In IHAMS, we addressed the five main limitations of the multi-site ACTIVE study by conducting an RCT of three methods of delivering the newest version of the visual speed of processing training that does not require ongoing supervision and which can be given to participants to use on their home PCs. IHAMS randomized 681 participants to 10 hours of on-site training, 10 hours of on-site training plus four hours of booster training at 11 months, 10 hours of self-administered at-home training, or 10 hours of on-site attention control (crossword puzzle program use). Among the 620 participants (91%) re-assessed at one-year, all three methods of delivering the visual speed of processing training had statistically significant small to medium standardized effect size (Cohen's d
) improvements (i.e., faster completion times) on the primary outcome (UFOV), with the on-site booster training group having the largest improvements. The larger improvements in the on-site with booster training group were expected, and the magnitude of these effects was consistent with those observed in previous studies using the original version of the visual speed of processing training with group (i.e., non-tailored) delivery protocols, including the ACTIVE study 
. The clinical relevance of these effects is that they translate into 3.0 to 4.1 years, depending on intervention group, of protection against normal age-related declines and/or improvements in UFOV performance.
What sets IHAMS apart from ACTIVE is that it was designed to be the first RCT to determine whether visual speed of processing training would work equally well for older and middle aged adults, and whether the training would affect other important neuropsychological outcomes. We found no significant differences in standardized effect sizes between the middle (50–64) and older (≥65) age bands. Thus, it is possible that visual speed of processing training may be used to address cognitive decline at least across those life course stages for which age-related cognitive decline has been demonstrated using the large, prospective Whitehall II cohort 
. Because substantial cross-sequential data exist suggesting that age-related cognitive decline actually begins as early as age 28 
, additional RCTs of visual speed of processing on adults at substantially earlier life course stages appear warranted.
IHAMS also breaks new ground in terms of visual speed of processing's ability to affect other important neuropsychological outcomes. We found significant effects reflected in small standardized effect size (Cohen's d
) improvements (i.e., faster completion times, more correct symbol to digit matches, or more correct words) on four of the secondary outcomes—the Trails A, Trails B, SDMT, and Stroop word tests. The clinical relevance of these effects is that they translate into 2.2 to 3.5 years of protection against age-related declines and/or years of improvement in cognitive performance on Trails A, 1.5 to 2.0 years on Trails B, 5.4 to 6.6 years on SDMT, and 2.3 to 2.7 years on Stroop Word. Moreover, while the improvements on the Stroop color and color-word, COWAT, and DVT times and errors tests were not statistically significant, they were all in the expected direction. That said, it is especially important to note here that several of these neuropsychological tests are more direct and commonly used measures of executive function than the primary outcome—UFOV. Therefore, these effects on the secondary outcomes suggest the potential for having beneficial cascading effects of as little as 10 hours of visual speed of processing training in many domains of everyday life that are highly affected by executive function.
Visual speed of processing training operates by requiring peripheral information processing (the Route 66 sign) in the presence of distractors (the rabbit crossing signs) simultaneously with performing a centrally located primary attention task (identification of the car or truck in the license plate). In addition to their effects on other aspects of everyday life 
, these targeted skills have repeatedly been shown to be especially important for the operation of motor vehicles and the retrospective, concurrent, and prospective reduction of accidents and collisions 
. Indeed, in a six-year prospective follow-up to participants in the ACTIVE study, motor vehicle collisions were reduced by 43% in person-mile analyses and by 48% in the person-time analyses for the visual speed of processing training group compared to the no-contact control group 
. And as previously noted, visual speed of processing training in ACTIVE has also been shown to result in significant and substantial long-lasting improvements on a number of health and quality of life outcomes 
For several reasons, our results have important implications for clinical practice and public health. First, age-related cognitive decline is common, and processing speed has been shown to play an early and central role in the cascading process that leads to many cognitive limitations 
. Second, having a PC in the home has become relatively common, and with minimal instruction at the time of a clinical or public health encounter, patients could be given the visual speed of processing training software to take home and load onto their PCs and then use it there in private and at convenient times. Third, although we observed some adherence issues in the at-home training group, this issue likely could be addressed either by (a) a brief weekly engagement reminder delivered by e-mail or telephone, both of which could be automated, and/or (b) shifting to the new web-based version of the visual processing speed training that would overcome the difficulties faced by some participants in successfully loading the software onto their home PCs. Therefore, given the substantial evidence that it improves processing speed on a number of standard neuropsychological tests that focus on executive function, visual speed of processing training would appear to be a worthy weapon for consideration in the armamentaria of both clinical and public health practitioners in their battle against the common enemy of age-related cognitive decline.
