R8 Flashcards
what does the dorsal stream do?
controls visually guided actions
what does the ventral stream do?
important for object recognition and perception
who was the participant in R8?
CB - 75y male who had a right occipital stroke
what condition does CB have and what does that mean for him (R8)
left visual field hemianopia - this means he has no left visual field in either eye
how did the researchers ensure that CB could not use self-generated precues to compute position of obstacles while reaching?
by controlling fixation, stabilizing his head, and removing visual feedback
who else was tested alongside CB? (R8)
two healthy and right-handed males, 83 and 70 yo (ECI1 and ECI2, resp.), and six young, healthy, right-handed males ~26yo
what was the task in R8?
reaching from a start button to 5cm wide target strip with the right hand as quickly and accurately as possible while avoiding obstacles that were either 10cm in or 15cm out from the midline of the visual field, in the right, left, or both visual fields, or no obstacles at all
what was the fixation protocol in R8?
stare at a pole just behind the center of the target strip, eyes were monitored using a camera to ensure fixation
what did CB wear during the experiment task (R8)
googles that could block his vision, they would open for 500ms at the start of each trial to allow initial visual feedback, but close before terminal visual feedback could be received (2 trials where he did look away were excluded from analysis)
what differed between exp 1 and 2 in R8?
experiment 1 was real-time obstacle avoidance task immediately after a 500ms period of visual feedback, and experiment 2 was an identical but delayed task - after the 500ms period, CB had to wait 2s before proceeding
what were the results of experiment 1? (R8)
exp 1 showed evidence of implicit visual processing in the blind field (blindsight)
what was the redundancy effect shown in preliminary behavioural testing in R8?
when visual target were presented simultaneously in his sighted and blind fields, CB was faster to respond with a button press compared to a target only being shown in his sighted field
what were the results of exp 1 for R8?
CB’s reach trajectories were significantly influenced by the presence of obstacles in BOTH his sighted and blind visual fields, at 20cm in (just in front of an obstacle), his trajectories deviated more when an obstacle was in rather than out
what were the results of exp 2 for R8?
similar to exp 1, CB was sensitive to obstacles in his blind field for the first 20cm into his reach, after that CB was no longer sensitive to obstacles, showing a complete overlap of error bars in figure 4C. But his sensitivity in his sighted field remained similar to exp 1
how did CB’s trajectories differ from the controls in R8?
his trajectories took longer to change to avoid obstacles, which can be attributed to retinal disparity signals in V1 that are critical for depth perception
