Neuropsychology 1999, Vol. 13, No. 4, 467-474
Copyright 1999 by the American Psychological Association, Inc. 0894-4105/99/S3.00
Source Memory and Divided Attention: Reciprocal Costs to Primary and Secondary Tasks Angela K. Troyer
Gordon Winocur
Rotman Research Institute of Baycrest Centre for Geriatric Care, University of Toronto
Rotman Research Institute of Baycrest Centre for Geriatric Care, University of Toronto, and Trent University
Fergus I. M. Craik
Morris Moscovitch
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Rotman Research Institute of Baycrest Centre for Geriatric Care, University of Toronto
Rotman Research Institute of Baycrest Centre for Geriatric Care, University of Toronto, Erindale College, and Baycrest Centre for Geriatric Care
Source memory, in comparison with item memory, is more sensitive to frontal lesions and may require more strategic processing. Divided attention was used to restrict attentional resources and strategic processing on memory tasks. Participants encoded and retrieved items (i.e., words) and source (i.e., voice or spatial location) while concurrently performing a fingertapping (FT) or visual reaction-time (VRT) task. Memory accuracy costs under divided attention were greater for retrieval of source than item and were greater with VRT than FT. Similarly, costs to the secondary task were greater when concurrently retrieving source as opposed to item and were greater for VRT than FT. Effects were stronger when spatial location was used as the source task. Findings support the idea that processing source information requires more attentional resources and effort than processing item information. Furthermore, concurrent performance of VRT produced greater interference with a task that was more dependent on intact frontal functioning and better simulated the performance of patients with frontal dysfunction.
Dissociations have been obtained between memory for items (e.g., words, facts, or pictures) and memory for the source or context in which the items occurred (e.g., voice, spatial location, color, or temporal order). For example, patients with lesions to the frontal lobes of the brain are less impaired on item memory tasks than on source memory tasks (e.g., Janowsky, Shimamura, & Squire, 1989; Schacter, 1987; Squire, 1982). Similarly, among healthy older adults—a population with neuron loss and atrophy in the frontal lobes (Bondareff, 1985)—there are smaller age differences for
item memory than for source memory (e.g., Kausler, Salthouse, & Saults, 1988; Mclntyre & Craik, 1987; Spencer & Raz, 1995; Troyer & Craik, 1997). These dissociations indicate that memory for source is more strongly related to intact frontal lobe functioning than memory for items. Dissociations between item and source memory among brain-injured patients and healthy older adults reflect the different processing requirements of these memory tasks. For example, item memory and source memory tasks differ in the degree to which effortful processes are required. According to Hasher and Zacks (1979), effortful memory processes, such as strategic elaboration and rehearsal, require considerable attentional resources and are performed intentionally. An analysis of the different requirements for remembering item and source suggests that source is not necessarily encoded completely and concurrently with the item; thus, strategic and effortful processes must be used during encoding and retrieval of source information to connect it to item information. Encoding and retrieving source information, therefore, may be relatively more effortful, and encoding and retrieving item information may be relatively more automatic. Indeed, recalling source information is considered to be a working-with-memory task that requires considerable effort and strategy (Moscovitch & Winocur, 1992). It is clear, however, that not all source memory tasks are the same. Some aspects of source information are intrinsic to the items, such as voice or color; this type of source information has been labeled associative (Moscovitch, 1992) or stimulus bound (Spencer & Raz, 1995). Associative
Angela K. Troyer and Fergus I. M. Craik, Rotman Research Institute of Baycrest Centre for Geriatric Care, University of Toronto, Toronto, Ontario, Canada. Gordon Winocur, Rotman Research Institute of Baycrest Centre for Geriatric Care, University of Toronto, and Department of Psychology, Trent University. Morris Moscovitch, Rotman Research Institute of Baycrest Centre for Geriatric Care, University of Toronto; Department of Psychology, Erindale College, Mississauga, Ontario, Canada; and Department of Psychology, Baycrest Centre for Geriatric Care, Toronto, Ontario, Canada. This research was supported by Medical Research Council of Canada Grant MT 6694 and by Natural Sciences and Engineering Research Council of Canada Grant 8261-98RGPIN. Angela K. Troyer was supported in part by the Ben and Hilda Katz Postdoctoral Fellowship. We thank Heidi Roesler for her assistance with data collection. Correspondence concerning this article should be addressed to Angela K. Troyer, who is now at Department of Psychology, Baycrest Centre for Geriatric Care, 3560 Bathurst Street, Toronto, Ontario, Canada M6A 2E1. Electronic mail may be sent to
[email protected].