Nonetheless, further research is needed to address several questions. These are whether: (1) the addition of brief weekly engagement reminders and/or the use of the web-based platform remediates the adherence issues observed for at-home training, (2) the training is effective for younger age bands (i.e., 30–50 year olds); (3) the observed effects last (although results from ACTIVE suggest endurance up to five years); and, (4) the training results in morphologic improvements to specific neural and structural mechanisms detectable using functional magnetic resonance imaging?
Finally, IHAMS is not without limitations, three of which warrant mention here. First, its respondents were predominantly white (95%), married (72%), college educated (71%), and healthy (68% reported excellent or very good health). Therefore, replication with more diverse and socioeconomically and health disadvantaged samples is needed. We note, however, that the ACTIVE study had a large (N
2,802), racially and ethnically diverse, and socioeconomically disadvantaged sample, and that the effects of visual speed of processing training in it were comparable across race, ethnicity, socioeconomic, and health characteristics 
Second, IHAMS participants were generally cognitively preserved. For example, among those 65 years old or older, the mean on the UFOV at baseline in IHAMS was 386 ms (standard deviation
182), which is noticeably faster than the mean of 485 ms (standard deviation
250) at baseline on the same three subtests in ACTIVE. And among those 50–64 years old in IHAMS, the mean on the UFOV at baseline was even faster at 247 ms (standard deviation
149; note that there are no age-comparable data from ACTIVE). Thus, a legitimate question is whether these statistically significant improvements on standard neuropsychological tests that target executive function are relevant. At this time we can only point to the empirical evidence shown in that 1.6 to 6.6 years of protection against age-related declines and/or years of improvement in cognitive performance were achieved, even among the cognitively preserved IHAMS participants. Further research on more cognitively challenged individuals is needed to determine if comparable or even greater effects of visual speed of processing training can be achieved.
Third, despite a well-developed and carefully executed randomization protocol, significant differences (p
<0.05) were observed when the two age bands were combined for the SDMT, Trails B, and Stroop Word outcomes (see ) at baseline between one or more of the intervention groups and the attention controls. For these significant differences, as well as for other differences that did not reach statistical significance, the attention control group was generally somewhat disadvantaged (i.e., fewer correct pairs, slower times, and fewer correct words). While this is unfortunate, we found no evidence that it led to arbitrary results. Indeed, in sensitivity analyses we re-estimated the linear mixed model within median splits on the UFOV (the primary outcome) at baseline. The standardized effect sizes (Cohen's d
) were statistically significant in both halves, but were larger in the slower performing half of the median split (Cohen's d
0.003; −0.671, p
0.001; and −0.318, p
0.004 for the on-site, on-site with boosters, and at-home training groups) than in the faster performing half (Cohen's d=
0.019; −0.464, p
0.001; and −0.375, p
In conclusion, we note that IHAMS successfully achieved all of its objectives and resolved the five limitations in the ACTIVE study. IHAMS demonstrated that all three modes of delivering the visual speed of processing training intervention significantly improved the primary outcome by clinically relevant amounts. Moreover, all three intervention arms also significantly improved several secondary outcomes that tap executive function (suggesting that the intervention effect was not merely “training to the test”), also by clinically relevant amounts. Finally, we observed comparable standardized effect sizes for both the middle and older age participants, underscoring the return on investment of beginning visual speed of processing training in middle age.