2 Adaptation of egocentric distance perception under 3 telestereoscopic viewing within reaching space

8 Abstract Telestereoscopic viewing provides a method to 9 distort egocentric distance perception by artificially 10 increasing the interpupillary distance. Adaptation to such a 11 visual rearrangement is little understood. Two experiments 12 were performed in order to dissociate the effects of a 13 sustained increased vergence demand, from those of 14 an active calibration of the vergence/distance mapping. 15 Egocentric distances were assessed within reaching space 16 through open-loop pointing to small targets in the dark. 17 During the exposure condition of the first experiment, 18 subjects were instructed to point to the targets without 19 feedback, whereas in the second experiment, hand visual 20 feedback was available, resulting in a modified relationship 21 between vergence-specified distance and reach distance. 22 The visual component of adaptation in the second experi-23 ment was assessed on the unexposed hand. In the post-tests 24 of both experiments, subjects exhibited a constant distance 25 overestimation across all targets, with a more than twice 26 larger aftereffect in the second one. These findings suggest 27two different processes: (1) an alteration in the vergence 28effort following sustained increased vergence; (2) a cali-29bration of the vergence/distance mapping uncovering the 30visual component of adaptation