Deborah Finkel, assistant professor of psychology at Indiana University Southeast, has compared different age groups and different levels of mental performance within age groups, and employed behavior genetics methods to determine the sources of individual differences. Behavior genetics--using the methods of genetic research in the investigation of human behavior--originated with the English scientist Sir Francis Galton (1822-1911), a cousin of Charles Darwin. Galton, Finkel says, "applied the ideas of his cousin to human traits such as intelligence, concluding that intelligence resulted solely from heredity, and environment had no influence." In her studies of memory, however, Finkel has found that environment plays an important role.
Consistent with the classical methods of behavior genetics, Finkel conducts much of her memory research with sets of twins as subjects. Since 1988, leading to her Ph.D. at the University of Minnesota in 1992, Finkel has been associated with that university's ongoing Minnesota Twin Study of Adult Development and Aging. Her collaborator has been Matt McGue, a professor of psychology at Minnesota and founder of the Minnesota Twin Study.
"The main scientific value of using sets of twins as subjects is that twins allow investigators to determine the extent to which the variability in a trait is genetically or environmentally determined," Finkel says. Studying twins and other closely related groups of people, she notes, provides an investigator with "information about both the genetic relatedness between a pair of individuals and the extent to which the rearing environment was shared." She adds, "Using this information, and increasingly sophisticated statistical models, behavior geneticists can determine what percentage of the variance in a trait results from genetic variance and what percentage results from environmental variance."
In a recent article in the journal Psychology and Aging (1993, volume 8), Finkel describes another of her memory experiments that probes the relative roles of heredity and environment by investigating the performance of 160 sets of twins, ranging in age from sixty to eighty-eight, on a variety of memory tasks. (For example, in one task, a subtest from the standardized Wechsler Memory Scale, subjects were asked to recall simple geometric figures.) In the overall investigation, Finkel and McGue report, "Behavior genetic analysis suggested that approximately 55 percent of the variance in memory performance could be attributed to genetic influences."
This percentage interests Finkel, in light of findings reported by other memory researchers. "I've found only two other twin studies of older adults that included measures of memory performance," she comments. "Both of those studies found estimates of heritability closer to 35 percent. However, both studies used very different measures of memory." Finkel emphasizes that the term memory embraces a complex assortment of processes.
For the next few months, as a visiting researcher at Sweden's Karolinska Institute, Finkel will collaborate with other scientists in the Swedish Adoption/Twin Study of Aging and possibly teach a course there on using the statistical software program LISREL to analyze twin study data.
At IU Southeast, Finkel's teaching, introductory and advanced, benefits from her research; her courses such as "Behavior Genetics" and "Adult Development and Aging" cover topics crucial to understanding modern psychology. She also has been conducting memory experiments at IUS. One experiment extends her earlier study of three age groups' performances on a memory task, and the other examines memory performance in college students. In addition, Finkel continues her involvement with the Minnesota Twin Study. In all of her research, the fragility of memory serves as a recurrent theme. Commenting on a study in which she and McGue compared parents' and children's memories of child-rearing experiences, Finkel says, "Memory is not a videotape stored in our heads that we can review at will. . . . Memory, by its very nature, is imperfect."