Table 2.

Results of included studies.

Search result #	Study	Control type	Control subtype	Description of conditions	Expectations measured?	Known limitation: expect-ations?	Known limitation: active control?	Positive result?	Transfer	Description of result
4	Cujzek & Vranic (2017) [28]	Active	Similar-form	Experimental: challenging computerized card game; active control: computerized dice-rolling game	No	No	—a	Yes	Far	Reasoning test (D-48) was different enough from skills required for the card game for authors to conclude that this was evidence of far transfer. Effect was maintained at 4-month follow up.
6	Souders et al (2017) [38]	Active	Similar-form	Experimental: Mind Frontiers suite; active control: puzzle game suite	Yes	—b	—a	Yes	Near	Corsi block tapping test (memory) was similar to game task. However, expectations for improvement may actually have MASKED observed improvement.
7	Kühn et al (2017) [47]	Both	Active: similar-form; passive: no-contact	Experimental: Inhibition training game on a tablet; active control: general-purpose cognitive training platform; passive: pretests and posttests only	No	No	—a	Yes	Near	Experimental group showed significant improvement on inhibition task while other groups did not.
8	Ballesteros et al (2017) [48]	Active	Similar-form	Experimental: Luminosity games; active control: The Sims or SimCity Build	No	No	—a	No	—c	Nonsignificant trend on n-back task for training; significant effect for group on oddball task in favor of active control
10	Pereira-Morales et al (2018) [49]	Passive	Passive-task	2 experimental groups: computerized training and computerized + pen and paper training; control: read brochure about cognitive training	No	No	No	Yes	Far	Experimental groups improved on cognitive tests more than passive control group. Experimental groups could not be considered active controls for each other because they were the same training, although one had additional training.
12	Lussier et al (2017) [50]	Passive	Passive-task	2 experimental groups: VPTd vs FPTe; passive control: computer classes	No	No	No	Yes	Both	VPT had larger effect than FPT for near transfer and smaller effect for far transfer.
13	Toril et al (2016) [51]	Passive	Passive-task	Experimental: Luminosity, 15 1-hr training sessions; control: met with experimenter once a month	No	Yes	Yes	Yes	Both	Jigsaw puzzle task, digit forward (short-term memory), and Faces I and Faces II (episodic memory), Corsi Blocks; also maintained after 3 months (except for Corsi blocks)
14	Hynes (2016) [43]	Passive	No-contact	Experimental: watched videos about cognitive training and played adaptive online training games; control: took pretests and posttests	Yes	—b	No	No	—c	No difference found; therefore, no evidence of transfer effects (but: exploratory study)
15	Vaportzis et al (2017) [52]	Passive	No-contact	Experimental: learned how to use regular apps on a tablet; passive control: only took pretests and posttests	No	No	Yes	Yes	Near	Improved processing speed compared to control group
17	Lussier et al (2017) [53]	Passive	Passive-task	2 experimental conditions: heterogeneous training context and homogeneous training context; control: computer lessons	No	No	No	Yes	Near	Training groups both had significantly better scores on near transfer tests than control. Heterogeneous training led to steeper improvement of dual-task coordination learning curve.
18	Grönholm-Nyman et al (2017) [11]	Active	Similar-form	Experimental: task-switching training games; control: fun games (Tetris, Angry Birds, and Bejeweled)	No	Yes	—a	Yes	Near	Very limited: only one near-transfer effect found: overall accuracy on a rule-based part. Training group also improved on the training tasks (very near transfer).
21	Guye and von Bastian (2017) [44]	Active	Similar-form	Experimental: WMf training games; control: visual search training games	Yes	—b	—a	No	—c	Bayesian analysis supported evidence for the null hypothesis. Expectation data went in opposite direction of observed result.
22	Chan et al (2016) [41]	Passive	Passive-task	Experimental: learned how to use a tablet; 2 control groups: games and radio programs at home, social groups met to discuss topics (to control for social interaction of training but limit new learning)	No	No	No	Yes	Far	iPad training improved processing speed and episodic memory compared with controls.
24	Perrot et al (2018) [54]	Both	Active: similar-for; passive: no-contact	Experimental: Kawashima Brain Training; active control: Super Mario Brothers; passive control: only pretests and posttests	No	Yes	—a	Yes	Near	Experimental training led to higher Stroop score than active control; both experimental training and active control had higher matrix reasoning scores than passive control; active control was significantly better at Corsi block test, spatial relations test, and number comparison test.
25	Nouchi et al (2016) [55]	Active	Similar-form	Experimental: processing-speed training game; active control: knowledge quiz training game	No	No	—a	Yes	Near	Improvements in processing speed, inhibition, and mood (depression scale) compared to active control
27	Belchior et al (2018) [56]	Both	Active control: similar-form; passive control: no-contact	Experimental: PositScience Insight (visual attention and processing speed); active control: Crazy Taxi; passive control: took pre and post-tests	No	Yes	—a	Yes	Near	Cognitive training improved visual attention and processing speed.
30	Yeo et al (2018) [45]	Passive	No-contact	Experimental: BrainFit software, which was controlled via BCI/dry EEGg headband; passive control: took pretests and posttests	Yes	—b	Yes	Yes	Near	Men in intervention group outperformed men in control group on RBANSh total score and subscore of Delayed Memory and Language.
31	Ordonez et al (2017) [42]	Passive	No-contact	Experimental: Actively Station cognitive training game suite, a series of games, many involving physical movement; passive control: took pretests and posttests	No	No	Yes	Yes	Far	Training group improved on global cognition, verbal fluency, memory complaints, and mood compared with control. Reported a significant result for language, which is contradicted by the data table, unless what was truly meant was verbal fluency. Other methodological problem: ACE-Ri is a dementia screening test.
34	Sosa and Lagana (2018) [57]	Passive	No-contact	Experimental: Brain Age; passive control: pretests and posttests	No	Yes	Yes	Yes	Near	Training group scored higher in brief syllable count and arithmetic assessments.

^aThe study included active control (not a limitation).

^bThe study controlled for expectations (not a limitation).

^cThe study reported no transfer effects.

^dVPT: variable priority training.

^eFPT: fixed priority training.

^fWM: working memory.

^gEEG: electroencephalogram.

^hRBANS: Repeatable Battery for the Assessment of Neuropsychological Status.

ⁱACE-R: Addenbrooke's Cognitive Examination Revised.