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Abstract
This research examines the effect of time of testing on adult age differences in resistance to interference, working memory, processing speed, and vocabulary. Results show that time of testing modulates age-related differences only in the ability to resist automatic and prepotent responses. Older adults tested in the afternoon were more susceptible to interference than young adults tested at the same time of the day, and than their peers tested in the morning. In contrast, age-related differences in working memory, processing speed, and vocabulary were not modulated by time of the day. Our findings suggest that age-related modulation of performance as a function of the time of the day is specific to resistance to interference.
Acknowledgments
This study was supported by the Swiss National Science Foundation (grants no 1114052565.97 and 1213065020.01).
Notes
1Studies on time of the day effects report large variations. For the morning session, testing time starts at 8 AM (Bugg et al., Citation2006), between 8 and 9 AM (May, Citation1999; Yoon et al., Citation1999; May, Hasher, & Foong, 2005; Li et al., Citation1998), between 8 and 9.15 AM (Hasher et al., Citation2002), between 8.30 and 10.30 AM (Intson-Peterson et al., Citation1998), at 9 AM (West et al., Citation2002; Brown et al., Citation1998; Murphy et al., Citation2007), or between 9 and 10 AM (Yang et al., Citation2007). With respect to the afternoon, testing time is reported to start after 12 PM (Murphy et al., Citation2007), between 3 and 6.30 PM (Intson-Peterson et al., 1998), between 4 and 5 PM (Yoon et al., 1998; Yang et al., Citation2007), between 4.15 and 5.15 PM (Hasher et al., Citation2002), or at 5 PM (Bugg et al., Citation2006; West et al., Citation2002).
*(RT in the experimental condition – RT in the control condition)/RT in the control condition.
2The same pattern of results was obtained selecting young and older participants that were tested between 8 and 10 AM, and between 5 and 7 PM (for the Color Stroop, Reading Span, Letter Comparison, and vocabulary tests). Nonetheless, in order to have a larger sample we decided to extend time of testing from 8 AM to 12 PM and from 2 to 6 PM.
3With respect to effect size values r, indices ranging from .000 to .147 indicate small effects, from .148 to .243 medium effects, and from .287 to .707 large effects.
4The same pattern of results was obtained using residual scores. Residual scores were computed using a regression procedure, entering the response times in the control condition (signs for the interference index and prime for the negative priming index) as predictors, and the response times in the incongruent condition (for interference index) and the probe (for the negative priming index) as dependent variables, respectively. Residual scores reflect performance in the target condition (incongruent and probe conditions, respectively) adjusted for an individual's performance in the control condition (signs and prime conditions, respectively) and performance in the probe condition for an individual's performance in the prime condition. This method can be used instead of difference scores to take into account baseline differences in speed of processing (e.g., Rush, Barch, & Braver, Citation2006; Uttl & Graf, Citation1997).
Note. Reading Span test: mean number of words correctly recalled; maximal possible score = 3.5. Mill Hill test: total number of correct answers; maximal possible score = 44.
Note. Raw correlations (pairwise method). Below the diagonal morning testing; above the diagonal afternoon testing. Reading Span test: mean number of words correctly recalled; Letter Comparison test: response latencies.
***p < .001; **p < .01; *p < .05.
Note. Reading Span test: mean number of words correctly recalled; Letter Comparison test: response completion time in seconds; Mill Hill test: total number of correct answers.
Note. Raw correlations (listwise method; N = 85). Reading Span test: mean number of words correctly recalled; Letter Comparison test: response completion time in seconds.
***p < .001; **p < .01; *p < .05.