Identification deficits in dementia of the Alzheimer
Type (DAT) often target specific classes of objects, sparing
others. Using line drawings to uncover the etiology of
such category-specific deficits may be untenable because
the underlying shape primitives used to differentiate one
line drawing from another are unspecified, and object form
is yoked to object meaning. We used computer generated
stimuli with empirically specifiable properties in a paradigm
that decoupled form and meaning. In Experiment 1 visually
similar or distinct blobs were paired with semantically
close or disparate labels, and participants attempted to
learn these pairings. By having the same blobs stand for
semantically close and disparate objects and looking at
shape–label confusion rates for each type of set,
form and meaning were independently assessed. Overall,
visual similarity of shapes and semantic similarity of
labels each exacerbated object confusions. For controls,
the effects were small but significant. For DAT patients
more substantial visual and semantic proximity effects
were obtained. Experiment 2 demonstrated that even small
changes in semantic proximity could effect significant
changes in DAT task performance. Labeling 3 blobs with
“lion,” “tiger,” and “leopard”
significantly elevated DAT confusion rates compared to
exactly the same blobs labeled with “lion,”
“tiger,” and “zebra.” In conclusion
both visual similarity and semantic proximity
contributed to the identification errors of DAT patients.
(JINS, 1999, 5, 330–345.)
Combined effects of planning and execution constraints on bimanual task performance
