{"id":"https://openalex.org/W7147472568","doi":"https://doi.org/10.1109/access.2026.3679348","title":"Unsupervised Continual Learning: A Review of Challenges, Techniques, and Evaluation Metrics","display_name":"Unsupervised Continual Learning: A Review of Challenges, Techniques, and Evaluation Metrics","publication_year":2026,"publication_date":"2026-01-01","ids":{"openalex":"https://openalex.org/W7147472568","doi":"https://doi.org/10.1109/access.2026.3679348"},"language":"en","primary_location":{"id":"doi:10.1109/access.2026.3679348","is_oa":true,"landing_page_url":"https://doi.org/10.1109/access.2026.3679348","pdf_url":null,"source":{"id":"https://openalex.org/S2485537415","display_name":"IEEE Access","issn_l":"2169-3536","issn":["2169-3536"],"is_oa":true,"is_in_doaj":true,"is_core":true,"host_organization":"https://openalex.org/P4310319808","host_organization_name":"Institute of Electrical and Electronics Engineers","host_organization_lineage":["https://openalex.org/P4310319808"],"host_organization_lineage_names":["Institute of Electrical and Electronics Engineers"],"type":"journal"},"license":null,"license_id":null,"version":"publishedVersion","is_accepted":true,"is_published":true,"raw_source_name":"IEEE Access","raw_type":"journal-article"},"type":"article","indexed_in":["crossref","doaj"],"open_access":{"is_oa":true,"oa_status":"gold","oa_url":"https://doi.org/10.1109/access.2026.3679348","any_repository_has_fulltext":true},"authorships":[{"author_position":"first","author":{"id":"https://openalex.org/A5132680283","display_name":"Hang Ruan","orcid":null},"institutions":[{"id":"https://openalex.org/I155043079","display_name":"University of Nottingham Malaysia Campus","ror":"https://ror.org/04mz9mt17","country_code":"MY","type":"education","lineage":["https://openalex.org/I142263535","https://openalex.org/I155043079"]}],"countries":["MY"],"is_corresponding":false,"raw_author_name":"Hang Ruan","raw_affiliation_strings":["School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia"],"raw_orcid":"https://orcid.org/0009-0008-4075-1489","affiliations":[{"raw_affiliation_string":"School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia","institution_ids":["https://openalex.org/I155043079"]}]},{"author_position":"middle","author":{"id":"https://openalex.org/A5011074138","display_name":"Tom\u00e1s Maul","orcid":"https://orcid.org/0000-0002-3563-1115"},"institutions":[{"id":"https://openalex.org/I155043079","display_name":"University of Nottingham Malaysia Campus","ror":"https://ror.org/04mz9mt17","country_code":"MY","type":"education","lineage":["https://openalex.org/I142263535","https://openalex.org/I155043079"]}],"countries":["MY"],"is_corresponding":false,"raw_author_name":"Tomas Maul","raw_affiliation_strings":["School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia"],"raw_orcid":"https://orcid.org/0000-0002-3563-1115","affiliations":[{"raw_affiliation_string":"School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia","institution_ids":["https://openalex.org/I155043079"]}]},{"author_position":"middle","author":{"id":null,"display_name":"Yifan Chen","orcid":"https://orcid.org/0000-0003-1353-7192"},"institutions":[{"id":"https://openalex.org/I155043079","display_name":"University of Nottingham Malaysia Campus","ror":"https://ror.org/04mz9mt17","country_code":"MY","type":"education","lineage":["https://openalex.org/I142263535","https://openalex.org/I155043079"]}],"countries":["MY"],"is_corresponding":false,"raw_author_name":"Yifan Chen","raw_affiliation_strings":["School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia"],"raw_orcid":"https://orcid.org/0000-0003-1353-7192","affiliations":[{"raw_affiliation_string":"School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia","institution_ids":["https://openalex.org/I155043079"]}]},{"author_position":"middle","author":{"id":"https://openalex.org/A5047739105","display_name":"Tissa Chandesa","orcid":"https://orcid.org/0000-0002-3453-1518"},"institutions":[{"id":"https://openalex.org/I155043079","display_name":"University of Nottingham Malaysia Campus","ror":"https://ror.org/04mz9mt17","country_code":"MY","type":"education","lineage":["https://openalex.org/I142263535","https://openalex.org/I155043079"]}],"countries":["MY"],"is_corresponding":false,"raw_author_name":"Tissa