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Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/uear20
Age, sex, and hemisphere asymmetry differences induced by a concurrent memory processing task a
b
Jeffrey W. Elias , Frank J. Winn Jr. & Linda L. Wright
c
a
Department of Psychology , Texas Tech University , Lubbock, TX, 79409, U.S.A. b
U.S. Coast Guard Support Center , Medical Unit Governor's Island , New York, NY, 10004, U.S.A. c
North Carolina Department of Mental Health , Division of Research , Raleigh, NC, 27611, U.S.A. Published online: 27 Sep 2007.
To cite this article: Jeffrey W. Elias , Frank J. Winn Jr. & Linda L. Wright (1979) Age, sex, and hemisphere asymmetry differences induced by a concurrent memory processing task, Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process, 5:3, 217-237, DOI: 10.1080/03610737908257200 To link to this article: http://dx.doi.org/10.1080/03610737908257200
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AGE, SEX, AND HEMISPHERE ASYMMETRY DIFFERENCES INDUCED BY A CONCURRENT MEMORY PROCESSING TASK JEFFREY W. ELIAS Department of Psychology Texas Tech University Lubbock, TX 79409 U.S.A.
F R A N K J. WINN, JR. U.S. Coast Guard Support Center, Medical Unit Governor’s Island, New York, NY JO004 U.S.A.
LINDA L. WRIGHT North Carolina Department of Mental Health Divkion of Research Raleigh, NC27611 U.S.A.
Elias, J.W., Winn, F.J., & Wright, L. Age, sex and hemisphere asymmetry differences induced by a concurrent memory processing task. Experimental Aging Research, 1979,5(3), 217-237. Subjects in three age groups matched simultaneously presented pairs of visual words or geometric shape stimuli as belonging in a “same” or “different” category. No age effects were observed unless .subjects were also required to repeat the sequence of the last three “same-different’’ responses immediately following each trial. Cerebral asymmetry effects were expected for the word and shape dimensions, but were not observed. Asymmetry effects for the same-different dimensions were noted and allowed inference regarding serial and parallel processing effects. When required to repeat the sequence of past responses following each trial, older males showed an increase in time to make the same judgments. Older females showed increased right vs left visual field processing times when required to repeat the sequence of same-different responses following each trial.
Preparation of this paper was supported by DHEW Research Grant NIH 5 Ro1 AG-00237-01 from the National Institute on Aging to J.W.E.
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The introduction and popularized use of noninvasive methods for the study of cerebral asymmetry has led to an increasing number of publications in this area since the mid-fifties. Early investigations in this area mostly concentrated on verifying the asymmetry phenomenon via the use of stimulus detection and accuracy of report type tasks (Kimura, 1973). More recent studies have investigated levels of processing effects (Moscovitch, Scullion, & Christie, 1976), decision making effects (Davis & Schmit, 1973), strategy effects (Levy & Trevarthen, 1976) hemisphere - hand of response interactions (Watson, Elias, & Pentz, 111, 1975), concurrent memory load (Hellige & Cox, 19761, and attention bias effects (Kinsbourne, 1973). As a result, the understanding of hemispheric function has become a bit more complicated, The characteristic functions of the hemispheres have been described less in terms of stimulus detection and more in terms of response to task demands. The developmental aspects of cerebral asymmetry have begun to be rather well investigated with infants and older children, but there have been relatively few investigations of asymmetry effects focused on age differences between young and old adults (Elias, 1979).
The present investigation focuses on age differences in asymmetry in the young to old adult age range with an emphasis on the effects of concurrent information processing. The concurrent information processing paradigm basically involves the introduction of a task secondary and concurrent to the principal asymmetry task. Kinsbourne (1973)was one of the first to introduce this paradigm to the literature in an attempt to provide an alternative explanation for asymmetry effects. Kinsbourne proposed that asymmetry effects occur to a large extent via a “hemisphere biasing” effect where a hemisphere is attentionally biased toward superior performance in an asymmetry paradigm. A task performed concurrently to a primary processing task can serve to bias attention of a hemisphere and in some cases produce an enhancement of performance by the “biased” hemisphere.
