Connor Dietz1, Andrea Albonico1, Jeremy Tree2, Jason Barton1
1The University of British Columbia, 2Swansea University
Objective:
To determine if posterior cortical atrophy (PCA) causes deficits in visual imagery, and if so, whether the imagery deficits are selective for certain visual properties.
Background:
Visual imagery has a close overlapping relationship with visual perception, sharing many common neural substrates. PCA is a neurodegenerative syndrome marked by early impairments in visuospatial processing and visual object recognition. We asked whether PCA would therefore also be marked by deficits in visual imagery, tested using objective forced-choice questionnaires.
Design/Methods:
We recruited four patients with PCA and, for comparison, one patient with an integrative general visual agnosia due to bilateral occipitotemporal strokes and thirty-five age- and sex-matched control subjects with no prior history of neurological disease. Standardized neuropsychological tests were used to assess each patient’s general cognitive function, language, memory, visual object processing, and visuospatial abilities, confirming complex visual object and visuospatial processing deficits with relative sparing of other cognitive domains. We then administered a battery of tests probing imagery for object shape, object size, colour lightness, hue, upper-case letters, lower-case letters, word shape, letter construction, and famous faces. Each patient was compared to the control group for each imagery test with single-case methodology using Crawford’s case-controls statistics.
Results:
All PCA patients showed a marked impairment in visual imagery. Imagery for lower-case letters was most likely to be spared, while several PCA patients found the word shape and letter construction tests too difficult to complete, likely reflecting the more complex demands of these tasks. The patient with bilateral occipitotemporal strokes showed similar impairments.
Conclusions:
PCA patients can show severe deficits in visual imagery. Further work is needed to establish how frequently this occurs, how early in the disease course it can be found, and whether a short test for visual imagery may prove to be a useful screening tool in the clinic.