The Use of Visual Cues in Gravity Judgements on Parabolic Motion

Abstract

Evidence suggests that humans rely on an earth gravity prior for sensory-motor tasks like catching or reaching. Even under earthdiscrepant conditions, this prior biases perception and action towards assuming a gravitational downwards acceleration of 9.81 m/s². This can be particularly detrimental in interactions with virtual environments employing earth-discrepant gravity conditions for their visual presentation. The present study thus investigates how sensitive humans are to visually presented gravities and which cues are used to extract the gravity values from the visual scene. To this end, we employed a Two-Interval Forced-Choice Design. In Experiment 1, participants had to judge which of two presented parabolas had the higher underlying gravity. We used two initial vertical velocities, two horizontal velocities and a constant target size. Experiment 2 added a manipulation of the reliability of the target size. Experiment 1 shows that participants are generally not very sensitive to visually presented gravities, with weber fractions of 13 to beyond 30 %. We identified the rate of change of the elevation angle () and the rate of change of the visual angle ( ) as major cues. Experiment 2 suggests furthermore that size variability has a small influence on sensitivity, while at the same time larger size variability increases reliance on ̇ and decreases reliance on . All in all, even though we use all available information, humans are not adept at extracting the governing gravity from a visual scene, which might further impact our capabilities of adapting to earth-discrepant gravity conditions with visual information alone.

Cognitive-perceptual traits influence use of physics laws to enhance visual motion tracking

“…Predictions of future positions of moving objects exploit gravity and participants' eye movements are guided by prediction to different extents (Jörges & López-Moliner, 2019). Observers are generally capable of distinguishing different settings of gravitational acceleration of parabolic trajectories with poor precision (Jörges, Hagenfeld, & López-Moliner, 2018). ASD has also been shown to drive deficits in ocular motor function with a recent review identifying saccade accuracy, inhibitory control and impaired tracking as common issues (Johnson, Lum, Rinehard & Fielding, 2016).…”

Estimations of the Passing Height of Approaching Objects

“…18,[24][25][26][27] For example, observers may use the visual direction of an approaching object (the angle between a horizontal line extending from the eyes and a line extending from the eyes to the object) to estimate the vertical passing distance. 25,27 Although the use of this variable cannot be discounted, judgments based on visual direction could be inaccurate because approaching objects that have different approach angles may at some point in time have identical visual angles. 26 Another variable that could help in estimating the vertical location of an approaching object upon arrival is the launch angle of the object.…”

“…26 Another variable that could help in estimating the vertical location of an approaching object upon arrival is the launch angle of the object. 9,27 In baseball, for example, slower pitches such as curveballs may be released with an upward trajectory, whereas faster pitches may be released with a downward trajectory. 9,28 Finally, the direction of rotation as determined by markings on an approaching object such as the seams on a baseball may serve as a cue to an object's approach direction.…”

“…23 On the other hand, judgments of where an object will arrive vertically (termed the vertical passing distance) could be based on a single variable or a combination of variables. 18,[24][25][26][27] For example, observers may use the visual direction of an approaching object (the angle between a horizontal line extending from the eyes and a line extending from the eyes to the object) to estimate the vertical passing distance. 25,27 Although the use of this variable cannot be discounted, judgments based on visual direction could be inaccurate because approaching objects that have different approach angles may at some point in time have identical visual angles.…”

Investigating Defensive Colouration in Nudibranch Molluscs using a Novel Analytical Framework for the Study of Animal Colour Patterns​​​​​​​

“…The best model fit was determined using AIC as per Yssaad-Fesselier & Knoblauch (2006) and Linares & Lopez-Moliner (2015). Thresholds between summed graphs for each scenario were compared as per Jörges et al (2018) using the Bootstrap (Boos, 2003) implemented in quickpsy (100 permutations). The Bonferroni method (Bland & Altman, 1995) was used to adjust the significance level of the confidence intervals to 1-0.05/n, with n corresponding to the number of comparisons.…”