Semantic memory structure: Evidence to be accounted for

1. Semantic memory structure:Evidence to be accounted for What evidence can be brought to bear on the question of semantic memory structure?

2. Long Term Memory (LTM) • Episodic memory - memory for events that we “remember” • Procedural memory - memory for how to do stuff; automatic processes • Semantic (declarative) memory - memory for facts about the world

3. Semantic memory • What is the purpose of semantic memory? • Beyond just storage, what functional role does semantic memory serve in our daily lives? Many-to-many mapping!

4. The Evidence • Category-specific deficits (e.g., Warrington & McCarthy, 1983, 1987; Warrington & Shallice, 1984; Gainotti & Silveri, 1996) • Patients show impairments in processing living things vs. man-made objects and vice versa. • Interesting exceptions: fruits, vegetables & other foods; musical instruments • Modality-specific deficits • Patients are unable to name visually presented objects, but can name them from other modalities and can access other semantic information about visually presented stimuli (Beauvois, 1982) • Other visual processing is fine.

5. More evidence • Brain-imaging (Martin et al., 1995; Martin et al., 1996) • Brain areas associated with visual processing more active when animals are being named; • Areas associated with generating action words or imagining actions active when naming man-made objects • Areas associated with color perception are active when color words are generated, even for man-made objects • Areas associated with motion perception are active when action words are generated for man-made object

6. Evidence (cont.) • Naming vs. Categorization (Potter & Faulconer, 1976; Guenther et al., 1980, Seifert, 1997) • Faster to name words vs. pictures • Faster to categorize pictures vs. words • Stroop-like effects (Glaser, 1992; Glaser & Glaser, 1989) • Incongruent words interfere with pictures more than pictures interfere with words in a naming task • Incongruent pictures interfere with words more than words interfere with pictures in a categorization task

7. Split-brain patients • An old treatment for epilepsy was to sever the corpus callosum, the band of neurons connecting the two hemispheres of the brain. • Verbal information is clearly processed in the left hemisphere, while more visual cognition seems to be processed in the right.

8. Competing theories • Unitary Content Hypothesis • Semantic information is stored in an abstract, amodal format organized by category. • Multiple Semantics Hypothesis • Semantic information is stored in many modality-specific semantic subsystems. Information in each subsystem is stored in a modality specific format. • Our intuitive sense of information being organized by categories is based on strong connections between related parts of these modality-specific semantic systems.

9. Unitary Content Hypotheses (UCH)(Caramazza et al., 1990; Caramazza & Shelton, 1998; Riddoch et al., 1988; Pylyshyn, 1973)

10. Multiple Semantics Hypotheses (MSH)(Paivio, 1971; Beauvois, 1982; Shallice, 1987, 1988; McCarthy & Warrington, 1988)