Dementia with Lewy bodies (DLB) and Posterior Cortical Atrophy (PCA), the visual variant of Alzheimer’s disease, are neurodegenerative diseases that present with progressive deterioration in visual perception. However, little is known about the precise nature underlying the complex visual deficits associated with both conditions. The present study compared DLB, PCA, and healthy control participants, in four visual tasks designed to measure the efficiency of the visual system at different levels of processing. In ascending order of complexity there were tasks of visual acuity, line orientation, contour integration, and rotated object comparison. DLB patients did not differ from controls in low level visual functions of visual acuity and line orientation, suggesting that early visual processing areas including V1 were relatively preserved, consistent with pathology evidence (Yamamoto et al., 2006). However, higher level visual functions of contour integration, mediated by extrastriatal areas, and the most complex task of object rotation, relying on processing within inferior temporal (IT), parietal, and frontal cortices, were impaired in DLB. In contrast, PCA patients were impaired in all tasks, consistent with evidence of widespread pathology within occipital and parietal areas in PCA. The latter suggests that both lower and higher level visual impairments contribute to the complex visual symptoms associated with PCA.