An examination of mediators of the transfer of cognitive speed of processing training to everyday functional performance.

The quality of life of older adults is negatively impacted by cognitive impairments. Although several approaches for improving cognitive functioning in older adults are available, few have actually transferred beyond the skills practiced in training (Noack, Lovden, Schmiedek, & Lindenberger, 2009), especially to everyday functional performance. Speed of processing training (SOPT) is one approach that has resulted in improvements in both cognitive and everyday functional abilities (Ball, Edwards, & McGwin, 2010; Edwards, Delahunt, & Mahncke, 2009; Edwards, Myers, et al., 2009; Edwards, Wadley, et al., 2005; Roenker, Cissell, Ball, Wadley, & Edwards, 2003). However, little is known about the mechanisms of SOPT. To this end, the present study examines mediators of SOPT transfer to everyday functioning. Over the past 25 years, many studies have demonstrated that, among older adults without dementia, cognitive abilities may be enhanced through training (e.g., Ball et al., 2002; Kramer, Larish, & Stayer, 1995; Labouvie-Veif & Gonda, 1976; Peretz, Korczyn, Shatil, Aharonson, & Birnboim, 2011; Rasmusson, Rebok, Bylsma, & Brandt, 1999; Rebok, Rasmusson, & Brandt, 1996; Schaie, Hertzog, Willis, & Schulenberg, 1987). Typically three general approaches for maintaining or improving cognitive function with increasing age have been employed (Smith et al., 2009): 1. strategy enhancement; 2. cognitively-stimulating activity; and, 3. perceptual-cognitive, also called process-based, training (Lustig, Shah, Seidler, & Reuter-Lorenz, 2009). The third approach, which is the focus of the present study, involves practice of exercises aimed at enhancing information processing. Speed of Processing Training (SOPT) SOPT is a process-based, computerized cognitive intervention that involves intensive practice of visual exercises designed to improve speed and accuracy of information processing (Ball, Edwards, & Ross, 2007; Edwards et al., 2002; Edwards, Wadley, et al., 2005; Roenker et al., 2003; Vance et al., 2007). This training program is aimed at enhancing performance on the Useful Field of View Test (UFOV1), a measure of processing speed for visual attention tasks which examines the speed at which one can rapidly process visual stimuli (Edwards, Vance, et al., 2005). This valid and reliable assessment has been used in prior research (e.g., Edwards, Wadley, et al., 2005) and consists of four subtests (processing speed; divided attention; selective attention; selective attention in conjunction with same/different discriminations) of increasing difficulty. Studies using SOPT have found large intervention effect sizes for UFOV performance as well as far transfer to real-world, performance-based tasks (which are not practiced in training) including driving outcomes (Ball et al., 2010; Edwards, Delahunt, et al., 2009; Edwards, Myers, et al., 2009; Roenker et al., 2003) and the Timed Instrumental Activities of Daily Living (TIADL) Test (Edwards et al., 2002; Edwards, Wadley, et al., 2005). To our knowledge, as compared to other cognitive intervention techniques, only SOPT has been shown to enhance performance of IADL. Edwards et al. (2002) examined the impact of SOPT among a community-dwelling sample of 97 older adults (with no vision, UFOV, or mental status exclusion criteria). Results indicated that SOPT resulted in a 0.61 sd improvement on UFOV as compared to a no-contact control group, and that training transferred to improved performance on the TIADL test (Edwards et al., 2002). In a subsequent study, Edwards et al. (2005) examined the cognitive and everyday functioning among older adults (N=126) randomized to either SOPT or a social- and computer-contact control group. SOPT training effect sizes averaged 1.94 sd of improvement in UFOV performance relative to the controls indicating that gains were not due to social- or computer-contact (Edwards, Wadley, et al., 2005). These training gains transferred to improved TIADL performance. Given that the participants in the control condition were learning a new cognitively-stimulating activity (internet training), the mechanism of SOPT gains is not likely to be merely cognitive stimulation. Dual-Task and Task Switching Training Other process-based cognitive interventions, task-switching training and dual-task training, have also resulted in near transfer to untrained tasks, with some evidence of far transfer (Baron & Mattila, 1989; Bherer et al., 2005, 2008; Gopher, Weil, & Bareket, 1994; Karbach & Kray, 2009; Karbach, Mang, & Kray, 2010; Kramer et al., 1995; Kramer, Larish, Weber, & Bardell, 1999; Li et al., 2010; McDowd, 1986). For example, Karbach and Kray (2009) examined the effects of task switching training, which involves perceptual practice to quickly make