Egocentric localization: visually directed alignment to projected head landmarks in binocular and monocular observers.
OBJECTIVE
To determine the accuracy and precision with which humans align moving, non-moving, point-like and linear stimuli to three head landmarks projected to a frontal plane. Monocularly enucleated and binocularly normal subjects, performing monocularly, were tested.


METHODS
Experimental tasks consisted of aligning the stimulus, a luminescent target, using a remote steering wheel control, to three projected landmarks; the nose, and the outside edge of each ear. Experiments were performed with a fixed [static] linear stimulus and a small dynamic stimulus, and then with a fixed stimulus at both a very close and an intermediate distance.


RESULTS
The data from the monocular enucleated observers showed better accuracy in some conditions but their variable errors were larger than those of the controls.


CONCLUSIONS
We propose that, for the alignments of the enucleated monocular subjects, a) the increase in accuracy is consistent with a shift of the egocenter in the direction of the remaining eye, and b) the decrease in precision may be due to the fact that the egocenter does not correspond to the mid-sagittal or median plane. This disparity would require adjustments to be learned in order to perform tasks involving visually directed alignments to the self.
González
E G
EG
Department of Ophthalmology, The Hospital for Sick Children, Toronto, Canada. gonzalez@yorku.ca
Steinbach
M J
MJ
Gallie
B L
BL
Ono
H
H
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D015353:Eye Enucleation; D005133:Eye Movements; D006801:Humans; D015588:Observer Variation; D010364:Pattern Recognition, Visual; D010775:Photic Stimulation; D015203:Reproducibility of Results; D014787:Vision Tests / Q000379:methods*; D015348:Vision, Binocular; D015349:Vision, Monocular