Vincent Roussarie

Does tilt/translation ratio affect perception of deceleration in driving simulators?

Tilt-coordination is a technique which uses the tilt-translation ambiguity of the vestibular system to simulate linear accelerations on dynamic driving simulators, in combination with real linear accelerations. However, the tilt/translation ratio is chosen empirically. We experimentally determine the most realistic tilt/translation ratio to simulate a given value of deceleration. Under specific conditions of driving simulation, five tilt/translation ratios were applied, with an inverse-proportional quantity of tilt and translation, so that the sum of the two (the proportion of the deceleration simulated by translational motion and the proportion simulated by tilt) was always equal to the same overall value (0.8 m/s(2)). We find that different ratios lead to different perceptions, depending on the quantity of tilt and translation. With a higher tilt ratio, the braking is perceived as being stronger than when there is a higher translation ratio and the most realistic tilt/translation ratio found is neither pure tilt, nor pure translation, but 35/65% tilt/translation. The way these different ratios are perceived during braking is discussed from vestibular and non-vestibular points of view.

Improving the realism in motion-based driving simulators by adapting tilt-translation technique to human perception

While modern dynamic driving simulators equipped with six degrees-of-freedom (6-DOF) hexapods and X-Y platforms have improved realism, mechanical limitations prevent them from offering a fully realistic driving experience. Solutions are often sought in the ”washout” algorithm, with linear accelerations simulated by an empirically chosen combination of translation and tilt-coordination, based on the incapacity of otolith organs to distinguish between inclination of the head and linear acceleration. In this study, we investigated the most effective combination of tilt and translation to provide a realistic perception of movement. We tested 3 different braking intensities (deceleration), each with 5 inverse proportional tilt/translation ratios. Subjects evaluated braking intensity using an indirect method corresponding to a 2-Alternative-Forced-Choice Paradigm. We find that perceived intensity of braking depends on the tilt/translation ratio used: for small and average decelerations (0.6 and 1.0m/s2), increased tilt yielded an increased overestimation of braking, inverse proportionally with intensity; for high decelerations (1.4m/s2), on half the conditions braking was overestimated with more tilt than translation and underestimated with more translation than tilt. We define a mathematical function describing the relationship between tilt, translation and the desired level of deceleration, intended as a supplement to motion cueing algorithms, that should improve the realism of driving simulations.

Towards timbre modeling of sounds inside accelerating cars

Quality investigations and design of interior car sounds constitute an important challenge for the car industry. Such sounds are complex and time-varying, inducing considerable timbre variations depending on the driving conditions. An interior car sound is indeed a mixture between several sound sources, with two main contributions, i.e. the engine noise on the one hand and the aerodynamic and tire-road noise on the other. Masking phenomena occur between these two components and should be considered when studying perceptive attributes of interior car sounds in order to identify relevant signal parameters. By combining sensory analysis and signal analysis associated with an auditory model, a relation between a reduced number of signal parameters and perceptive attributes can be found. This approach has enabled us to propose timbre descriptors based on the tristimulus criterion that reflect the dynamic behavior of a sound inside an accelerating car.

Formant shifting for speech intelligibility improvement in car noise environment

In this paper, we propose a novel approach aiming at improving the intelligibility of speech in the context of in-car applications. Speech produced in noisy environments is subject to the Lombard effect which gathers a number of voice transformation effects compared to the speech produced in calm environments. To improve intelligibility of in car speech (radio, message alerts, ...), we propose to modify the original speech signal by incorporating one of the important Lombard effect, namely the shift of the lower formant center frequencies away from the competing noise regions. The proposed approach exploits traditional Linear Prediction analysis and overlap and add synthesis. We explore several modification strategies and the merit of each modification is evaluated using both objective and subjective tests. It is in particular shown that the improvement of speech intelligibility in car noise is significantly improved for a majority of listeners.

Effect of additional warning sounds on pedestrians’ detection of electric vehicles: An ecological approach

Virtually silent electric vehicles (EVs) may pose a risk for pedestrians. This paper describes two studies that were conducted to assess the influence of different types of external sounds on EV detectability. In the first study, blindfolded participants had to detect an approaching EV with either no warning sounds at all or one of three types of sound we tested. In the second study, designed to replicate the results of the first one in an ecological setting, the EV was driven along a road and the experimenters counted the number of people who turned their heads in its direction. Results of the first study showed that adding external sounds improve EV detection, and modulating the frequency and increasing the pitch of these sounds makes them more effective. This improvement was confirmed in the ecological context. Consequently, pitch variation and frequency modulation should both be taken into account in future AVAS design.

