Date Published: January 26, 2017
Publisher: Public Library of Science
Author(s): Alessandro Nesti, Ksander de Winkel, Heinrich H. Bülthoff, Robert J. van Beers.
While moving through the environment, our central nervous system accumulates sensory information over time to provide an estimate of our self-motion, allowing for completing crucial tasks such as maintaining balance. However, little is known on how the duration of the motion stimuli influences our performances in a self-motion discrimination task. Here we study the human ability to discriminate intensities of sinusoidal (0.5 Hz) self-rotations around the vertical axis (yaw) for four different stimulus durations (1, 2, 3 and 5 s) in darkness. In a typical trial, participants experienced two consecutive rotations of equal duration and different peak amplitude, and reported the one perceived as stronger. For each stimulus duration, we determined the smallest detectable change in stimulus intensity (differential threshold) for a reference velocity of 15 deg/s. Results indicate that differential thresholds decrease with stimulus duration and asymptotically converge to a constant, positive value. This suggests that the central nervous system accumulates sensory information on self-motion over time, resulting in improved discrimination performances. Observed trends in differential thresholds are consistent with predictions based on a drift diffusion model with leaky integration of sensory evidence.
Everyday life requires humans to move through the environment, while completing crucial tasks such as maintaining balance or controlling a vehicle. Success in these tasks largely relies on a veridical perception of self-motion, i.e., the continuous estimation of one’s body position, and its derivatives, with respect to the world. This estimation process is performed by the central nervous system (CNS) by combining visual, auditory and inertial (i.e., somatosensory and vestibular) sensory information–seemingly without effort. Whereas a considerable body of neurophysiological and behavioural studies address how information on self-motion is accumulated across the senses (see e.g., [1–10]), much less is known about how information on self-motion is accumulated over time. Given the dynamic nature of natural self-movements, it is rather intuitive that the CNS must accumulate sensory information not only across the senses, but also over time. For instance, it has been shown that humans walking on a straight path in darkness can estimate their travelled distance, suggesting a path integration mechanism that continuously updates based on sensory information [11,12]. Nevertheless, the perceptual processes underlying the accumulation of sensory evidence, and in specific the effect of stimulus exposure time on the human ability to perceive and discriminate self-motion, remains largely unexplored.
Averaged DTs are presented in Fig 5. As confirmed by linear regression analysis, DTs significantly decrease with the duration of the yaw stimuli (t(38) = 2.87, p = 0.007, r2 = 0.72). Over the tested range of stimulus durations, the highest DTs were measured for the 1 s condition (3.42 deg/s), while the lowest DTs were measured for the 5 s condition (2.57 deg/s).
In this study, we measured DTs for discriminating two consecutive head-centred sinusoidal rotations of different amplitude. We found that stimulus duration has a significant effect on DTs, with lower DTs (i.e., better discrimination performances) for longer as compared to shorter stimulus durations. We further showed that a DDM with a leaky integration of sensory evidence can account for this effect. The following sections discuss the implications that methodological choices may have on the experimental results, the relation of the results to the literature and the tenability of DDMs.