Effects of Magnocellular Selective Inhibition on Dorsal Stream Vision-For-Action Tasks

Megan McFadyen, Thompson Rivers University

Abstract

Milner and Goodale's action-perception theory proposes that the dorsal stream enables vision-for-action, like reaching out to grasp an object, whereas the ventral stream enables vision-for-perception, such as recognizing that object. There is evidence that magnocellular (M) and parvocellular (P) pathways map on to the dorsal and ventral streams but there is no behavioural evidence that the M pathway selectively enables vision-for-action and the P pathway vision-for-perception. We hypothesized that if the action-perception theory extends to the M and P pathways then selective inhibition of the M pathway should impair dorsal stream vision-for-action tasks, but not ventral stream vision-for-perception tasks. Participants performed a grasping (vision-for-action) task by reaching out to grasp a target embedded within an ebbinghaus illusion. They also performed an estimating (vision-for-perception) task by simply opening their index finger and thumb to match the perceived size of that same target. These tasks were performed in a white light condition and a red light condition as diffuse red light is known to selectively inhibit the M pathway. Maximum opening of the index finger and thumb was recorded during both tasks using electromagnetic sensors attached to the participants' fingers. It was expected that the accuracy of index-thumb opening would be impaired on the grasping, but not estimating task in the red light condition. The results are discussed in relation to whether or not this supports the proposition to extend the action-perception theory to the M and P pathways.

 

Effects of Magnocellular Selective Inhibition on Dorsal Stream Vision-For-Action Tasks

Milner and Goodale's action-perception theory proposes that the dorsal stream enables vision-for-action, like reaching out to grasp an object, whereas the ventral stream enables vision-for-perception, such as recognizing that object. There is evidence that magnocellular (M) and parvocellular (P) pathways map on to the dorsal and ventral streams but there is no behavioural evidence that the M pathway selectively enables vision-for-action and the P pathway vision-for-perception. We hypothesized that if the action-perception theory extends to the M and P pathways then selective inhibition of the M pathway should impair dorsal stream vision-for-action tasks, but not ventral stream vision-for-perception tasks. Participants performed a grasping (vision-for-action) task by reaching out to grasp a target embedded within an ebbinghaus illusion. They also performed an estimating (vision-for-perception) task by simply opening their index finger and thumb to match the perceived size of that same target. These tasks were performed in a white light condition and a red light condition as diffuse red light is known to selectively inhibit the M pathway. Maximum opening of the index finger and thumb was recorded during both tasks using electromagnetic sensors attached to the participants' fingers. It was expected that the accuracy of index-thumb opening would be impaired on the grasping, but not estimating task in the red light condition. The results are discussed in relation to whether or not this supports the proposition to extend the action-perception theory to the M and P pathways.