Biomedical subjects
T G Babler
Publications and source records attributed to T G Babler.
Role of image acceleration in judging landing location of free-falling projectiles.
The vertical acceleration of the projective image of a free-falling object specifies whether the object will land behind or in front of the observation site. Human sensitivity to this visual cue was investigated in 4 studies. Experiments 1 and 2 examined sensitivity to both constant and accelerating vertical acceleration. Detection of acceleration required a total change in velocity that was about 20% of the average velocity. In Experiments 3 and 4, subjects judged where computer-simulated free-falling objects would land relative to the observation site by viewing the initial segment of the flight objects whose trajectories remained in the sagittal plane of the observer. Judgments were influenced significantly by the magnitude and direction of the image velocity change even when no error feedback was available, implicating image acceleration as a source of information for judging the landing site of free-falling objects.
Effects of peripheral circular contours on dynamic spatial orientation.
The rod-and-frame effect (RFE) was investigated with the use of a frame that oscillated about an axis at its center at five different frequencies, ranging from .013 to .213 Hz. The resultant RFE shifted continuously with the roll motion of the frame, and it was significantly larger at the lowest frequency (.013 Hz) than under comparable static conditions. The dynamic RFE was lowest at the higher oscillation frequencies. Oscillatory roll vection--apparent self-motion--was reported by 3 of the 9 subjects when the frame was oscillating at its highest frequency (.213 Hz). The subjects yielded large increases in the RFE during the sessions with reports of vection. Surrounding the kinetic frame with a circular contour eliminated all reports of vection and significantly interacted with frequency to reduce the RFE--but only at low frequencies. The reduction amounted to 21.2% averaged over all 9 subjects at the three lowest frequencies. A surrounding contour, therefore, suppressed low-frequency kinetic visual orientation information that might otherwise have produced larger changes in apparent self-orientation and perceived vertical. Vection-sensitive subjects differed from nonvection subjects by exhibiting (1) a high-frequency fall-off in real-motion gain, (2) a high-frequency enhancement in illusory-motion gain, and (3) only a small and nonsignificant increase in illusory-movement phase lag with increases in frequency.