The double dissociation between cortical blindness and aphantasia: A review of 55 cases

A long-standing assumption in cognitive neuroscience is that visual mental imagery (VMI) is "visual perception in reverse" and, as such, requires reactivation of the primary visual cortex (V1). On this view, total destruction of V1 should abolish VMI and provoke neurological aphantasia. We tested this prediction by reviewing 55 published cases of cortical blindness (CB) in which VMI abilities were assessed. Vivid VMI is repeatedly documented in CB patients with complete or near-complete bilateral destruction, disconnection, or functional loss of V1; in impaired-VMI cases with informative anatomical or functional evidence, the lesion extends well beyond V1, typically into left temporal or temporo-occipital cortex. No impaired-VMI case with informative anatomical or functional evidence shows damage confined to V1. These data are difficult to reconcile with a necessary role for V1 in VMI. They are also compatible with, but do not by themselves establish, network accounts that assign an important role to ventral temporal and frontoparietal systems. We outline practical guidelines for future neuropsychological studies of visual mental imagery in CB.