Edited by: Susan Mérillat, University of Zurich, Switzerland
Reviewed by: Tilo Strobach, Medical School Hamburg, Germany; Zsófia Anna Gaál, Hungarian Academy of Sciences (MTA), Hungary
This article was submitted to Cognitive Neuroscience, a section of the journal Frontiers in Human Neuroscience
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Healthy aging is associated with deficits in focused and sustained attention and executive functions. However, cognitive training (CT) provides a promising method to counteract these deficits. In the present randomized controlled study, we examined to what extent CT regimes can improve attention, verbal skills, and inhibition capacities. Over a period of 16 weeks, healthy older adults (65 years and older, mean: 70 years) received a trainer-guided multidomain paper-and-pencil and computerized CT. Pre- and post-training, a battery of psychometric tests was applied that measured the critical functions. This study used two control groups: a passive control and an active control group performing a relaxation training. Compared to a passive control group, the CT led to enhanced performance in the attentional endurance test and the interference list of the Stroop test, whereas no benefits in verbal and crystalized tests were found. Similar effects were found on the attentional endurance compared to the active control group. Additionally, word fluency was enhanced after CT, but the improvement in the Stroop test did not reach significance compared to the active control. The contents of CT were dissimilar to the psychometric tests showing far transfer, whereas no transfer to attentional or memory functions in the daily life assessed by the Cognitive Failures Questionnaire was found. This demonstrates specific gains of multidomain CT on cognitive functions not explicitly trained and lack of transfer to daily activities.
People in western societies are living longer and longer, and the incidence of mild cognitive impairment (MCI) and dementia has increased rapidly from decade to decade. The expected number of people who will be suffering from dementia is estimated at about 150 million in 2050 (
One method for improving cognitive fitness in older age is cognitive training (CT). CT for older adults is increasingly used to improve their performance in cognitive functions which are essential for activities in daily life and to maintain self-sufficiency but prone to age-related decline. In most CT studies, test-like tasks or serous games were trained by applying paper-and-pencil tasks or PC-based tasks for a period of several weeks or months. In particular, computer-based games were frequently used to assess the efficacy of CT. Indeed, a number of controlled studies showed effects of computer-based CT on attention (
An important aspect of CT research is the transfer effect referring to the ability to use the knowledge and skills learned in one scenario to achieve different goals in other scenarios (
The outcome of CT is usually indicated by performance changes in psychometric or neuropsychological tests. As outlined above, studies using behavioral measures showed training-related improvements of mnemonic and executive functions (
Moreover, a potential shortcoming of CT regimes is a rather inconsistent transfer to other, not explicitly trained cognitive functions. On the one hand, there are several positive findings regarding near or even far transfer (
The aim of the present study was to evaluate effects of multidomain adaptive paper-and-pencil and computerized CT in older individuals in a randomized controlled trial. Multidomain CTs are not limited to a single cognitive process (such as memory or processing speed) but involve a number of cognitive processes that interact and increase the demands on the cognitive system (
The data presented here are from a large training study of which some PC-based tasks using electrophysiological measures have already been reported (
We compared the performance of older participants before and after a complex adaptive multidomain CT with the performance of an active control (relaxation training) and no-contact control groups. The no-contact control group was implemented to evaluate test–retest effects (
Data of 69 participants aged 65–88 years (
Design of the study.
The study was carried out in accordance with the Declaration of Helsinki and was approved by the local Ethical Committee of the Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany. All participants gave written informed consent and received 100 Euro to recompense them for travel expenses.
Participants of the CT group were trained for 16 weeks, twice per week and 90 min per session. The CT was supervised by a professional trainer and a student assistant in small groups of no more than 12 participants. Participants who had missed regular sessions had the opportunity to take part in two additional sessions after the regular training had been completed. In the first step, participants were given basic information on cognitive functions and their relevance for the daily life to enhance compliance and motivation to train. The subsequent multidomain CT consisted of paper-and-pencil tasks and PC-based games. The difficulty of the tasks was adapted and adjusted to the current individual performance of the trainees.
