Abstract
To successfully perform daily activities such as maintaining posture or running, humans need to be sensitive to self-motion over a large range of motion intensities. Recent studies have shown that the human ability to discriminate self-motion in the presence of either inertial-only motion cues or visual-only motion cues is not constant but rather decreases with motion intensity. However, these results do not yet allow for a quantitative description of how self-motion is discriminated in the presence of combined visual and inertial cues, since little is known about visual–inertial perceptual integration and the resulting self-motion perception over a wide range of motion intensity. Here we investigate these two questions for head-centred yaw rotations (0.5 Hz) presented either in darkness or combined with visual cues (optical flow with limited lifetime dots). Participants discriminated a reference motion, repeated unchanged for every trial, from a comparison motion, iteratively adjusted in peak velocity so as to measure the participants’ differential threshold, i.e. the smallest perceivable change in stimulus intensity. A total of six participants were tested at four reference velocities (15, 30, 45 and 60 °/s). Results are combined for further analysis with previously published differential thresholds measured for visual-only yaw rotation cues using the same participants and procedure. Overall, differential thresholds increase with stimulus intensity following a trend described well by three power functions with exponents of 0.36, 0.62 and 0.49 for inertial, visual and visual–inertial stimuli, respectively. Despite the different exponents, differential thresholds do not depend on the type of sensory input significantly, suggesting that combining visual and inertial stimuli does not lead to improved discrimination performance over the investigated range of yaw rotations.
Highlights
When moving through the environment, humans need to constantly estimate their own motion for performing a variety of crucial tasks
As extensively discussed in Nesti et al (2014b), analysing the noise introduced in the stimulus by the simulator provides important insights into the study of self-motion perception, as it allows dissociation of the mechanical noise of the experimental setup from the noise that is inherent in the perceptual processes
Average signalto-noise ratio (SNR) were computed for every reference stimulus and tested by means of an ANCOVA to investigate the effect of motion intensity on the motion SNRs
Summary
When moving through the environment, humans need to constantly estimate their own motion for performing a variety of crucial tasks (e.g. maintaining posture in presence of external disturbances or controlling a vehicle). This estimate of self-motion, computed by the central nervous system (CNS), is the result of complex multisensory information processing of mainly visual and inertial cues and is inevitably affected by noise, and uncertainty. We investigate the human ability to discriminate rotations centred on the head-vertical axis (yaw) by measuring DTs for different supra-threshold motion intensities in the presence of congruent visual–inertial cues.
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