This article was downloaded by: [University of Arizona] On: 01 February 2015, At: 10:53 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
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 differences in dark-interval threshold across the life-span a
a
a
Jants I. Amberson , Beverly M. Atkeson , Robert H. Pollack & Victor J. Malatesta
a
a
Department of Psychology , University of Georgia , Athens, Georgia, 30602, U.S.A. Published online: 27 Sep 2007.
To cite this article: Jants I. Amberson , Beverly M. Atkeson , Robert H. Pollack & Victor J. Malatesta (1979) Age differences in dark-interval threshold across the life-span, Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process, 5:5, 423-433, DOI: 10.1080/03610737908257217 To link to this article: http://dx.doi.org/10.1080/03610737908257217
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 distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
423
AGE DIFFERENCES IN DARK-INTERVAL THRESHOLD ACROSS THE LIFE-SPAN
Downloaded by [University of Arizona] at 10:53 01 February 2015
J A N I S I. AMBERSON, B E V E R L Y M. ATKESON, ROBERT H. POLLACK. and VICTOR J. MALATESTA Department of Psychology Universiry of Georgia Athens, Georgia 30602 U.S.A. Amberson, J . I., Atkeson, B. M., Pollack, R. H., & Maltesta, V. J. Age differences in dark-interval threshold across the life span. Experimental Aging Research, 1979, 5 ( 3 ,423-433. The threshold for the dark interval between two flashes was used to examine differences in stimulus persistence in 72 subjects aged 20 to 79 years. The data were then combined with results from two previous studies involving children and adolescents; thus, a cross sectional, adult, life-span view of differences in the dark-interval threshold was presented. Results showed that during childhood and adolescence there is a decline in stimulus persistence as a result of decreased receptor sensitivity. In adulthood, however, the dark-interval threshold remains fairly stable until the 70s where it increases significantly. Two possible explanations for this increase in stimulus persistence in old age are discussed.
Decline in visual functioning for older as compared to younger age groups has been shown in previous studies. Backward monoptic masking ( N i n e & Szafran, 1975), backward dichoptic masking (Kline & Birren, 1975), critical flicker frequency (Misiak, 1951; McFarland, Warren, & Karls, 1958; Brozek & Keys, 19451, recognition ability (Burg, 19671, and ability to recover from glare (Burg, 1967) have all been shown to be poorer for older age groups. One hypothesis offered to account for these findings is the idea that “in the senescent nervous system, there may be an
This study was supported by a grant from the National Institute of Aging, Department of‘ Health, Education, and Welfare, grant no. ROI AG00297. Department of Psychology. University of Georgia, Athens, Georgia, 30602.
Downloaded by [University of Arizona] at 10:53 01 February 2015
424
AMBERSON/ATKESON/POLLACK/MALATESTA
increased persistence of the activity evoked by a stimulus” (Axelrod, Thompson, & Cohen, 1968). Support for this hypothesis has come from a study by Mundy-Castle (1962) in which older subjects showed lengthened electroemcephalographic afteractivity to photic stimuli; from backward masking studies (Kline & Birren, 1975;Kline & Szafran, 1975) in which subjects exhibited a significant decrease with age in “stimulus clearing speed”; and in critical flicker frequency studies (Misiak, 1951) in which older subjects showed elevated thresholds for flicker fusion. However, more recent studies have produced equivocal evidence. Data have supported (Kline & Nestor, 1977; mine & Orme-Rogers, 1978) and conflicted (Till, 1978; Walsh & Thompson, 1978) with the persistence hypothesis. Thus, to test further the hypothesis of “stimulus persistence”, a simplified version of intermittent stimulation, the Dark-Interval Threshold (Pollack, Ptashne, & Carter, 1968) was utilized. Instead of presenting a long series of repeated flashes of varying cycles per second, only two flashes of light were presented in quick temporal succession with a varying interflash interval. The task for the subject was simply to report whether she detected an interval between the two flashes. Pollack, Ptashne. and Carter (1968, 1969) found that Dark-Interval Threshold showed a significant linear decline with increasing chronological age for subjects aged 6 to 17 years. This finding was attributed to the physiological aging of the receptor system and, more specifically, to diminishing stimulus persistence with increasing age. At younger ages, the apparent duration of the first flash is extended into the dark interval because of the persistence of the stimulus trace in the nervous system. Consequently, the younger children report seeing onIy one flash a t longer interflash intervals than the older children. With increasing age, the stimulus persistence of the first light bridges less and less of the dark interval between the two flashes; thus, the older children can detect the dark interval more easily and report seeing two flashes at shorter interflash intervals.