The basic principle of the training was to construct exercises that are as diverse as possible. Therefore, each exercise was performed two times at most, which should ensure that participants find the training interesting and entertaining. It was not intended to train a particular cognitive ability, for example, spatial awareness or reasoning, but to employ different exercises requiring different cognitive abilities. Hence, each participant got the chance to become familiar with different types of training and to find out which ones were most suitable to him or her. Furthermore, every participant was motivated to integrate the training into his or her everyday life after the study was finished. While selecting the training programs, we took care that a low-cost continuation of the training is possible.
During the first 4 weeks, a mental activation training (MAT;
The participants of the active control group were trained similar to the CT group for a period of 4 months, twice per week and 90 min per session. This group received a relaxation training consisting of progressive muscle relaxation, autogenic training, breathing exercises, back training, massage, and Qigong. The aim of this training was to provide interesting and varied exercises which did not involve and hence should not train cognitive functions. The passive control group did not participate in any intervention.
Participants completed a number of sociodemographic questionnaires at home. During the test session, a number of paper-and-pencil psychometric tests that assessed a broad spectrum of cognitive abilities like perceptual speed, sustained and focused attention, short and working memory, long-term memory, interference processing, divergent thinking, and verbal abilities were used. After a 1-h break, a second test session using computer-based tasks with EEG recording was conducted, which was not the focus of analysis here (for further details, see
The focus of interest in the present study was fluid cognitive functions like focused and sustained attention, processing speed, cognitive flexibility, and interference control as one of the crucial executive functions. The selected tests are sensitive to subtle changes in cognitive performance of healthy adults and are mainly used in non-clinical populations. Thus, the tests are even more able to differentiate between persons with normal cognition and those with just the beginnings of MCI. The detailed description of the tests and their psychometric properties are provided in more detail in
The d2 test (
The digit symbol test (DST) is an evaluation tool used to assess psychomotor functions. Initially, it was part of the Wechsler Adult Intelligence Test (WAIS;
In the word fluency test (from LPS,
The Stroop test (from NAI,
The MWT-B (
To assess a possible far transfer of CT to the performance in daily activities, the CFQ (
A series of two-way mixed analyses of variance with repeated measures (mixed ANOVAs) with the factors Group (CT vs. active control group and CT vs. passive control group) and Session (t1 vs. t2) were conducted. Significant interactions were further analyzed using
The repeated-measures ANOVA for the comparison between the CT and the passive control groups for the number of correctly crossed d2 symbols (
Number of correctly marked symbols in the d2 test at pre- and post-measures in the CT group (CT), passive control group (Control), and active control group (Active Control). Error bars reflect standard errors.
The number of correct symbols in the d2 test for the comparison between the CT and the active control group revealed a main effect of Session, indicating a larger number of crossed symbols at t2 than at t1 (t1: 370 ± 9.5 vs. t2: 403 ± 10.5;
The total number of correctly substituted digit–symbol items for the comparison CT vs. passive control groups (
Total number of correctly substituted symbols in the DST at pre- and post-measures in the CT group (CT), passive control group (Control), and active control group (Active Control). Error bars reflect standard errors.
The total number of correctly substituted digit–symbol items for the comparison CT vs. active control increased from t1 to t2 (t1: 45.4 ± 1.0 vs. t2: 47.4 ± 1.1;
The total number of words for the comparison between CT and passive control groups (
Total number of correctly produced words in the word fluency task at pre- and post-measures in the CT group (CT), passive control group (Control), and active control group (Active Control). Error bars reflect standard errors.
The number of words for the comparison between CT and active control groups increased only slightly from t1 to t2 (t1: 41.9 ± 1.3 vs. t2: 44.0 ± 1.6;
In the first step, a series of ANOVAs were conducted for the CT vs. passive control group and CT vs. active control group for parts 1, 2, and 3 of the Stroop test.
In part 1 of the Stroop test (
Time to perform part 1 of the Stroop task (reading of color words) at pre- and post-measures in the CT group (CT), passive control group (Control), and active control group (Active Control). Error bars reflect standard errors.
For the comparison between the CT and active control groups in part 1, no effect of Session was observed (t1: 14.8 ± 0.4 s, t2: 14.6 ± 0.3 s;
The time to name color blocks in part 2 of the Stroop test for the CT and passive control groups (
Time to perform part 2 of the Stroop task (naming of color squares) at pre- and post-measures in the CT group (CT), passive control group (Control), and active control group (Active Control). Error bars reflect standard errors.