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The task requirement of holding some information in short-term storage while concurrently processing new information has been shown to have a hemisphere biasing effect. Hellige and Cox (1976) demonstrated this effect by having subjects concurrently hold 0 , 2 , 4 , or 6 nouns in memory while performing a primary asymmetry task. An easy memory load of 2 or 4 nouns enhanced performance in the left hemisphere but the more difficult memory load of 6 nouns decreased visual recognition accuracy below levels observed in the no-memory condition. Apparently hemisphere biasing can produce enhanced or diminished performance depending on the degree of concurrent competition for time and space in the “biased” hemisphere. Using a monaural same-different matching paradigm, with young, middle aged, and older males and females as subjects, Elias, Wright, and Winn (1976) observed that a requirement of having to repeat the sequence of the last three same-different responses after each identification response resulted in increased response times to right ear verbal stimuli for middle aged and older men. For middle aged and older women, the effects of the concurrent task were less clear - some showed an increase in right ear processing times, some showed an increase in left ear processing times, and some showed no effect at all. The age effect was interpreted as representing increased competition for “time and space” in the left hemisphere of the middle aged and older males. The sex effect could potentially be a function of greater bilateral representation for verbal processing in females than males (Waber, 1976) resulting in less concurrent task interference for left hemisphere processing. The present set of studies was planned in an attempt to verify in the visual mode the relationships observed by Elias et al. (1977)in the auditory mode. Based on previous research it would be predicted that a concurrent memory task would produce greater interference effects for old subjects relative to younger subjects, and that the effects of the concurrent memory task might differ by sex of subject, especially in the older age
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groups. Although the monaural concurrent memory paradigm did not produce an enhancement of performance by young subjects, other research has suggested an enhancement of performance may occur with a concurrent task if the concurrent task is not too difficult. Thus enhancement of performance due to the biasing effect would not be completely unexpected in the present study.
Subjects in the present study were asked to participate in two experiments, with the first experiment serving as a basis on which to judge the effects of the concurrent memory task required in the second experiment. Since investigation of hemisphere biasing effects was the primary purpose of the study stimulus presentation methods were designed to avoid inadvertant biasing of hemisphere function. As a result methods of presentation were at variance with common tachistoscopic hemisphere asymmetry paradigms. The primary processing task was a same-different identification task involving two stimuli. These stimuli could not be presented successively since the presentation of the initial stimulus could be considered a form of hemisphere attention bias in itself (Hellige & Cox,1976). Control of anticipatory eye movements is considered an essential feature of concurrent information processing paradigms. In the present study control for such eye movements was aided by having one stimulus present in the midfield viewing area and one present in the left or right lateral visual field. Day (1976) has reported that similar methodology was successful in showing asymmetry effects for abstract vs. concrete noun identification. Moscovitch et al. (1976) have argued that when the dependent variable is reaction time rather than number of correct detections, exposure of a stimulus to both hemispheres should not offset the initial advantage of processing in a hemisphere superior for the processing of that stimulus. Since one of the stimuli to be matched was projected only to a lateral visual field a hemisphere advantage for processing stimuli should still be observed, especially if stimuli presented to a non-dominant
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hemisphere have to be transferred to a dominant hemisphere for processing (Gazzaniga, 1973; Kimura, 1973).
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METHOD Subjects
There were 10 males and 10 females in each age group: Young (18-26),middle aged (38-51)and older (58-77).The middle aged. and older subjects were recruited from a Southwestern community and were all healthy, noninstitutionalized individuals who, if retired, had continued to remain“ active in their communities. Younger persons were volunteers who were fulfilling a college course requirement during a summer school session. All subjects were right-handed as classified by a modified form of the Harris Lateral Dominance Test (Harris, 1958). Questioning of subjects revealed no uncorrectable visual difficulties. Some subjects were not included in the study since the type of bifocal they wore restricted their lateral vision. Persons indicating a history of neurological problems, hypertension or cardio-vascular disease were not included in the sample. Stimuli
Pairs of stimuli were presented simultaneously to the center of the visual field and to either the left or right visual hemifield. Each presentation consisted of two words or two geometric shapes presented for 50 msec. By presenting the stimuli simultaneously, both lateral and midfield stimuli could begin prbcessing within the same time frame. A successive presentation of stimuli would have permitted one stimulus to be potentially further encoded than the stimulus to which it was to be matched.
Stimulus field background luminance was 1.1 log ftl. The field was dark between trials. Viewing was binocular.
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Words and geometric shapes were presented on separate blocks of trials. The presentation order of words or shapes was counterbalanced within sex groups. Subjects were required to respond correctly to 28 word pairs and 28 geometric shape pairs. Incorrect responses were replaced by correct responses mixed randomly within the trials so that subjects could not anticipate the response. Within word and shape blocks of trials subjects were required to respond correctly to 14 right and 14 left lateral hemifield stimuli. One-half of the stimuli in each hemifield required a “same” and half required a response of “different.” The name stimuli were chosen as stimuli that would be verbally encoded (VE) easily and consisted of names of animate objects (names JOHN and JILL) or inanimate objects (names JARS and JADE ) . These stimuli were drawn using a Pickett 26 V lettering guide with a “Modern Bold” style, x” (635cm) vertical height. Letters in names were all upper case, and lateral VE stimuli subtended an angle from 2.5 to 5.0 degrees to the left or right of midline. Stimuli were black on a white background. The shape stimuli were chosen as stimuli that would be easily encoded nonverbally (NVE ) . They consisted of circles and equilateral triangles, black on a white background, of the same height as the VE stimuli. Lateral NVE stimuli subtended an angle 2.5 to 4.4 degrees to the left or right of visual midline. As has been noted by Elias and Kinsbourne (1976), the classification of a stimulus as easily verbally encodable or easily nonverbally encodable depends as much on the task demands as on the nature of the stimulus itself. Thus, the stimuli in the present study are classified as VE or NVE on the basis of how the task would allow the subjects to process the stimuli in the most efficient manner. It is recognized that mder certain circumstances V E stimuli could be processed on the basis of physical characteristics only or that W E stimuli could be verbally labeled.