Chandesa","raw_affiliation_strings":["School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia"],"raw_orcid":"https://orcid.org/0000-0002-3453-1518","affiliations":[{"raw_affiliation_string":"School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia","institution_ids":["https://openalex.org/I155043079"]}]},{"author_position":"middle","author":{"id":"https://openalex.org/A5033249915","display_name":"Iman Yi Liao","orcid":"https://orcid.org/0000-0001-5165-4539"},"institutions":[{"id":"https://openalex.org/I155043079","display_name":"University of Nottingham Malaysia Campus","ror":"https://ror.org/04mz9mt17","country_code":"MY","type":"education","lineage":["https://openalex.org/I142263535","https://openalex.org/I155043079"]}],"countries":["MY"],"is_corresponding":false,"raw_author_name":"Iman Yi Liao","raw_affiliation_strings":["School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia"],"raw_orcid":"https://orcid.org/0000-0001-5165-4539","affiliations":[{"raw_affiliation_string":"School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia","institution_ids":["https://openalex.org/I155043079"]}]},{"author_position":"middle","author":{"id":"https://openalex.org/A5128328916","display_name":"Zhiyuan Chen","orcid":null},"institutions":[{"id":"https://openalex.org/I155043079","display_name":"University of Nottingham Malaysia Campus","ror":"https://ror.org/04mz9mt17","country_code":"MY","type":"education","lineage":["https://openalex.org/I142263535","https://openalex.org/I155043079"]}],"countries":["MY"],"is_corresponding":false,"raw_author_name":"Zhiyuan Chen","raw_affiliation_strings":["School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia"],"raw_orcid":"https://orcid.org/0000-0002-4915-1593","affiliations":[{"raw_affiliation_string":"School of Computer Science, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia","institution_ids":["https://openalex.org/I155043079"]}]},{"author_position":"last","author":{"id":null,"display_name":"Man Zhou","orcid":"https://orcid.org/0000-0002-1602-7369"},"institutions":[{"id":"https://openalex.org/I47720641","display_name":"Huazhong University of Science and Technology","ror":"https://ror.org/00p991c53","country_code":"CN","type":"education","lineage":["https://openalex.org/I47720641"]}],"countries":["CN"],"is_corresponding":false,"raw_author_name":"Man Zhou","raw_affiliation_strings":["School of Cyber Science and Engineering, Huazhong University of Science and Technology, Wuhan, China"],"raw_orcid":"https://orcid.org/0000-0002-1602-7369","affiliations":[{"raw_affiliation_string":"School of Cyber Science and Engineering, Huazhong University of Science and Technology, Wuhan, China","institution_ids":["https://openalex.org/I47720641"]}]}],"institutions":[],"countries_distinct_count":2,"institutions_distinct_count":2,"corresponding_author_ids":[],"corresponding_institution_ids":[],"apc_list":{"value":1850,"currency":"USD","value_usd":1850},"apc_paid":{"value":1850,"currency":"USD","value_usd":1850},"fwci":0.0,"has_fulltext":false,"cited_by_count":0,"citation_normalized_percentile":{"value":0.36361541,"is_in_top_1_percent":false,"is_in_top_10_percent":false},"cited_by_percentile_year":null,"biblio":{"volume":"14","issue":null,"first_page":"56919","last_page":"56937"},"is_retracted":false,"is_paratext":false,"is_xpac":false,"primary_topic":{"id":"https://openalex.org/T11307","display_name":"Domain Adaptation and Few-Shot Learning","score":0.9045000076293945,"subfield":{"id":"https://openalex.org/subfields/1702","display_name":"Artificial Intelligence"},"field":{"id":"https://openalex.org/fields/17","display_name":"Computer Science"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},"topics":[{"id":"https://openalex.org/T11307","display_name":"Domain Adaptation and Few-Shot Learning","score":0.9045000076293945,"subfield":{"id":"https://openalex.org/subfields/1702","display_name":"Artificial Intelligence"},"field":{"id":"https://openalex.org/fields/17","display_name":"Computer Science"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},{"id":"https://openalex.org/T10036","display_name":"Advanced Neural Network Applications","score":0.005900000222027302,"subfield":{"id":"https://openalex.org/subfields/1707","display_name":"Computer Vision and Pattern