Motion can convey the spatial relationship between origin and destination

What it is

The direction, path, and endpoint of a motion — whether real motion or apparent motion — carries information on its own: it tells the observer where something came from and where it's going, a spatial relationship that a plain pair of before/after static images cannot convey by itself. This is exactly why interfaces deliberately use motion transitions to express relationships between states — an icon flying from one location to another, a panel sliding in from a screen edge — the trajectory itself is telling the user where this thing used to be and where it is now.

Why it happens

The visual pathway that computes motion direction and trajectory (the same pathway that underlies motion's attentional priority) extracts not just "something moved" but the specific vector — origin, path, endpoint — and this spatial-relational information gets bound into the observer's mental representation of the scene (technically related to the object-tracking/correspondence mechanisms that maintain an object's identity across a movement). Because trajectory information is extracted automatically as part of motion perception itself, a motion transition connecting two static states lets an observer read off "this came from there, and went there" at a much lower cognitive cost than deliberate inference. Presenting only the two static states with no connecting motion in between forces the observer to reconstruct that relationship purely from spatial position or semantic cues, at a noticeably higher cognitive cost.

Studying it

• Object tracking/correspondence experiments: comparing a connected-motion transition against an instantaneous cut, testing whether observers can correctly maintain an object's identity across the transition — e.g. correctly answering "where did that object go" or "where did this newly appeared object come from" — to measure the role motion trajectory plays in preserving identity.
• Applied UI studies: comparing an animated transition against an instant cut, measuring the time and accuracy with which users relocate a moved or minimized element's new position, as a proxy for whether the origin-destination information carried by the trajectory was actually used.
• Typical independent variables: presence of connecting motion (animated transition versus instant cut), how direct the trajectory is (straight versus roundabout), motion duration.
• Typical dependent variables: accuracy of origin/destination judgments, time needed to relocate a target, subjective certainty about "where did that go."

Where it stops holding

• This benefit requires the motion to be perceivable as a coherent trajectory — real motion, or apparent motion that stays within the range where it reads as a coherent path. An instant cut, or a transition too fast to be perceived as continuous motion, conveys none of this origin-destination information and functions exactly like a plain cut.
• An overly long or roundabout (winding, indirect) motion path can cost more than it saves: once the time and attention it consumes exceed the cognitive-inference cost it was meant to save, this "considerate" animation stops being considerate — the same duration/smoothness trade-off that applies to apparent motion generally.
• This entry is about conveying a spatial relationship, not about drawing attention (that's the territory of motion's attentional priority) — a trajectory can be subtle or low-contrast enough that it isn't the first thing noticed during scanning, yet still correctly convey origin and destination once it is noticed; the two are separable.

Applying it

• Use a directed, traceable motion path — not a plain opacity fade or an instant cut — specifically when the "where did this come from, where is it going" relationship matters to the user's mental model: minimizing a window to a taskbar icon, adding an item to a cart icon, expanding a thumbnail into a detail view — in these cases the trajectory itself is what conveys the relationship.
• Keep the path direct and its duration short enough that it still reads as one continuous motion, following the same constraints that keep apparent motion reading as smooth, rather than designing a long, roundabout path just to look elaborate.
• Skip the connecting-motion transition when the origin-destination relationship carries no real meaning for the user (purely decorative animation), since the extra motion then only costs time without conveying useful spatial information.
• Verification: remove the connecting motion and replace it with an instant cut, then test whether users can still correctly say where an element went — if performance drops noticeably with the cut, the original motion was doing real work conveying the spatial relationship.

Related

• Same group: A1.14.1 Motion takes attentional priority over static content · A1.14.2 Apparent motion turns discrete positional jumps into perceived continuous movement
• Nearby: A5.15 Space- and object-based attention
• Search terms: motion trajectory · object correspondence · object tracking · motion path