Probing the involvement of the earliest levels of cortical processing in motion extrapolation with rapid forms of visual motion priming and adaptation

Prediction of time to contact under perceptual and contextual uncertainties

Accurately estimating time to contact (TTC) is crucial for successful interactions with moving objects, yet it is challenging under conditions of sensory and contextual uncertainty, such as occlusion. In this study, participants engaged in a prediction motion task, monitoring a target that moved rightward and an occluder. The participants' task was to press a key when they predicted the target would be aligned with the occluder's right edge. We manipulated sensory uncertainty by varying the visible and occluded periods of the target, thereby modulating the time available to integrate sensory information and the duration over which motion must be extrapolated. Additionally, contextual uncertainty was manipulated by having a predictable and unpredictable condition, meaning the occluder either reliably indicated where the moving target would disappear or provided no such indication. Results showed differences in accuracy between the predictable and unpredictable occluder conditions, with different eye movement patterns in each case. Importantly, the ratio of the time the target was visible, which allows for the integration of sensory information, to the occlusion time, which determines perceptual uncertainty, was a key factor in determining performance. This ratio is central to our proposed model, which provides a robust framework for understanding and predicting human performance in dynamic environments with varying degrees of uncertainty.

Seeing and extrapolating motion trajectories share common informative activation patterns in primary visual cortex

The natural environment is dynamic and moving objects become constantly occluded, engaging the brain in a challenging completion process to estimate where and when the object might reappear. Although motion extrapolation is critical in daily life-imagine crossing the street while an approaching car is occluded by a larger standing vehicle-its neural underpinnings are still not well understood. While the engagement of low-level visual cortex during dynamic occlusion has been postulated, most of the previous group-level fMRI-studies failed to find evidence for an involvement of low-level visual areas during occlusion. In this fMRI-study, we therefore used individually defined retinotopic maps and multivariate pattern analysis to characterize the neural basis of visible and occluded changes in motion direction in humans. To this end, participants learned velocity-direction change pairings (slow motion-upwards; fast motion-downwards or vice versa) during a training phase without occlusion and judged the change in stimulus direction, based on its velocity, during a following test phase with occlusion. We find that occluded motion direction can be predicted from the activity patterns during visible motion within low-level visual areas, supporting the notion of a mental representation of motion trajectory in these regions during occlusion.

Effect of Repetitive Transcranial Magnetic Stimulation on a Target Moving in Front of a Static or Random Dynamic Visual Noise

Observers report seeing as slower a target disk moving in front of a static visual noise (SVN) background than the same object moving in front of a random dynamic visual noise (rDVN) background when the speed is the same. To investigate in which brain region (lower vs. higher visual areas) the background and the target signals might be combined to elicit this misperception, the transcranial magnetic stimulation (TMS) was delivered over the early visual cortex (V1/V2), middle temporal area (MT) and Cz (control site) while participants performed a speed discrimination task with targets moving in front of an SVN or an rDVN. Results showed that the TMS over MT reduced the perceived speed of the target moving in front of an SVN, but not when the target was moving in front of an rDVN background. Moreover, the TMS do not seem to interfere with encoding processing but more likely affected decoding processing in conditions of high uncertainty (i.e., when targets have similar speed).

Brain activity during time to contact estimation: an EEG study

Understanding the neural mechanisms associated with time to contact (TTC) estimation is an intriguing but challenging task. Despite the importance of TTC estimation in our everyday life, few studies have been conducted on it, and there are still a lot of unanswered questions and unknown aspects of this issue. In this study, we intended to address one of these unknown aspects. We used independent component analysis to systematically assess EEG substrates associated with TTC estimation using two experiments: (1) transversal motion experiment (when a moving object passes transversally in the frontoparallel plane from side to side in front of the observer), and (2) head-on motion experiment (when the observer is on the motion path of the moving object). We also studied the energy of all EEG sources in these two experiments. The results showed that brain regions involved in the transversal and head-on motion experiments were the same. However, the energy used by some brain regions in the head-on motion experiment, including some regions in left parietotemporal and left frontal lobes, was significantly higher than the energy used by those regions in the transversal motion experiment. These brain regions are dominantly associated with different kinds of visual attention, integration of visual information, and responding to visual motion.

The effect of symbolic meaning of speed on time to contact

The effects of moving task-irrelevant objects on time-to-contact (TTC) judgments are examined in six experiments. In particular, we investigated the effects of the symbolic meaning of speed on TTC by presenting images of objects recalling the symbolic meaning of high speed (motorbike, rocket, formula one, rabbit, cheetah and flying Superman) and low speed (bicycle, hot-air balloon, tank, turtle, elephant and static Superman). In all experiments, participants judged the TTC of these moving objects with a black line, indicating the end of the occlusion. Experiment 7 was conducted to disambiguate whether the effects on TTC, found in the previous experiments, were either a by-product of a speed illusion or they were rather elicited by the implicit timing task. In a two-interval forced choice task, participants were instructed to judge if "high-speed objects" moved actually faster than "slow-speed objects". The results revealed no consistent speed illusion. Taken together the results showed shorter TTC estimated with stimuli recalling the meaning of high compared to low speed, but only with the long occlusion duration (3.14 s). At shorter occlusion durations, the pattern was reversed (participant tend to have shorter TTC with stimuli recalling the meaning of low speed). We suggest that the symbolic meaning of speed works mainly at low speed and long TTC, because the semantic elaboration of the stimulus needs a deeper cognitive elaboration. On the other hand, at higher speeds, a small erroneous perceptual judgment affects the TTC, perhaps due to a speed expectancy violation of the expected "slow object".