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Apparatus
Stimuli were presented via a Gerbrands three-field tachitoscope, Model #T-3A. A Lafayette Multichoice Reaction Timer was used to record choice reaction time to the nearest msec. The subject’s console contained two precision telegraph keys which were held in a depressed position with the index finger, and were released to respond. Procedure: Experiment 1
Prior to testing, subjects were given several practice trials where they were required to respond as rapidly as possible to the onset of a light. Subjects responded by lifting a telegraph key held in a down position. The releasing of a key, rather than pushing it down, seems to reduce warm-up effects considerably and in this particular study resulted in no significant differences between age groups in simple reaction time. Following the warm-up period, subjects were instructed that they would be participating in two experiments, and that approximately one hour would be required to complete both tasks. The participants were told that they would be required to identify simultaneously presented lateral and midfield stimuli as belonging to the “same” or “different” category based on a concept of “sameness” or “difference.” For VE stimuli, a response of “same” was required for the simultaneous appearance of animate objects (names JOHN and JILL) or inanimate objects (names JARS-JADE). A response of ‘ ‘different” was required if the name of an animate and inanimate object appeared together (e.g., JOHN-JADE). The purpose of devising the identification task in this particular manner was so that the participants would have to identify the words prior to responding, rather than being able to merely make a physical match.
For NVE stimuli the concept for “sameness” was the presence or absence of a line drawn through the center of the figure. That is, a circle and a triangle appearing simultaneously
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required a response of “same” if both had a line through the center, or if neither had a line drawn through the center. A response of “different” was required if only one of the figures had a line drawn through the center. This identification procedure prevented the subjects from merely verbally labeling the stimuli as “two triangles,” or “a triangle and a cirlce,” since the appearance of a triangle and a circle or two circles, or two triangles could either produce a “same” or a ”different” response depending on the presence or absence of the line through the center of the figures. Reaction time was the dependent variable but subjects were instructed to respond both quickly and accurately. The right and left hand position of the “same” and “different” keys was counterbalanced within sex groups. This was necessary to avoid ipsilateral-contralateral stimulus presentation by hand of response, biasing the response times (Simon, Craft, & Small, 1971).
A t the beginning of each test trial subjects were requested to focus on a dark circle (fixation point, duration 50 msec) presented a t the midpoint of the visual field. This was followed by a plain gray visual field for 25 msec prior to the 50 msec stimulus presentation of test stimuli. The msec duration of the midpoint, gray visual field, and stimuli were designed so that subjects could not shift their gaze from the midpoint to the lateral stimuli. This was necessary so that the lateral visual stimulus would be presented in the left or right visual hemifield. The midpoint stimulus was presented to both visual fields.
Procedure, Experiment S
Participants received a few minutes’ rest following the completion of Experiment 1while the procedure for Experiment 2 was explained. All procedures for stimulus presentation and response remained the same as in Experiment 1, with one
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exception. After every key response the subject was to repeat back to the experimenter the sequence of the last three “samedifferent’’ responses. If subjects made a mistake they were supplied with the proper sequence. This sequence of responses changed after every response to accommodate the latest key response. There were no time limits placed on the repeating of the sequence. This has the effect of having subjects store information while preparing for the input of similar information. RESULTS The reaction time data were analyzed as an age by stimulus by hemifield by same-different (3 x 2 x 2 x 2) analysis of variance with age as a between subjects factor and all other factors analyzed within subjects. Data from the Concept tasks and Concept plus Memory Tasks were analyzed separately for males and females (Elias et al., 1977). Only reaction time data from correct responses are reported. Male Concept Task [Experiment I ]
Perhaps the most outstanding feature of this analysis was the lack of age differences and interactions with the age factor. Figure 1shows that matching reaction times, summed over all conditions but age were 843 msec for young subjects, 774 msec for middle aged subjects, and 955 msec for old subjects ( p = .24). The age by stimulus by Hemifield interaction, that would have depicted an inferred change with age in the ability of the left and right hemispheres to process V E and NVE information, was not significant ( p = .30). Cerebral asymmetry effects could be inferred for the processing of “same” and “different” judgments as the result Of a hemifield by same-different interaction ( p = .06). It can be seen (Table 1) that the greatest disparity in same and different processing time occurred when same and different judgments were presented via the left visual hemifield, and by inference processed laterally by the right hemisphere. From the analysis it
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[ALES
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l2Ol
I10
n
0
100
Q)
E
Y
IK
90
z a w
8C
E 7c
6(
5( YOUNG
MIDDLE AGED
OLDE
Figure 1. Mean RT for males and females summed over all conditions but Age for Experiment 1 (Concept Task) and Experiment 2 (Concept + Memory Task).
