Does delay impair localisation in blindsight?

The unconscious sensorimotor skills which survive compromise of the geniculostriate visual pathway have been linked with activity of the dorsal stream of extrastriate occipitoparietal cortex. These sensorimotor circuits are thought to operate in real time. Therefore, an introduction of a delay between visual stimulus presentation and the patient's subsequent motor response should severely compromise sensorimotor tasks such as localisation (moving hand or eye to the location of a previously presented visual target). We tested this hypothesis in patient DB, a well-studied case of blindsight whose localisation abilities were first documented in the 1970s. Using eye tracking and hand movement recording technologies, as well as stimuli that control for light scatter, we verified the original observations of DB's manual and saccadic localisation. Remarkably, the introduction of a 4s delay did not compromise his ability to localise with either eye or hand. A control experiment reveals that this skill does not depend on an opportunity to make a decision at the time of stimulus presentation, circumventing the delay using memory. These data suggest that DB's manual and saccadic localisation skills do not depend on the circuits of the dorsal stream, or that delay, contrary to theory, does not severely compromise dorsal sensorimotor skills. ► A cortically-blind patient can localise targets with fixation and luminance controls. ► Four second delays do not impair localisation blindsight in this patient. ► Blindsight after delays cannot be explained by guessing at presentation times.