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source information is bound to, and thus more directly connected with, the item itself. This type of source information may be encoded strongly because it is encoded concurrently with the item information. A similar pattern of performance is obtained for item memory and associative source memory, most likely because of the close link between associative source information and item information. For example, in a large meta-analysis, the magnitude of age differences in associative source memory were small and were equivalent to age differences in item memory (Spencer & Raz, 1995). In contrast, other aspects of source are not intrinsic to the items, such as spatial location or temporal order; this type of source information has been labeled organizational (Moscovitch, 1992) or spatial temporal (Spencer & Raz, 1995). Organizational source information is not as closely bound to the items. It is not as strongly encoded because location and order are outside of the items themselves; thus, more effort is required to link such source information with the item. Clear distinctions between item memory and organizational source memory have been obtained. A meta-analysis indicated that the magnitude of age differences in organizational source memory is larger than that of item memory (Spencer & Raz, 1995). Given the predominance of frontal lobe changes in the aging population, this pattern of age differences suggests that memory for associative context may be less dependent on frontal functioning than memory for organizational context. Divided attention (DA) paradigms have been used to model frontal lobe dysfunction. When required to perform a concurrent, interfering task, young healthy adults produce patterns of performance that are similar to those of patients with frontal dysfunction. For example, young adults under conditions of DA, in comparison with conditions of full attention, made more perseverative errors on the Wisconsin Card Sorting Test (Dunbar & Sussman, 1995), had difficulty inhibiting reflexive eye saccades (Roberts, Hager, & Heron, 1994), failed to release from proactive inhibition (Moscovitch, 1994), and performed more poorly on fluency tests sensitive to frontal dysfunction (Moscovitch, 1994; Troyer, Moscovitch, & Winocur, 1997). Concurrent performance of a secondary task appears to have its greatest effect on primary tasks that are more dependent on frontal lobe related abilities. For example, context memory, in comparison with item memory, is thought to be more dependent on frontal lobe functioning and is also impaired to a greater extent by DA (Troyer & Craik, 1997). There is some evidence that secondary tasks differ in the degree to which they interfere with the primary task. A visual reaction-time (VRT) task in which the stimuli were unpredictable produced greater interference on a memory task than a similar VRT task in which the stimuli were predictable (Fletcher, Shallice, & Dolan, 1998). There may also be an interaction between the primary and secondary tasks. The unpredictable VRT task had its greatest effects on an unorganized word list, whereas the predictable VRT task had equal effects on an organized and unorganized word list (Fletcher et al., 1998). The greatest interference appears to occur when the primary and secondary tasks involve similar processes or rely on similar brain regions. For example, in a
study of verbal fluency performance, a sequential-motor finger-tapping task had its greatest effects on performance on a phonemic fluency task (both of which are thought to rely most heavily on frontal lobe functioning), whereas an object-decision task had its greatest effects on a semantic fluency task (both of which are thought to rely most heavily on temporal lobe functioning; Martin, Wiggs, Lalond, & Mack, 1994). Thus, the specific characteristics of the secondary task determine the extent to which it interferes with the primary task. In addition to the effects of DA on the primary task, the primary task may also influence the secondary, interfering task. For example, reaction times on a VRT secondary task were faster when the secondary task was performed alone than when performed during encoding on a memory task, and reaction times were faster during encoding than during retrieval (e.g., Craik, Govoni, Naveh-Benjamin, & Anderson, 1996; Johnston, Griffith, & Wagstaff, 1972). These effects are interpreted as reflecting the degree to which the primary task requires attentional resources (e.g., Johnston et al., 1972). That is, primary tasks requiring more attention are especially detrimental to performance on the secondary task.
