The patient groups performed worse than the control group on the task when vision was not available to compensate for the deficient vestibular system. The patient groups walked slower and veered earlier. Angle of veering seemed to be affected by cognitive tasks, such as talking, in the VVD group, and approached significance in the BPPV group.
The VVD group was comprised of patients with chronic vestibular disorders. The majority of these patients did not take part in the study during their original presentation of acute symptoms. Due to the chronic nature of their vestibular disorders, most patients likely had some compensation for their vestibular deficiency. The performance of these patients was between the post-operative acoustic neuroma (AN) patients and the chronic vestibulopathy (CV) patients described in a previous study, in which both groups veered earlier than controls, the CV patients’ angle was significantly greater and the acutely post-operative AN group veered more than controls [9
]. The compensated post operative AN group did not veer more than controls, however. The less significant findings when analyzing angle in this study was likely due to the heterogonous diseases that composed the VVD group.
Both patient groups in the present experiment walked significantly slower, with eyes open or closed, or approached significance, especially when performing the cognitive task. Dual task performance was not tested in Cohen’s initial study. The decrease in velocity reinforces the idea of competing attention demands, especially when a deficiency in the vestibular system is an exacerbating factor. During a passive orientation task in Yardley’s experiment, healthy volunteers were less accurate in returning to a starting position with a competing cognitive task [18
]. In her follow up study, the inaccuracy in judging orientation was increased in patients with vestibular imbalance and was correlated with the severity of the symptoms [14
]. Our patients did not show as significant an inaccuracy in finding their way to the correct position, but they took longer to perform the task. Our patients were not tested on their responses to the cognitive task; therefore, they could easily prioritize the path integration task over the cognitive task. They were able to walk slower while performing the various tasks and achieve an accurate result.
Peruch et al. found that Meniere’s patients performance was correlated with the complexity of an accompanying mental task [19
]. Our cognitive task was not complex. This low complexity may have contributed to the ability to complete the task more accurately. The effect of the dual tasks may be on a continuum, with less complex tasks only affecting the velocity, while as the task becomes more complex the patients may begin to veer more.
This experiment added a motor component to the dual task performance. The addition of nodding, however, did not significantly affect the variables. Only one patient in this study was greater than 70 years old. In Harley’s study on dual task performance with a cognitive and motor (stepping over an obstacle) tasks, she found that only the performance of healthy subjects aged 70–79 decreased with the addition of an obstacle when compared to subjects aged 20–29 and 60–69 [20
]. Our patients, who had no additional orthopedic or neurologic diseases, could easily adjust to performing the simple task of nodding.
The BPPV group did not perform differently from the VVD group. All of the BPPV patients were tested during an acute presentation with active vertigo on Dix Hallpike maneuvers. One may expect the BPPV patients to behave no differently than controls unless one of the movements during the task was in plane with the respective, diseased semicircular canal. Their consistent similarity may be due to the unloading of the utricle. In BPPV, otoconial matter becomes removed from the utricle to the posterior semicircular canal, probably changing the inertial properties of the otoconial membrane. These patients can have changes in standing balance most likely due to the change in the otolithspinal reflexes and probably have additional changes in their walking balance [21
]. Since linear acceleration signals are important for path completion, the altered linear acceleration signal from the utricle may have decreased the ability of BPPV patients to perform this task [3
The patient groups walked significantly slower than the controls. Using a similar task Dickstein et al found that when healthy individuals were blindfolded they departed less from a straight-ahead path while running [23
], suggesting that speed of gait may play a role. Patients with acute vestibulopathies also veer less when performing path integration tasks at faster speeds. Brandt et al. observed four patients with vestibular neuritis performing a linear path integration task at varying speeds [24
]. In contrast to these previous studies, velocity did not affect the performance of our subjects even though the patient groups walked significantly slower, probably because none of the subjects ran while performing the task. Their gait speeds varied slightly by individual but walking did not allow the variation in foot placement that Dickstein et al hypothesized would lead to improved performance while running.
In conclusion, the patients’ performance on this linear path was affected by adding additional, simple tasks. Performing this task requires attentional demands, and the effect on adding tasks exacerbated the decreased performance by vestibular patients. Patients with vestibular disorders need counseling to perform daily tasks safely in this world of multitasking, especially at night, when there are less visual cues.