Alzheimer’s Disease and Herpes Simplex Encephalitis

to show the same significant category effect on three
tasks: A (picture naming), B (drawing), and C (attribute
verification). Nevertheless, what if another patient is
impaired on A and B, but not C? This patient may still
have a category disorder and tell us something poten-
tially more important about the true nature of category
effects (e.g., that they might be related to visual knowl-
edge alone).

Finally, although the vast majority of category-specific
studies use a case study approach (for a review, see
Laws, in press), a minority have used between-group
comparisons. One reason that group studies have been
less popular in this area is because group analyses may
cancel out individual category effects. For example, if
some patients showed a living deficit and some a
nonliving deficit, then the overall pattern might simply
reveal poor performance on both (see Gonnerman,
Anderson, Devlin, Kempler, & Seidenberg, 1997). This
is especially likely with severely neurologically impaired
cases. The following experiments compare category
knowledge on three tasks in healthy controls with
patients with Alzheimer’s disease and Herpes Simplex
Encephalitis (HSE); and are designed to explore how
category effects might be determined.

EXPERIMENT 1: THE LIVING-NONLIVING
DISCREPANCY IN ALZHEIMER’S DISEASE

The incidence and pattern of category specificity across
Alzheimer’s patients as a group (Tippett, Grossman, &
Farah 1996; Silveri, Daniele, Guistolisi, & Gainotti 1991)
and for individual Alzheimer’s patients (Laws, Leeson, &
Gale, 2003; Garrard, Patterson, Watson, & Hodges, 1998;
Gonnerman et al., 1997; Mauri, Daum, Satori, Riesch, &
Birbaumer, 1994) have been inconsistent.

Most analyses of Alzheimer’s patients have reported
living deficits, a minority has reported nonliving deficits,
some report both, and still others find no category
specificity in Alzheimer’s patients (for a review, see
Laws, Gale, et al., 2005). Some of this variability may
stem from previously ignored methodological problems.
In particular, Laws, Gale, et al. (2005) note that controls
in these studies are often performing at ceiling level, and
have shown how this may distort the incidence and even
direction of category effects. An additional issue con-
cerns the observation that almost all of the studies
examining category effects in Alzheimer’s patients have
relied exclusively on picture naming as the test of
category. The current study addresses these points by
testing picture naming, naming-to-description, and fea-
ture verification in Alzheimer’s patients and controls.

Results

The criterion for a living-nonliving dissociation was that
a patient must show a discrepancy that would be
estimated to occur in <1% of the population of healthy
matched controls. Two of the Alzheimer’s patients were
impaired on all three category tasks (see Table 1). Nine
were impaired on picture naming (7 living and 2 non-
living), 10 on feature verification (all living), and 3 on
naming to description (all living).

Critically, the analyses revealed category inconsisten-
cies across tasks. One patient showed a paradoxical
dissociation: patient LZ had a differential deficit for living
things on the feature verification task, but for nonliving
things on the picture naming task.

Summary

The comparison with results from x² points to a number
of both false positives (7) and false negatives (5). In one
patient (SL), x² produced significant dissociations on all
three tasks, however, when referenced to control data,

Table 1. Category Performance in Alzheimer’s Patients
(% Living and Nonliving)

*L = differential living deficit; NL = differential nonliving deficit; x² =
patient impaired using x²; s = strong dissociation; c = classical
dissociation.

+ = living advantage; — = nonliving advantage.

1454 Journal of Cognitive Neuroscience

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