can be inferred that the right hemisphere is more efficient for processing same judgments than different judgments, while the left hemisphere is more equally proficient in the processing of same and different judgments. The lack of a significant
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TABLE 1 Male and Female Mean Reaction Times and Standard Deviations in msec for the Concept Task [Experiment11
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MALES Left Hemi-field
Same Choice Different Choice
Right Hemi-field
FEMALES Left Right Hemi-field Hemi-field
743 1 853 l(202) 1 (292) 83 52 929 ' " : 9058 2 6 1 (331) (308) (254)
808 (277)
29 8 2 7 1 (286)
interaction with the age factor suggests that this relationship does not differ for the different age groups. A significant stimulus by same-different interaction was also present. The pattern of means for same and different judgments indicated that same judgments were made only slightly faster than different judgments when the stimuli were geometric shapes (mean same judgment = 771 msec; mean different judgment = 804 msec). When the stimuli were words, same judgments were made on an average of 139 msec faster than different judgments (mean same judgment = 891 msec; mean different judgment = 1030 msec). The lack of a significant age by stimulus by same-different interaction suggests that the stimulus by same-different relationship does not differ greatly with age.
Male Concept Plus Sequential Task [Experiment 21
In contrast to the results of Experiment 1, the most outstanding feature of this analysis was the appearance and the nature of age differences. Figure 1 shows that matching reaction times, summed over all conditions but age, were 637 msec for young subjects, 673 for middle aged subjects, and 1114 msec for
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TABLE 2 M e and F a d e Mean Recetkn"her, mdStandud Deviations in maec for the Concept plus SeqwntitJMemOry Task [Experiment21
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MALES
Left Hemi-field
Right Hemi-field
FEMALES Left Hemi-field
Right Hemi-field
old subjects. This Age effect ( p < .001) reflects the fact mat only the oldest subjects increase their reaction times with the addition of the sequential memory task. Young and middle aged subjects show a substantial reduction in reaction times with the added sequential memory requirements. It can be seen in Table 2 that the hemifield by same-different interaction is of less magnitude in this second analysis ( p = .105). It can also be seen in Table 2 that same judgments were longer than different judgments for males but the difference did not reach statistical significance. A significant age x samedifferent interaction (p .05).
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TABLE 3 Same-DifferentMean Reaction Times and Standard Deviations in m8Bt for Young, Middle Aged and Older Males and F e d e s on the Concept plus SequentialMemory Task
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-
MALES Same
YOUNG
634-1
MIDDLE AGED
(156) 6
(%I-'
Different
640 (153)
692 .-I (248)
Females Same
Young
Middle Aged
-
:G-I
192
1062 (418)
-
Older
(E, 1
(E-1 26
(KT-1 21
637 (161)
675 (193)
933 (413)
37
Different
38
OLDER
Female Concept Task [Experiment 11
The results of this analysis for females parallels the results for the males with the exception that females in the older age group have much shorter reaction times than their male counterparts. As with the males there were no age differences or interactions with the age factor. Figure 1 shows matching reaction times, summed over all conditions but age, were 637 msec for young subjects, 773 msec for middle aged subjects, and 809 msec for old subjects ( p = .55). The hemifield by same-different interaction was significant at the p = .0575 level. It can be seen in Table 1that the greatest disparity in same and different processing times occurred when same and different judgments were presented via the left visual hemifield, and by inference to the right hemisphere. The lack Of an interaction with age for these factors suggests the relationship did not change across age.
ELIAS/ WINN/ WRIGHT
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120' LEFT VISUAL HEMIFIELD
1101
MALES
100'
901
80
70
1 MlDDl
AGED
011
YOUNG
MlDDl AGE
OLD
Figure 2. Mean RT for males and females in Experiment 2 (Concept + Memory Task)showing the Age by Visual Hemi-field interaction which was significant for the females and nonsignificant for the males.
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The female groups also exhibited a significant stimulus by same-different interaction ( p g.05). When geometric shapes were the stimuli, same judgments (mean = 668 msec) were made only slightly faster than different judgments (mean = 687 msec). When the stimuli were words, same judgments were made on an average of 93 msec faster than different judgments (mean same judgment = 873 msec; mean different judgment = 966 msec. These effects did not interact with the age factor. Female Concept and Sequential Memory Task [Experiment 21
Similar to results for the males, the addition of the sequential memory task resulted in the appearance of age differences. A significant main effect for age occurred ( p < .01) with mean reaction times of 618, 662, and 944 msec for the young, middle aged, and older groups, respectively. The young and middle aged subjects showed decreases in reaction time in comparison to Experiment 1 performance. Only the older age group showed increased reaction times with the addition of the sequential memory factor. For the'males, the addition of the sequential memory task resulted in a significant age by same-different interaction. For the females, the addition of the sequential memory factor also resulted in a significant age by samedifferent interaction ( p C . 0 5 ) and a significant age x visual hemifield interaction (p
Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/uear20
Age, sex, and hemisphere asymmetry differences induced by a concurrent memory processing task a
b
Jeffrey W. Elias , Frank J. Winn Jr. & Linda L. Wright
c
a
Department of Psychology , Texas Tech University , Lubbock, TX, 79409, U.S.A. b
U.S. Coast Guard Support Center , Medical Unit Governor's Island , New York, NY, 10004, U.S.A. c
North Carolina Department of Mental Health , Division of Research , Raleigh, NC, 27611, U.S.A. Published online: 27 Sep 2007.
