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Eli Brenner, Lotte Laan, Erik van Lopik, Jeroen BJ Smeets, Irene A Kuling; Can you look at your finger in the dark?. Journal of Vision 2019;19(10):147b. doi: https://doi.org/10.1167/19.10.147b.
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© ARVO (1962-2015); The Authors (2016-present)
There is a tight coupling between the eyes and the hand in many aspects of human behaviour. One might therefore expect people to be able to direct their gaze to their finger without seeing the finger. However, there are two reasons to doubt whether they can. Firstly, the eyes are known to drift in the dark, so people may not be able to maintain their gaze on anything in complete darkness. Secondly, people make reproducible idiosyncratic errors of up to a few centimetres when they try to align a visible target to their own finger hidden below a surface. Thus, they fail to notice the offset between the position of their finger and where they are looking when guiding the visible target. We measured ten participants’ finger and eye movements to examine how accurately they could look at their finger in the dark. Their task was to place their finger on a frontal surface and then to look at the finger, first in the dark and then under dim illumination. Not surprisingly, they were less precise when they could not see their finger. They could fixate in the dark, but made idiosyncratic errors. The magnitude of these errors was similar to that when matching a visual target to their hidden finger. We propose that the systematic errors in both tasks arise when relating arm proprioception to direction of gaze.
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