Studies week 2

Williams et al

Found that brain volume loss in the anterior temporal lobes strongly correlates with semantic memory deficits in those with semantic dementia.

KC

Case KC, a woman with bilateral temporal lobe (anterior ventral and medial parts of the temporal lobes) damage from herpes simplex encephalitis, showed selective impairment in animal concepts, highlighting the role of the anterior temporal lobes in category-specific semantic knowledge.

RS

Case RS, a 64-year-old man who suffered a stroke affecting left temporal, occipital, and thalamic regions, showed selective difficulty with fruit and vegetable concepts, suggesting category-specific semantic impairment linked to these brain areas.

Only 4 reported SD cases showed category-specific patterns

Most people with semantic dementia (SD) show general loss of conceptual knowledge.

• 1 case was better with living things (Lambon Ralph et al., 1998)

• 3 cases were better with non-living things (Barbarotto et al., 1995; Li et al., 2006; Lambon Ralph et al., 2003)

Category Impairments Are More Common in Herpes Simplex Encephalitis (HSE)

• HSE often causes more focal damage, especially to the anterior temporal lobes.

• Patients have shown:

  • Worse performance with living things (Warrington & Shallice, 1984; Silveri & Gainotti, 1989)

  • Worse performance with non-living things (Warrington & McCarthy, 1992)

• This provides evidence of double dissociation, suggesting separable neural systems for different semantic categories.

Large-Scale Findings (Capitani et al., 2003)

• Analyzed many HSE cases:

  • 61 cases had living thing deficits

  • 17 cases had non-living deficits, but only 1 of these had HSE

• Suggested Brain Areas:

  • Living thing deficits → bilateral anterior medial inferior temporal lobes

  • Non-living thing deficits → left posterior superior temporal + inferior parietal lobes

Different types of knowledge may rely on different brain networks.

Selective Preservation of Fruit and Vegetable Knowledge in SD (Merck et al., 2013)

• Studied 35 SD cases

• Only consistent pattern: relative preservation of fruit/vegetable knowledge

Why?

• May be due to preservation of colour knowledge

• Colour info is processed in the left posterior fusiform gyrus (FG)

  • This area is often spared early in SD

• Fruit and vegetables rely heavily on colour for identification (Crutch & Warrington, 2003)

So this apparent category effect may actually reflect preserved feature knowledge (colour), not category per se.

Important Consideration: Confounding Variable

• The authors admit they did not control for familiarity.

• Familiarity could explain why some items (like common fruits/veg) are remembered better, not necessarily category-specific memory.

Some studies didn’t control for important variables in their test items

• Visual complexity: Some pictures (like Michelangelo sculptures) were more detailed than others, which may have affected how well patients recognized them (Sartori & Job, 1988).

• Familiarity vs. frequency: Some studies matched how often people encounter a word (frequency), but not how well-known it felt to them (familiarity) (Funnell & Sheridan, 1992; Stewart et al., 1992).

Farah et al. (1995)

• They showed that when you test a patient only once, you might get misleading results (random errors).

• But when tested over multiple sessions, a real pattern appears — like a true category-specific problem.

(Caramazza & Shelton, 1998).

• Many patients do show more trouble with living things than nonliving things.

• But this can be confusing because:

  • Living things are often more familiar, so they should be easier — yet patients still struggle.

• When researchers control for familiarity, living thing deficits still happen