Rationale and Hypotheses Secondary tasks may differ in the degree to which they demand attentional resources and rely on frontal lobe functioning. We examined the reciprocal effects of two memory tasks (one of which is more dependent on frontal functioning than the other) and two secondary tasks (both dependent to some degree on frontal functioning). The two memory tasks used in the present study were item memory, which is relatively less dependent on frontal functioning, and source memory, which is relatively more dependent on frontal functioning, as previously reviewed. Two types of source tasks were used. In Experiment 1, we used a source task that was primarily associative in nature (i.e., voice) and may be less dependent on frontal functioning; in Experiment 2, we used a source task that was primarily organizational (i.e., spatial location) and may be more dependent on frontal functioning (Moscovitch, 1992; Spencer & Raz, 1995). The two secondary tasks were a sequential-motor fingertapping task (FT; Moscovitch, 1994) and a four-choice VRT task (Craik et al., 1996). The FT task required the participant to press keys continuously on a keyboard in a fixed and predictable order using the four fingers of the right hand. This task involves several activities that are mediated at least in part by the frontal lobes, including motor sequencing (Stuss, Eskes, & Foster, 1994), internal pacing of finger responses (Gerloff et al., 1998), and sustained attention (Stuss et al., 1994; Stuss, Shallice, Alexander, & Picton, 1995). The VRT task required the participant to monitor continuously four horizontally aligned stimuli and, as the stimuli were randomly highlighted, to press the corresponding key with one of the four fingers of the right hand. The frontal lobe related activities required by this task include stimulus-response matching (Petrides, 1985; Winocur, 1992), conscious and effortful control of responses (Moscovitch, 1992), and sustained attention (Stuss et al., 1994, 1995). Direct evidence of the frontal lobe involvement in this task
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SOURCE MEMORY AND DIVIDED ATTENTION
has been provided by a positron emission tomography study. The left prefrontal cortex was preferentially activated during performance of the VRT task (Fletcher et al., 1998). We made several predictions regarding patterns of memory and secondary task performance. We expected to find that (a) there would be greater costs to source memory than to item memory associated with concurrent performance of the secondary task and (b) costs to the secondary task would be greater during concurrent performance of the source memory task than by concurrent performance of the item memory task. Within source memory, we expected greater costs to memory for spatial location than to memory for voice and similarly greater costs to the secondary task when performed concurrently with the spatial-location source task rather than the voice source task.
Experiment 1 Method Participants. Twenty-nine undergraduate students at the University of Toronto participated for extra credit in a psychology course. Five additional participants were unable to perform one of the memory tasks above chance level under full attention and were not included in the final sample. Ages ranged from 18 to 30 years, with a mean age of 21.5 years (SD = 3.1). The mean level of education was 13.3 years (SD = 1.6), and the male-to-female ratio was 11:18. All participants were right handed and proficient in English. Potential participants who were skilled at playing a musical instrument requiring rapid finger movement were excluded from the study because of the possibility that such skill would decrease the difficulty of the FT task. General procedures. Memory for items (i.e., words) and memory for source (i.e., voice) were each tested under three conditions: full attention (FA), divided attention using the fingertapping task (DA-FT), and divided attention using the visual reaction-time task (DA-VRT). For each of these attention conditions, a word list was presented, and participants were asked to learn both the words and the voice in which each word was presented. After list presentation, item and source memory were tested separately by presenting a yes-no recognition test for items and a two-alternative (i.e., male or female) forced-choice recognition test for voice. During the DA trials, the secondary task was performed both at list presentation and at test. We told participants that the memory and secondary tasks were equally important and that they should put equal effort into both. Participants were given practice with each of the tasks before proceeding with the experimental trials. That is, practice was provided for each of the secondary tasks alone, for the memory task alone, and for a memory task concurrent with each secondary task. In addition, to establish baseline task performance, participants performed each of the secondary tasks alone for 75 s, either before or after completion of the experimental trials. Memory tasks. Three presentation lists were created, one for each attention condition (e.g., FA, DA-FT, and DA-VRT), using two-syllable nouns from Thorndike and Lorge (1944). Each list consisted of 48 words, and the mean word frequency was equivalent on each list. We presented the lists on audiocassette tape at the rate of 2 s per word. The first 24 words were presented in a female voice and the second 24 words were presented in a male voice. We gave participants general instructions to learn the words and the voice but provided no specific encoding instructions. For each of the three presentation lists, two 24-word test lists were created. One test list was used for testing item memory, and
