Abstract
Understanding the dynamics of vestibular perception is important, for example, for improving the realism of motion simulation and virtual reality environments or for diagnosing patients suffering from vestibular problems. Previous research has found a dependence of direction discrimination thresholds for rotational motions on the period length (inverse frequency) of a transient (single cycle) sinusoidal acceleration stimulus. However, self-motion is seldom purely sinusoidal, and up to now, no models have been proposed that take into account non-sinusoidal stimuli for rotational motions. In this work, the influence of both the period length and the specific time course of an inertial stimulus is investigated. Thresholds for three acceleration profile shapes (triangular, sinusoidal, and trapezoidal) were measured for three period lengths (0.3, 1.4, and 6.7 s) in ten participants. A two-alternative forced-choice discrimination task was used where participants had to judge if a yaw rotation around an earth-vertical axis was leftward or rightward. The peak velocity of the stimulus was varied, and the threshold was defined as the stimulus yielding 75 % correct answers. In accordance with previous research, thresholds decreased with shortening period length (from ~2 deg/s for 6.7 s to ~0.8 deg/s for 0.3 s). The peak velocity was the determining factor for discrimination: Different profiles with the same period length have similar velocity thresholds. These measurements were used to fit a novel model based on a description of the firing rate of semi-circular canal neurons. In accordance with previous research, the estimates of the model parameters suggest that velocity storage does not influence perceptual thresholds.
Highlights
The vestibular system, important for our perception of selfmotion and our sense of balance, has been intensively studied in animals
Threshold measurements for stimuli varying in frequency as well as in profile shape are presented, and we show that our model can accurately fit these measurements
As expected from the characteristics of semi-circular canal neurons and as suggested or assumed from perceptual threshold modeling of others (Hosman and van der Vaart 1978; Benson et al 1989; Heerspink et al 2005; Grabherr et al 2008), it was found that the discrimination process mainly depends on the peak velocity of the stimulus
Summary
The vestibular system, important for our perception of selfmotion and our sense of balance, has been intensively studied in animals. Perceptual thresholds for sinusoidal accelerations are often measured using motion simulators in order to study the vestibular system. The aim of the present study is twofold: to extend threshold measurements for rotational stimuli to non-sinusoidal accelerations and to explain these threshold measurements with a model based on the firing rate of semi-circular canal neurons. Threshold measurements for non-sinusoidal accelerations are important for at least two reasons. When using a motion simulator to present stimuli, high-frequency movements can exhibit distortions from the commanded sinusoidal motion. This latter problem will be discussed in detail in the ‘‘Methods’’ section. Current models of perceptual thresholds do not distinguish between sinusoidal and non-sinusoidal accelerations; rather, they only take into account the period length of the motion. We propose a new model that can take into account both the period length and the specific time course of the acceleration for a given stimulus
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