| Abstract | The ‘balance system’ comprises the peripheral and central components of the vestibular and visual systems. The peripheral structures code information pertaining to the spatial relationships and motion of the whole body. The central networks modulate and integrate this ‘space-motion information’. Coding or modulatory disturbances, due to pathology or incongruous environmental conditions, can lead to a syndromic ‘balance disorder’. This is because such disturbances result in the execution of balance system functions based on aberrant space-motion information.
The cardinal manifestations of balance disorders include instability and dizziness. Higher cognitive dysfunction is also a possible sequela, but the mechanisms that give rise to it are unclear. Prevailing theory implies that disruption of higher cognition is an indirect, mediated consequence of balance disorders. The specific objective of this research programme was to determine if aberrant space-motion information can affect higher cognition directly.
To fulfil this objective, the effects of experimentally-induced balance disorders on spatial cognitions were examined using tasks that call upon space-motion information to different extents. The results of the first study did not reveal a differential disruption of performance variables because the spatial perspective-taking (SPT) task did not reliably evoke mental self-translocation (MS-TL). Therefore, it did not call upon space-motion information any more than the control task. This led to the creation and validation of new experimental and control tasks in the second study. There was a monotonic response time function on the new SPT task, the ‘SASS task’, but not on the new control task (interaction effect: F(1, 29) = 16.58, p < .001, η2p = .364). This was the first study to show empirically that performance monotonicity on a SPT task is not accounted for by graded spatial compatibil ity effects.
In studies 3 and 4, participants completed the new tasks while exposed to two forms of aberrant stimulation. In study 3, disruption of performance caused by optokinetic stimulation was not found to be selective to the SASS task. However, in study 4, responses on that task after impulse stimulation were characterised by smaller boundary separations (simple effect: t(14) = 2.89, p = .014, r = .612). This effect was selective to the SASS task according to a significant task by cue congruity interaction (F(2, 40) = 4.07, p = .025, η2p = .169), and was not due to the effects of anxiety according to mediation analyses. In the absence of concurrent inordinate disturbances of the physiological states of the participants in the SASS task group, the selective effect implied that aberrant space-motion information can have a direct effect on higher cognition.
This was the first empirical study to show the direct effect. Erroneous self-motion velocity information caused by impulse stimulation may have disrupted the temporal integration of covert body movements during MS-TL. The direct effect of aberrant space-motion information, specifically on MS-TL, has clinical implications. This cognitive function and its dependent cognitions, including ‘theory of mind’, may be particularly vulnerable. According to the results of this project, further research is warranted to explore the integrity of social functioning in persons contending with balance disorders. |
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