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one was used for testing source memory. All test lists were read aloud by a third (female) voice. To minimize primacy and recency effects, the first 2 words and last 2 words from each presentation list were not included on the test lists. To test item memory, a yes-no recognition paradigm was used in which words were read one at a time, and participants indicated whether each word was on the presentation list. Six of the test words were originally presented in a female voice, 6 words were originally presented in a male voice, and 12 words were distractors that were not previously presented on either list. Participants were allowed 3 s to respond to each item. To correct for guessing, item memory was scored as hit rate minus false alarm rate. To test source memory, a different test list was read to the participant. Twelve of the test words were originally presented by a female voice and 12 words were originally presented by a male voice. A two-alternative forced-choice recognition paradigm was used, in which participants indicated whether each word was originally presented by a male or female voice. We allowed participants 3 s for each response. Similar to item memory, source memory was scored as hit rate minus false alarm rate (for female-voice items and responses). Secondary tasks. The two secondary tasks were programmed in Micro Experimental Laboratory (Version 2.0; Schneider, 1995) and performed on a computer. For each task, participants placed the four fingers of the right hand on the "g," "h," "j," and "k" keys of the keyboard. For the FT task, participants were asked to tap continuously the fingers of the right hand in the following order: index, ring, middle, pinkie. Participants were instructed to proceed as quickly and as accurately as possible. The sequence and timing of each tap were internally generated; no visual stimuli were present to guide these responses. Accuracy rate and intertap intervals were recorded by the computer. For the VRT task, a grid of four horizontally aligned boxes was shown on the computer screen. On each trial, one of the squares was highlighted, and the participant was asked to press the corresponding key (i.e., the first, second, third, or fourth) with the corresponding finger (i.e., index, middle, ring, or pinkie, respectively) as quickly and as accurately as possible. Performance was continuous, with each trial beginning immediately after the key press of the preceding trial. Accuracy rate and reaction times were recorded by the computer. Previous experience with these secondary tasks indicated that participants' hands can become fatigued when performing the tasks for extended periods of time. To minimize such fatigue, 30-s rest periods were provided several times throughout each memory task, including halfway through the presentation list, between the presentation list and the first test list, and between the two test lists. During the rest period, participants discontinued any memory or secondary task and, to prevent subvocal rehearsal of memory items, counted backward by 3 or 7 from a specified number. Counterbalancing. Two formats of the presentation word lists (A and B) were created, with the same words rearranged onto different lists and presented by different voices. Two formats of the test lists (A and B) were created, with the words that were used to test item and source exchanged. The use of Presentation List A or B and Test List A or B was counterbalanced across participants. Additionally, the order in which attention conditions were used (FA, DA-FT, DA-VRT), the word lists used for each condition (Lists 1,2, or 3), the order of test trials (item or source first), and the timing of baseline secondary task administration (before or after the experimental memory trials) were counterbalanced across participants.
Results and Discussion Memory tasks. Raw scores on the item and source tasks are presented in Table 1. Because performance under FA
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Table 2 Raw Speed Scores (in Milliseconds) on the Secondary Task
Table 1 Raw Accuracy Scores on the Memory Task Item
Source
Item
FT
Source
VRT
FT
VRT
Condition
M
SD
M
SD
M
SD
M
SD
Condition
M
SD
M
SD
M
SD
M
SD
FA DA-FT DA-VRT
.70 .53 .45
.22 .23 .30
.55 .34 .24
.25 .30 .32
.12 .54 .51
.19 .26 .20
.51 .26 .17
.22 .25 .23
Baseline Item Source
286 326 328
67 76 81
480 584 617
82 113 127
269 314 336
56 78 84
460 578 670
67 135 194
Note. FA = full attention; DA-FT = divided attention using the finger-tapping task; DA-VRT = divided attention using the visual reaction-time task.
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Experiment 2
Experiment 1
Experiment 2
Experiment 1
showed different base rates for item and source (i.e., .70 and .55), DA performance was converted to a proportion change score for each participant with the formula: 1 - DA/FA. Larger scores, therefore, indicate a greater cost to the memory task associated with secondary task performance. These response cost data are shown in Figure 1. All subsequent analyses, including analyses of memory and secondary tasks, were on response cost data. We performed a 2 (memory task: item and source) X 2 (DA condition: FT and VRT) repeated measures analysis of variance (ANOVA). The main effect of memory task was significant, F(l, 28) = 6.63, p = .016, indicating a greater DA cost to source memory than item memory, consistent with our predictions. There was no main effect of DA condition, F( 1, 28) = 1.69, p = .204, indicating that costs to the memory task were similar when performed during FT and VRT. The interaction was not significant, F( 1, 23) < 1. Secondary tasks. Accuracy rates on the secondary tasks were generally high (i.e., .92 to .97) with low variability between conditions. Raw speed scores on the FT and VRT secondary tasks are shown in Table 2. Because of baseline differences in secondary task performance (i.e., 286 and 480 ms), DA performance was converted to a proportion change score from baseline for each participant using the formula: (DA - Baseline)/Baseline. Larger scores, therefore, indicate a greater cost to the secondary task associated with concurrent performance of the memory task. These response cost data are shown in Figure 2.
Note.
FT = finger-tapping task; VRT = visual reaction-time task.