To cite this article: Jeffrey W. Elias , Frank J. Winn Jr. & Linda L. Wright (1979) Age, sex, and hemisphere asymmetry differences induced by a concurrent memory processing task, Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process, 5:3, 217-237, DOI: 10.1080/03610737908257200 To link to this article: http://dx.doi.org/10.1080/03610737908257200
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or
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distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions
217
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AGE, SEX, AND HEMISPHERE ASYMMETRY DIFFERENCES INDUCED BY A CONCURRENT MEMORY PROCESSING TASK JEFFREY W. ELIAS Department of Psychology Texas Tech University Lubbock, TX 79409 U.S.A.
F R A N K J. WINN, JR. U.S. Coast Guard Support Center, Medical Unit Governor’s Island, New York, NY JO004 U.S.A.
LINDA L. WRIGHT North Carolina Department of Mental Health Divkion of Research Raleigh, NC27611 U.S.A.
Elias, J.W., Winn, F.J., & Wright, L. Age, sex and hemisphere asymmetry differences induced by a concurrent memory processing task. Experimental Aging Research, 1979,5(3), 217-237. Subjects in three age groups matched simultaneously presented pairs of visual words or geometric shape stimuli as belonging in a “same” or “different” category. No age effects were observed unless .subjects were also required to repeat the sequence of the last three “same-different’’ responses immediately following each trial. Cerebral asymmetry effects were expected for the word and shape dimensions, but were not observed. Asymmetry effects for the same-different dimensions were noted and allowed inference regarding serial and parallel processing effects. When required to repeat the sequence of past responses following each trial, older males showed an increase in time to make the same judgments. Older females showed increased right vs left visual field processing times when required to repeat the sequence of same-different responses following each trial.
Preparation of this paper was supported by DHEW Research Grant NIH 5 Ro1 AG-00237-01 from the National Institute on Aging to J.W.E.
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The introduction and popularized use of noninvasive methods for the study of cerebral asymmetry has led to an increasing number of publications in this area since the mid-fifties. Early investigations in this area mostly concentrated on verifying the asymmetry phenomenon via the use of stimulus detection and accuracy of report type tasks (Kimura, 1973). More recent studies have investigated levels of processing effects (Moscovitch, Scullion, & Christie, 1976), decision making effects (Davis & Schmit, 1973), strategy effects (Levy & Trevarthen, 1976) hemisphere - hand of response interactions (Watson, Elias, & Pentz, 111, 1975), concurrent memory load (Hellige & Cox, 19761, and attention bias effects (Kinsbourne, 1973). As a result, the understanding of hemispheric function has become a bit more complicated, The characteristic functions of the hemispheres have been described less in terms of stimulus detection and more in terms of response to task demands. The developmental aspects of cerebral asymmetry have begun to be rather well investigated with infants and older children, but there have been relatively few investigations of asymmetry effects focused on age differences between young and old adults (Elias, 1979).
The present investigation focuses on age differences in asymmetry in the young to old adult age range with an emphasis on the effects of concurrent information processing. The concurrent information processing paradigm basically involves the introduction of a task secondary and concurrent to the principal asymmetry task. Kinsbourne (1973)was one of the first to introduce this paradigm to the literature in an attempt to provide an alternative explanation for asymmetry effects. Kinsbourne proposed that asymmetry effects occur to a large extent via a “hemisphere biasing” effect where a hemisphere is attentionally biased toward superior performance in an asymmetry paradigm. A task performed concurrently to a primary processing task can serve to bias attention of a hemisphere and in some cases produce an enhancement of performance by the “biased” hemisphere.
