Resolving visual motion through perceptual gaps

Abstract

Perceptual gaps can be caused by objects in the foreground temporarily occluding objects in the background or by eyeblinks, which briefly but frequently interrupt visual information. Resolving visual motion across perceptual gaps is particularly challenging, as object position changes during the gap. We examine how visual motion is maintained and updated through externally driven (occlusion) and internally driven (eyeblinks) perceptual gaps. Focusing on both phenomenology and potential mechanisms such as suppression, extrapolation, and integration, we present a framework for how perceptual gaps are resolved over space and time. We finish by highlighting critical questions and directions for future work.

Keywords: extrapolation; eyeblinks; motion; occlusion; prediction; suppression.

Figure 1.. Illustration of perceptual gaps.

Perceptual gaps can be externally-driven (occlusion) or internally-driven (eyeblinks). In both cases, even though incoming visual information is unavailable during the gap, we still perceive visual events as continuous.

Figure 2.. Physical and illusory motion processing.

(A) Physical motion processing pathway. The earliest motion-selective cells are within the retina. From there information is relayed upstream to the LGN, which projects mostly to V1 but with some direct projections to V5/MT. V1 also projects directly onto V5/MT, which has dense connections with regions around the intraparietal sulcus (IPS). While V1 neurons have small receptive fields and are thought to represent local motion, V5/MT represents global motion. (B) Apparent motion occurs when the position of an object is varied quickly over time between discrete locations. The subjective experience is that the object moves smoothly between those locations.

Figure 3.. Involuntary motion extrapolation through a perceptual gap.

Participants observed a stimulus moving along a circular trajectory. When an involuntary blink occurred, the stimulus disappeared, and the participants were asked to indicate where the last visible position was. The results showed that independent of blink duration the response was biased to reflect a perception of the moving stimulus ahead of time. When the stimulus disappeared without a blink occurring, this overshoot was not observed suggesting that the sudden offset overwrote the extrapolated trajectory. (Maus et al. 2020, Figure 2b, redrawn with permission [54])

Figure 4.. Position-specific information during occlusion.

Participants viewed an object moving on a circular trajectory. In the occlusion condition, the object moved behind an occluder without visible edges (quadrant and trajectory lines depicted were added for demonstration only). Then the object re-appeared on the other side of the occluder. In the disappearance condition, the object vanished as soon as it came in contact with the occluder and re-appeared after a delay on the other side of the occluder. In the occlusion condition, the object was perceived to persist behind the occluder, while no object was perceived during the gap in the disappearance condition. In line with this perceptual experience, the neuroimaging results showed that there was position-specific information in visual cortex for the occlusion but not the disappearance condition. (Erlikhman & Caplovitz (2017), Figure 3, redrawn with permission [87])

Figure 5.. Evidence for extrapolation and suppression.

(A) The flash-lag effect (FLE) describes the illusion that a stationary flash is perceived to lag behind a stimulus in motion when they are actually aligned. This effect is due to extrapolation of the moving object resulting in the moving object being perceived ahead in time. The FLE scales with speed and this relationship can be fit along a horizontal asymptote (blue). When training a model, extrapolation occurs spontaneously with the receptive field (RF) of each neuron biasing perception ahead of time. This shift in RF also scales with motion speed (red). When correlating the FLE lag with the RF shift, there is a near perfect correlation, suggesting that the mechanism of extrapolation occurs artificially in a similar way as behaviorally. (Burkitt and Hogendoorn (2021), Figures 7 and 8, redrawn with permission [9]) (B) In another study (Golan et al., 2016), neural responses were recorded intracranially from visual cortex while patients viewed images of different things such as faces, houses, and objects. In some trials, a gap was inserted (i.e., black screen) to interrupt visual information and in other trials the authors looked at the interruption of visual information by spontaneous eyeblinks. Looking at the results, there was a strong evoked response after the stimulus re-appeared after the gap but not after the spontaneous eyeblink. This indicates that re-appearance signals are suppressed after an eyeblink but not after an artificial gap. (Golan et al. (2016), Figure 5, redrawn with permission [112])