We analyzed performance on the secondary tasks in a 2 (secondary task: FT and VRT) X 2 (memory task: item and source) repeated measures ANOVA. There was a significant main effect of secondary task, F(l, 28) = 7.16, p = .012, with a greater cost to VRT speed than FT speed. There was no main effect of memory task on secondary task costs, F(\, 28) = 1.29, p = .266. The interaction, however, was significant, F(l, 28) = 5.89, p = .022, indicating a greater cost to the VRT task when performed during source retrieval than during item retrieval and indicating no such pattern for the FT task. Taken together, these results suggest several differences between item and source memory in the degree to which they are demanding of attentional resources. When we examined costs to the memory tasks, DA was associated with greater costs to source memory than item memory. When we examined costs to the secondary tasks, there was no overall difference in cost to the secondary tasks when performed concurrently with an item or source memory task. However, a significant interaction between source memory task and secondary task cost indicated greater costs to the VRT task when performed concurrently with a source memory rather than an item memory task and indicated no such pattern for the FT task. In Experiment 1, our source memory task involved recalling the voice in which the items were presented. This source task is primarily associative in nature, as voice is intrinsically bound to the item itself. There was an organizational component to this task as well, as voice (i.e., male or Experiment 1: Secondary-task costs
Experiment 1: Memory-task costs
VRT
VRT Secondary task
Secondary task
Figure I. Bars show the standard error of the mean. FT = finger tapping; VRT = visual reaction time.
Figure 2. Response costs to secondary tasks. Bars show the standard error of the mean. FT = finger tapping; VRT = visual reaction time.
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SOURCE MEMORY AND DIVIDED ATTENTION
female) and list inclusion (i.e., first or second presentation list) overlapped. Thus, this task could be accomplished by relying either on associative or organizational information. As previously discussed, associative source memory tasks do not always show reliably different performance patterns from item memory tasks. Thus, it is perhaps not surprising that we did not obtain consistent differences between our item and source tasks. To increase the differences between the item and source tasks, in Experiment 2, we used a source task that could be accomplished only by relying on organizational source information (i.e., the spatial location of items). As previously discussed, organizational source in comparison with associative source may be more dependent on the functioning of the frontal lobes. Among healthy older adults, a population in which changes in the frontal lobes are predominant, there are greater age differences in memory for organizational than associative source (Spencer & Raz, 1995).
Experiment 2 Method Participants. Twenty-four undergraduate students at the University of Toronto participated for extra credit in their psychology course. Five additional participants were unable to perform one of the memory tasks above chance level under full attention and were not included in the final sample. Age ranged from 19 to 24 years, with a mean age of 21.0 years (SD = 1.5). The mean level of education was 14.6 years (SD = 0.9), and the male-to-female ratio was 11:13. As in Experiment 1, all participants were right handed, proficient in English, and not skilled at playing any musical instrument that required rapid finger movement. Procedures. Word lists from Experiment 1 were used. All words were recorded in a female voice. Word lists were presented to the participant through stereo headphones, with each word presented only to the left or the right ear. On each list, half of the words were presented to the left ear and half of the words were presented to the right ear in a pseudorandom order (i.e., no more than 3 words in a row were presented to the same ear). Item memory was tested as in Experiment 1. To test source, a list of words was read by a second female voice, and participants indicated whether each word was originally presented to the left or right ear. The remaining procedures were identical to those of Experiment 1.
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Experiment 2: Memory-task costs
FT
VRT
Secondary task Figure 3. Response costs to memory task with spatial location as source. Bars show the standard error of the mean. FT = finger tapping; VRT = visual reaction time.
.111, indicating equivalent costs to memory when performed with either secondary task. The interaction approached significance, F(l, 23) < 3.63,p = .069, indicating a possibly greater difference between source costs and item costs during VRT performance than during FT performance. To examine the effect on memory performance of using voice (in Experiment 1) versus spatial location (in Experiment 2) as the source memory task, we performed a 2 (source task) X 2 (memory task) X 2 (DA condition) ANOVA. There was no main effect of source task (F < 1). None of the interactions involving the source task variable were significant. Secondary tasks. Accuracy rates on the secondary tasks were generally high (i.e., .94 to .98), with low variability between conditions. Raw speed scores are presented in Table 2, and task costs are shown in Figure 4. We analyzed performance on the secondary tasks in a 2 (secondary task) X 2 (memory task) repeated measures ANOVA. There was a significant main effect of memory task, F(l, 23) = 38.89, p < .001, indicating a greater secondary task cost when performed concurrently with source retrieval than with item retrieval. There was a significant main effect of Experiment 2: Secondary-task costs
Results and Discussion Memory tasks. Raw scores are presented in Table 1. As in Experiment 1, raw scores were converted to proportion change scores to examine response costs. These data are shown in Figure 3. All subsequent analyses, including analyses of memory and secondary tasks, were on response cost data. We performed a 2 (memory task: item and source) X 2 (DA condition: FT and VRT) repeated measures ANOVA. The main effect of memory task was significant, F(l, 23) = 12.50, p = .002, indicating a greater cost to source memory than to item memory, consistent with our prediction. There was no main effect of DA condition, F(l, 23) = 2.75, p =
FT
VRT
Secondary task Figure 4. Response costs to secondary tasks. Bars show the standard error of the mean. FT = finger tapping; VRT = visual reaction time.