Downloaded by [McGill University Library] at 22:59 07 February 2015
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The task requirement of holding some information in short-term storage while concurrently processing new information has been shown to have a hemisphere biasing effect. Hellige and Cox (1976) demonstrated this effect by having subjects concurrently hold 0 , 2 , 4 , or 6 nouns in memory while performing a primary asymmetry task. An easy memory load of 2 or 4 nouns enhanced performance in the left hemisphere but the more difficult memory load of 6 nouns decreased visual recognition accuracy below levels observed in the no-memory condition. Apparently hemisphere biasing can produce enhanced or diminished performance depending on the degree of concurrent competition for time and space in the “biased” hemisphere. Using a monaural same-different matching paradigm, with young, middle aged, and older males and females as subjects, Elias, Wright, and Winn (1976) observed that a requirement of having to repeat the sequence of the last three same-different responses after each identification response resulted in increased response times to right ear verbal stimuli for middle aged and older men. For middle aged and older women, the effects of the concurrent task were less clear - some showed an increase in right ear processing times, some showed an increase in left ear processing times, and some showed no effect at all. The age effect was interpreted as representing increased competition for “time and space” in the left hemisphere of the middle aged and older males. The sex effect could potentially be a function of greater bilateral representation for verbal processing in females than males (Waber, 1976) resulting in less concurrent task interference for left hemisphere processing. The present set of studies was planned in an attempt to verify in the visual mode the relationships observed by Elias et al. (1977)in the auditory mode. Based on previous research it would be predicted that a concurrent memory task would produce greater interference effects for old subjects relative to younger subjects, and that the effects of the concurrent memory task might differ by sex of subject, especially in the older age
Downloaded by [McGill University Library] at 22:59 07 February 2015
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groups. Although the monaural concurrent memory paradigm did not produce an enhancement of performance by young subjects, other research has suggested an enhancement of performance may occur with a concurrent task if the concurrent task is not too difficult. Thus enhancement of performance due to the biasing effect would not be completely unexpected in the present study.
Subjects in the present study were asked to participate in two experiments, with the first experiment serving as a basis on which to judge the effects of the concurrent memory task required in the second experiment. Since investigation of hemisphere biasing effects was the primary purpose of the study stimulus presentation methods were designed to avoid inadvertant biasing of hemisphere function. As a result methods of presentation were at variance with common tachistoscopic hemisphere asymmetry paradigms. The primary processing task was a same-different identification task involving two stimuli. These stimuli could not be presented successively since the presentation of the initial stimulus could be considered a form of hemisphere attention bias in itself (Hellige & Cox,1976). Control of anticipatory eye movements is considered an essential feature of concurrent information processing paradigms. In the present study control for such eye movements was aided by having one stimulus present in the midfield viewing area and one present in the left or right lateral visual field. Day (1976) has reported that similar methodology was successful in showing asymmetry effects for abstract vs. concrete noun identification. Moscovitch et al. (1976) have argued that when the dependent variable is reaction time rather than number of correct detections, exposure of a stimulus to both hemispheres should not offset the initial advantage of processing in a hemisphere superior for the processing of that stimulus. Since one of the stimuli to be matched was projected only to a lateral visual field a hemisphere advantage for processing stimuli should still be observed, especially if stimuli presented to a non-dominant
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hemisphere have to be transferred to a dominant hemisphere for processing (Gazzaniga, 1973; Kimura, 1973).
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METHOD Subjects
There were 10 males and 10 females in each age group: Young (18-26),middle aged (38-51)and older (58-77).The middle aged. and older subjects were recruited from a Southwestern community and were all healthy, noninstitutionalized individuals who, if retired, had continued to remain“ active in their communities. Younger persons were volunteers who were fulfilling a college course requirement during a summer school session. All subjects were right-handed as classified by a modified form of the Harris Lateral Dominance Test (Harris, 1958). Questioning of subjects revealed no uncorrectable visual difficulties. Some subjects were not included in the study since the type of bifocal they wore restricted their lateral vision. Persons indicating a history of neurological problems, hypertension or cardio-vascular disease were not included in the sample. Stimuli
Pairs of stimuli were presented simultaneously to the center of the visual field and to either the left or right visual hemifield. Each presentation consisted of two words or two geometric shapes presented for 50 msec. By presenting the stimuli simultaneously, both lateral and midfield stimuli could begin prbcessing within the same time frame. A successive presentation of stimuli would have permitted one stimulus to be potentially further encoded than the stimulus to which it was to be matched.
Stimulus field background luminance was 1.1 log ftl. The field was dark between trials. Viewing was binocular.
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Words and geometric shapes were presented on separate blocks of trials. The presentation order of words or shapes was counterbalanced within sex groups. Subjects were required to respond correctly to 28 word pairs and 28 geometric shape pairs. Incorrect responses were replaced by correct responses mixed randomly within the trials so that subjects could not anticipate the response. Within word and shape blocks of trials subjects were required to respond correctly to 14 right and 14 left lateral hemifield stimuli. One-half of the stimuli in each hemifield required a “same” and half required a response of “different.” The name stimuli were chosen as stimuli that would be verbally encoded (VE) easily and consisted of names of animate objects (names JOHN and JILL) or inanimate objects (names JARS and JADE ) . These stimuli were drawn using a Pickett 26 V lettering guide with a “Modern Bold” style, x” (635cm) vertical height. Letters in names were all upper case, and lateral VE stimuli subtended an angle from 2.5 to 5.0 degrees to the left or right of midline. Stimuli were black on a white background. The shape stimuli were chosen as stimuli that would be easily encoded nonverbally (NVE ) . They consisted of circles and equilateral triangles, black on a white background, of the same height as the VE stimuli. Lateral NVE stimuli subtended an angle 2.5 to 4.4 degrees to the left or right of visual midline. As has been noted by Elias and Kinsbourne (1976), the classification of a stimulus as easily verbally encodable or easily nonverbally encodable depends as much on the task demands as on the nature of the stimulus itself. Thus, the stimuli in the present study are classified as VE or NVE on the basis of how the task would allow the subjects to process the stimuli in the most efficient manner. It is recognized that mder certain circumstances V E stimuli could be processed on the basis of physical characteristics only or that W E stimuli could be verbally labeled.