For the CT and active control groups, the time to name color blocks in part 2 of the Stroop test was shorter at t2 than at t1 (21.4 ± 0.4 vs. 22.3 ± 0.6;
For the CT and the passive control groups, the time for processing the interference list in part 3 (
Time to perform part 3 of the Stroop task (interference list) at pre- and post-measures in the CT group (CT), passive control group (Control), and active control group (Active Control). Error bars reflect standard errors.
The time for processing the interference list in part 3 for the CT and active control groups was shorter at t2 than at t1 (41.0 ± 0.8 vs. 44.0 ± 1.2 s;
Finally, we analyzed the time difference between Stroop 3 and Stroop 2 to assess the baseline-corrected interference effect (see
Interference score in seconds (Stroop 3–Stroop 2) at pre- and post-measures in the CT group (CT), passive control group (Control), and active control group (Active Control). Error bars reflect standard errors.
For the comparison between CT and active control, no Group effect or interaction between Group and Session was found (both
The number of correctly detected words in the test measuring crystallized intelligence (
Total number of correctly crossed words in the MWT-B at pre- and post-measures in the CT group (CT), passive control group (Control), and active control group (Active Control). Error bars reflect standard errors.
Similarly, no effect of Group or Session (both
To assess the training-related gains and transfer effects,
Cohens’
Psychometric task | CT | Passive control | Active control |
d2 test | 1.00 | 0.29 | 0.24 |
Digit symbol test | 0.48 | 0.06 | 0.08 |
Word fluency test | 0.46 | 0.15 | 0.07 |
Stroop task (part 1) | –0.25 | –0.01 | –0.11 |
Stroop task (part 2) | –0.41 | –0.19 | –0.16 |
Stroop task (part 3) | –0.43 | –0.09 | –0.32 |
Stroop (part 3–part 2) | –0.32 | –0.01 | –0.27 |
MWT-B | 0.30 | 0.12 | 0.05 |
No group differences in the CFQ were found at the post-test measurement (CT group: 29.2, passive control group: 28.4, active control group: 27.2; both
The present study evaluated effects of a 16-week multidomain CT on different cognitive functions in older participants. Compared to an active control group receiving relaxation training and a passive (no-contact) control group, participants in the CT group showed enhancement of sustained and focused attention (attentional endurance) as assessed by the d2 test. The same pattern was found for the digit symbol substitution test assessing focused attention and psychomotor speed, although the interaction Group × Session showed only a trend compared to both control groups. However, whereas no significant interaction was observed in the word fluency test after CT compared to the passive control group, this difference was substantial in comparison to the active control group. In the simple tasks of the Stroop task (word reading and color naming), no interactions between Group and Session were found (though descriptively, the participants of the CT group showed faster responses than did the control groups). Interestingly, the results of the interference list (Stroop 3), in which interference processing and inhibitory control were required, revealed divergent patterns: while there was a similar improvement of performance in the CT and in the active control groups from pre- to post-measure, the participants of the CT group showed a clear performance improvement after training compared to the passive controls. No effects or interactions were found in the MWT-B that evaluates crystallized intelligence. Thus, crystallized cognitive functions were not improved after training. The findings indicate also that basic cognitive functions like sensory abilities and psychomotor speed were not affected by the CT, whereas higher-order cognitive functions were enhanced. Additionally, though some interactions between Group and Session did not reach significance, the effect sizes of the CT group were consistently larger compared to those of the control groups. For example, the improvement in the d2 task after CT corresponded to one standard deviation. Taken together, these observations indicate that a multidimensional training consisting of a number of short exercises is suitable to improve some attentional and executive functions in older adults. The findings are consistent with a number of previous training studies reporting positive effects of CT on executive functions in older age (
The comparison between the CT and the two control groups provided similar effects, but there were also some interesting differences in the results. First, word fluency was improved after CT and reached significance relative to the active control group but did not reach significance compared to the passive control group. In contrast, performance in the interference list of the Stroop test was significantly faster in comparison to the passive control group, but not to the active control group. While the first observation was probably due to differences in power, the unspecific enhancement in the interference list of Stroop 3 suggests that relaxation training, which was used in the present study as active control and was supposed not to involve cognitive resources, may reduce distractibility (
Our study also aimed at transfer effects. Near transfer indicates performance enhancement in structurally similar tasks involving overlapping neural circuits, whereas far transfer denotes effects on structurally dissimilar tasks (
However, it has to be noted that near and far transfers have been differently defined in the literature. Some authors proposed that far transfer is given when dissimilar tasks were used for training and evaluating CT effects. For example,
Nevertheless, as outlined above, far transfer to dissimilar cognitive tasks was found in the present study. This is in line with behavioral and electrophysiological findings obtained in the same study and reported previously, including computer-based versions of task switching (
Overall, transfer effects are controversially discussed as the results are rather inconsistent (
There are some limitations of the study that have to be acknowledged. Firstly, the functional overlap between the training and test tasks is not easy to evaluate because of a variety of different games and subtasks that were used. Additionally, paper-and-pencil trainings that trained working memory and speed of processing as well logical thinking were used. The goal of our multidomain training was to maximally enhance cognitive functioning in older adults by offering them an interesting and varying program with a large fun factor to fill more than 30 training sessions and to maintain their motivation to train across this relatively long time.