Downloaded by [University of Arizona] at 10:53 01 February 2015
DARK-INTERVAT, THRESHOLD
425
Dark-interval threshold has been used with adults ranging in age from 18 to 50 years (Farley, 1969). However, the mean age of the sample employed was 22.73 years, suggesting an inadequate representation of older individuals. On the other hand, Critical Flicker Frequency has been studied extensively in both children and older adults. Cross (1963) performed a study of Flicker Frequency in children with a n age range of 6 to 12 years. This young age group showed a significant increase in Critical Flicker Frequency (i.e.. better performance) with age. Misak (1951) tested subjects with an age range of 7 to 89. They were divided into five-year age groups: 7-11, 12-16, 17-21, etc. Critical Flicker Frequency increased through the second age group (12-161, then decreased throughout the rest of the life span. McFarland, Warren, and Karis (1958) used subjects ranging in age from 13 to 89 years. They divided the groups into ten year periods: 13-19, 130-29. 30-38. etc. Their results showed that there is a steady decline in Critical Flicker Frequency over all age groups from the youngest age group to the oldest. Using adults only, from ages 18 to 60, Brozek and Keys (1945) found a steady decrease in Flicker Frequency with advancing age. Combining five studies, Weale (1965) estimated that between the ages of 20 and 60 years the average decline in fusion frequency is about seven cycles per second. However, Misiak (1951) pointed out that the drop does not become ‘significant until later in life (i.e., after 551, and Coppinger (1955) did not find a significant decrease until age 70. A review of these studies, then, shows a consistent decline in Critical Flicker Frequency, but because of the grouping of the children’s data in these earlier studies it is possible only to say that the decline starts a t about age 13 or 14. Several reasons have been offered to account for the decline in Critical Flicker Frequency over age. According to Weale (19651, senile rniosis is able to account for about 70 percent of the decline and lenticular yellowing for another 10 percent. However, Weekers and Roussel (19461, using pupil dilation with atropine, still found a Flicker Frequency decrement with age, although the decrement was reduced. Misiak (1951) does not feel that diminished pupil size can be the entire explanation, in view of the
Downloaded by [University of Arizona] at 10:53 01 February 2015
426
AMRERSON/ATKESON/POLLACK/MALATESTA
gradual decrease in Flicker Frequency before the age of a diminished mobility of the pupil and in view of the fact that injuries of the cerebrum lower Flicker Frequency. In a later study, Misiak (1961) reported a positive, although low, correlation between Critical Flicker Frequency and intelligence test scores. These date provide another indication that central factors may be involved. The Dark-Interval Threshold and Critical Flicker Frequency a r e similar tasks and possibly measure the same function. The only difference in the curves for these two tasks over the life span is a different inflection point during adolescence. Critical Flicker Frequency starts declining at about age 13 o r 14. In contrast, dark interval-threshold does not start its decline until early 20s. There are two possible explanations for this difference. The adolescent data in many studies, including the earlier dark-interval threshold study, are highly variable; also, as stated before, the groupings of the adolescent Flicker Frequency data prohibit accurate comparisons. The other explanation is offered in a study by Herrick (1974). Herrick found that the minimum interval which a subject can detect between two successive flashes must be longer than the minimum interval for many flashes. This information indicates that Critical Flicker Frequency is easier to detect than dark-interval threshold and may account for the earlier inflection point for Flicker Frequency. Finally, it is important to note that critical flicker frequency has been questioned as a measure due to the light-dark ratio confound (McFarland, Warren, & Karis, 1958). The dark-interval threshold appears to overcome this problem. The present study extends the age-range of the earlier study by Pollack, Ptashn,e, and Carter (1968,1969) and provides new data on age differences in the dark-interval threshold from young adulthood through old age. In children, stimulus persistence is a function of the interaction between the sensitivity of the receptors in the eye and the intensity of the stimulus. Receptor sensitivity decreases with age. If this process continues in adults unmediated by any other process, one would expect a
DARK-INTERVAL THRESHOLD
427
continual decline in dark-interval threshold throughout adulthood as stimulus persistence in the receptors diminishes through normal aging. METHOD Downloaded by [University of Arizona] at 10:53 01 February 2015
Subjects:
The subjects were 72 female adults who verbally reported good health. They were volunteers from the community. There = were 12 subjects in each of six age groups: 20-29 years 26.21,40-49years = 43.9),50-59 years = 55.61, 60-69years = 64.1), and 70-79 years = 76.3). Although no cohort controls were employed, all subjects possessed between 12-14 years of formal education. All subjects had a t least 20/30 corrected or uncorrected vision in both eyes as measured by the Master Orthorater.