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Apparatus
Stimuli were presented via a Gerbrands three-field tachitoscope, Model #T-3A. A Lafayette Multichoice Reaction Timer was used to record choice reaction time to the nearest msec. The subject’s console contained two precision telegraph keys which were held in a depressed position with the index finger, and were released to respond. Procedure: Experiment 1
Prior to testing, subjects were given several practice trials where they were required to respond as rapidly as possible to the onset of a light. Subjects responded by lifting a telegraph key held in a down position. The releasing of a key, rather than pushing it down, seems to reduce warm-up effects considerably and in this particular study resulted in no significant differences between age groups in simple reaction time. Following the warm-up period, subjects were instructed that they would be participating in two experiments, and that approximately one hour would be required to complete both tasks. The participants were told that they would be required to identify simultaneously presented lateral and midfield stimuli as belonging to the “same” or “different” category based on a concept of “sameness” or “difference.” For VE stimuli, a response of “same” was required for the simultaneous appearance of animate objects (names JOHN and JILL) or inanimate objects (names JARS-JADE). A response of ‘ ‘different” was required if the name of an animate and inanimate object appeared together (e.g., JOHN-JADE). The purpose of devising the identification task in this particular manner was so that the participants would have to identify the words prior to responding, rather than being able to merely make a physical match.
For NVE stimuli the concept for “sameness” was the presence or absence of a line drawn through the center of the figure. That is, a circle and a triangle appearing simultaneously
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required a response of “same” if both had a line through the center, or if neither had a line drawn through the center. A response of “different” was required if only one of the figures had a line drawn through the center. This identification procedure prevented the subjects from merely verbally labeling the stimuli as “two triangles,” or “a triangle and a cirlce,” since the appearance of a triangle and a circle or two circles, or two triangles could either produce a “same” or a ”different” response depending on the presence or absence of the line through the center of the figures. Reaction time was the dependent variable but subjects were instructed to respond both quickly and accurately. The right and left hand position of the “same” and “different” keys was counterbalanced within sex groups. This was necessary to avoid ipsilateral-contralateral stimulus presentation by hand of response, biasing the response times (Simon, Craft, & Small, 1971).
A t the beginning of each test trial subjects were requested to focus on a dark circle (fixation point, duration 50 msec) presented a t the midpoint of the visual field. This was followed by a plain gray visual field for 25 msec prior to the 50 msec stimulus presentation of test stimuli. The msec duration of the midpoint, gray visual field, and stimuli were designed so that subjects could not shift their gaze from the midpoint to the lateral stimuli. This was necessary so that the lateral visual stimulus would be presented in the left or right visual hemifield. The midpoint stimulus was presented to both visual fields.
Procedure, Experiment S
Participants received a few minutes’ rest following the completion of Experiment 1while the procedure for Experiment 2 was explained. All procedures for stimulus presentation and response remained the same as in Experiment 1, with one
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exception. After every key response the subject was to repeat back to the experimenter the sequence of the last three “samedifferent’’ responses. If subjects made a mistake they were supplied with the proper sequence. This sequence of responses changed after every response to accommodate the latest key response. There were no time limits placed on the repeating of the sequence. This has the effect of having subjects store information while preparing for the input of similar information. RESULTS The reaction time data were analyzed as an age by stimulus by hemifield by same-different (3 x 2 x 2 x 2) analysis of variance with age as a between subjects factor and all other factors analyzed within subjects. Data from the Concept tasks and Concept plus Memory Tasks were analyzed separately for males and females (Elias et al., 1977). Only reaction time data from correct responses are reported. Male Concept Task [Experiment I ]
Perhaps the most outstanding feature of this analysis was the lack of age differences and interactions with the age factor. Figure 1shows that matching reaction times, summed over all conditions but age were 843 msec for young subjects, 774 msec for middle aged subjects, and 955 msec for old subjects ( p = .24). The age by stimulus by Hemifield interaction, that would have depicted an inferred change with age in the ability of the left and right hemispheres to process V E and NVE information, was not significant ( p = .30). Cerebral asymmetry effects could be inferred for the processing of “same” and “different” judgments as the result Of a hemifield by same-different interaction ( p = .06). It can be seen (Table 1) that the greatest disparity in same and different processing time occurred when same and different judgments were presented via the left visual hemifield, and by inference processed laterally by the right hemisphere. From the analysis it
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[ALES
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l2Ol
I10
n
0
100
Q)
E
Y
IK
90
z a w
8C
E 7c
6(
5( YOUNG
MIDDLE AGED
OLDE
Figure 1. Mean RT for males and females summed over all conditions but Age for Experiment 1 (Concept Task) and Experiment 2 (Concept + Memory Task).
