The overall goal of this procedure is to investigate the role of stereoscopic or three dimensional cues and the recognition of viewpoint rotated figures. This is accomplished by first simulating the appearance of a shape or an object that has undergone a rotation in depth. A rotation in depth is akin to a change in viewpoint.
The second step is to present viewpoint rotated objects to the observer through the mirror stereoscopic device. The viewpoint change presented to the observer can be two or three dimensional. Next, the experimenter runs the trials to determine an observer's sensitivity to viewpoint change.
This experiment is repeated for 2D and 3D stimuli. The final step is to analyze the behavioral data in order to determine the observer's sensitivity to viewpoint change and how the sensitivity is affected by the presence or absence of stereoscopic cues. Ultimately, the method is used to show how human observers recognize shapes and objects when they are viewed from a different viewpoint.
This method can be used to help answer key questions in the field of vision science, such as which stages of cortical processing incorporates stereoscopic information in their representation demonstrating the procedures. Today will be Shannon Webb and honor student in my laboratory. Prior to the experiment, perform a pre-screening to assure the subject's eligibility for the study.
Be sure to ask if he or she has normal or corrected to normal visual acuity via either glasses or contact lenses. Also, obtain written and informed consent from the participant. Next, verify the stereo acuity of the participant using a simple handheld stereo test.
Then seat the participant at the desk in front of the mirror stereoscope and adjust the height of the chair for comfort. Turn off the lights and allow the subject to dark adapt for a minimum of three minutes. Since the visual system performs best when it is adapted to the prevailing lighting conditions.
Now have the participant look through the stereoscope. Instruct the subject to adjust The horizontal position of the fixation crosses until they see only one cross in the center of the field of view. If the subject sees two crosses, then the separation is incorrect and horizontal adjustment is needed.
In the following experiment, the targets will be entered on the crosses when displayed, and this procedure ensures fusion at the correct distance. Once all equipment is set up and binocular fusion is achieved, assure that the participant is ready to commence the experiment, then give the following instructions for the task as stated Here on each trial, you'll see two curves that have rotation in depth, or RID. You are required to decide which of the two curves have a greater RID.
In other words, which is more rotated away from your view, press the left mouse button. If the first stimulus has a greater RID, press the right mouse button. If the second curve has more RID, this is a forced choice task in which the next trial does not commence until a response has been made to a previous trial.
If you are not sure which stimulus has more RID, please take your best guess to evaluate the role of stereoscopic. Cue and judgments of RID. Measure the performance of the participants separately in both stereo conditions and non-steroid conditions.
To present stereoscopic cues, the computer should display a different RID angle of curve to each eye of the observer through the stereoscope to present the curves without stereo cues. Present the same RID curve to both eyes. Initiate the procedure, which should be composed of 140 trials.
Use the method of constant stimuli to ensure equal numbers of trials. For each value of RID of the test curve employed. The rids can be either greater than less than or equal to 45 degrees with a particular value being randomly chosen from the set for each trial.
The RID of the reference curve should be held constant at 45 degrees. RID randomize the presentation. Order of reference and test stimuli on each trial.
Allow the program to record how often the test is chosen as being at the greater RID angle and give the participant a break. After each block of trials here, the 140 trials consist of 20 repetitions at each of seven different RID angles for the test curve, three angles are less than 45 degrees, three angles are greater than 45 degrees, and one RID is precisely 45 degrees being the same as the reference curve. At the end of each run, have the computer plot out data describing the proportion of times that the participant chose the test stimulus as being at RID angle greater than 45 degrees as a function of the presented RID angle.
Let the software fit the data with the cumulative SIAN function in order to determine the precision with which the subject was able to make the RID discrimination obtain the slope from each plot. The slope estimates for the stereo and non-steroid conditions can then be statistically compared in order to determine whether stereoscopic cues have contributed to an observer's ability to detect the change in RID. This movie demonstrates the change in the two dimensional retinal image of a shape that is being subjected to a rotation and depth around the vertical axis.
The main change to the image is a horizontal compression of its shape. Here we can see example results for three observers showing sensitivity to RID viewpoint change as a function of the RID angle of the stimuli. The Y axis in each figure describes the proportion of times that the test pattern was chosen as having a greater RID.
The X axis describes the physical RID of the test pattern. The reference pattern was held at a constant 45 degrees RID. After watching this video, you should have a good understanding of how to measure sensitivity to viewpoint rotation of objects with and without stereo cues.
You should understand the way in which a viewpoint change can be simulated and how the per at the observer can be altered between a two dimensional and a three dimensional perspective.