(x
(x
(x
(x
(x
Stimulus Figures
Pairs of flashes were presented binocularly in a 3-channel electronic tachistoscope (Scientific Prototype, Model G ) . Each flash was generated by the illumination passing through an aperture 6 mm in diameter cut from the center of a black background card. The visual angle subtended by the flash was 18 min. 40 sec. Both flashes were generated in a single channel and were separated by a dark interval which varied from 0 to 250 msec. in 10 msec. steps. The brightness level was 7.704 mL as measured by the Macbeth Illuminometer at the eye piece. PROCEDURE
Initially each subject was seated in the experimental chamber for 3 minutes. Because foveal fixation was employed, this period was used in order to allow for cone adaptation (Weale, 1965). The subject then received 3 practice trials of double and single flashes in order to become familiar with the task. She was instructed to report “two” if she saw two flashes or a dark interval between the flashes and to report “one” when she
Downloaded by [University of Arizona] at 10:53 01 February 2015
saw one flash or no dark interval. Each subject was informed that there were no right or wrong answers because people judge the flashes differently. The subject had to respond with a “one” or a “two”. This forced choice procedure was used in order to minimize the possibility of a criterion shift in the older subjects. Swets (19611, employing signal detection methodology showed that by using a forced choice procedure “few observers show a bias in their responses large enough to affect the sensitivity of d’ appreciably ...and (forced choice) may be used to advantage in studies having an emphasis on sensory, rather than on motivational or response, processes.”
Thresholds for the subjects were obtained from five ascending (beginning at 0 msc) and five descending trials (beginning at 250 msec) in counterbalanced order. Employing a method of limits procedure, a trial ended when the subject reported either three consecutive “one’s’’ or “two’s.” These three consecutive responses were then averaged to obtain a measure of threshold. a t each trial. Flash durations 1and 2 were kept constant at 20 msec.
RESULTS and‘DISCUSSION The dark-interval threshold for each trial was computed and the 10 trails were averaged to obtain a threshold for each subject. An F test for homogeniety of variance was performed. Variances were not significantly different. A one-way analysis of variance revealed a significant effect of age [ P (5,66) = 4.07, 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 differences in dark-interval threshold across the life-span a
a
a
Jants I. Amberson , Beverly M. Atkeson , Robert H. Pollack & Victor J. Malatesta
a
a
Department of Psychology , University of Georgia , Athens, Georgia, 30602, U.S.A. Published online: 27 Sep 2007.
To cite this article: Jants I. Amberson , Beverly M. Atkeson , Robert H. Pollack & Victor J. Malatesta (1979) Age differences in dark-interval threshold across the life-span, Experimental Aging Research: An International Journal Devoted to the Scientific Study of the Aging Process, 5:5, 423-433, DOI: 10.1080/03610737908257217 To link to this article: http://dx.doi.org/10.1080/03610737908257217
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 distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
423
AGE DIFFERENCES IN DARK-INTERVAL THRESHOLD ACROSS THE LIFE-SPAN
Downloaded by [University of Arizona] at 10:53 01 February 2015
J A N I S I. AMBERSON, B E V E R L Y M. ATKESON, ROBERT H. POLLACK. and VICTOR J. MALATESTA Department of Psychology Universiry of Georgia Athens, Georgia 30602 U.S.A. Amberson, J . I., Atkeson, B. M., Pollack, R. H., & Maltesta, V. J. Age differences in dark-interval threshold across the life span. Experimental Aging Research, 1979, 5 ( 3 ,423-433. The threshold for the dark interval between two flashes was used to examine differences in stimulus persistence in 72 subjects aged 20 to 79 years. The data were then combined with results from two previous studies involving children and adolescents; thus, a cross sectional, adult, life-span view of differences in the dark-interval threshold was presented. Results showed that during childhood and adolescence there is a decline in stimulus persistence as a result of decreased receptor sensitivity. In adulthood, however, the dark-interval threshold remains fairly stable until the 70s where it increases significantly. Two possible explanations for this increase in stimulus persistence in old age are discussed.
Decline in visual functioning for older as compared to younger age groups has been shown in previous studies. Backward monoptic masking ( N i n e & Szafran, 1975), backward dichoptic masking (Kline & Birren, 1975), critical flicker frequency (Misiak, 1951; McFarland, Warren, & Karls, 1958; Brozek & Keys, 19451, recognition ability (Burg, 19671, and ability to recover from glare (Burg, 1967) have all been shown to be poorer for older age groups. One hypothesis offered to account for these findings is the idea that “in the senescent nervous system, there may be an
This study was supported by a grant from the National Institute of Aging, Department of‘ Health, Education, and Welfare, grant no. ROI AG00297. Department of Psychology. University of Georgia, Athens, Georgia, 30602.
