Normal aging effects in a priming-free Stroop test

The present study investigated age differences in selective attention and the modulatory effect that variables such as verbal and spatial intelligence have on its decline.We used a Stroop colour test with no feature repetitions between subsequent trials to avoid priming effects. Sixteen healthy older (65-79 years, 8 females, MMSE=28-30/30) and sixteen younger (18-34 years, 8 females) volunteers participated in the study. The two age-groups were matched for education years and for four WAIS-R subtests (Wechsler, 1981): Block Design, Arithmetic, Vocabulary and Similarities. Error percentage was similar in the two groups [<4%, F(1,30)=.04, p=.84]. A classical Stroop effect was instead present in both younger [t(15)=-5.34, p<.001] and older adults [t(15)=-12.45, p<.001]. Older adults were 250 ms slower than younger controls, even after the data were logarithmically transformed to partially correct for general slowing [F(1,30)=58.89, p<.001]. The older group suffered from the word-colour Stroop interference more than younger adults as shown by the interaction between age and congruency [F(1,30)=20.44, p<.01]. This finding confirms that older adults have difficulty in ignoring non-target features (colour word) with respect to a target feature (word colour). However, a negative correlation between Similarities test scores and Stroop effect in the older group (r= -.58, p<.05) was obtained, indicating that those older adults with higher verbal similarities scores are those who cope better with Stroop interference. This finding suggests that there is a specific type of cognitive reserve, probably related to verbal intelligence, which preserves selective attention in normal aging.