M Di Luca

Influence of visual and haptic delays on stiffness perception in augmented reality

Visual delays are unavoidable in augmented reality setups and occur in different steps of the rendering pipeline. In the context of haptic interaction with virtual objects, it has been shown that delayed force feedback can alter the perception of object stiffness. We hypothesize that delays in augmented reality systems can have similar consequences. To test this, we carried out a user study to investigate the effect of visual and haptic delays on the perception of stiffness. The experiment has been performed in an optimized visuo-haptic augmented reality setup, which allows to artificially manipulate delays during visual and haptic rendering. In line with previous results, delays for haptic feedback resulted in decreased perceived stiffness. In contrast, visual delays caused an increase in perceived stiffness. However, the simultaneous occurrence of delays in both sensory channels led to a partial compensation of these effects. This could potentially help to correct stiffness perception of virtual objects in visuo-haptic augmented reality systems.

Perceived compliance in a pinch

Handling a compliant object using a pinch grasp provides sensory information about deformation and resistive force from both index finger and thumb. In this paper, an object with rigid surfaces and composed of two compliant materials fixed on a central position is used to address how information from the two fingers is integrated into a holistic percept of compliance. Results indicate that with small differences in material compliance there is a small tendency to rely more on the information at the index finger. With larger differences in material compliance participants adopt different movement patterns with the two fingers to explore the objects. Compliance judgments depend on the relative amount of motion and force exerted-the finger that presses more contributes more to the final estimate. This tendency is consistent with the utilization of a unique force signal for the two fingers. The uneven contribution of the sensory information in the pinch leads to predictable compliance discrimination performance from the performance obtained using the fingers independently.0042-6989/

Inconsistency of perceived 3D shape

see front matter 2011 Elsevier Ltd. A doi:10.1016/j.visres.2011.02.021 E-mail address: max@tuebingen.mpg.de URLs: http://www.kyb.mpg.de~max Handling a compliant object using a pinch grasp provides sensory information about deformation and resistive force from both index finger and thumb. In this paper, an object with rigid surfaces and composed of two compliant materials fixed on a central position is used to address how information from the two fingers is integrated into a holistic percept of compliance. Results indicate that with small differences in material compliance there is a small tendency to rely more on the information at the index finger. With larger differences in material compliance participants adopt different movement patterns with the two fingers to explore the objects. Compliance judgments depend on the relative amount of motion and force exerted—the finger that presses more contributes more to the final estimate. This tendency is consistent with the utilization of a unique force signal for the two fingers. The uneven contribution of the sensory information in the pinch leads to predictable compliance discrimination performance from the performance obtained using the fingers independently. 2011 Elsevier Ltd. All rights reserved.

Does audiovisual temporal recalibration store without stimulation

Internal consistency of local depth, slant, and curvature judgments was studied by asking participants to match two 3D surfaces rendered by different mixtures of 3D cues (velocity, texture, and shading). We found that perceptual judgments were not consistent with each other, with cue-specific distortions. Adding multiple cues did not eliminate the inconsistencies of the judgments. These results can be predicted by the Intrinsic Constraint (IC) model according to which the perceptual metric local estimates are a monotonically increasing function of the Signal-to-Noise Ratio of the optimal combination of direct information of 3D shape (Domini, Caudek, & Tassinari, 2006).

Time and time again: temporal influences of repeated stimuli

Recent studies have investigated adaptation to temporal discrepancies between different sensory modalities by first exposing participants to asynchronous multisensory signals, and subsequently assessing the magnitude of the adaptation effect (the size of the shift in subjective simultaneity). Although never reported, there is reason to assume that the strength of the adaptation effect declines during this measurement period. Usually, short re-exposures are interleaved with testing to prevent such declining. In the present study, we show that a decrease in the strength of adaptation still can take place, even when a common re-exposure procedure is used. In a second experiment, we investigated whether the observed decline is due to: (1) a dissipation of adaptation with the passage of time or, (2) a new adaptation induced by the test stimuli. We find that temporal adaptation does not dissipate with time but is stored until new sensory information, i.e., stimuli that differ from those used during the adaptation procedure, is presented. An alternative explanation, namely that adaptation decays over time but is re-established before the first test trial due to the experimental procedure we chose, is addressed in a control experiment. This finding is discussed in terms of Helsons adaptation level (AL) theory [1947, Adaptation-level as frame of reference for prediction of psychophysical data. The American Journal of Psychology, 60, 1–29], according to which the null point of any perceptual dimension, in our case the perception of simultaneity on the dimension of temporal order, is a summarizing statistic of all stimuli presented in the past. Any single stimulus pulls the AL toward its own value, and any single stimulus is judged as though it was being compared with the current AL.

Effects of visual–haptic asynchronies and loading–unloading movements on compliance perception

Temporal perception does not always correspond to objective time. Several factors contribute to distort perceived timing of stimuli. This work investigates the effect of repeated stimulus presentation (either a sound or a light) on perceived timing of a subsequent audiovisual pair. At the beginning of each trial, a series of sounds or lights is presented with a constant interval. One final stimulus is presented either rhythmically or with a temporal shift. In a psychophysical task, participants judged whether the last stimulus in the sequence is presented before or after a temporal probe in the other modality. Results indicate two types of effects. First, the last stimulus of the sequence appears to be delayed with respect to the probe in the other modality. Second, deviations from regular rhythm tend to be perceptually compensated. Overall, perceived stimulus timing is shown to be affected by the temporal context, and the effect is consistent with a change in perceptual latency. The change depends on the modality of the repeated stimulus and can be explained as a combined effect of an temporal adaptation (i.e., slowing down perception) plus a temporal expectation acting on the slightly arrhythmic stimuli.