ExoLog

What the research says, and what we did with it.

ExoLog is designed around three bodies of evidence: what aphantasia takes away, what SDAM takes away, and what decades of memory rehabilitation say about putting it back. Every claim below links to its source.

Aphantasia: memory without pictures

About 1% of people report a complete absence of voluntary mental imagery, and a further 3% report imagery that is at best vague and dim. Their autobiographical memories contain fewer details and less episodic richness, and they report lower confidence in those memories, while working memory and reasoning stay intact. Around 40% report difficulty recognising faces.

The research community is explicit that aphantasia is not a disorder. It is a variation in human experience, and it comes with strengths: people with aphantasia are over-represented in analytical and scientific work. Most discover the name for their experience in their teens or twenties, often by accident.

SDAM: facts without reliving

Severely Deficient Autobiographical Memory was described in 2015, in healthy, high-functioning adults. People with SDAM know the facts of their lives but cannot re-experience past events from the inside. Recognition memory sits near normal. Everything else about cognition is preserved. Their own description is consistent: they remember the information, not the moment.

Prevalence is unknown. The research team behind the original paper suspects 1 to 2% of the population, and thousands of people have come forward to their surveys. Aphantasia and SDAM overlap often, but each occurs without the other.

What works: reference instead of replay

External memory aids are standard practice in memory rehabilitation. In controlled trials, smartphone-based aids improved everyday remembering beyond what paper notebooks achieved. The principle transfers: these tools do not repair memory, they replace replay with reference. That is the substitution people with aphantasia and SDAM already perform with photos, lists and notes.

ExoLog formalises that substitution. Entries carry their cues with them (place, weather, time, people), answers cite their sources, and originals stay provable. The design plays to what this population does well: facts, words and structure.

Sources

  • Wright, D.J. et al. (2024). An international estimate of the prevalence of differing visual imagery abilities. Frontiers in Psychology. The largest prevalence study to date (n = 9,063): aphantasia 0.9–1.2%, hypophantasia 3.0–3.3%, combined about 4%. pmc.ncbi.nlm.nih.gov/articles/PMC11518826
  • Zeman, A. (2024). Aphantasia and hyperphantasia: exploring imagery vividness extremes. Trends in Cognitive Sciences. The field’s founding researcher reviews a decade of work: familial patterns, face-recognition difficulty in about 40%, preserved general cognition, and the position that these are variations, not disorders. cell.com/trends/cognitive-sciences/fulltext/S1364-6613(24)00034-2
  • University of Exeter (2024). A decade of aphantasia research. Accessible summary of Zeman’s review, including the “not a disorder” position and late-discovery pattern. news.exeter.ac.uk
  • University of Bonn (2024). Memories with a blind mind. People with aphantasia recall autobiographical events with fewer details and less vivid narratives, report diminished confidence, and show lower hippocampal activation during recall. sciencedaily.com/releases/2024/11/241104124140.htm
  • Palombo, D.J. et al. (2015). Severely deficient autobiographical memory (SDAM) in healthy adults: a new mnemonic syndrome. Neuropsychologia. The original description: lifelong absence of first-person reliving with intact factual memory and near-normal recognition, in healthy high-functioning adults. pubmed.ncbi.nlm.nih.gov/25892594
  • SDAM research team FAQ (Levine group, Rotman Research Institute). Prevalence suspected at 1–2% of the population, similar to other neurodevelopmental variants. Many self-identified cases have come forward beyond the published five. sdamstudy.weebly.com/faq.html
  • BBC Future (2018). Could you have this memory disorder? Report on the SDAM research programme: thousands of survey respondents, and the conclusion that the condition might not be rare. bbc.com/future
  • Efficacy of memory aids after traumatic brain injury (2017). Brain Injury. Controlled trial: smartphone-based aids improved prospective memory task completion over and above traditional memory notebooks. pubmed.ncbi.nlm.nih.gov/29036840
  • The utilisation of internal and external memory strategies (Pearson evidence-based practice brief). Review across populations: users of handheld electronic aids showed measurably fewer memory failures than users of non-electronic strategies. pearsonassessments.com (PDF)
  • Smartphones helping memory-impaired individuals (2024). Case research describing the smartphone as a valid tool for compensating for memory disorder, restoring daily independence even where memory test scores never change. pmc.ncbi.nlm.nih.gov/articles/PMC11391420

A note on method: ExoLog makes no clinical claims. The research above describes the population the product is designed for and the compensatory principle it applies. Nothing here implies that using ExoLog treats, improves or restores memory.