Directional Asymmetries and Age Effects in Human Self-Motion Perception

Abstract

Directional asymmetries in vestibular reflexes have aided the diagnosis of vestibular lesions; however, potential asymmetries in vestibular perception have not been well defined. This investigation sought to measure potential asymmetries in human vestibular perception. Vestibular perception thresholds were measured in 24 healthy human subjects between the ages of 21 and 68 years. Stimuli consisted of a single cycle of sinusoidal acceleration in a single direction lasting 1 or 2 s (1 or 0.5 Hz), delivered in sway (leftright), surge (forward-backward), heave (up-down), or yaw rotation. Subject identified self-motion directions were analyzed using a forced choice technique, which permitted thresholds to be independently determined for each direction. Non-motion stimuli were presented to measure possible response bias. A significant directional asymmetry in the dynamic response occurred in 27% of conditions tested within subjects, and in at least one type of motion in 92% of subjects. Directional asymmetries were usually consistent when retested in the same subject but did not occur consistently in one direction across the population with the exception of heave at 0.5 Hz. Responses during null stimuli presentation suggested that asymmetries were not due to biased guessing. Multiple models were applied and compared to determine if sensitivities were direction specific. Using Akaike information criterion, it was found that the model with direction specific sensitivities better described the data in 86% of runs when compared with a model that used the same sensitivity for both directions. Mean thresholds for yaw were 1.3±0.9°/s at 0.5 Hz and 0.9±0.7°/s at 1 Hz and were independent of age. Thresholds for surge and sway were 1.7±0.8 cm/s at 0.5 Hz and 0.7±0.3 cm/s at 1.0 Hz for subjects G50 and were significantly higher in subjects 950 years old. Heave thresholds were higher and were independent of age.

Vestibular Perception and the Vestibulo-Ocular Reflex in Young and Older Adults

“…We found no significant difference between the detection thresholds of younger and older subjects undergoing 0.5 Hz earth-vertical sinusoidal rotations determined using a two-alternative, two-interval forced choice paradigm. This confirms an earlier study of detection thresholds, which also found no relationship to age while using a somewhat different, single-interval paradigm consisting of solitary raised-cosine rotations at 0.5 Hz (Roditi and Crane 2012). Others have also failed to find a difference with age, with one study finding that thresholds to motion along a 0.5 Hz triangular velocity trajectory about the earth-vertical axis remained stable across a range of ages (Seemungal et al 2004).…”

“…It was uncertain based on their study whether the changes seen with aging were specific to the higher frequency or might have actually been more closely dependent on the higher accelerations also inherent in that higher stimulus. As our discrimination stimulus tested function at the same frequency but higher accelerations, and we found no elevation of thresholds with aging, it could be concluded that the effect seen by Roditi and Crane (2012) may have indeed been determined by frequency more than acceleration.…”

“…Others, however, have found that other stimulus conditions did result in age-related changes in detection thresholds. Roditi and Crane (2012) found that detection thresholds to rotations about the earth-vertical axis at higher stimulus frequencies than 0.5 Hz increased with age, and Kingma (2005) showed a similar age-related effect measuring linear accelerations along the nasal-occipital axis (Kingma 2005; Roditi and Crane 2012). …”

“…This allowed us to examine further the findings of Roditi and Crane, who found that thresholds did not change with aging during an earth-vertical rotation task at 0.5 Hz but did at a higher frequency (Roditi and Crane 2012). It was uncertain based on their study whether the changes seen with aging were specific to the higher frequency or might have actually been more closely dependent on the higher accelerations also inherent in that higher stimulus.…”

Determining thresholds using adaptive procedures and psychometric fits: evaluating efficiency using theory, simulations, and human experiments

“…To simplify interpretation of results, we did not perform the scaling of the biased-reduced estimates (Chaudhuri and Merfeld 2013) to further improve accuracy, but this could easily be done in combination with the approaches described in this paper. For simplicity, we opted not to include a nonlinear asymmetry (Roditi and Crane 2012a) or a lapse rate (Wichmann and Hill 2001a), though either could be readily included as independent effects when necessary.…”