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secondary task, F(l, 23) = 13.05, p = .001, with an overall greater cost to VRT speed than FT speed. In addition, the interaction was significant, F(l, 23) = 10.85, p = .003, indicating a greater item-source cost difference on VRT than on FT. To examine the effect on secondary task performance of using voice versus spatial location as the source memory task, we performed an additional ANOVA. There was no main effect of source task on overall secondary task cost, F(l, 52) = 2.21, p = .144. The interaction between source task and secondary task was not significant (F < I). However, the interaction between memory task and source task was significant, F(l, 52) = 6.23, p = .016, indicating that the greater secondary task cost associated with concurrent performance of a source versus item task is accentuated with a spatial location source task. The three-way interaction was not significant.
General Discussion Greater costs to source retrieval, in comparison with item retrieval, were associated with concurrent performance of a secondary task. Similarly, greater costs to the secondary tasks were associated with concurrent performance of the source task in comparison with the item task. These findings suggest that source retrieval requires greater attentional resources and thus arguably greater amounts of strategic processing than item retrieval. This is consistent with findings that source retrieval is more sensitive to frontal lobe dysfunction than item retrieval (e.g., Schacter, 1987; Squire, 1982). Source retrieval draws more heavily on frontal lobe resources (e.g., strategic retrieval) and is thus disrupted to a greater extent when these resources are reduced under conditions of divided attention. This pattern of costs was moderated by the source task used. In general, fewer cost differences were obtained when using a source task that was primarily associative in nature (i.e., voice in Experiment 1) than when using a source task that was primarily organizational (i.e., spatial location in Experiment 2). For example, a direct comparison indicated that the cost to the secondary task was smaller when concurrently performed with an associative rather than an organizational source memory task. Relative difficulty of the two source tasks does not explain the pattern of costs obtained because accuracy rates on the source tasks under FA were similar in Experiments 1 and 2 (i.e., .55 and .51). Rather, this pattern is consistent with the idea that associative source tasks share some similarity with item tasks (e.g., Spencer & Raz, 1995) and require less strategic processing than organizational source tasks. This pattern was also moderated by the secondary task used. Although concurrent performance of either secondary task was associated with costs to the memory task, this effect was generally greater with VRT than FT. Furthermore, VRT was associated with greater costs specifically to source versus item memory. There are several differences between FT and VRT that may explain these patterns, including
difficulty level, information-processing requirements, and dependence on frontal lobe related strategic abilities. First, regarding level of difficulty, VRT was more difficult than FT, as shown by a slower speed of performance under FA. As well, source retrieval was more difficult than item retrieval, as shown by decreased accuracy rates under FA. Thus, the interaction between memory and secondary tasks may reflect a greater amount of interference related to the performance of more difficult tasks. The information-processing requirements of the FT and VRT tasks differ, and this may provide a second explanation of the differential effects of the secondary tasks on item and source memory. VRT is a more difficult task that likely requires more attentional or processing resources than FT. In other words, VRT requires more conscious effort for success than FT. Additionally, as previously discussed, processing source information is a more effortful task than processing item information. Effortful processes require considerable attentional resources and tend to interfere with other effortful tasks (Hasher & Zacks, 1979). Thus, one would expect source memory (the more effortful memory task) to be interrupted to the greatest extent by VRT (the more effortful secondary task). A third explanation for the different effects of FT and VRT on memory task performance focuses on the frontal lobe related strategic abilities required by each task. VRT involves more of these abilities, including conscious control of each response, stimulus-response matching, and sustained attention. As previously reviewed, source memory is relatively more impaired by frontal lobe lesions than item memory. Thus, concurrent performance of VRT may interfere more with source memory because both tasks are heavily dependent on the same type of cognitive abilities. This explanation is consistent with