parameter) X 2 (age group) univariate split-plot ANOVA was performed for the young (n=80) and older (n=50) adults, with memory parameter as the within- subjects factor and age group as the between-subjects factor.

There was a main effect of memory parameter F(1,128)=388.07, p<.001, η²=.752 and a main effect of age group F(1,128)=96.20, p<.001, η²=.429 but the interaction was not significant, F(1,128)=2.17, p=.143, η²=.017. The familiarity parameter was larger than the recollection parameter, for both age groups. Older adults had significantly smaller memory parameters overall, but were not specifically impaired on recollection compared to young adults.

Because some of the subjects in Experiment 3 did not participate in Experiment 1, another analysis was performed excluding the people who did not participate in Experiment 1. Of the people who participated in Experiment 3, there were 31 young and 33 older adults who

participated in Experiment 1. The results were the same, no interaction was present F(1,61)=.002, p=.969, η²<.0001 but there were main effects of memory parameter F(1,61)=263.2, p<.001, η²=.812 and age group F(1,61)=, p<.001, η²=.337. Note that the effect size for the age group parameter is similar for this smaller group that participated in both Experiment 3 and Experiment 1 (η²=.337) and for the larger group of all Experiment 3 participants (η²=.429), regardless of whether they participated in Experiment 1.

In this subset, older adults had significantly slower reaction times for correct responses than young adults (t(61)= -5.30, p<.001, Cohen’s d=1.36). Correct response mean RT for older adults was 1333 ms and mean RT for correct responses for young adults was 1004 ms. For the inclusion task, some subjects did not have enough incorrect responses to compute reliable median RT so the RT for each subject was the average of median RT only for correct responses across the two conditions.

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Figure 4. Recollection and familiarity parameters for young and older adults. Error bars represent

standard error of the mean.

4.4              DISCUSSION

 

 

The most commonly accepted explanation for the episodic impairment in healthy older adults  has been put forth by Jacoby (1991). His hypothesis is that aging decreases controlled  processing ability, that is, the ability to do tasks that require the allocation of attentional resources. According to this view, recollective memory requires controlled processing whereas familiarity is supported by automatic processes that do not require attentional control. This hypothesis has been researched extensively by others often making use of an experimental  design called the process-dissociation procedure (Jacoby, 1998) which teases out the respective contributions of recollection and familiarity to memory performance.

If the age-related memory impairment is due to degradation of attentional functions that support strategic memory search, then there should be larger differences between old and young adults for tasks that rely on recollection compared to tasks that rely on familiarity. Here, controlled processing was not specifically tested, but the process-dissociation procedure was used to provide a baseline for age-related differences among the current participant sample by which to judge the results of the other experiments.

In the process-dissociation paradigm there are two types of tests. In the inclusion test, the participants must say “yes” to items from either study list and it is believed that recollection and familiarity are working together in this task (Jacoby, 1991; Jacoby, 1998; Hay & Jacoby, 1999). In the exclusion test, the participants must say “yes” only to items from the second study list and it is believed that recollection and familiarity are working against each other in this task. Therefore, incorrectly including List 1 items in the exclusion task is evidence of the reliance on familiarity instead of recollection because recollection is an all-or-none process.

The difference between older and young adults for recollection was not significantly bigger than the difference between older and young adults for familiarity. This finding is inconsistent with several previous findings in studies which used the same process-dissociation procedure (Hay & Jacoby, 1999; Jennings & Jacoby, 1993; Jennings & Jacoby, 1997). When using the process-dissociation procedure to separate the relative contributions of recollection and familiarity, older adults have shown greater impairment in recollection than for familiarity compared to young adults. Those studies differed in regard to the modality of each list the and more notably the instructions given to the participants for the study session. In one of the studies (Jennings & Jacoby, 1993; Exp. 2) items were given to the participants as text on one list and verbally on the other list. That is, the lists differed on perceptual details, while the current study had the same delivery modality (text presentation) for both lists. In all the previous studies the older adults were told to read the words aloud in the study sessions. Auditory perceptual processing may be more impaired than visual perceptual processing which would explain why other studies showed a supposed “recollection-specific” deficit but the current study did not.   The current study also had a larger group of older adults than most previous studies and a more representative sample of older adults than most previous studies. Therefore, the lack of recollection-specific deficit in the current study casts some doubt upon Jacoby’s assumption that memory processes are neatly divided into recollection and familiarity components and that recollection is impaired while familiarity is spared.