Recognition"},"field":{"id":"https://openalex.org/fields/17","display_name":"Computer Science"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},{"id":"https://openalex.org/T11714","display_name":"Multimodal Machine Learning Applications","score":0.0034000000450760126,"subfield":{"id":"https://openalex.org/subfields/1707","display_name":"Computer Vision and Pattern Recognition"},"field":{"id":"https://openalex.org/fields/17","display_name":"Computer Science"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}}],"keywords":[{"id":"https://openalex.org/keywords/key","display_name":"Key (lock)","score":0.616599977016449},{"id":"https://openalex.org/keywords/unsupervised-learning","display_name":"Unsupervised learning","score":0.6071000099182129},{"id":"https://openalex.org/keywords/scalability","display_name":"Scalability","score":0.5418999791145325},{"id":"https://openalex.org/keywords/task","display_name":"Task (project management)","score":0.5370000004768372},{"id":"https://openalex.org/keywords/adaptation","display_name":"Adaptation (eye)","score":0.4763000011444092},{"id":"https://openalex.org/keywords/task-analysis","display_name":"Task analysis","score":0.3598000109195709},{"id":"https://openalex.org/keywords/sequence","display_name":"Sequence (biology)","score":0.35670000314712524}],"concepts":[{"id":"https://openalex.org/C41008148","wikidata":"https://www.wikidata.org/wiki/Q21198","display_name":"Computer science","level":0,"score":0.8450000286102295},{"id":"https://openalex.org/C26517878","wikidata":"https://www.wikidata.org/wiki/Q228039","display_name":"Key (lock)","level":2,"score":0.616599977016449},{"id":"https://openalex.org/C154945302","wikidata":"https://www.wikidata.org/wiki/Q11660","display_name":"Artificial intelligence","level":1,"score":0.6148999929428101},{"id":"https://openalex.org/C8038995","wikidata":"https://www.wikidata.org/wiki/Q1152135","display_name":"Unsupervised learning","level":2,"score":0.6071000099182129},{"id":"https://openalex.org/C119857082","wikidata":"https://www.wikidata.org/wiki/Q2539","display_name":"Machine learning","level":1,"score":0.5910000205039978},{"id":"https://openalex.org/C48044578","wikidata":"https://www.wikidata.org/wiki/Q727490","display_name":"Scalability","level":2,"score":0.5418999791145325},{"id":"https://openalex.org/C2780451532","wikidata":"https://www.wikidata.org/wiki/Q759676","display_name":"Task (project management)","level":2,"score":0.5370000004768372},{"id":"https://openalex.org/C139807058","wikidata":"https://www.wikidata.org/wiki/Q352374","display_name":"Adaptation (eye)","level":2,"score":0.4763000011444092},{"id":"https://openalex.org/C175154964","wikidata":"https://www.wikidata.org/wiki/Q380077","display_name":"Task analysis","level":3,"score":0.3598000109195709},{"id":"https://openalex.org/C2778112365","wikidata":"https://www.wikidata.org/wiki/Q3511065","display_name":"Sequence (biology)","level":2,"score":0.35670000314712524},{"id":"https://openalex.org/C48103436","wikidata":"https://www.wikidata.org/wiki/Q599031","display_name":"State (computer science)","level":2,"score":0.3257000148296356},{"id":"https://openalex.org/C136389625","wikidata":"https://www.wikidata.org/wiki/Q334384","display_name":"Supervised learning","level":3,"score":0.31940001249313354},{"id":"https://openalex.org/C28006648","wikidata":"https://www.wikidata.org/wiki/Q6934509","display_name":"Multi-task learning","level":3,"score":0.28290000557899475},{"id":"https://openalex.org/C77967617","wikidata":"https://www.wikidata.org/wiki/Q4677561","display_name":"Active learning (machine learning)","level":2,"score":0.275299996137619},{"id":"https://openalex.org/C108583219","wikidata":"https://www.wikidata.org/wiki/Q197536","display_name":"Deep learning","level":2,"score":0.262800008058548},{"id":"https://openalex.org/C2522767166","wikidata":"https://www.wikidata.org/wiki/Q2374463","display_name":"Data science","level":1,"score":0.26109999418258667},{"id":"https://openalex.org/C19768560","wikidata":"https://www.wikidata.org/wiki/Q320727","display_name":"Dependency (UML)","level":2,"score":0.2515999972820282}],"mesh":[],"locations_count":2,"locations":[{"id":"doi:10.1109/access.2026.3679348","is_oa":true,"landing_page_url":"https://doi.org/10.1109/access.2026.3679348","pdf_url":null,"source":{"id":"https://openalex.org/S2485537415","display_name":"IEEE