Spatial orientation: Visual-vestibular-somatic interaction

We are able to orient lines with respect to environmentally or egocentrically defined reference axes. To do this we must be able to compensate for disturbances produced by displacement of our eyes relative to other parts of our bodies and for visual disturbances such as tilted frames or moving visual fields. Compensation signals from somatosensory and vestibular receptors were examined in this investigation. Disturbances were produced by tilting the head and by rotating a large visual display. Compensation signals associated with gravity were manipulated by placing the observers horizontally on a board or seating them verticatly. Experiment 1 examined effects of visual disturbance on the ability of supine observers to set a line to the longitudinal body axis while the head was tilted toward one shoulder or while the head was straight. Effects of the visual disturbance were greater when the head was tilted than when it was straight. This indicates that the effects of visual disturbance were greater for a task that required compensation. Experiment 2 compared the performance of supine and erect observers. No differences between the performance of observers on a task requiring the use of compensation signals were obtained under these two conditions. This suggests that enrichment of compensatory signals did not reduce the effects of visual disturbance. Experiment 2 did replicate the result from Experiment 1 that the effects of visual disturbance were greater when observers performed a task that required them to use compensation signals. Finally, Templeton’s (l973) previous report that supine observers undercompensate for head tilt was replicated.

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