can be inferred that the right hemisphere is more efficient for processing same judgments than different judgments, while the left hemisphere is more equally proficient in the processing of same and different judgments. The lack of a significant
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TABLE 1 Male and Female Mean Reaction Times and Standard Deviations in msec for the Concept Task [Experiment11
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MALES Left Hemi-field
Same Choice Different Choice
Right Hemi-field
FEMALES Left Right Hemi-field Hemi-field
743 1 853 l(202) 1 (292) 83 52 929 ' " : 9058 2 6 1 (331) (308) (254)
808 (277)
29 8 2 7 1 (286)
interaction with the age factor suggests that this relationship does not differ for the different age groups. A significant stimulus by same-different interaction was also present. The pattern of means for same and different judgments indicated that same judgments were made only slightly faster than different judgments when the stimuli were geometric shapes (mean same judgment = 771 msec; mean different judgment = 804 msec). When the stimuli were words, same judgments were made on an average of 139 msec faster than different judgments (mean same judgment = 891 msec; mean different judgment = 1030 msec). The lack of a significant age by stimulus by same-different interaction suggests that the stimulus by same-different relationship does not differ greatly with age.
Male Concept Plus Sequential Task [Experiment 21
In contrast to the results of Experiment 1, the most outstanding feature of this analysis was the appearance and the nature of age differences. Figure 1 shows that matching reaction times, summed over all conditions but age, were 637 msec for young subjects, 673 for middle aged subjects, and 1114 msec for
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TABLE 2 M e and F a d e Mean Recetkn"her, mdStandud Deviations in maec for the Concept plus SeqwntitJMemOry Task [Experiment21
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MALES
Left Hemi-field
Right Hemi-field
FEMALES Left Hemi-field
Right Hemi-field
old subjects. This Age effect ( p < .001) reflects the fact mat only the oldest subjects increase their reaction times with the addition of the sequential memory task. Young and middle aged subjects show a substantial reduction in reaction times with the added sequential memory requirements. It can be seen in Table 2 that the hemifield by same-different interaction is of less magnitude in this second analysis ( p = .105). It can also be seen in Table 2 that same judgments were longer than different judgments for males but the difference did not reach statistical significance. A significant age x samedifferent interaction (p .05).
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TABLE 3 Same-DifferentMean Reaction Times and Standard Deviations in m8Bt for Young, Middle Aged and Older Males and F e d e s on the Concept plus SequentialMemory Task
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MALES Same
YOUNG
634-1
MIDDLE AGED
(156) 6
(%I-'
Different
640 (153)
692 .-I (248)
Females Same
Young
Middle Aged
-
:G-I
192
1062 (418)
-
Older
(E, 1
(E-1 26
(KT-1 21
637 (161)
675 (193)
933 (413)
37
Different
38
OLDER
Female Concept Task [Experiment 11
The results of this analysis for females parallels the results for the males with the exception that females in the older age group have much shorter reaction times than their male counterparts. As with the males there were no age differences or interactions with the age factor. Figure 1 shows matching reaction times, summed over all conditions but age, were 637 msec for young subjects, 773 msec for middle aged subjects, and 809 msec for old subjects ( p = .55). The hemifield by same-different interaction was significant at the p = .0575 level. It can be seen in Table 1that the greatest disparity in same and different processing times occurred when same and different judgments were presented via the left visual hemifield, and by inference to the right hemisphere. The lack Of an interaction with age for these factors suggests the relationship did not change across age.
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120' LEFT VISUAL HEMIFIELD
1101
MALES
100'
901
80
70
1 MlDDl
AGED
011
YOUNG
MlDDl AGE
OLD
Figure 2. Mean RT for males and females in Experiment 2 (Concept + Memory Task)showing the Age by Visual Hemi-field interaction which was significant for the females and nonsignificant for the males.
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The female groups also exhibited a significant stimulus by same-different interaction ( p g.05). When geometric shapes were the stimuli, same judgments (mean = 668 msec) were made only slightly faster than different judgments (mean = 687 msec). When the stimuli were words, same judgments were made on an average of 93 msec faster than different judgments (mean same judgment = 873 msec; mean different judgment = 966 msec. These effects did not interact with the age factor. Female Concept and Sequential Memory Task [Experiment 21
Similar to results for the males, the addition of the sequential memory task resulted in the appearance of age differences. A significant main effect for age occurred ( p < .01) with mean reaction times of 618, 662, and 944 msec for the young, middle aged, and older groups, respectively. The young and middle aged subjects showed decreases in reaction time in comparison to Experiment 1 performance. Only the older age group showed increased reaction times with the addition of the sequential memory factor. For the'males, the addition of the sequential memory task resulted in a significant age by same-different interaction. For the females, the addition of the sequential memory factor also resulted in a significant age by samedifferent interaction ( p C . 0 5 ) and a significant age x visual hemifield interaction (p