Access","issn_l":"2169-3536","issn":["2169-3536"],"is_oa":true,"is_in_doaj":true,"is_core":true,"host_organization":"https://openalex.org/P4310319808","host_organization_name":"Institute of Electrical and Electronics Engineers","host_organization_lineage":["https://openalex.org/P4310319808"],"host_organization_lineage_names":["Institute of Electrical and Electronics Engineers"],"type":"journal"},"license":null,"license_id":null,"version":"publishedVersion","is_accepted":true,"is_published":true,"raw_source_name":"IEEE Access","raw_type":"journal-article"},{"id":"pmh:oai:doaj.org/article:5fb012aed4964919a9d0c02049a9a757","is_oa":true,"landing_page_url":"https://doaj.org/article/5fb012aed4964919a9d0c02049a9a757","pdf_url":null,"source":{"id":"https://openalex.org/S4306401280","display_name":"DOAJ (DOAJ: Directory of Open Access Journals)","issn_l":null,"issn":null,"is_oa":false,"is_in_doaj":false,"is_core":false,"host_organization":null,"host_organization_name":null,"host_organization_lineage":[],"host_organization_lineage_names":[],"type":"repository"},"license":"cc-by-sa","license_id":"https://openalex.org/licenses/cc-by-sa","version":"submittedVersion","is_accepted":false,"is_published":false,"raw_source_name":"IEEE Access, Vol 14, Pp 56919-56937 (2026)","raw_type":"article"}],"best_oa_location":{"id":"doi:10.1109/access.2026.3679348","is_oa":true,"landing_page_url":"https://doi.org/10.1109/access.2026.3679348","pdf_url":null,"source":{"id":"https://openalex.org/S2485537415","display_name":"IEEE Access","issn_l":"2169-3536","issn":["2169-3536"],"is_oa":true,"is_in_doaj":true,"is_core":true,"host_organization":"https://openalex.org/P4310319808","host_organization_name":"Institute of Electrical and Electronics Engineers","host_organization_lineage":["https://openalex.org/P4310319808"],"host_organization_lineage_names":["Institute of Electrical and Electronics Engineers"],"type":"journal"},"license":null,"license_id":null,"version":"publishedVersion","is_accepted":true,"is_published":true,"raw_source_name":"IEEE Access","raw_type":"journal-article"},"sustainable_development_goals":[],"awards":[],"funders":[{"id":"https://openalex.org/F4320320324","display_name":"University of Nottingham","ror":"https://ror.org/01ee9ar58"}],"has_content":{"grobid_xml":false,"pdf":false},"content_urls":null,"referenced_works_count":0,"referenced_works":[],"related_works":[],"abstract_inverted_index":{"Unsupervised":[0],"continual":[1,40],"learning":[2,7,38,41],"(UCL)":[3],"aims":[4],"to":[5,113],"develop":[6],"systems":[8],"that":[9],"can":[10],"acquire":[11],"knowledge":[12],"from":[13],"a":[14,45,56],"sequence":[15],"of":[16,59,62],"unlabeled":[17],"and":[18,74,91,95,100,105,111,120,127],"potentially":[19],"non-stationary":[20],"data":[21],"while":[22],"retaining":[23],"previously":[24],"learned":[25],"information,":[26],"without":[27],"relying":[28],"on":[29],"task":[30],"labels":[31],"or":[32],"explicit":[33],"supervision.":[34],"By":[35],"combining":[36],"unsupervised":[37],"with":[39],"(CL),":[42],"UCL":[43,116,132],"provides":[44],"framework":[46],"for":[47,130],"autonomous":[48],"adaptation":[49],"in":[50,65,88,93],"dynamic":[51],"environments.":[52],"This":[53],"review":[54,107],"presents":[55],"comprehensive":[57],"synthesis":[58],"the":[60,63],"state":[61],"art":[64],"UCL,":[66],"covering":[67],"fundamental":[68],"principles,":[69],"representative":[70],"methods,":[71],"key":[72,125],"challenges,":[73],"evaluation":[75],"practices.":[76],"Despite":[77],"recent":[78],"progress,":[79],"major":[80],"obstacles":[81],"remain,":[82],"including":[83],"catastrophic":[84],"forgetting,":[85],"distribution":[86],"shift":[87],"streaming":[89],"data,":[90],"scalability":[92],"memory":[94],"computation.We":[96],"summarize":[97],"these":[98],"challenges":[99],"organize":[101],"mainstream":[102],"solutions":[103],"accordingly,":[104],"we":[106,123],"commonly":[108],"used":[109],"benchmarks":[110],"metrics":[112],"clarify":[114],"how":[115],"methods":[117],"are":[118],"evaluated":[119],"compared.":[121],"Finally,":[122],"identify":[124],"gaps":[126],"suggest":[128],"directions":[129],"future":[131],"research.":[133]},"counts_by_year":[],"updated_date":"2026-04-21T06:05:55.347736","created_date":"2026-04-02T00:00:00"}