PubMed · 593793
A solid object--a frame enclosing rods--can be seen as having an illusory 'line' joining the tips of the rods.
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C Ware, J M Kennedy. 1977. Illusory line linking solid rods.. https://doi.org/10.1068/p060601
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Ptolemy (127-148 AD) studied physiological diplopia, correspondence and the horopter. He had all the data to build a theory of depth perception through disparity detection, but left that undone. Alhazen (1000 AD) associated depth perception with the sensation of binocular convergence, just as Kepler (1611) and Descartes (1637). With the development of the concept of retinal correspondence and the fusion of the retinal images in the brain (Huygens 1667, Newton 1704) a cerebral mechanism of disparity detection became thinkable. The rise of Empiricism (Molyneux' Premise, the case of Cheselden) postponed the solution of the problem, finally reached by Wheatstone (1838). Physiological proof of Wheatstone's theory came from the experiments of Barlow et al. (1967).
We investigated observers' ability to extrapolate a linear trajectory of a moving point, in order to determine how effectively the visual system can combine orientation and position information for moving stimuli. Observers saw a probe dot moving along a straight line toward a stationary target dot. The probe dot extinguished before reaching the target, and the observers' task was to judge whether an extrapolation of the trajectory of the probe would pass to the left or right of the target. Performance was measured as a function of probe velocity, length of the visible trajectory, and location of the target. The empirical results indicated that over a range of conditions, performance on this task is qualitatively similar to, but somewhat less accurate than, that on an analogous task with static stimuli. A four-component model is presented to account for the results. The model specifies an accurate extraction of probe motion parameters, extrapolation of the motion by an ideal observer, and limitations on the input to these processes in the form of visual field spatial inhomogeneity and temporal decay of position information.
Looming objects comprise many 2D unidirectional motion elements changing over time. However, observers assign a single 3D speed to looming objects, not many independent unidirectional speeds to different regions of the object. These experiments examined speed discrimination for looming stimuli to illuminate the mechanisms underlying the perception of 3D motion. Speed discrimination thresholds for looming displays were comparable to those of fronto-parallel translating and rotating displays (approximately 5%), and thresholds were predicted from the simple linear combination of 2D unidirectional thresholds. These results suggest that 2D unidirectional motion and looming motion are not independent: the simple pooling of unidirectional motion units limits sensitivity to looming stimuli. These results do not support the notion that the visual system directly encodes relative motion within a distinct channel.