Alzheimer’s Disease and Herpes Simplex Encephalitis

none emerged as significant. Using the criterion of
category-consistent dissociations across all three tasks,
two patients (MS and AE) showed living impairments.

A further six patients were impaired on two tasks;
critically, in patient LZ, the deficits were paradoxical,
that is, impaired for living on one task (feature verifica-
tion) and nonliving (picture naming) on another task.
The case of LZ is of particular importance. Given that
the features used in the features verification task were
all perceptual/visual, and given that semantic activation
from pictures is triggered from visual features of the
picture itself, this paradoxical dissociation is particularly
surprising. The lack of consistency across analyses and
the finding of a paradoxical dissociation across tasks
emphasize why performance on any one task cannot
provide a reliable indicator of the direction of a category
effect.

EXPERIMENT 2: THE LIVING-NONLIVING
DISCREPANCY IN HERPES
SIMPLEX ENCEPHALITIS

In contrast to the studies of category effects in groups of
Alzheimer’s patients, many of the reported case studies
of patients with category-specific disorders are people
who have suffered from HSE (22/47 living cases, and not
one nonliving case; see anatomical review by Gainotti,
2000). The original report of category effects was in a
series of four HSE patients (Warrington & Shallice,
1984). As Gainotti (2000) argues, when referring to
HSE, that ‘‘the selective impairment of Living things,
far from being an occasional phenomenon resulting
from idiosyncratic factors, is strongly associated with a
certain kind of brain pathology.’’

Following the initial reports of Warrington and
Shallice (1984), other patients suffering from the same
pathology who also displayed living thing deficits in-
creased confidence in the claim that ‘‘real’’ category
specificity can be found predominantly in this group of
patients. Capitani, Laiacona, Mahon, and Caramazza
(2003) reported, in their database, 26/61 patients with
HSE in the group impaired for living and 1/18 in that
impaired for nonliving. Nevertheless, these figures refer
to the incidence of HSE category-specific patients in the
total population of category-specific patients. No data
are available regarding the incidence of category speci-
ficity among the HSE population. For this reason, the
second part of this study examines the incidence and
type of category effects that occur in a series of patients
following HSE.

Results

The data were analyzed using the same methods out-
lined in Experiment 1. One HSE patient was impaired
across all three tasks (SR). Five patients were impaired
on two of the three tasks. Two HSE patients (DD
and MF) also displayed paradoxical dissociations (see
Table 2).

Summary

Again, a large number of false negatives occur when
using x² (11 for HSE patients). As with Alzheimer’s
patients, an absolute (nonreferenced) comparison is
likely to underestimate rather than overestimate the
incidence of category dissociations. Inconsistency across
tasks for an individual patient again highlights the fact
that performance on any one task cannot provide a
reliable marker for a category effect—this includes
feature verification (which was the most sensitive and
reliable task in both groups for detecting significant
category differences).

Furthermore, the analysis of HSE patients accentuates
how absolute scores can be misleading. Consider BM,
who showed a significant differential deficit for living
things on feature verification in the x² analysis (76% vs.
90%), but not when compared to controls (although the

Table 2. Category Performance in HSE 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.

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