Our overall goal is perceptual tests for vestibular function. Why Study Perception? Because of discrepancies between eye movement responses and self-motion perception, especially during adaptation.
Some possible advantages of animations to study Self-Motion Perception are:
Animations Study Procedure
The stimulus is cross-coupled angular acceleration (head roll during earth-vertical rotation). Subjects manipulate real doll's head so that the virtual doll's head displayed on monitor moves in manner that corresponds to perceived head motion (magnetic field tracker embedded in real doll's head). Animations are recorded for later analysis. We then record vertical eye movements (experiment 3).
Fig. 1. Illusory self-motion was produced
by head roll during yaw axis, earth-vertical rotation. For leftward
head roll during counter-clockwise rotation, illusory rearward
head pitch and downward slow phase eye movements would be expected.
Fig. 2. 2A.
Selected frames from animation. Stimulus: head roll from
right to left during CCW rotation. The real leftward head roll
accompanied by illusory forward head pitch; as the roll motion
was completed, brief leftward yaw was recorded. The subject reported
verbally that her head went "forward and then slight rotation."
2B. "Pitch", "roll" and "roll"
path signals (ordinate) as a function of frame (24 frames / s).
Frames 15-75 illustrate leftward head roll which was accompanied
by forward pitch (frames 15-50). Leftward head yaw is illustrated
in frames 45-120.
Perceived pitch head directions did not correspond to predictions.
-Head Roll Direction
-Head Roll Direction
Results: Experiments 1 And 2
Experiment 1
Stimulus
Expected Perception
% Observed
Rotation Direction
Cw-R / Ccw-L
Rearward
76%
Ccw-R / Cw-L
Forward
38%
Experiment 2
Stimulus
Expected Perception
% Observed
Rotation Direction
Cw-R / Ccw-L
Rearward
54%
Ccw-R / Cw-L
Forward
33%
Fig. 3. Four-second segment of EOG for Subject 3, Trail 1. Chair rotation was counter-clockwise (viewed from above). At time 57.7, the subject rolled her head from her right to her left shoulder (indicated by step function). Slow-phase down nystagmus appeared after about 1.3 s. Slow-phase direction was as predicted.
Slow phase eye movement directions corresponded to predictions; but perceived pitch head directions did not.
Table 3 | ||||||||
Stimulus | Expected Perception | % Observed | Expected Slow-Phase Direction | % Observed | ||||
Rotation Direction
-Head Roll Direction | ||||||||
Cw-R / Ccw-L | Rearward | 38% | Down | 96% | ||||
Ccw-R / Cw-L | Forward | 22% | Up | 100% |
In conclusion, we found the following. Our non-verbal perceptual reporting procedure supports self-motion perception reporting. Perceptual reports did not correspond to expectations based on mechanical stimuli to vestibular apparatus and previous reports (guedry & montague, 1961; guedry, 1974). Differences between the results of the present study and previous ones may be due to subjects' training and expectations. Our eye movement data support those reported by guedry and montague.