ÔÇÿSelf-Occlusion’ during a manual control task

Physiology 2012 (Edinburgh) (2012) Proc Physiol Soc 27, PC253

Poster Communications: ÔÇÿSelf-Occlusion’ during a manual control task

T. Osborne1, M. Lakie1

1. University of Birmingham, Birmingham, United Kingdom.

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Introduction: There is evidence to suggest that sensory information is gated during, and immediately following movements. We wished to test this hypothesis using a novel paradigm in a manual control task. Methods: With ethical permission and their informed consent, subjects (n = 20) sat in a self selected position holding a small uniaxial joystick and wore a pair of PLATO visual occlusion spectacles. A computer screen in front of them displayed both a red circle, which represented the angle of a virtual inverted pendulum, and a white cross which marked the centre of the screen. Subjects were required to maintain the position of the circle as close to the centre of the screen as possible via gentle taps of the joystick (Loram et al., 2010). As subjects performed the task, their vision was occluded for a period of 200 ms following each contact with the joystick. In different trials, the delay between joystick contact and the 200 ms visual occlusion was varied among the following values: 1 ms, 50 ms, 100 ms, 150 ms, 200 ms, 250 ms and 2000 ms. There was also a control condition where no occlusions were presented throughout the whole trial. Results: In the control condition, and in the 2000 ms condition, the modal tapping intervals were 398 and 384 ms respectively. In the 1, 50, 100 and 150 ms conditions the modal tapping intervals consistently occurred at a relatively fixed interval following the end of the occlusion (263 ± 10 ms, mean ± SD). In the 200 and 250 ms conditions, there were two common tapping intervals. The modal tapping intervals were 381 and 376 ms respectively, and there was a secondary peak at 258 and 257 ms following the end of the occlusion. Performance in the task was least impaired compared to the control condition when the occlusion was presented after only a 1 ms delay. Discussion: These observations suggest that, in this particular task, subjects were able to compute, select and execute a corrective response (a tap of the joystick) within ≈ 260 ms of the presentation of visual information. However, when subjects were not occluded, or when the delay between the tap and the occlusion was long (2000 ms), subjects elected to make corrective responses at longer intervals (approximately 390 ms). We suggest this discrepancy may be explained if each tap is immediately followed by a brief period of ‘self-occlusion’ where subjects make little use of sensory information. This may also explain why performance was least impaired when the visual occlusion was presented immediately following each tap because in this case, the visual occlusion is partly concurrent with the self-occlusion.



Where applicable, experiments conform with Society ethical requirements.

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