Downloaded by [University of Arizona] at 10:53 01 February 2015
424
AMBERSON/ATKESON/POLLACK/MALATESTA
increased persistence of the activity evoked by a stimulus” (Axelrod, Thompson, & Cohen, 1968). Support for this hypothesis has come from a study by Mundy-Castle (1962) in which older subjects showed lengthened electroemcephalographic afteractivity to photic stimuli; from backward masking studies (Kline & Birren, 1975;Kline & Szafran, 1975) in which subjects exhibited a significant decrease with age in “stimulus clearing speed”; and in critical flicker frequency studies (Misiak, 1951) in which older subjects showed elevated thresholds for flicker fusion. However, more recent studies have produced equivocal evidence. Data have supported (Kline & Nestor, 1977; mine & Orme-Rogers, 1978) and conflicted (Till, 1978; Walsh & Thompson, 1978) with the persistence hypothesis. Thus, to test further the hypothesis of “stimulus persistence”, a simplified version of intermittent stimulation, the Dark-Interval Threshold (Pollack, Ptashne, & Carter, 1968) was utilized. Instead of presenting a long series of repeated flashes of varying cycles per second, only two flashes of light were presented in quick temporal succession with a varying interflash interval. The task for the subject was simply to report whether she detected an interval between the two flashes. Pollack, Ptashne. and Carter (1968, 1969) found that Dark-Interval Threshold showed a significant linear decline with increasing chronological age for subjects aged 6 to 17 years. This finding was attributed to the physiological aging of the receptor system and, more specifically, to diminishing stimulus persistence with increasing age. At younger ages, the apparent duration of the first flash is extended into the dark interval because of the persistence of the stimulus trace in the nervous system. Consequently, the younger children report seeing onIy one flash a t longer interflash intervals than the older children. With increasing age, the stimulus persistence of the first light bridges less and less of the dark interval between the two flashes; thus, the older children can detect the dark interval more easily and report seeing two flashes at shorter interflash intervals.
Downloaded by [University of Arizona] at 10:53 01 February 2015
DARK-INTERVAT, THRESHOLD
425
Dark-interval threshold has been used with adults ranging in age from 18 to 50 years (Farley, 1969). However, the mean age of the sample employed was 22.73 years, suggesting an inadequate representation of older individuals. On the other hand, Critical Flicker Frequency has been studied extensively in both children and older adults. Cross (1963) performed a study of Flicker Frequency in children with a n age range of 6 to 12 years. This young age group showed a significant increase in Critical Flicker Frequency (i.e.. better performance) with age. Misak (1951) tested subjects with an age range of 7 to 89. They were divided into five-year age groups: 7-11, 12-16, 17-21, etc. Critical Flicker Frequency increased through the second age group (12-161, then decreased throughout the rest of the life span. McFarland, Warren, and Karis (1958) used subjects ranging in age from 13 to 89 years. They divided the groups into ten year periods: 13-19, 130-29. 30-38. etc. Their results showed that there is a steady decline in Critical Flicker Frequency over all age groups from the youngest age group to the oldest. Using adults only, from ages 18 to 60, Brozek and Keys (1945) found a steady decrease in Flicker Frequency with advancing age. Combining five studies, Weale (1965) estimated that between the ages of 20 and 60 years the average decline in fusion frequency is about seven cycles per second. However, Misiak (1951) pointed out that the drop does not become ‘significant until later in life (i.e., after 551, and Coppinger (1955) did not find a significant decrease until age 70. A review of these studies, then, shows a consistent decline in Critical Flicker Frequency, but because of the grouping of the children’s data in these earlier studies it is possible only to say that the decline starts a t about age 13 or 14. Several reasons have been offered to account for the decline in Critical Flicker Frequency over age. According to Weale (19651, senile rniosis is able to account for about 70 percent of the decline and lenticular yellowing for another 10 percent. However, Weekers and Roussel (19461, using pupil dilation with atropine, still found a Flicker Frequency decrement with age, although the decrement was reduced. Misiak (1951) does not feel that diminished pupil size can be the entire explanation, in view of the
Downloaded by [University of Arizona] at 10:53 01 February 2015
426
AMRERSON/ATKESON/POLLACK/MALATESTA
