The science behind Lumessa

Testing yourself beats rereading

The idea

Trying to recall a word strengthens your memory of it more than reading it again does. It also pays to go on testing a word after you first get it right: dropping it from practice at that point loses much of the benefit.

What Lumessa does

• Every new word in Learn ends with questions, the same ones Review asks, rather than a summary to reread.
• Review is questions only. It never runs the lesson again.
• Reading a word again in My Dictionary does not count as a review and does not change when the word is next asked.

The evidence

• Roediger, H. L. & Karpicke, J. D. (2006). Test-enhanced learning. Psychological Science 17(3), 249–255.
• Karpicke, J. D. & Roediger, H. L. (2008). The critical importance of retrieval for learning. Science 319(5865), 966–968.
• Rowland, C. A. (2014). The effect of testing versus restudy on retention: a meta-analytic review of the testing effect. Psychological Bulletin 140(6), 1432–1463.

How strong: strong. One of the most often repeated findings in learning research, from many laboratory and classroom studies and a review that pooled their results.

Spreading practice out

The idea

Memory fades fastest soon after learning. Practice spread over several days beats the same amount of practice crammed into one sitting. And the longer you want to remember something, the longer the best gap between reviews tends to be.

What Lumessa does

• Review quizzes you on the words you have already learnt at progressive intervals: the next day, then after 3 days, a week, 3 weeks and 2 months, then every 3 months.
• Every word due for review is available, on free and Pro. Review has no daily limit.

The exact gaps are our choice, not a schedule any study found best: see Where we used judgement.

The evidence

• Ebbinghaus, H. (1885; English translation 1913). Memory: a contribution to experimental psychology. Teachers College, Columbia University.
• Murre, J. M. J. & Dros, J. (2015). Replication and analysis of Ebbinghaus’ forgetting curve. PLOS ONE 10(7), e0120644.
• Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T. & Rohrer, D. (2006). Distributed practice in verbal recall tasks: a review and quantitative synthesis. Psychological Bulletin 132(3), 354–380.
• Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T. & Pashler, H. (2008). Spacing effects in learning: a temporal ridgeline of optimal retention. Psychological Science 19(11), 1095–1102.
• Kim, S. K. & Webb, S. (2022). The effects of spaced practice on second language learning: a meta-analysis. Language Learning 72(1), 269–319.

How strong: strong for spreading practice out. One review pooled 317 experiments; another pooled 48 experiments with people learning a second language and found a medium to large effect. Ebbinghaus’s own curve came from one person learning nonsense syllables, though a modern repeat found much the same shape.

A missed word comes back the next day

The idea

Getting a missed item right again, soon, and then again on later days, is among the most effective ways to study. Researchers call it successive relearning.

What Lumessa does

• Miss a word in Review and it goes back to the start: it is asked again the next day, then at growing gaps once more.

The evidence

• Rawson, K. A. & Dunlosky, J. (2011). Optimizing schedules of retrieval practice for durable and efficient learning: how much is enough? Journal of Experimental Psychology: General 140(3), 283–302.
• Higham, P. A., Zengel, B., Bartlett, L. K. & Hadwin, J. A. (2022). The benefits of successive relearning on multiple learning outcomes. Journal of Educational Psychology 114(5), 928–944.

How strong: strong. Laboratory studies and a study in a real course, which also found lower anxiety among the students who used it.

Seeing the right answer after a mistake

The idea

Showing the right answer after a mistake is what turns the mistake into learning. Without it, a wrong option picked from a list can be remembered as the right one.

What Lumessa does

• You get two tries at each question. A second miss, or tapping “I don’t know this one”, shows you the right answer.

The evidence

• Butler, A. C. & Roediger, H. L. (2008). Feedback enhances the positive effects and reduces the negative effects of multiple-choice testing. Memory & Cognition 36(3), 604–616.
• Metcalfe, J. (2017). Learning from errors. Annual Review of Psychology 68, 465–489.

How strong: strong. Controlled experiments and a major review.

Building the word, not just recognising it

The idea

Recalling an answer does more for memory than picking it from a list. Practising from the meaning to the word builds the ability to say and write words; practising from the word to the meaning builds the ability to recognise them. Most learners understand more words than they can produce.

What Lumessa does

• Each word is asked up to four questions: choose its English, choose it in the language you are learning, build it from pieces of two or three letters, and build it one letter at a time.
• Three of the four show you the English and ask for the word, the direction you need to speak.
• Words too long to spell on a phone screen are asked the first two questions only.

Building a word from letters on the screen is easier than recalling it from nothing, so the research on recall applies to it only in part. And building it on a screen is not the same as saying it.

