May the Force be against you:

Better sensitivity to speed changes that

appear to resist gravity

Beyond seemingly lower-level features such as color and motion, visual perception also recovers properties that are more commonly associated with higher-level thought — as when an upwardly accelerating object is seen as self-propelled, and resisting the force of gravity. Past work has explored how speed changes drive the perception of physical forces, but might the reverse also be true? Does seeing a speed change as self-propelled make us more likely to notice it in the first place? In four experiments, online observers were more sensitive to objects’ accelerations when they moved upward (i.e. when those accelerations opposed gravity), and they were more sensitive to objects’ decelerations when they moved downward (i.e. when those decelerations appeared as ‘braking’ against gravity). We conclude that the perception of self-propelledness is not merely an ‘endpoint’ in visual processing, but rather determines the perception of other, seemingly lower-level, features of how objects move.

Demonstrations

Experiment 1 — Acceleration Detection

In an initial experiment, observers viewed animations featuring single moving objects. After each animation, they reported whether the object accelerated, or remained at a constant speed (see Figure 1). We predicted that observers would be more sensitive to the acceleration of upward-moving objects (i.e. when the object’s acceleration would need to resist the force of gravity) compared to downward-moving objects (i.e. when its acceleration could be attributed to the force of gravity).

Observers were better at detecting speed-ups for Upward moving objects than for Downward moving objects. These results indicate that we are more sensitive to an object’s acceleration when that acceleration appears to be self-propelled, and resisting the force of gravity.

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Experiment 2 — Deceleration Detection

The hypothesis that observers are more sensitive to speed changes that appear to resist gravity makes the *opposite* prediction for the detection of deceleration. If an upward-moving object slows down, then this slow-down is attributable to the force of gravity, and observers should be relatively insensitive to this. By contrast, if a downward-moving object slows down, then this slow-down may be attributed to a ‘braking’ force that resists gravity, in which case observers should be more sensitive to this. To test this prediction, we next ran a Deceleration Detection Experiment, which was analogous to the Acceleration Detection Experiment, except that now observers were instead tasked with detecting slow-downs.

Observers were more sensitive to the slow-downs of downwardly-moving objects (i.e. to slow-downs which appear to resist gravity) than to the slow-downs of upwardly moving objects (i.e. to slow-downs which appear consistent with gravity).

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Downward Accelerating Object
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Downward Constant Moving Object (Slow)
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Downward Constant Moving Object (Fast)
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Upward Accelerating Object
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Upward Constant Moving Object (Slow)
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Upward Constant Moving Object (Fast)
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Downward Decelerating Object
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Downward Constant Moving Object (Slow)
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Downward Constant Moving Object (Fast)
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Upward Decelerating Object
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Upward Constant Moving Object (Slow)
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Upward Constant Moving Object (Fast)
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