Knowledge, implicit metaknowledge in visual agnosia and pure alexia

Todd E. Feinberg, Diana Dyckes-berke, Christian R. Miner, David M. Roane

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Residual or implicit knowledge has been observed in patients with object agnosia, optic aphasia and pure alexia. Previous investigators have considered implicit knowledge in these patients to be dissociated from awareness on the basis of intact semantic capabilities that are consistent with right hemisphere processing. The absence of explicit verbal identification is presumably dependent upon damaged left hemisphere systems. We describe a 72-year-old woman with a left occipital infarction, object agnosia and pure alexia who was unable to explicitly identify visual stimuli (objects and words), but was able to make reliable judgements of her residual knowledge on forced-choice matching tasks. While the patient could not consistently demonstrate awareness of knowledge prior to stimulus matching ('Do you know what this is?'), she was able to reliably demonstrate awareness of knowledge for response accuracy ('Are you sure?') assessed after stimulus matching. Further, the extent of the patient's metaknowledge corresponded to her degree of preserved knowledge. We propose that this pattern of performance suggests limited or partial access to preserved semantic knowledge which, though degraded, is not 'non-conscious'.

Original languageEnglish
Pages (from-to)789-800
Number of pages12
Issue number3
StatePublished - Jun 1995
Externally publishedYes


  • Associative visual agnosia
  • Implicit knowledge
  • Metaknowledge
  • Pure alexia


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