The evidence

• Rowland, C. A. (2014). The effect of testing versus restudy on retention: a meta-analytic review of the testing effect. Psychological Bulletin 140(6), 1432–1463.
• Kang, S. H. K., McDermott, K. B. & Roediger, H. L. (2007). Test format and corrective feedback modify the effect of testing on long-term retention. European Journal of Cognitive Psychology 19(4–5), 528–558.
• Webb, S. (2008). Receptive and productive vocabulary sizes of L2 learners. Studies in Second Language Acquisition 30(1), 79–95.
• Webb, S. (2009). The effects of receptive and productive learning of word pairs on vocabulary knowledge. RELC Journal 40(3), 360–376.

How strong: moderate. A review that pooled many studies found larger benefits from recalling than from recognising, and one study found short written answers beat multiple choice when the right answer was shown afterwards. The finding about direction rests on a single study.

Scored by your answers, not your feelings

The idea

People are poor judges of what they have learnt. Most believe cramming worked better even when spacing worked better; letting learners drop the words they feel they know does slight harm; overconfident learners do worse; and a session that feels smooth can mislead you about how much has gone in.

What Lumessa does

• Review is scored from your answers and how long they took. There are no buttons asking you to rate how well you knew a word.
• Review ends when the words due that day are done.

The evidence

• Kornell, N. (2009). Optimising learning using flashcards: spacing is more effective than cramming. Applied Cognitive Psychology 23(9), 1297–1317.
• Kornell, N. & Bjork, R. A. (2008). Optimising self-regulated study: the benefits — and costs — of dropping flashcards. Memory 16(2), 125–136.
• Soderstrom, N. C. & Bjork, R. A. (2015). Learning versus performance: an integrative review. Perspectives on Psychological Science 10(2), 176–199.
• Dunlosky, J. & Rawson, K. A. (2012). Overconfidence produces underachievement: inaccurate self evaluations undermine students’ learning and retention. Learning and Instruction 22(4), 271–280.

How strong: strong. Several experiments and a major review.

A memory hook for every word

The idea

Linking a new foreign word to a familiar word or a vivid picture, known as the keyword method, speeds up learning and helps recall soon afterwards. Words learnt this way can fade faster later on, so a hook works best with spaced review behind it. Pictures in the mind help memory in general; strange or bizarre pictures help only in some conditions.

What Lumessa does

• Every word has a memory hook, shown straight after the word, before the grammar note.
• A hook links sounds only where the sounds really match.
• A word with a hook goes into Review like any other, so the hook is never the only help.

The evidence

• Atkinson, R. C. & Raugh, M. R. (1975). An application of the mnemonic keyword method to the acquisition of a Russian vocabulary. Journal of Experimental Psychology: Human Learning and Memory 1(2), 126–133.
• Wang, A. Y., Thomas, M. H. & Ouellette, J. A. (1992). Keyword mnemonic and retention of second-language vocabulary words. Journal of Educational Psychology 84(4), 520–528.
• Clark, J. M. & Paivio, A. (1991). Dual coding theory and education. Educational Psychology Review 3(3), 149–210.
• McDaniel, M. A. & Einstein, G. O. (1986). Bizarre imagery as an effective memory aid: the importance of distinctiveness. Journal of Experimental Psychology: Learning, Memory, and Cognition 12(1), 54–65.

How strong: strong for recall soon after learning, with many studies since 1975. Moderate to limited over the long term, where one study found faster forgetting. Mixed for “the stranger the picture, the better”.

Common words first

The idea

A small number of very common words make up most of what people say and read. Learning the commonest words first gives you the most understanding for each word you learn.

What Lumessa does

• Each language’s words are ordered by how often they are used, then adjusted so that easy, useful words come early and more abstract ones later.

The evidence

• Nation, I. S. P. (2006). How large a vocabulary is needed for reading and listening? The Canadian Modern Language Review 63(1), 59–82.
• Adolphs, S. & Schmitt, N. (2003). Lexical coverage of spoken discourse. Applied Linguistics 24(4), 425–438.
• van Zeeland, H. & Schmitt, N. (2013). Lexical coverage in L1 and L2 listening comprehension: the same or different from reading comprehension? Applied Linguistics 34(4), 457–479.
• Webb, S. & Rodgers, M. P. H. (2009). The lexical coverage of movies. Applied Linguistics 30(3), 407–427.
• Nation, I. S. P. (2001). Learning vocabulary in another language. Cambridge University Press.

How strong: strong for how much of real speech and writing the commonest words cover, though these counts are of English. Moderate for frequency as the best order to teach in, which we treat as a starting point rather than a settled fact.

