A study of implicit memory and temporal gradients in retrograde amnesia and semantic dementia.
This thesis sets out to test some of the predictions proposed by a recent
connectionist model of memory and amnesia. The model proposes a time limited role for
the hippocampus in memory consolidation in which memories once dependent on the
hippocampus become independent of the hippocampus over time and fully supported by
the neocortex. The predictions that are made by the model are that there will be
memories in retrograde amnesia that are only available through implicit tests of memory;
that implicit memory in retrograde amnesia will show a temporal gradient; that semantic
dementia patients will show a 'reverse temporal gradient' in retrograde amnesia; and that
implicit learning in semantic dementia will be impaired.
Chapter 1 reviews some of the current literature relevant to these predictions.
Chapter 2 contains the psychometric details of the patient groups taking part, relating
these to the underlying neuropathology. Chapter 3 describes three studies which examine
recognition and familiarity of famous faces and names from the retrograde period and
temporal gradients in familiarity responses. The results are discussed in terms of face and
name recognition models. Chapter 4 describes a study that provides evidence of implicit
knowledge of famous faces using an indirect method of testing. Chapter 5 is a single-case
study using a reaction time measure for new words introduced into the English language
during the retrograde period. Chapter 6 is a single-case study of a patient with semantic
dementia. The three experiments in this chapter investigate implicit learning in a
repetition priming task and the relationship between forced choice recognition of famous
faces and famous names.
Finally, Chapter 7 discusses the findings in terms of the predictions of the
connectionist model of memory and amnesia. The conclusion is that whilst there is
evidence of implicit memory in retrograde amnesia, this is unlikely to show a temporal
gradient. The prediction that there would be a 'reverse temporal gradient' and impaired
implicit memory in semantic dementia was not upheld, and this is discussed in terms of
the underlying neuropathology and how it relates to this and other models of memory.