previous findings by Moscovitch and Ziegler (personal communication, August 1,1997) examining the effects of concurrent performance of VRT or FT on another test sensitive to frontal lobe functioning. The number of words generated on a verbal fluency task was lower when performed concurrently with VRT than with FT. Thus, concurrent performance of VRT, in comparison with FT, results in performance patterns on other cognitive tasks that more closely resemble those of patients with frontal dysfunction. Performing the VRT task requires a conscious decision for each response because each is directed by a visual stimulus. Performing the FT task, in contrast, requires less conscious control and may be more automatic because each response is based on a repetitive and predictable pattern. Given these different task requirements, it is not surprising that VRT results in performance resembling that of patients with frontal dysfunction. VRT requires more frontal lobe related resources, leaving fewer resources for the concurrent memory task. The findings obtained in these experiments do not reflect a trade-off between memory task and secondary task performance. That is, participants did not simply expend more effort on one task at the expense of the other. Rather, decreased accuracy on the memory tasks was always
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SOURCE MEMORY AND DIVIDED ATTENTION associated with slower performance speed on the secondary tasks. The question arises as to why one type of source task requires more processing resources than the other. In the visual modality, the ventral visual stream is involved in the recognition of objects such as visual words (Ungerleider & Mishkin, 1982). This system may also be involved in the recognition of object-bound or associative characteristics such as color. If these pieces of information are indeed coded by the same system, they may be bound together into one unit. Visual spatial location, however, is coded by a separate, dorsal visual stream (Ungerleider & Mishkin, 1982). Binding and retrieving the object with its spatial location, therefore, may be less successful and require more effort. Brain regions involved in the control of attentional resources, such as the frontal or parietal lobes, may be called into play on such organizational source tasks. Although this research has focused exclusively on the visual system, the same may also be true of the auditory system. Studies of auditory event-related brain potentials indicate that the pitch and spatial location of a tone are processed in distinct cortical regions (e.g., Woods & Alain, 1993; Woods, Alho, & Algazi, 1994). As well, there is preliminary evidence for parallel streams in the auditory system that are similar to the streams in the visual system (Rauschecker, 1998). Thus, the differential cortical involvement in processing object-bound characteristics versus spatial location parallel the dissociations we obtained using behavioral manipulations.
References Bondareff, W. (1985). The neural basis of aging. In J. E. Birren & K. W. Schaie (Eds.), Handbook of the psychology of aging (2nd ed., pp. 95-112). New York: Van Nostrand Reinhold. Craik, F. I. M., Govoni, R., Naveh-Benjamin, M., & Anderson, N. D. (1996). The effects of divided attention on encoding and retrieval processes in human memory. Journal of Experimental Psychology: General, 125, 159-180. Dunbar, K., & Sussman, D. (1995). Toward a cognitive account of frontal lobe function: Simulating frontal lobe deficits in normal subjects. Annals of the New York Academy of Sciences, 769, 289-304. Fletcher, P. C., Shallice, T., & Dolan, R. J. (1998). The functional roles of prefrontal cortex in episodic memory: Encoding. Brain, 121, 1239-1248. Gerloff, C., Richard, J., Hadley, J., Schulman, A. E., Honda, M., & Hallett, M. (1998). Functional coupling and regional activation of human cortical motor areas during simple, internally paced and externally paced finger movements. Brain, 121, 1513-1531. Hasher, L., & Zacks, R. T. (1979). Automatic and effortful processes in memory. Journal of Experimental Psychology: General, 108, 356-388. Janowsky, J. S., Shimamura, A. P., & Squire, L. R. (1989). Source memory impairment in patients with frontal lobe lesions. Neuropsychologia, 27, 1043-1056. Johnston, W. A., Griffith, D., & Wagstaff, R. R. (1972). Speed, accuracy, and ease of recall. Journal of Verbal Learning and Verbal Behavior, 11, 512-520. Kausler, D. H., Salthouse, T. A., & Saults, J. S. (1988). Temporal
473
