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Brittney Hartle, Laurie Wilcox; Scaling stereoscopic depth: The role of reaching. Journal of Vision 2020;20(11):533. doi: https://doi.org/10.1167/jov.20.11.533.
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Biases in suprathreshold depth estimation from stereopsis have been reported over a wide variety of viewing distances, stimulus geometry, and estimation methods - particularly for virtual stimuli. These depth distortions are often attributed to incorrect scaling of binocular disparity via absolute distance. This assumption supported by the fact that physical stimuli tend to produce more accurate depth scaling, but systematic errors often persist. However, we do not just look at the world around us; we interact with objects and potentially obtain proprioceptive cues to distance. There is strong evidence that stereopsis aids actions such as reaching and grasping (Loftus et al., 2004); is the reverse also true? Here we assessed the impact of proprioceptive distance information from arm’s reach on depth estimation. We compared depth magnitude estimates before and after observers performed reaching movements in a virtual environment. Observers estimated the relative depth between a rectangle and reference frame using a pressure-sensitive strip before and after performing a reaching task. When reaching, observers used hand-held controlllers with their index finger extended. The finger tip was tracked and represented by a dot while they touched a virtual square within a reference frame presented at 50cm for a total of 60 trials. In a control experiment, observers performed this same task without reaching, using head movements alone. We found that depth estimation accuracy improved after observers engaged with the target in the reaching task. However, without reaching movements observers showed no such improvement. Further, there was no change in the precision of depth estimates after either type of task (reach or no-reach). The observed improvement in depth estimation reflects a cross-modal calibration of visual space that may be important for everyday interactions. Further, it is likely that this relationship could be exploited in immersive environments to improve accuracy of visuomotor performance.
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