Planning Lane Changes using Advance Visual and Haptic Information

International audienceTaking a motor planning perspective, this study investigates whether haptic force cues displayed on the steering wheel are more effective than visual cues in signaling the direction of an upcoming lane change. Licensed drivers drove in a fixed-base driving simulator equipped with an active steering system for realistic force-feedback. They were instructed to make lane changes upon registering a directional cue. Cues were delivered according to the movement precuing technique employing a pair of precues and imperative cues which could be either visual, haptic, or crossmodal (a visual precue with a haptic imperative cue, and vice versa). The main dependent variable was response time. Additional analyses were conducted on steering wheel angle profiles and the rate of initial steering errors. Conditions with a haptic imperative cue produced considerably faster responses than conditions with a visual imperative cue, irrespective of the precue modality. Valid and invalid precues produced the typical gains and costs, with one exception. There appeared to be little cost in response time or initial steering errors associated with invalid cueing when both cues were haptic. The results are consistent with the hypothesis that imperative haptic cues facilitate action selection while visual stimuli require additional time-consuming cognitive processing

The effect of visual degradation on anticipatory and compensatory steering control

International audienceIt has long been long held that steering a vehicle is subserved by two distinct visual processes, a compensatory one for maintaining lane position and an anticipatory one for previewing the curvature of the upcoming road. In this study we investigated the robustness of these two steering control processes by systematically degrading their visual inputs. Performance was measured at the level of vehicle position and at the level of the actions on the steering wheel. The results show that the compensatory process is more robust to visual degradation than the anticipatory process. The results are also consistent with the idea that steering is under the supervision of a combination of compensatory and anticipatory mechanisms, although they suggest that the quality of the sensory information will determine how information is combined

Upper limits of auditory motion perception: the case of rotating sounds

Presented at the 15th International Conference on Auditory Display (ICAD2009), Copenhagen, Denmark, May 18-22, 2009We report two experiments investigating rotating sounds presented on a circular array of 12 speakers. Velocity thresholds were mea- sured for three different types of stimuli (broadband noises, white noise, harmonic sounds). In the first experiment, we gradually in- creased or decreased the velocity and asked participants to indicate the point at which they stopped or started (respectively) perceiving a rotating sound. The thresholds ranged between 1.95-2.80 rot/s for noises and 1.65-2.75 rot/s for harmonic sounds. We observed significant effects of the direction of velocity change (accelera- tion or deceleration), stimulus type and fundamental frequencies for harmonic sounds, but no effect of centre frequency was ob- served for broadband noises. In the second experiment, stimuli were presented at constant velocities in a single-interval forced- choice paradigm: listeners were asked to indicate if the sound was rotating or not. The thresholds obtained were within the range of those of the first experiment. The effect of frequency for harmonic sounds was confirmed

Effect of Sound Source Stimuli on the Perception of Reverberation in Large Volumes

International audienceThe aim of the presented research is to determine whether the perception of reverberation is dependent on the type of sound stimuli used. We quantified the discrimination thresholds for reverberations that are representative for large rooms such as concert halls (reverberation times around 1.8 s). For exponential decays, simulating an ideal simple room, thresholds are around 6% (Experiment 1). We found no difference in thresholds between a short noise burst and a male voice spoken word, suggesting that discrimination is not dependent on the type, or spectral content, of the sound source (Experiment 2). In two further experiments using a magnitude estimation paradigm we assessed the perceived amount of reverberation as a function of various types of stimuli. Whereas the discrimination of reverberant stimuli does not seem to be affected by the sound stimulus, the perceived amount of reverberation is affected. Vocal stimuli are perceived as being more reverberant than non-vocal stimuli. The results are discussed in light of current neuroscientific models of auditory processing of complex stimuli but also with respect to their consequences for the use of reverberation in auditory display

The aftereffects of ventriloquism: Generalization across sound-frequencies

Exposure to synchronous but spatially discordant auditory and visual inputs produces, beyond immediate cross-modal biases, adaptive recalibrations of the respective localization processes that manifest themselves in aftereffects. Such recalibrations probably play an important role in maintaining the coherence of spatial representations across the various spatial senses. The present study is part of a research program focused on the way recalibrations generalize to stimulus values different from those used for adaptation. Considering the case of sound frequency, we recently found that, in contradiction with an earlier report, auditory aftereffects generalize nearly entirely across two octaves. In this new experiment, participants were adapted to an 18° auditory-visual discordance with either 400 or 6400 Hz tones, and their subsequent sound localization was tested across this whole four-octave frequency range. Substantial aftereffects, decreasing significantly with increasing difference between test and adapter frequency, were obtained at all combinations of adapter and test frequency. Implications of these results concerning the functional site at which visual recalibration of auditory localization might take place are discussed. © 2004 Elsevier B.V. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

The aftereffects of ventriloquism: Are they sound-frequency specific?

