On the time course of short-term forgetting: a human experimental model for the sense of balance

Abstract

The primary aim of this study was to establish whether the decline of the memory of an angular displacement, detected by the semicircular canals, is best characterized by an exponential function or by a power function. In 27 subjects a conflict was created between the semicircular canals and the graviceptive systems. Subjects were seated, facing forwards, in the gondola of a large centrifuge. The centrifuge was accelerated from stationary to 2.5Gz. While the swing out of the gondola (66°) during acceleration constitutes a frontal plane angular-displacement stimulus to the semicircular canals, the graviceptive systems persistently signal that the subject is upright. During 6 min at 2.5Gz the perceived head and body position was recorded; in darkness the subject repeatedly adjusted the orientation of a luminous line so that it appeared to be horizontal. Acceleration of the centrifuge induced a sensation of tilt which declined with time in a characteristic way. A three-parameter exponential function (Y = Ae−bt + C) and a power function (Y = At−b + C) were fitted to the data points. The inter-individual variability was considerable. In the vast majority of cases, however, the exponential function provided a better fit (in terms of RMS error) than the power function. The mean exponential function was: y = 27.8e−0.018t + 0.5°, where t is time in seconds. Findings are discussed with connection to possible underlying neural mechanisms; in particular, the head-direction system and short-term potentiation and persistent action potential firing in the hippocampus are considered.

Factors of significance for the ability of fighter pilots to visually indicate the magnitude of roll tilt during simulated turns in a centrifuge

“…Both in a previous study at 2.0 G (Tribukait et al, 2011) and in the present study at the 1.1- and 1.8-G loads, the majority of the pilots maintained their initial perception throughout the exposure (Table 1), which is at variance with naïve participants (nonpilots) in whom the initial SVH is typically considerably smaller and declines exponentially with a time constant of 1–2 min (Tribukait & Eiken, 2016). Such a response is attributable to the transient semicircular canal stimuli, induced by the planetary acceleration of the centrifuge and swing-out of the gondola, with a combination of canal stimuli in the transversal (yaw), frontal (roll), and sagittal (pitch) planes (Tribukait & Eiken, 2005b).…”

Visual measures of perceived roll tilt in pilots during coordinated flight and gondola centrifugation

“…Subjects who displayed a pronounced decline in the SVH tilt during the 2-G exposure often responded with a large but short-lasting after-effect upon deceleration of the centrifuge and when the aircraft reassumed straight ahead flight after being in a left-turn. near-zero to more than 40 degrees [22,23]. A suggested explanation for the general underestimation of the roll tilt angle is that the graviceptive systems, which during gondola centrifugation persistently signal that the subject is upright in roll, contradict the semicircular canal response to the swing out of the gondola [7,22,29].…”

“…The SVH responses, corrected for minor differences in the roll tilt stimulus, were very similar in the two conditions. There were substantial inter- individual differences, but for each individual, data obtained in the aircraft corresponded to those obtained during centrifugation [ 23 ]. However, the quantitative and qualitative differences between non-pilots and pilots, revealed in several earlier centrifuge studies, warrants further investigations of this kind, with pilots as test subjects.…”

Spatial orientation during gondola centrifugation with subjects upright versus supine: Evidence for Gestalt psychological mechanisms in vestibular perception

“…Time 0 is defined as the beginning of the 2-G plateau. The constant A represents the initial deviation (response) with respect to an asymptote C. This third parameter (C) is motivated by the fact that normal individuals, while gravitationally upright in the static 1-g environment, often have a deviation (albeit usually < 2.5°) from the true gravitational horizontal [ 6, 46 ]; at an increased gravitoinertial force vector, acting in parallel with the subject’s head-to-seat (z) axis, this static component of the SVH can be considerably greater [ 51 ]. T is the time constant for exponential decay, t is time.…”