Dissociating Speed from Automaticity in the Stroop Task: Evidence from a Case of Progressive Posterior Cortical Atrophy

There have been clinical reports within the last decade (Benson, Davis, & Snyder, 1958; Victoroff, Ross, Benson, Verity, & Vinters, 1994) of a progressive dementia arising from atrophy of the posterior regions of the cerebral cortex. These patients often show an early development of visual agnosia, alexia, anomia, and difficulties in controlling visual gaze. Problems in memory are mild or absent in the early stages, but become severe with the later stages of the illness. Insight is also preserved. According to the Victoroff et al. (1994) report, the three patients who shared this early onset pattern progressed to three different forms of dementia: subcortical gliosis, Alzheimer’s disease, and Creutzfeldt-Jakob disease. The implication of this finding is that this form of posterior cortical atrophy is not a disease entity in itself, but, rather, represents an occasional onset pattern of a number of different dementias. In this paper we describe the clinical course of a patient (J.D.) with a very similar progression of posterior cortical atrophy. He presented initially with focal symptoms of hemianopia and alexia, secondary to parietal lobe atrophy, without a focal lesion. In addition to some unusual clinical observations during the course of his disease, this patient is of interest because of experimental studies carried out on his reading processing, which have theoretical implications for contributions of speed and automaticity during reading.