An innovative method for the sonification of quiet cars

With the development of electric motorizations, the acoustic feedback that the driver perceives in the passenger compartment has deeply changed. The vanishing of engine noise is often associated with better comfort, but it also represents a substantial loss of information for the driver. Internal combustion engine noise indeed plays a major role in the acoustic contribution of the multisensory perception of motion. In a previous experiment, we showed that it was more difficult for drivers to correctly estimate the vehicle speed without engine noise. Thus, more attention is needed from the driver to correctly regulate the speed in electric cars than in internal combustion engine cars. Consequently, we developed an innovative sonification method to compensate for the loss of auditory information in electric cars. The generated sounds are directly controlled by the vehicle’s driving parameters, which give relevant cues on motion. This method has been tested in a driving simulator study to validate its suitab...

Relations between acoustic parameters and perceptual properties: an approach by regressions tree applied to car door closure sounds

The aim of this study is to identify perceptually pertinent parameters for the evaluation of car door closure sounds. For this purpose, door closing sounds are finely decomposed into perceptual properties: analytical properties (which are obtained thanks to sensory analysis), natural properties (linked to perception of sources and events) and evocations. The acoustic characterisation of the sound is then processed by means of an analysis-synthesis model which aims, not at reproducing the exact replica of the door closing sounds, but to synthesize sounds that preserve perceptual properties with a reduced number of signal parameters. The model consists in decomposing the sound in several independent impact sources, each impact being modelled by a set of gains and damping factors in frequency bands. Listening tests on controlled sounds are then carried out to observe the eects of acoustic parameters on the perceptual properties. The complex relations between acoustic parameters and perceptual properties are finally established via regressions tree analyses.

Speech intelligibility improvement in car noise environment by voice transformation

Abstract The typical application targeted by this work is the intelligibility improvement of speech messages when rendered in car noise environment (radio, message alerts,...). The main idea of this work is to transform the original speech to “Lombard” speech or more precisely to simulate some of the strategies followed by humans to render their speech clearer when they are surrounded by noise. Three main effects are considered in this work, namely non uniform-time scale modification, formant shifting and a combination of these modifications along with energy redistribution between speech regions. All effects are studied with specific transformations for voiced and unvoiced segments. The proposed modifications are then evaluated by means of subjective and objective tests. The results of these tests conducted with normal hearing and impaired listeners demonstrate the potential of the selected transformations for voice intelligibility improvement.

Visuo-vestibular interaction in the perception of curvilinear trajectories for passive and active drivers

Self-motion perception, which partly determines the realism of dynamic driving simulators, is based on multisensory integration. For curved trajectories, adding linear translations to visual stimulation seems to improve the perception of motion (Bertin et al., 2004). However, cornering means not only translational motion but also rotational motion in yaw. Wikie and Wand (2005) found no effect of yaw motion on steering performance, but it seems that higher rates of physical stimulation could have a more visible effect. However, the influence of yaw acceleration on cornering perception is still a matter of debate, especially when associated to optic flow. Therefore, the present study aims to analyze the respective role of vestibular (yaw acceleration) and visual stimulations for the perception of curvilinear trajectories. We designed two experiments in which the subjects had 1/to orally estimate their angular displacements as passive drivers, 2/to generate angular displacements by controlling the steering wheel as active drivers. In both experiments, subjects were submitted to three different conditions: (1) visual motion, (2) physical yaw acceleration, (3) combined visual and physical motions. Preliminary results of the first experiment show that visual stimulation produces greater overestimations of angular displacements than physical yaw motion, this overestimation being in between in the visuo-vestibular condition. They also suggest that the weights of visual and vestibular cues in cornering perception depend on the amplitude of the angular displacements. The second experiment should allow us to observe the evolution of visuo-vestibular interaction when subjects are active rather than passive drivers.

Is there a perceptive signature of vehicles vibrations

The vibro‐acoustic comfort of vehicles running at low speed has been studied for several years by car manufacturers. Even if car passengers are exposed to a complex environment involving sight, hearing and touch, it is generally agreed that vibrations transmitted through the seat is a very significant parameter in such situations. Previous laboratory experimentations revealed that vehicles were strongly discriminated even when subjects were submitted to seat vibrations only. The ranking of vehicles was also identical for different tested roads. All these observations raised the question of the existence of an identifiable signature of vehicles, independent of the road type. A perceptive experiment designed to evaluate the influence of such phenomenon was conducted. Subjects were submitted to a free sorting test. The categorisation task consisted in grouping vibrations stimuli recorded in 9 cars running on 3 differents roads according to their similarity. The RMS level of stimuli was normalised so that its...