Autokinesis illusion in fighter flying revisited

Introduction: Autokinesis refers to the perception of motion which is experienced by an aircrew when he fixates his gaze on a stationary point/source of light in an otherwise completely darkened environment. A study was conducted in the Department of Acceleration Physiology and Spatial Orientation, Institute of Aerospace Medicine to determine the time taken for onset of autokinesis in the disorientation simulator (Air Fox DISO) and the effectiveness of various intervention strategies to break the illusion. Material and Methods: A total of 103 randomly selected fighter pilots participated in the study. They were briefed about the illusion and the various interventions used to counteract it, such as: (a) Shrugging of shoulders without breaking gaze, (b) stretching of arms without breaking gaze, (c) breaking of gaze for 5 s and (d) breaking of gaze for 10 s (if the illusion is not broken after breaking of gaze for 5 s). Time taken for autokinesis to set in and the effectiveness of the interventions used were noted. Subjective feedback from the participating aircrew was also obtained on their experience on autokinesis illusion in active flying through a structured questionnaire. Results: The average time required for onset of the autokinesis illusion in the DISO was observed to be 20.3 ± 15.5 s (range 4.1–121.4 s). Of the 103 aircrew participants, 100 (97.1%) reported that the intervention of stretching of arms was effective, 94 aircrew (91.3%) reported that the intervention of shoulder shrug was effective in breaking the illusion and 99 aircrew (96.1%) were able to counter the illusion by breaking their gaze for duration of 5 s. Autokinesis was experienced in active flying by 17 aircrew, accounting for an incidence of 16.5%. This study reveals that autokinesis involves the interplay of vision, vestibular system, as well as the proprioceptive stimulus in counteracting this illusion. A combination of gaze break and shoulder shrug/arm stretch could be the most appropriate intervention strategy under such circumstances. The operational scenarios conducive for causing this illusion and the physiological basis for the various intervention strategies have been discussed. Conclusion: The autokinesis illusion though considered benign has got significant potential for distraction during operational flying. The intervention strategies discussed in the study are effective in breaking the illusion. The pilot community needs to be aware of the preconditions, mechanism, and effectiveness of the intervention strategies in countering this illusion.

Abnormal microscale neuronal connectivity triggered by a proprioceptive stimulus in dystonia

We investigated modulation of functional neuronal connectivity by a proprioceptive stimulus in sixteen young people with dystonia and eight controls. A robotic wrist interface delivered controlled passive wrist extension movements, the onset of which was synchronised with scalp EEG recordings. Data were segmented into epochs around the stimulus and up to 160 epochs per subject were averaged to produce a Stretch Evoked Potential (StretchEP). Event-related network dynamics were estimated using a methodology that features Wavelet Transform Coherency (WTC). Global Microscale Nodal Strength (GMNS) was introduced to estimate overall engagement of areas into short-lived networks related to the StretchEP, and Global Connectedness (GC) estimated the spatial extent of the StretchEP networks. Dynamic Connectivity Maps showed a striking difference between dystonia and controls, with particularly strong theta band event-related connectivity in dystonia. GC also showed a trend towards higher values in dystonia than controls. In summary, we demonstrate the feasibility of this method to investigate event-related neuronal connectivity in relation to a proprioceptive stimulus in a paediatric patient population. Young people with dystonia show an exaggerated network response to a proprioceptive stimulus, displaying both excessive theta-band synchronisation across the sensorimotor network and widespread engagement of cortical regions in the activated network.

Persistent visual and vestibular impairments for Postural control following concussion

ObjectiveThe purpose of this study was to examine sensory reweighting for upright stance in three groups (i.e., sub-acute concussion, concussion history, control).BackgroundBalance impairments are common following concussion; however, the physiologic mechanisms underlying these impairments are not well understood.Design/methodsThere were 13 participants (8 women, 21 ± 3 years) between 2 weeks and 6 months post-injury who reported being asymptomatic at the time of testing (i.e., sub-acute concussion group), 13 participants (8 women, 21 ± 1 year) with a history of concussion (i.e., concussion history group, >1 year following concussion), and 26 participants (8 women, 22 ± 3 years) with no concussion history (i.e., control group). We assessed sensory reweighting by simultaneously perturbing participants' visual, vestibular, and proprioceptive systems. The visual stimulus was a sinusoidal translation of the visual scene at 0.2Hz, the vestibular stimulus was ±1 mA binaural monopolar galvanic vestibular stimulation (GVS) at 0.36Hz, and the proprioceptive stimulus was Achilles' tendon vibration at 0.28Hz. The visual stimulus was presented at two different amplitudes (low vision = 0.2m, high vision = 0.8m). We computed center of mass gain to each modality.ResultsThe sub-acute concussion group (95% confidence interval = 0.078-0.115, p = 0.001) and the concussion history group (95% confidence interval = 0.056-0.094, p = 0.038) had higher gains to the visual stimulus than the control group (95% confidence interval = 0.040-0.066). The sub-acute concussion group (95% confidence interval = 0.795–1.159, p = 0.002) and the concussion history group (95% confidence interval = 0.633–1.012, p = 0.018) had higher gains to the vestibular stimulus than the control group (95% confidence interval = 0.494-0.752). There were no group differences in gains to the proprioceptive stimulus and there were no group differences in sensory reweighting.ConclusionsFollowing concussion, participants responded more strongly to visual and vestibular stimuli during upright stance, suggesting they may have abnormal dependence on visual and vestibular feedback. These findings may indicate an area for targeted rehabilitation interventions.