Exposing different sense modalities (like sight, hearing or touch) to repeated simultaneous but spatially discordant stimulations generally causes recalibration of localization processes in one or both of the involved modalities, which is manifested through aftereffects. These provide opportunities for determining the extent of the changes induced by the exposure. Taking the so-called ventriloquism situation, in which synchronized sounds and light flashes are delivered in different locations, we examine if auditory recalibration produced by exposing tones of one frequency to attraction by discordant light flashes generalizes to different frequencies. Contrary to an earlier report, generalization was obtained across two octaves. This result did not depend on which modality attention was forced on through catch trials during exposure. Implications concerning the functional site of recalibration are briefly discussed. © 2003 Elsevier Science B.V. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Walking along curved paths of different angles: the relationship between head and trunk turning

Sreenivasa MN, Frissen I, Souman JL, Ernst MO. Walking along curved paths of different angles: the relationship between head and trunk turning. Experimental Brain Research. 2008;191(3):313-320.Walking along a curved path requires coordinated motor actions of the entire body. Here, we investigate the relationship between head and trunk movements during walking. Previous studies have found that the head systematically turns into turns before the trunk does. This has been found to occur at a constant distance rather than at a constant time before a turn. We tested whether this anticipatory head behavior is spatially invariant for turns of different angles. Head and trunk positions and orientations were measured while participants walked around obstacles in 45 degrees, 90 degrees, 135 degrees or 180 degrees turns. The radius of the turns was either imposed or left free. We found that the head started to turn into the direction of the turn at a constant distance before the obstacle (similar to 1.1 m) for turn angles up to 135 degrees. During turns, the head was consistently oriented more into the direction of the turn than the trunk. This difference increased for larger turning angles and reached its maximum later in the turn for larger turns. Walking speeds decreased monotonically for increasing turn angles. Imposing fixed turn radii only affected the point at which the trunk started to turn into a turn. Our results support the view that anticipatory head movements during turns occur in order to gather advance visual information about the trajectory and potential obstacles

Walking Straight into Circles

Souman JL, Frissen I, Sreenivasa MN, Ernst MO. Walking Straight into Circles. Current Biology. 2009;19(18):1538-1542.Common belief has it that people who get lost in unfamiliar terrain often end up walking in circles. Although uncorroborated by empirical data, this belief has widely permeated popular culture. Here, we tested the ability of humans to walk on a straight course through unfamiliar terrain in two different environments: a large forest area and the Sahara desert. Walking trajectories of several hours were captured via global positioning system, showing that participants repeatedly walked in circles when they could not see the sun. Conversely, when the sun was visible, participants sometimes veered from a straight course but did not walk in circles. We tested various explanations for this walking behavior by assessing the ability of people to maintain a fixed course while blindfolded. Under these conditions, participants walked in often surprisingly small circles (diameter < 20 m), though rarely in a systematic direction. These results rule out a general explanation in terms of biomechanical asymmetries or other general biases [1-6]. Instead, they suggest that veering from a straight course is the result of accumulating noise in the sensorimotor system, which, without an external directional reference to recalibrate the subjective straight ahead, may cause people to walk in circles

Making Virtual Walking Real: Perceptual Evaluation of a New Treadmill Control Algorithm

Souman JL, Giordano PR, Frissen I, De Luca A, Ernst MO. Making Virtual Walking Real: Perceptual Evaluation of a New Treadmill Control Algorithm. ACM Transactions on Applied Perception. 2010;7(2):1-14.For us humans, walking is our most natural way of moving through the world. One of the major challenges in present research on navigation in virtual reality is to enable users to physically walk through virtual environments. Although treadmills, in principle, allow users to walk for extended periods of time through large virtual environments, existing setups largely fail to produce a truly immersive sense of navigation. Partially, this is because of inadequate control of treadmill speed as a function of walking behavior. Here, we present a new control algorithm that allows users to walk naturally on a treadmill, including starting to walk from standstill, stopping, and varying walking speed. The treadmill speed control consists of a feedback loop based on the measured user position relative to a given reference position, plus a feed-forward term based on online estimation of the user's walking velocity. The purpose of this design is to make the treadmill compensate fully for any persistent walker motion, while keeping the accelerations exerted on the user as low as possible. We evaluated the performance of the algorithm by conducting a behavioral experiment in which we varied its most important parameters. Participants walked at normal walking speed and then, on an auditory cue, abruptly stopped. After being brought back to the center of the treadmill by the control algorithm, they rated how smoothly the treadmill had changed its velocity in response to the change in walking speed. Ratings, in general, were quite high, indicating good control performance. Moreover, ratings clearly depended on the control algorithm parameters that were varied. Ratings were especially affected by the way the treadmill reversed its direction of motion. In conclusion, controlling treadmill speed in such a way that changes in treadmill speed are unobtrusive and do not disturb VR immersiveness is feasible on a normal treadmill with a straightforward control algorithm