gradual decrease in Flicker Frequency before the age of a diminished mobility of the pupil and in view of the fact that injuries of the cerebrum lower Flicker Frequency. In a later study, Misiak (1961) reported a positive, although low, correlation between Critical Flicker Frequency and intelligence test scores. These date provide another indication that central factors may be involved. The Dark-Interval Threshold and Critical Flicker Frequency a r e similar tasks and possibly measure the same function. The only difference in the curves for these two tasks over the life span is a different inflection point during adolescence. Critical Flicker Frequency starts declining at about age 13 o r 14. In contrast, dark interval-threshold does not start its decline until early 20s. There are two possible explanations for this difference. The adolescent data in many studies, including the earlier dark-interval threshold study, are highly variable; also, as stated before, the groupings of the adolescent Flicker Frequency data prohibit accurate comparisons. The other explanation is offered in a study by Herrick (1974). Herrick found that the minimum interval which a subject can detect between two successive flashes must be longer than the minimum interval for many flashes. This information indicates that Critical Flicker Frequency is easier to detect than dark-interval threshold and may account for the earlier inflection point for Flicker Frequency. Finally, it is important to note that critical flicker frequency has been questioned as a measure due to the light-dark ratio confound (McFarland, Warren, & Karis, 1958). The dark-interval threshold appears to overcome this problem. The present study extends the age-range of the earlier study by Pollack, Ptashn,e, and Carter (1968,1969) and provides new data on age differences in the dark-interval threshold from young adulthood through old age. In children, stimulus persistence is a function of the interaction between the sensitivity of the receptors in the eye and the intensity of the stimulus. Receptor sensitivity decreases with age. If this process continues in adults unmediated by any other process, one would expect a
DARK-INTERVAL THRESHOLD
427
continual decline in dark-interval threshold throughout adulthood as stimulus persistence in the receptors diminishes through normal aging. METHOD Downloaded by [University of Arizona] at 10:53 01 February 2015
Subjects:
The subjects were 72 female adults who verbally reported good health. They were volunteers from the community. There = were 12 subjects in each of six age groups: 20-29 years 26.21,40-49years = 43.9),50-59 years = 55.61, 60-69years = 64.1), and 70-79 years = 76.3). Although no cohort controls were employed, all subjects possessed between 12-14 years of formal education. All subjects had a t least 20/30 corrected or uncorrected vision in both eyes as measured by the Master Orthorater.
(x
(x
(x
(x
(x
Stimulus Figures
Pairs of flashes were presented binocularly in a 3-channel electronic tachistoscope (Scientific Prototype, Model G ) . Each flash was generated by the illumination passing through an aperture 6 mm in diameter cut from the center of a black background card. The visual angle subtended by the flash was 18 min. 40 sec. Both flashes were generated in a single channel and were separated by a dark interval which varied from 0 to 250 msec. in 10 msec. steps. The brightness level was 7.704 mL as measured by the Macbeth Illuminometer at the eye piece. PROCEDURE
Initially each subject was seated in the experimental chamber for 3 minutes. Because foveal fixation was employed, this period was used in order to allow for cone adaptation (Weale, 1965). The subject then received 3 practice trials of double and single flashes in order to become familiar with the task. She was instructed to report “two” if she saw two flashes or a dark interval between the flashes and to report “one” when she
Downloaded by [University of Arizona] at 10:53 01 February 2015
saw one flash or no dark interval. Each subject was informed that there were no right or wrong answers because people judge the flashes differently. The subject had to respond with a “one” or a “two”. This forced choice procedure was used in order to minimize the possibility of a criterion shift in the older subjects. Swets (19611, employing signal detection methodology showed that by using a forced choice procedure “few observers show a bias in their responses large enough to affect the sensitivity of d’ appreciably ...and (forced choice) may be used to advantage in studies having an emphasis on sensory, rather than on motivational or response, processes.”
Thresholds for the subjects were obtained from five ascending (beginning at 0 msc) and five descending trials (beginning at 250 msec) in counterbalanced order. Employing a method of limits procedure, a trial ended when the subject reported either three consecutive “one’s’’ or “two’s.” These three consecutive responses were then averaged to obtain a measure of threshold. a t each trial. Flash durations 1and 2 were kept constant at 20 msec.
RESULTS and‘DISCUSSION The dark-interval threshold for each trial was computed and the 10 trails were averaged to obtain a threshold for each subject. An F test for homogeniety of variance was performed. Variances were not significantly different. A one-way analysis of variance revealed a significant effect of age [ P (5,66) = 4.07, p
