neuropsych week 4

• Semantic Memory


  Our fact and general knowledge
• Episodic Memory


  Our knowledge of personal events
• Procedural Memory


  Our knowledge about certain complex motor activities
• Patients with Amnesic syndrome typically present with varying degrees of episodic memory impairment
• Neurological damage can also result in patients who present with varying degrees of semantic memory impairment
• Semantic Memory Architectural Principles


  How the store of all our semantic knowledge (or mental lexicon) is organised
• Collins & Quillian (1969) model of semantic memory


  • Word meanings are represented in a semantic network, with each word consisting of conceptual 'nodes' that are connected to each other such that activation of a single node passes activation on to other interconnected nodes
• Collins & Loftus (1975) revision of the semantic memory model


  • Included the principle of 'spreading activation' such that connections between nodes in the model vary both in activation strength and relative distance
• Warrington (1975) used the hierarchical model as the basis for understanding a patient with a progressive deterioration of semantic memory (Semantic Dementia)
• Semantic Dementia


  As the patient declines, they don't simply lose all information about a concept at once, instead they lose fine-grained item specific information first, retaining higher order semantic information about items
• Acquisition of semantic information for children


  They learn broad conceptual information before more fine-grained information
• The initial semantic memory model still produces several unanswered questions
• Imageability/Concreteness effect


  Patients with disruption of semantic memory are typically far superior at accessing conceptual information specific to words that are highly imageable or concrete relative to low imageability or abstract words
• Deep Dyslexia


  • Patients who not only demonstrated better performance reading high relative to low imageability words, but also make semantic errors in reading
• Deep Dysphasia


  • The equivalent type of patient performance has also been reported in repetition
• Some patients have been reported with the reverse imageability/concreteness effect, performing better on abstract relative to concrete words
• The presence of cases with the reverse concreteness effect remains controversial, but there have been more recent studies in which such a pattern has been observed
• Imageability/Concreteness importance


  The more concrete a word is, the easier predicates can be generated for them
• Plaut & Shallice (1993) connectionist model of reading


  • Concrete words have more semantic 'features' and therefore have richer overall conceptual representations, making them more robust to disruption
• McClelland, McNaughton & O'Reilly (1995) Complementary Learning Systems Theory


  Semantic information can be obtained by two complementary processes: a slow-learning semantic system and a fast learning system in the medial temporal lobes that rapidly generates connections within this system
• Patients with Amnesia have little semantic memory impairment, but are very poor at acquiring new factual information
• Temporal lobes' role in semantic memory


  • The anterior part of the inferior temporal gyrus is considered the terminus of the ventral visual processing stream, the middle temporal gyrus integrates input from multiple modalities, and the superior temporal gyrus is important for speech and auditory perception
• Damasio's model of semantic memory


  Semantic features are stored within particular primary association areas, with 'convergence zones' in the temporal lobe acting as a 'relay' station for conceptual representations
• Rogers et al. (2004) model of semantic memory


  The anterior temporal lobes act as a 'hidden layer' that drives amodal semantic representations, helping determine semantic similarity independent of surface features
• Category Specific Deficits in Semantic Memory


  Patients can present with impaired comprehension or semantic processing of a particular category of items (e.g., living things) relative to other categories
• Patients who were survivors of herpes simplex encephalitis were amongst the first reported to exhibit category specific semantic deficits
• Functional imaging studies have also provided findings implicating neural regions specific to particular semantic categories
• Criticisms of category specific deficits include differences in visual complexity and failure to control for variables like familiarity
• Michaelangelo was better at naming inanimate objects relative to animals/fruits and vegetables
• Michaelangelo's case was very poor at object decision (i.e., is this picture a 'real' item or 'unreal' item?) with both animals and inanimate items
• Sartori & Job (1988) suggested that on the basis of their case's poor performance at visually processing objects, that apparent category specific deficits may not implicate semantic memory, rather they reflect damage to 'structural descriptions' of visual objects (in other words category specific deficits may well arise due to a pre-semantic impairment)
• Funnell & Sheridan (1992) and Stewart, Parkin & Hunkin, (1992) pointed out that previous studies reporting a living/non-living dissociation did match testing stimuli for name frequency, but not for an additional variable considered to be vital in psycholinguistic research, namely familiarity
• It was shown that apparent category specific impairments demonstrated by their cases disappeared when other cognitive variables such as familiarity, visual complexity and structural similarity were sufficiently matched across living and non-living category stimuli
• The notion of personal familiarity is very difficult to quantify, since it is clear dependent on the types of things individuals are exposed to, interested in etc
• Familiarity (on the basis of personal experience) may even differ across gender –lines; Albanese, Capitani, Barbarotto & Laiacona, (2000) reviewed cases with greater living or non-living impairments and found that all cases with greater impairment of animals versus fruits were female, whereas all cases of the reverse were male
• Farah, Meyer & McMullen (1995) demonstrated in their patient that although category specific (inanimate > animate) differences in performance could be explained by familiarity and visual complexity on the basis of a single testing session, the presence of a category specific impairment (over and above possible artifactual effects) was statistically reliable across several testing sessions
• The very first patients reported with category specific impairments had survived herpes simplex encephalitis (Warrington & Shallice, 1984; Sartori & Job, 1988; Silveri & Gainotti, 1988) and in most cases damage implicated bilateral temporal, hippocampal and possibly even frontal regions (Sartori, Job, Miozzo, Zago & Marchiori, 1993)
• Category specific disorders have also been reported in cases of closed head injury (Farah et al., 1995; Funnell & Sheridan, 1992)
• There is conflicting evidence as to whether category specific disorders are present in neurodegenerative conditions (namely Alzheimer's disease - AD)
• Tippett, Grossman & Farah (1996) reported no category specific impairments in their sample of 14 probable AD cases using Funnell & Sheridan's well balanced stimuli, suggesting this may reflect the diffuse nature of neurodegeneration in AD