5.0 CORRELATIONAL ANALYSIS OF BEHAVIORAL EXPERIMENTS

 

 

 

Many of the same participants participated in all three behavioral experiments. Correlational analyses were conducted to determine if there were patterns of performance across the experiments. Reaction times were highly correlated across all three experiments for both older and young adults (see Table 1). The proportion of correct responses was significantly correlated for Experiments 1 & 3 for older adults (R=.555, p<.001) and marginally correlated for Experiments 1 & 2 (R=.331, p-.069) and for Experiments 2 & 3 (R=.259, p=.075). The proportion of correct responses was significantly correlated for Experiments 1 & 3 (R=.511, p=.006) and for Experiments 2 & 3 (R=.292, p=.009) and marginally correlated for Experiments 1 & 2 (R=.344, p=.073). Thus, based on correct responses and reaction times, individuals’ performance was quite consistent across the three experiments. An additional analysis compared the magnitudes of the age-related effects across experiments to determine whether the hypothesized age effects in each task were associated with the same underlying mechanisms. Significant correlations would suggest that similar cognitive processes were being measured in each experiment.

The measures used to represent the specific age-related impairment in each experiment were based on the predictions of each experiment. For Experiment 1, the difference in old/new discrimination (hits-lure false alarms) between pictures and words was used as a measure of age- related impairment (perceptual processing impairment). Age-related impairment should

correspond to a greater difference in discrimination between pictures and words. For Experiment 2, the level of old/new discrimination (hits-false alarms) in the “List 1 & 2 Exact” condition represented the ability of older adults to use associative information. Age-related impairment should correspond to worse discrimination in this task. For Experiment 3, discrimination in the “exclusion” task was used (hits-false alarms to List 1 items). Age-related impairment should correspond to worse discrimination in this task. Only Experiments 1 and 2 were significantly correlated and only for young adults (R=-.669, p<.001). The negative correlation indicates that a greater benefit in the picture lure condition in Experiment 1 was related to worse pair memory in the “List 1 & 2 Exact” condition in Experiment 2.

The lack of correlation of performance on Experiment 3 with Experiments 1 & 2 is consistent with the finding that there was no specific age-related impairment and with the conclusion that the process-dissociation procedure is not the best method for detecting age- related memory impairments. The lack of correlation between Experiments 1 & 2 suggests that the specific age-related impairments may not have the same underlying causes. The perceptual impairment hypothesis and the associative encoding impairment hypothesis might represent two separate and independent age-related memory impairments. However, it is impossible to draw strong conclusions from the lack of correlation because this lack of correlation might simply reflect the noisiness of the data.

Table 1. Reaction time correlations across Experiments 1, 2, & 3 for older and young adults.

 

Group	Experiments	N	Correlation	Significance
	Exp. 1, 2	31	R = .567	p = .001
Old	Exp. 1, 3	31	R = .530	p = .002
	Exp. 2, 3	48	R = .508	p < .001
	Exp. 1, 2	28	R = .571	p = .002
Young	Exp. 1, 3	27	R = .407	p = .035
	Exp. 2, 3	78	R = .554	p < .001

 

 

 

 

 

6.0              EXPERIMENT 4

 

 

 

6.1              RATIONALE

 

 

Experiment 1 found that older adults had difficulty using perceptual details to distinguish lures from targets, and that this difficulty affected words more than pictures. If there are behavioral differences between older adults and young adults and if cognitive processes are supported by neural processes, then it stands to reason that electrophysiological differences between age groups should also exist for this task. Specifically, there should be differences between age groups in the topography and amplitude of waveforms associated with memory, such as the old/new left parietal effect (Curran & Cleary, 2003; Curran, 2000; Henson, et al., 1999) and the slow-wave late positivity (Ruchkin, et al., 2003). Therefore, the interesting results from Experiment 1 were further supplemented and extended by an event-related potential (ERP) experiment that used the same stimuli and similar experimental paradigm.

6.2              METHODS

 

 

6.2.1        Participants

 

 

Seventeen healthy older adults were recruited from a healthy older adult participant database at the University of Pittsburgh and received $15.00 for participation. The healthy older adults were

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