The overall goal of this procedure is to develop a methodology using a 3D depth inversion illusion to clarify the role of top-down visual processes on motor action. This is accomplished by first constructing an apparatus that presents a robust 3D reverse perspective stimulus to perform reaches under different perceptual states. The second step of the procedure is to set up a motion capture system to record a participant's interaction with this stimulus.
The third step is to create a platform that allows participants to reach for where they last perceived a target located on the stimulus without any online visual corrections or haptic feedback. The final step is to analyze both the forward reach data as well as the non instructed retraction of the arm to build a comprehensive model of visual motor behavior in this context. Ultimately, results can show changes in reach dynamics under different perceptual states through the kinematic assessment provided in this paradigm.
The main advantage of this technique over existing methods like those that utilize the hollow face illusion is that the respective stimulus allows for nearly 90 degrees maximal differences in surface orientation under vertical and illusory perceptual states. This new method can help answer key questions in the field of perceptual science and begin building towards a more objective psychological science with new techniques that go above and beyond human verbal self reports or key presses, The very different predictions of the two hypothesis. In other words, whether the motor control system is influenced or not by the illusion enable us to test this hypothesis.
Demonstrating the procedure today will be Jay Val, CD pathak, and R Sadik, who are research assistants in our laboratories. First construct a movable platform that is 65 by 55 centimeters and moves on a sliding track that is 55 centimeters long. The various stimuli will be placed on the platform.
The stimuli must be presented at eye level to a seated participant, so the track should be secured at the appropriate height. The platform should have a retractable spring mechanism. Connect this mechanism to a circuit board that synchronizes various events behind the participant's seat.
Set up lamps to evenly illuminate the platform. Connect the lamps to the same circuit board below the hand rests of the participant's seat. Secure a switch box that is easily depressed by the participant lifting their hand.
Connect the switch to the circuit board on the circuit board. Connect the output pins to the pins of the microcontroller for the stimulus activation. The platform should retract and the light should go off when the trigger box is depressed by the participant reaching outward with their arm.
Use MATLAB to control the microcontroller to record the trial sequence and to instruct the experimenter to which viewing conditions are needed for each trial. Now construct the proper perspective stimulus and construct the reverse perspective stimulus. Even though it appears that the central building is convex, it is physically concave to the right of the midline on both stimuli.
Attach a red planar disc. Build the two training stimuli from rectangular panels on each panel. Represent one of the isolated right surfaces of the middle building with the red disc.
One panel is for the reverse perspective stimulus and the other for the proper perspective stimulus. First, test the stereopsis of the participants using a Rand dot stereo test. Also determine their eye dominance.
Next, set up the motion capture system composed of 14 electromagnetic sensors at 240 hertz and motion tracking software. Place 12 of the 14 sensors on the participant using sport bands. Attach them to the head, the trunk, the two shoulders, the upper arms, the forearms, and the index finger and thumb of the hand operating the switch.
Place the other two sensors on the backs of the two stimuli behind the red discs. The participant should not see the stimuli prior to the test. Turn off all the lights except the lamps used to illuminate the stimulus platform.
Dim any computer screens and keep them turned away from the experimental setup. Brief the participant on the experimental flow and how they will trigger the switch box. Demonstrate how the participant should only grab at the platform where it is visible.
Now, conduct a practice trial for a stimulus. Send only a blackboard with a pole on it to hang objects. Ask the participant to reach for the pole and bring their hand back to rest.
Do this three times at the comfort pace of the participant. Begin the initiation trials using the two training stimuli. Have the participant close their eyes after each trial so they do not see the stimuli being swapped.
The software randomly sets the order of showing the two stimuli four times each. Now begin the experimental trials. These trials consist of three conditions.
One is viewing the reverse spec under illusory percept. The next condition is viewing the reverse perspective under vertical percept. The third, of course, is the proper perspective.
Present the reverse perspective stimulus first and ask if the participant can stabilize the illusory percept of the middle building popping out. If the participant cannot stabilize the illusion playing a defocusing lens on the non-dominant eye, if the lens is needed, use it for each retrospective illusory trial. The order for the remainder of the trials should be randomized.
A total of 12 trials for each condition are presented resulting in 36 experimental trials. The overall total number of trials is 47. This includes the practice training and experimental trials.
Give verbal instructions for each trial for the retrospective illusory trial and the proper perspective trial instructs the participant to view the middle building as popping out for the spective. Vertical trials instructs the participant to view the middle building as caving in away. Always ask the participant to reach out only once the perception has stabilized.
The most critical part of the protocol is ensuring that the participant maintains the illusory or vertical percept for the entire duration of the trial. We allow for the participant to take his or her time to achieve this, and if there is doubt, the trial is repeated. The Wilkes Lambda test statistic is one metric used for the analysis.
Hand path data for a representative. Subject showed significant differences in the hand path trajectory profiles for the subject reaches performed under the vertical percept in green and illusory percept in blue of the respective stimulus. This difference in hand path curvature under vertical and illusory per percept is also seen in the arms non instructed retraction.
Comparing the spective vertical proper perspective, data revealed as expected significant differences for both the forward reach extension and in the hand retraction discussions on the statistics are detailed in the text protocol when examining the orientation of the hand during approach to the stimuli. Hand approach vectors under the reverse spective vertical stimulus in green differed from the other two stimulus condition. Hand approach vectors in hand.
Orientations were markedly similar. Once mastered, this technique can be performed in approximately one hour if it is done correctly. While attending this procedure, it's very important to remember to record a continuous full motion of the arm, including both the forward hand reaching motion towards the target and the spontaneous hand retraction.
The ladder performed automatically without any Instructions after its development. This technique can pave the way for researchers in the field of neuroscience to explore the relationship between top-down control and sensory motor processing in both typically developing and pathological populations.