memory over the adult lifespan. American Journal of Psychology, 101, 207-215. Martin, A., Wiggs, C. L., Lalond, F., & Mack, C. (1994). Word retrieval to letter and semantic cues: A double dissociation in normal subjects using interference tasks. Neuropsychologia, 32, 1487-1494. Mclntyre, J. S., & Craik, F. I. M. (1987). Age differences in memory for item and source information. Canadian Journal of Psychology, 41, 175-192. Moscovitch, M. (1992). Memory and working-with-memory: A component process model based on modules and central systems. Journal of Cognitive Neuroscience, 4, 257-267. Moscovitch, M. (1994). Cognitive resources and dual-task interference effects at retrieval in normal people: The role of the frontal lobes and medial temporal cortex. Neuropsychology, 8, 524-534. Moscovitch, M., & Winocur, G. (1992). The neuropsychology of memory and aging. In F. I. M. Craik & T. A. Salthouse (Eds.), The handbook of aging and cognition (pp. 315-372). Hillsdale, NJ: Erlbaum. Petrides, M. (1985). Deficits on conditional associative-learning tasks after frontal- and temporal-lobe lesions in man. Neuropsychologia, 23, 601-614. Rauschecker, J. P. (1998). Parallel processing in the auditory cortex of primates. Audiology & Neuro-otology, 3, 86-103. Roberts, R. J., Hager, L. D., & Heron, C. (1994). Prefrontal cognitive processes: Working memory and inhibition in the antisaccade task. Journal of Experimental Psychology: General, 123, 374-393. Schacter, D. L. (1987). Memory, amnesia, and frontal lobe dysfunction. Psychobiology, 15, 21-36. Schneider, W. (1995). MEL professional: User's guide [Computer program manual]. Pittsburgh, PA: Psychology Software Tools. Spencer, W. D., & Raz, N. (1995). Differential effects of aging on memory for content and context: A meta-analysis. Psychology and Aging, 10, 527-539. Squire, L. R. (1982). Comparisons between forms of amnesia: Some deficits are unique to Korsakoffs syndrome. Journal of Experimental Psychology: Learning, Memory, and Cognition, 8, 560-571. Stuss, D. T., Eskes, G. A., & Foster, J. K. (1994). Experimental neuropsychological studies of frontal lobe functions. In F. Boiler & J. Graffman (Eds.), Handbook of neuropsychology (Vol. 9, pp. 149-185). Amsterdam: Elsevier. Stuss, D., Shallice, T., Alexander, M. P., & Picton, T. W. (1995). A multidisciplinary approach to anterior attentional functions. Annals of the New York Academy of Sciences, 769, 191-212. Thorndike, E. L., & Lorge, I. (1944). The teacher's word book of 30,000 words. New York: Teacher's College Bureau of Publications. Troyer, A. K., & Craik, F. I. M. (1997). The effect of divided attention on memory for item versus context [Abstract]. Journal of the International Neuropsychological Society, 3, 10. Troyer, A. K., Moscovitch, M., & Winocur, G. (1997). Clustering and switching as two components of verbal fluency: Evidence from younger and older healthy adults. Neuropsychology, 11, 138-146. Ungerleider, L. G., & Mishkin, M. (1982). Two visual cortical systems. In D. J. Ingle, M. A. Goodale, & R. J. Mansfield (Eds.), Analysis of visual behavior (pp. 549-586). Cambridge, MA: MIT Press. Winocur, G. (1992). A comparison of normal old rats and young
TROVER, WINOCUR, CRAIK, AND MOSCOVITCH
474
This document is copyrighted by the American Psychological Association or one of its allied publishers. This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.
adult rats with lesions to the hippocampus or prefrontal cortex on a test of matching-to-sample. Neuropsychologia, 30, 769-781. Woods, D. L., & Alain, C. (1993). Feature processing during high-rate auditory selective attention. Perception and Psychophysics, 53, 391-402. Woods, D. L., Alho, K., & Algazi, A. (1994). Stages of auditory feature conjunction: An event-related brain potential study.
Journal of Experimental Psychology: Human Perception and Performance, 20, 81-94.
Received September 22, 1998 Revision received January 22, 1999 Accepted January 26, 1999
Call for Nominations The Publications and Communications Board has opened nominations for the editorships of Behavioral Neuroscience, JEP: Applied, JEP: General, Psychological Methods, and Neuropsychology for the years 2002-2007. Michela Gallagher, PhD; Raymond S. Nickerson, PhD; Nora S. Newcombe, PhD; Mark I. Appelbaum, PhD; and Laird S. Cermak, PhD, respectively, are the incumbent editors. Candidates should be members of APA and should be available to start receiving manuscripts in early 2001 to prepare for issues published in 2002. Please note that the P&C Board encourages participation by members of underrepresented groups in the publication process and would particularly welcome such nominees. Self-nominations are also encouraged. To nominate candidates, prepare a statement of one page or less in support of each candidate. The search chairs are as follows: • • • • •
Joe L. Martinez, Jr., PhD, for Behavioral Neuroscience Lauren B. Resnick, PhD, and Margaret B. Spencer, PhD, for JEP: Applied Sara B. Kiesler, PhD, for JEP: General Lyle E. Bourne, Jr., PhD, for Psychological Methods Lucia A. Gilbert, PhD, for Neuropsychology
Address all nominations to the appropriate search committee at the following address: [Name of journal] Search Committee c/o Karen Sellman, P&C Board Search Liaison Room 2004 American Psychological Association 750 First Street, NE Washington, DC 20002-4242 The first review of nominations will begin December 6,1999.