one of two possible judgments about visual stimuli (i.e., category or size). Results indicated that training enhanced task switching and transferred to improved performance on other measures of fluid ability including Stroop, verbal and spatial working memory, and reasoning. Similarly, Bherer and colleagues (Bherer et al., 2005, 2008) examined dual-task training in which participants practice quickly making perceptual discriminations of visual and auditory targets that are either presented simultaneously, or with an inter-stimulus interval of 200 ms. Results indicated improvement in dual-task performance with new stimuli similar to those practiced in the training. Li and colleagues (2010) further examined the impact of this training paradigm and demonstrated far transfer of dual-task training to improved standing balance. Kramer and colleagues trained dual-task performance of older adults by requiring participants to practice two tasks concurrently and individually (Kramer et al., 1995; Kramer et al., 1999). The training tasks involved monitoring visual displays and required tracking a moving target by moving a cursor, and making an appropriate key press corresponding to the spatial position of a particular target in an array. Two training conditions were used in which participants applied a strategy to either devote equivalent priority to the two concurrent tasks (fixed), or to vary priority between the two tasks across practice trials. Dual-task training, particularly the variable priority condition, transferred to improved performance on a task unlike those practiced in training, alphabetic arithmetic (i.e., K-3= ? answer: H). Training also transferred to a task requiring monitoring of an array of 6 gauges (in which participants were required to reset the gauge with a key press); a task that could potentially have everyday functional relevance (Kramer et al., 1999). Gopher and colleagues found that a similar dual-task training paradigm in a game-context, Space Fortress, transferred to improved flight simulator performance (Gopher et al., 1994). Research on these techniques of cognitive training (e.g., SOPT, task switching, dual task training) has led to the assertion that process-based training techniques may be most likely to result in far transfer to tasks dissimilar to those practiced in training (Karbach et al., 2010; Lustig et al., 2009). However, the underlying mechanisms of transfer of these techniques are not well explored. Mechanisms of Cognitive Training Studies of the mechanisms of cognitive training are few, although some studies have examined how cognitive benefits are derived from training by exploring neural correlates (Berry et al., 2010; Scalf et al., 2007; Takeuchi et al., 2011). Takeuchi and colleagues (2011) used functional Magnetic Resonance Imaging (fMRI) with young adults to show that cognitive training designed to enhance processing speed reduced regional gray matter volume, which was interpreted as reflecting more efficient cognitive processing. Scalf and colleagues used fMRI to examine how practice on a functional field of view task resulted in cognitive improvements among older adults. Results indicated training-related increased activation in brain regions associated with shifting and reorienting attentional focus to relevant stimuli. Similarly, Erickson and colleagues (Erickson et al., 2007a; Erickson et al., 2007b) examined mechanisms of dual task training using fMRI. Improvements in dual task performance were associated with shifts in regions of brain activation. The authors concluded that training led to more efficient processing, perhaps due to enhanced allocation of attention. In an Event Related Potential (ERP) study, Berry et al. (2010) found that training on perceptual processing of Gabor patches (Sweep Seeker task of the InSight cognitive training program) resulted in a decrease in the amplitude of the N1 ERP component following training. The N1 is indicative of early visual motion detection and is modulated by attention. The results suggest attentional focus was more efficient following training. Caution is advised in interpreting the results of such studies, as the effects are likely to be specific to the given training program (Takeuchi et al., 2011). To our knowledge no published studies to date have examined the mechanisms of far transfer of cognitive training. The present analyses are designed to further examine transfer of SOPT. Specifically we sought to determine whether the IADL performance improvements can be attributed to cognitive improvements in UFOV as a result of SOPT, and, if so, whether training transfer was mediated by performance on a particular UFOV subtest. One way to explore causal pathways, or mechanisms of action, is through statistical mediation analyses. Thus, mediators of the transfer of SOPT to improved TIADL performance are explored.