Words in sentences, with their sound

The idea

The linguist Stephen Krashen argued that people pick up a language mainly from meaningful language they understand, rather than from conscious study. It is an influential theory, but a theory, and its central split between picking up and studying is disputed. And in conversation, a word arrives by ear.

What Lumessa does

• Every word has a recording.
• Every word comes with two example sentences, each with its English.
• Pro: each example sentence has its own recording too.

The evidence

• Krashen, S. D. (1982). Principles and practice in second language acquisition. Oxford: Pergamon. A book, with no DOI.

How strong: limited. Most of Lumessa (the questions, the spelling, the schedule) is deliberate study, which is where the strong evidence is; this theory supports the example sentences only. We found no study comparing listening-first vocabulary questions with written ones, so the recordings rest on the skill they practise, not on a tested result.

Your own note on a word

The idea

Material you produce yourself is remembered better than the same material read; researchers call this the generation effect. In one study, learners who made their own flashcards learnt more than learners given ready-made ones.

What Lumessa does

• Pro: you can add a short note of your own to any word in My Dictionary.
• Your note is never shown during a question, so it cannot give the answer away.

The evidence

• Slamecka, N. J. & Graf, P. (1978). The generation effect: delineation of a phenomenon. Journal of Experimental Psychology: Human Learning and Memory 4(6), 592–604.
• Bertsch, S., Pesta, B. J., Wiscott, R. & McDaniel, M. A. (2007). The generation effect: a meta-analytic review. Memory & Cognition 35(2), 201–210.
• Pan, S. C., Zung, I., Imundo, M. N., Zhang, X. & Qiu, Y. (2023). User-generated digital flashcards yield better learning than premade flashcards. Journal of Applied Research in Memory and Cognition 12(4), 574–588.

How strong: strong in the laboratory, limited for this use. No study has tested a short personal note in a vocabulary app.

A streak that forgives a missed day

The idea

Habits form through repetition in a steady routine, and in one study, missing a single day did not make a real difference to how a habit formed. A streak shown as broken makes people less likely to carry on than one shown as unbroken, and less so when a break can be repaired. And one slip read as total failure can lead people to give up altogether, an effect first described in dieting.

What Lumessa does

• Miss one day and the streak forgives it; nothing scolds.
• Miss two in a row and it quietly resets.
• Days you choose not to practise do not count as missed.
• There is nothing to buy to protect a streak.

The evidence

• Lally, P., van Jaarsveld, C. H. M., Potts, H. W. W. & Wardle, J. (2010). How are habits formed: modelling habit formation in the real world. European Journal of Social Psychology 40(6), 998–1009.
• Silverman, J. & Barasch, A. (2023). On or off track: how (broken) streaks affect consumer decisions. Journal of Consumer Research 49(6), 1095–1117.
• Polivy, J. & Herman, C. P. (1985). Dieting and binging: a causal analysis. American Psychologist 40(2), 193–201.

How strong: limited to moderate. One study of habits in daily life, with 96 people; a set of studies of streaks among consumers; and an effect first seen in eating, not in language learning. Whether the forgiven day itself helps learners has not been tested.

Calm by design

The idea

Anxiety about a new language goes with lower achievement in it, and the fear of being judged is at the heart of that anxiety. Krashen proposed that anxiety blocks language from being taken in at all; that is a hypothesis, and a hard one to test.

What Lumessa does

• No countdowns or timers on screen.
• No leaderboards and no comparisons with other learners.
• When more than ten words are due, Review shows you ten, then offers once to carry on, without saying how many are left.

The evidence

• Horwitz, E. K., Horwitz, M. B. & Cope, J. (1986). Foreign language classroom anxiety. The Modern Language Journal 70(2), 125–132.
• MacIntyre, P. D. & Gardner, R. C. (1994). The subtle effects of language anxiety on cognitive processing in the second language. Language Learning 44(2), 283–305.
• Teimouri, Y., Goetze, J. & Plonsky, L. (2019). Second language anxiety and achievement: a meta-analysis. Studies in Second Language Acquisition 41(2), 363–387.
• Krashen, S. D. (1982). Principles and practice in second language acquisition. Oxford: Pergamon. A book, with no DOI.

How strong: moderate that anxiety goes with worse learning: a review of 105 groups of learners shows a link, though not that one causes the other, and one experiment points the same way. Limited for Krashen’s idea of a filter. No study has tested these particular design choices.

No points, no prizes

The idea

Rewards people expect for doing a task can lower their own interest in it. In learning, points and badges help a little, and their effect on motivation is small and unsteady.

What Lumessa does

• No points, no levels and no leaderboards.
• No advertising.

