PubMed · 676094
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N Kawabata, K Yamagami, M Noaki. 1978. Visual fixation points and depth perception.. https://doi.org/10.1016/0042-6989(78)90127-x
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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.
A prospective study was performed over a 4-year period of 56 infants presenting with infantile esotropia to assess development of binocularity after surgical alignment before 2 years of age. In 50% of cases infantile esotropia was associated with neurological problems or prematurity. Forty-three cases have undergone surgery (mean age 15.7 months +/- 3.46); 86% were aligned (+/- 10 dioptres) at 2 years. Eighty-seven per cent of normal children and 74% of children with neurological problems or prematurity were aligned at last follow-up (mean 27.2 months since surgery). Tests of fusion and stereopsis have to date been possible upon 21 'successfully' aligned infants and although most have evidence of peripheral sensory fusion none showed stereopsis to more than one test. Although early surgery achieves a good cosmetic result in normal children and those with neurological problems, our findings question its ability to promote the development of even gross stereopsis in most children.