Secondly, it was not possible to evaluate individual training data to assess interindividual differences in the progress of training-induced gains. This was due to partly using a number of freely available internet games that did not record or permanently store the training data. Moreover, the training difficulty was individually adjusted to the training progress of the participants who absolved individually different training units, making the analysis and interpretation less meaningful.
The present study provides further evidence for positive effects of trainer-guided multidomain CT on fluid intelligence in older age. In particular, a 16-week-long CT substantially improved attentional endurance and interference processing. These effects were specifically evident for tests that require verbal fluency or selection of predefined targets and ignoring distractors, indicating enhancement of executive functioning like inhibitory control. Moreover, a transfer effect was observed to non-explicitly trained functions, but not to performance in daily life activities. The study contributes to the literature showing positive effects of CT in old age, especially on executive functions that reflect a crucial aspect of cognitive performance highly susceptible to aging.
The raw data supporting the conclusions of this article can be provided by the authors on request.
The studies involving human participants were reviewed and approved by Ethical Committee of the Leibniz Research Centre for Working Environment and Human Factors, Dortmund. The patients/participants provided their written informed consent to participate in this study.
PG designed the study, analyzed the data, and wrote the manuscript. MF designed the study. ST, EW, and SG wrote and revised the manuscript. All authors approved the final version of the manuscript.
MF was employed by the company Institut für Arbeiten Lernen Altern GmbH. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We thank Claudia Frieg, Ines Mombrei, and Christiane Westedt for conducting the testing and Ludger Blanke for developing the software and technical support. We thank the trainers of the CT, Rita Pfeiffer, and of the relaxation training, Antje Dreikaus. We would also like to thank the reviewers for their valuable comments on the previous version of the manuscript. The research reported in the present article was partly funded by the German Insurance Association (GDV, Gesamtverband der Deutschen Versicherungswirtschaft). The publication was supported by the open-access fund of the Leibniz Association.
The appendix contains a detailed description of the exercises included in the cognitive training and the schedule of the cognitive training procedures.
The training begins with easy exercises to make quick effects possible. By creating more challenging instructions and by allowing less time for task performance, the level of difficulty gets enhanced gradually.
The training consists of the following modules:
Information processing speed: Time limited visual search. Different forms, numbers and letters are used. Identification of single words in randomly assembled sequences of letters. The hidden words are arranged forwards, backwards, vertically, horizontally or diagonally.
Memory span: Keep several numbers, words or pictures in memory and immediate recall of words or identifying missing words.
Basic learning speed: Memorization of faces with personal data and memorization of faces with distracting stimuli.
Double:
There is a yellow ball and a red box presented on the screen. With one hand, the participant has to use the computer mouse in a certain way in order to put the ball into the box. With the other hand, the participant has to type the presented words as quickly as possible. This exercise trains peripheral visual attention as well as the coordination of multiple operations.
Euro Coins:
There are many different coins in a purse. The task is to assemble specific coins in order to reach a given amount. This should be done as often as possible within a specific interval. Visual perception, selective attention and mental arithmetic are trained.
Response:
Balloons float past the window of an aircraft. The task is to click as quickly as possible on the relevant balloon appearing on the left side of the window. This exercise trains selective attention and distractor inhibition.