The evidence

• Deci, E. L., Koestner, R. & Ryan, R. M. (1999). A meta-analytic review of experiments examining the effects of extrinsic rewards on intrinsic motivation. Psychological Bulletin 125(6), 627–668.
• Sailer, M. & Homner, L. (2020). The gamification of learning: a meta-analysis. Educational Psychology Review 32(1), 77–112.

How strong: strong for the effect of expected rewards on interest, from a review of many experiments. Moderate for points and badges in learning.

Where we used judgement

Not every choice in an app can be settled by a study. These are ours, made with care, and we list them here so that nobody takes them for research findings.

• The exact gaps between reviews (the next day, 3 days, a week, 3 weeks, 2 months, then every 3 months) follow a long-standing convention, not a schedule any study found best. Studies comparing growing gaps with equal ones found no reliable difference over the long term.
• A right answer that takes more than 8 seconds halves the next gap. A slow answer may mean a weaker memory, but one study suggests a hard-won right answer can strengthen memory more, so this is an open question.
• Words you have missed several times in a row are asked first in Review.
• A word counts as remembered only if all its questions are answered right, with two tries at each.
• You spell by tapping letters on the screen rather than typing, to keep practice quick on a phone.
• The number of new words a day (3 on free; 3, 7 or 12 on Pro) and Review’s ten words at a time.
• Review asks its questions in a random order. This is not “interleaving”: research on mixing different kinds of material advises caution for vocabulary.
• A word and its opposite are taught on the same day. Studies of learning closely related words together found they can be confused with each other, so we treat it as a choice to keep watching.
• The rules for writing memory hooks are our own editorial standards.
• The lock-screen widget shows the day’s words through the day. Seeing a word is not the same as recalling it, so the widget never replaces a review.
• The lights, chime and buzz after a right answer are there for enjoyment, not learning.
• Review is free on every plan. That is a choice about fairness, though it follows from the research on testing and spacing above.

The evidence behind these cautions

• Pimsleur, P. (1967). A memory schedule. The Modern Language Journal 51(2), 73–75.
• Karpicke, J. D. & Roediger, H. L. (2007). Expanding retrieval practice promotes short-term retention, but equally spaced retrieval enhances long-term retention. Journal of Experimental Psychology: Learning, Memory, and Cognition 33(4), 704–719.
• Kim, S. K. & Webb, S. (2022). The effects of spaced practice on second language learning: a meta-analysis. Language Learning 72(1), 269–319.
• Pyc, M. A. & Rawson, K. A. (2009). Testing the retrieval effort hypothesis: does greater difficulty correctly recalling information lead to higher levels of memory? Journal of Memory and Language 60(4), 437–447.
• Brunmair, M. & Richter, T. (2019). Similarity matters: a meta-analysis of interleaved learning and its moderators. Psychological Bulletin 145(11), 1029–1052.
• Tinkham, T. (1993). The effect of semantic clustering on the learning of second language vocabulary. System 21(3), 371–380.
• Waring, R. (1997). The negative effects of learning words in semantic sets: a replication. System 25(2), 261–274.
• Nation, P. (2000). Learning vocabulary in lexical sets: dangers and guidelines. TESOL Journal 9(2), 6–10.

Coming in the next update

These are built and planned for the next version of the app. They are not in the version in the stores today.

Next update

Each word on its own schedule

Instead of the same gaps for every word, each word’s next review will be worked out from your own answers to it, using a published memory model, with today’s gaps kept as a fallback. A missed word will still come back the next day.

• Lindsey, R. V., Shroyer, J. D., Pashler, H. & Mozer, M. C. (2014). Improving students’ long-term knowledge retention through personalized review. Psychological Science 25(3), 639–647.
• Ye, J., Su, J. & Cao, Y. (2022). A stochastic shortest path algorithm for optimizing spaced repetition scheduling. Proceedings of the 28th ACM SIGKDD Conference on Knowledge Discovery and Data Mining, 4381–4390.

How strong: moderate. One classroom study found review timed from each student’s own answers beat ordinary spacing. The model’s accuracy figures come from its own developers and have not been tested independently.

Next update

Look again after a miss

After you miss a word in Review, its card (the sound, the memory hook and an example) will be shown before you go on. This rests on the research in Seeing the right answer after a mistake.

Next update

Once more before you finish

Each word you miss in Review will be asked once more at the end of the run, the other way round. This rests on the research in A missed word comes back the next day.

How we check this page

Every study on this page has been checked to exist, and its authors, year, title and journal matched against its record in Crossref, the registry behind DOI links. The one book without a DOI was checked against library catalogue records. Each description of the app was checked against the version in the stores. When the app changes, or the research does, this page changes with it.