Combining biological motion perception with optic flow analysis for self-motion in crowds

Hülemeier, Anna-Gesina; Lappe, Markus

doi:10.1167/jov.20.9.7

Cited by 6 publications

(36 citation statements)

References 41 publications

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“…As the nonrigid motion of the Intact walker disturbs optic flow necessary for estimating self-motion (Riddell & Lappe, 2017 ; Hülemeier & Lappe, 2020 ) it could be a potential source of uncertainty for flow parsing estimates. To investigate whether nonrigid motion of a walker affected flow parsing we first tested for differences between the Intact and the Cloud (i.e., a non-human stimulus without nonrigid motion) walkers and then for differences between the Intact and the Scrambled (i.e., a non-human stimulus with the same nonrigid motion as the Intact walker) walkers.…”

Section: Methodsmentioning

confidence: 99%

“…The Scrambled walkers served as a control for possible effects on flow parsing of the nonrigid motion produced by the walker. This was critical for our study because the presence of nonrigid motion of humans (and scrambled versions of human PLWs) affects optic flow perception (Riddell & Lappe, 2017 ; Koerfer & Lappe, 2020 ; Hülemeier & Lappe, 2020 ) and, therefore, might also affect flow parsing. For the Intact walker, we induced conflicts between biological features (i.e., facing and articulation) and the direction of scene-relative motion.…”

Section: Introductionmentioning

confidence: 99%

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Flow parsing and biological motion

Mayer¹,

Riddell

Lappe

2021

Atten Percept Psychophys

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Flow parsing is a way to estimate the direction of scene-relative motion of independently moving objects during self-motion of the observer. So far, this has been tested for simple geometric shapes such as dots or bars. Whether further cues such as prior knowledge about typical directions of an object’s movement, e.g., typical human motion, are considered in the estimations is currently unclear. Here, we adjudicated between the theory that the direction of scene-relative motion of humans is estimated exclusively by flow parsing, just like for simple geometric objects, and the theory that prior knowledge about biological motion affects estimation of perceived direction of scene-relative motion of humans. We placed a human point-light walker in optic flow fields that simulated forward motion of the observer. We introduced conflicts between biological features of the walker (i.e., facing and articulation) and the direction of scene-relative motion. We investigated whether perceived direction of scene-relative motion was biased towards biological features and compared the results to perceived direction of scene-relative motion of scrambled walkers and dot clouds. We found that for humans the perceived direction of scene-relative motion was biased towards biological features. Additionally, we found larger flow parsing gain for humans compared to the other walker types. This indicates that flow parsing is not the only visual mechanism relevant for estimating the direction of scene-relative motion of independently moving objects during self-motion: observers also rely on prior knowledge about typical object motion, such as typical facing and articulation of humans.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Flow parsing and biological motion

Mayer¹,

Riddell

Lappe

2021

Atten Percept Psychophys

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“…Due to the similar to identical motion speed of the observer and the walkers, the optic flow was reduced to a minimum. Here, participants must infer visual self-motion from the articulation of the walkers in the crowd ( Seno & Sato, 2012 ; Masselink & Lappe, 2015 ; Riddell & Lappe, 2017 ; Hülemeier & Lappe, 2020 ). In the approaching condition, participants visually traversed a crowd that walked toward them.…”

Section: Discussionmentioning

confidence: 99%

“…In natural environments, however, we are often confronted with dynamic scenes in which other people walk alongside us. The motion of other walking humans, known as biological motion ( Johansson, 1973 ), introduces noise to the optic flow field, thereby biasing optic flow analysis for heading, the direction of one's self-motion ( Riddell & Lappe, 2017 ; Riddell & Lappe, 2018 ; Riddell, Li, & Lappe, 2019 ; Hülemeier & Lappe, 2020 ; Koerfer & Lappe, 2020 ) and concerning flow parsing, the estimation of independent object motion within a flow field ( Mayer, Riddell, & Lappe, 2021 ). Biological motion consists of limb articulation and its associated translation through space.…”

Section: Introductionmentioning

confidence: 99%

Visual perception of travel distance for self-motion through crowds

Hülemeier

Lappe

2023

Journal of Vision

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Humans can use visual motion to estimate the distance they have traveled. In static environments, optic flow generated by self-motion provides a pattern of expanding motion that is used for the estimation of travel distance. When the environment is populated by other people, their biological motion destroys the one-to-on correspondence between optic flow and travel distance. We investigated how observers estimate travel distance in a crowded environment. In three conditions, we simulated self-motion through a crowd of standing, approaching, or leading point-light walkers. For a standing crowd, optic flow is a veridical signal for distance perception. For an approaching crowd, the visual motion is the sum of the self-motion–induced optic flow and the optic flow produced by the approaching walkers. If only optic flow were to be used, travel distance estimates would be too high because of the approaching direction of the crowd toward the observer. If, on the other hand, cues from biological motion could be used to estimate the speed of the crowd, then the excessive optic from the approaching crowd flow might be compensated. In the leading crowd condition, in which walkers of the crowd keep their distance from the observer as they walk along with the observer, no optic flow is produced. In this condition, travel distance estimation would have to rely solely on biological motion information. We found that distance estimation was quite similar across these three conditions. This suggests that biological motion information can be used (a) to compensate for excessive optic flow in the approaching crowd condition and (b) to generate distance information in the leading crowd condition.

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“…In scenes that violate the assumption of rigidity, for example, if objects move in the scene, heading perception becomes biased by the independent object motion ( Warren & Saunders, 1995 ; Royden & Hildreth, 1996 ; Layton & Fajen, 2016 ; Li, Ni, Lappe, Niehorster, & Sun, 2018 ). A particularly relevant situation occurs when other people move in the scene, such as when a traveling observer encounters another walker or a group of walkers ( Riddell & Lappe, 2017 ; Riddell & Lappe, 2018 ; Riddell, Li, & Lappe, 2019 ; Hülemeier & Lappe, 2020 ; Koerfer & Lappe, 2020 ; Mayer, Riddell, & Lappe, 2021 ).…”

Section: Introductionmentioning

confidence: 99%

Illusory percepts of curvilinear self-motion when moving through crowds

Hülemeier,

Lappe

2023

Journal of Vision

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Self-motion generates optic flow, a pattern of expanding visual motion. Heading estimation from optic flow analysis is accurate in rigid environments, but it becomes challenging when other human walkers introduce independent motion to the scene. Previous studies showed that heading perception is surprisingly accurate when moving through a crowd of walkers but revealed strong heading biases when either articulation or translation of biological motion were presented in isolation. We hypothesized that these biases resulted from misperceiving the self-motion as curvilinear. Such errors might manifest as opposite biases depending on whether the observer perceived the crowd motion as indication of his/her self-translation or self-rotation. Our study investigated the link between heading biases and illusory path perception. Participants assessed heading and path perception while observing optic flow stimuli with varying walker movements. Self-motion perception was accurate during natural locomotion (articulation and translation), but significant heading biases occurred when walkers only articulated or translated. In this case, participants often reported a curved path of travel. Heading error and curvature pointed in opposite directions. On average, participants perceived the walker motion as evidence for viewpoint rotation leading to curvilinear path percepts.

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Combining biological motion perception with optic flow analysis for self-motion in crowds

Cited by 6 publications

References 41 publications

Flow parsing and biological motion

Flow parsing and biological motion

Visual perception of travel distance for self-motion through crowds

Illusory percepts of curvilinear self-motion when moving through crowds

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