Electrophysiological correlates of motion extrapolation: An investigation on the CNV

Motion extrapolation (ME), the ability to estimate the current position of moving objects hidden by an occluder, is critical to interact with a dynamic environment. In a typical paradigm, participants estimate time to contact (TTC) by pressing a button when they estimate the occluded moving target reaches a certain cue. Research using this paradigm has shown that motion adaptation of the occluded area produces a shift in the TTC estimate (Gilden et al., 1995). We examined the effect of motion adaptation on the contingent negative variation (CNV), a frontal electrophysiological component (Tecce, 1972) that could reflect the activity of an accumulator (Buhusi and Meck, 2005) for time processing. We predicted that longer TTC estimates due to previous visual motion adaptation would result in a larger CNV because the accumulator can collect more time units. Results showed that motion adaptation actually modulates the CNV, but the CNV amplitude did not correlate with TTC duration, falsifying the accumulator hypothesis. We suggest that motion adaptation interferes with the remembered speed (stored during the visible part of the trajectory) that may be used as input by higher cognitive function to guide the temporal update of target position, regardless of the TTC estimate.

Fast moving texture has opposite effects on the perceived speed of visible and occluded object trajectories

In a series of psychophysical experiments, we altered the perceived speed of a spot (target) using a grayscale texture moving in the same (iso-motion) or opposite (anti-motion) direction of the target. In Experiment 1, using a velocity discrimination task (2IFC), the target moved in front of the texture and was perceived faster with anti-motion than iso-motion texture. The integration and segregation of motion signals in high-level motion areas may have accounted for the illusion. In Experiment 2, by asking observers to estimate the time-to-contact (TTC) with a bar indicating the end of the invisible trajectory, we showed that this illusory visible speed, due to anti- (iso-) texture, reduced (increased) the subsequent estimated duration of occluded target trajectory. However, in Experiment 3, when the target disappeared behind the iso-motion texture, the TTC was estimated shorter than anti- and static textures. In Experiment 4, using an interruption paradigm, we found negative Point of Subjective Equalities (PSEs) with iso-motion but not static texture, suggesting that iso-motion led to overestimation of the hidden speed. However, sensitivity to target speed differences, as assessed by JNDs and d'values was not affected. Results of Experiments 3 and 4 indicate that only the iso-texture affected the estimated target speed, but with opposite polarity compared to visible motion, suggesting a different origin of speed bias. Because our results show that visuospatial tracking was facilitated by the fast iso-motion, we conclude that motion of the occluded target was tracked by shifting visuospatial attention.

Contribution of Visuospatial and Motion-Tracking to Invisible Motion

People experience an object's motion even when it is occluded. We investigate the processing of invisible motion in three experiments. Observers saw a moving circle passing behind an invisible, irregular hendecagonal polygon and had to respond as quickly as possible when the target had “just reappeared” from behind the occluder. Without explicit cues allowing the end of each of the eight hidden trajectories to be predicted (length ranging between 4.7 and 5 deg), we found as expected, if visuospatial attention was involved, anticipation errors, providing that information on pre-occluder motion was available. This indicates that the observers, rather than simply responding when they saw the target, tended to anticipate its reappearance (Experiment 1). The new finding is that, with a fixation mark indicating the center of the invisible trajectory, a linear relationship between the physical and judged occlusion duration is found, but not without it (Experiment 2) or with a fixation mark varying in position from trial to trial (Experiment 3). We interpret the role of central fixation in the differences in distinguishing trajectories smaller than 0.3 deg, by suggesting that it reflects spatiotemporal computation and motion-tracking. These two mechanisms allow visual imagery to form of the point symmetrical to that of the disappearance, with respect to fixation, and then for the occluded moving target to be tracked up to this point.

Tracking Visual Events in Time in the Absence of Time Perception: Implicit Processing at the ms Level

Previous studies have suggested that even if subjects deem two visual stimuli less than 20 ms apart to be simultaneous, implicitly they are nonetheless distinguished in time. It is unclear, however, how information is encoded within this short timescale. We used a priming paradigm to demonstrate how successive visual stimuli are processed over time intervals of less than 20 ms. The primers were two empty square frames displayed either simultaneously or with a 17ms asynchrony. The primers were followed by the target information after a delay of 25 ms to 100 ms. The two square frames were filled in one after another with a delay of 100 ms between them, and subjects had to decide on the location of the first of the frames to be filled in. In a second version of the paradigm, only one square frame was filled in, and subjects had to decide where it was positioned. The influence of the primers is revealed through faster response times depending on the location of the first and second primers. Experiment 1 replicates earlier results, with a bias towards the side of the second primer, but only when there is a delay of 75 to 100 ms between primers and targets. The following experiments suggest this effect to be relatively independent of the task context, except for a slight effect on the time course of the biases. For the temporal order judgment task, identical results were observed when subjects have to answer to the side of the second rather than the first target, showing the effect to be independent of the hand response, and suggesting it might be related to a displacement of attention. All in all the results suggest the flow of events is followed more efficiently than suggested by explicit asynchrony judgment studies. We discuss the possible impact of these results on our understanding of the sense of time continuity.