Audiovisual estimation of Time-to-contact

Abstract

Time-to-contact (TTC) is the remaining time for a moving object to reach its observer. A good estimation of TTC is essential in everyday situations such as crossing a road or catching a ball. So far, most studies have only looked at estimation of TTC at constant speed, and in visual condition, whereas it is a multisensory task by essence. In our study, we investigated TTC estimation at constant or accelerated speed for three modalities: Auditory, Visual and Audiovisual. At constant speed, it has been demonstrated that TTC estimation performance is already accurate so the addition of auditory cues would not lead to significant performance changes. However, at accelerated speed, visual estimation of TTC becomes more impaired. In this context, auditory cues were expected to play a more prominent role in improving performance. For this reason, we hypothesized that V and AV performance would be identical at constant speed, whereas at accelerated speed, auditory cues would allow a better performance in AV compared to V. Our results show that observers do use both modalities in the AV condition and therefore demonstrate a multisensory integration, but for both levels of acceleration and better performance is not always observed in the multimodal condition. Specifically, auditory cues lead to an underestimation of TTC, which compensates for the visual overestimation. Therefore, whether multisensory integration has a beneficial or detrimental effect on the performances of TTC estimation depends on the level of baseline error in the visual-only and auditory-only conditions.

Keywords: Attention: Selective; Attentional capture; Visual search.

Fig. 1

Experimental paradigm. Participants performed a TTC estimation task with visual-only (V), auditory-only (A) or audiovisual (AV) stimuli. On each trial, a ball moving towards the participant was visible for 2000 milliseconds and occluded during its trajectory for a TTC of 750, 1500, 2250 or 3000 milliseconds. The ball could move at a constant or accelerated speed. In the visual-only modality, the perception of motion was induced by changing the size of the ball. In the auditory modality, motion perception was induced by changing the intensity of the complex tone (see Supplementary Materials Table 1 and Table 2 for details)

Fig. 2

Mean CE as a function of Modality (A=Auditory-only, V=Visual-only, AV=Audiovisual). Points and lines with the same colour belong to the same participant. The red dots correspond to the average of CE. Error bars indicate the 95% confidence interval (CI95). * indicates a significant difference at the p < 0.05 threshold

Fig. 3

Mean CE as a function of Acceleration. Points and lines with the same colour belong to the same participant. An acceleration of 0 m/s² corresponds to a constant speed. The red dots correspond to the average of CE. Error bars indicate the 95% confidence interval (CI95). * indicates a significant difference at the p < 0.05 threshold

Fig. 4

Mean CE as a function of Acceleration for each Modality (A=Auditory-only, V=Visual-only, AV=Audiovisual). Points and lines with the same colour belong to the same participant. An acceleration of 0 m/s² corresponds to a constant speed. The red dots correspond to the average of CE. Error bars indicate the 95% confidence interval (CI95). * indicates a significant difference at the p < 0.05 threshold

Fig. 5

Repeated measures correlation between TTC and CE for the different Acceleration and Modality levels. Points and lines with the same colour belong to the same participant. Panels of the top line correspond to the constant speed condition (Acceleration = 0 m/s²) while the lower line panels correspond to the accelerated speed condition (Acceleration = 7 m/s²). Panels on the left, middle and right are respectively representing the Audio, Visual and Audiovisual modalities

Fig. 6

Mean CE as a function of Modality (A=Auditory-only, V=Visual-only, AV=Audiovisual). Points and lines with the same colour belong to the same participant. The red dots correspond to the average of CE. Panels of the top line correspond to the constant speed condition (Acceleration = 0 m/s²) while the lower line panels correspond to the accelerated speed condition (Acceleration = 7 m/s²). TTC varies from left to right panels to represent the 750, 1500, 2250, 3000 ms levels. * indicates a significant difference at the p < 0.05 threshold