Palpation:
At the time when a green light appears on the screen, one of five given forms is hidden behind a big picture. The participant’s task is to touch the form by use of the computer mouse in order to decide which form is hidden in the current trial. To make a choice, the participant has to click on the corresponding picture. There is only one attempt in each trial. This exercise trains perception and spatial-visual memory.
Double Words:
A pool of words is given, which contains each single word twice. The task is to click on the currently relevant word by use of the computer mouse. There are five attempts in each trial to find the correct word. This exercise trains the participant’s memory.
Chimpanzee test:
Nine fields are presented containing single digits for a short time. After the digit’s disappearance, the participants are instructed to click on the fields in ascending order to reproduce the positions, where the respective figures were shown. Here, visual perception, short-term memory and spatial-visual memory can be trained.
Colors:
The participants have to memorize the colors of a presented picture. The task is to “repaint” the image by first clicking on a “paint pot” and then clicking on the image area. The participants receive one point for each correctly chosen color. Visual perception, short-term memory and spatial-visual memory can be trained by this exercise.
Figurative Thinking:
In each trial, two, almost identical pictures are presented. There are exactly three differences between the two pictures, which the participant has to detect as quickly as possible. This exercise is designed to support selective attention.
Capacity:
The task is to catch vertically falling balls with a basket as accurately and quickly as possible. To adjust the basket, the participant has to use the computer mouse. Simultaneously, as many numerical and alphabetical tasks as possible have to be performed. Spatial-visual attention, arithmetic, concentration and of multiple task performance should be improved by this task.
Concentration:
In each trial, an “E” surrounded by a certain number of dots is presented. The task is to identify every E which is surrounded exactly by three dots as quickly as possible. Concentration and visual attention are trained by this task.
Pattern Matching:
Four pictures are presented in each trial. There is always one original, two rotated versions of the original and one differing picture, which the participant has to identify by clicking on it. This exercise trains the abilities of mental rotation and visual search.
Person Memory:
This exercise aims at memorizing and recognizing names and faces. First, a sequence of faces and names is presented and the participants explicitly have to memorize the names. Then, faces are displayed with various names. The participant has to decide which name is related to a particular face. This exercise specifically trains object recognition.
Visual Acuity:
In each trial, two pictures are presented. As quickly as possible, the participant has to decide whether the two pictures are identical. Visual acuity and visual search are trained by this task.
Response Capacity:
Two objects are presented side by side. The participant has to decide whether the objects are identical. A response is required if the objects are identical. This exercise aims at improving visual search and decision time.
Memory for Numbers:
The participant has to memorize and reproduce numbers presented on the screen. The length of each number is adapted to the participant’s capacity. The more digits a number contains, the more time is granted for memorizing and reproducing the number. Primarily, this exercise trains the memory for numbers, but also working memory in general.
A schedule of the cognitive training program.
Week | Session | Exercise |
1 | 1 | MAT |
2 | MAT | |
2 | 3 | MAT |
4 | MAT | |
3 | 5 | MAT |
6 | MAT/Sudoku | |
4 | 7 | MAT/Sudoku |
8 | MAT/Sudoku | |
5 | 9 | Mental-Aktiv/Ahano/Sudoku |
10 | Mental-Aktiv/Ahano | |
6 | 11 | Mental-Aktiv/Ahano |
12 | Mentaga/Mental-Aktiv/Ahano | |
7 | 13 | Mentaga/Mental-Aktiv/Ahano |
14 | Mentaga/Ahano | |
8 | 15 | Mentaga/Ahano |
16 | Mentaga/Ahano/Sudoku | |
9 | 17 | Mentaga/Ahano/Sudoku |
18 | Mentaga/Sudoku | |
10 | 19 | Mentaga/Sudoku |
20 | Mentaga/Sudoku | |
11 | 21 | Mentaga |
22 | Mentaga | |
12 | 23 | Mentaga/Ahano |
24 | Mentaga/Ahano | |
13 | 25 | Mentaga/Sudoku |
26 | Mentaga/Ahano | |
14 | 27 | Mentaga/Ahano |
28 | Mentaga/Ahano | |
15 | 29 | Mentaga/Ahano |
30 | Mentaga | |
16 | 31 | Mentaga/Ahano/Sudoku |
32 | Mentaga/Sudoku |