Add perceived performance section to motion-design reference

- 80ms threshold for "instant" perception
- Active vs passive time (preemptive start, early completion)
- Optimistic UI patterns with appropriate use cases
- Easing affects perceived duration (peak-end effect)
- Caution: too-fast can decrease perceived value

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude/skills/frontend-design/reference/motion-design.md

@@ -74,6 +74,22 @@ This is not optional. Vestibular disorders affect ~35% of adults over 40.
 
 **What to preserve**: Functional animations like progress bars, loading spinners (slowed down), and focus indicators should still work—just without spatial movement.
 
+## Perceived Performance
+
+**Nobody cares how fast your site is—just how fast it feels.** Perception can be as effective as actual performance.
+
+**The 80ms threshold**: Our brains buffer sensory input for ~80ms to synchronize perception. Anything under 80ms feels instant and simultaneous. This is your target for micro-interactions.
+
+**Active vs passive time**: Passive waiting (staring at a spinner) feels longer than active engagement. Strategies to shift the balance:
+
+- **Preemptive start**: Begin transitions immediately while loading (iOS app zoom, skeleton UI). Users perceive work happening.
+- **Early completion**: Show content progressively—don't wait for everything. Video buffering, progressive images, streaming HTML.
+- **Optimistic UI**: Update the interface immediately, handle failures gracefully. Instagram likes work offline—the UI updates instantly, syncs later. Use for low-stakes actions; avoid for payments or destructive operations.
+
+**Easing affects perceived duration**: Ease-in (accelerating toward completion) makes tasks feel shorter because the peak-end effect weights final moments heavily. Ease-out feels satisfying for entrances, but ease-in toward a task's end compresses perceived time.
+
+**Caution**: Too-fast responses can decrease perceived value. Users may distrust instant results for complex operations (search, analysis). Sometimes a brief delay signals "real work" is happening.
+
 ## Performance
 
 Don't use `will-change` preemptively—only when animation is imminent (`:hover`, `.animating`). For scroll-triggered animations, use Intersection Observer instead of scroll events; unobserve after animating once. Create motion tokens for consistency (durations, easings, common transitions).

dist/claude-code/.claude/skills/frontend-design/reference/motion-design.md

@@ -74,6 +74,22 @@ This is not optional. Vestibular disorders affect ~35% of adults over 40.
 
 **What to preserve**: Functional animations like progress bars, loading spinners (slowed down), and focus indicators should still work—just without spatial movement.
 
+## Perceived Performance
+
+**Nobody cares how fast your site is—just how fast it feels.** Perception can be as effective as actual performance.
+
+**The 80ms threshold**: Our brains buffer sensory input for ~80ms to synchronize perception. Anything under 80ms feels instant and simultaneous. This is your target for micro-interactions.
+
+**Active vs passive time**: Passive waiting (staring at a spinner) feels longer than active engagement. Strategies to shift the balance:
+
+- **Preemptive start**: Begin transitions immediately while loading (iOS app zoom, skeleton UI). Users perceive work happening.
+- **Early completion**: Show content progressively—don't wait for everything. Video buffering, progressive images, streaming HTML.
+- **Optimistic UI**: Update the interface immediately, handle failures gracefully. Instagram likes work offline—the UI updates instantly, syncs later. Use for low-stakes actions; avoid for payments or destructive operations.
+
+**Easing affects perceived duration**: Ease-in (accelerating toward completion) makes tasks feel shorter because the peak-end effect weights final moments heavily. Ease-out feels satisfying for entrances, but ease-in toward a task's end compresses perceived time.
+
+**Caution**: Too-fast responses can decrease perceived value. Users may distrust instant results for complex operations (search, analysis). Sometimes a brief delay signals "real work" is happening.
+
 ## Performance
 
 Don't use `will-change` preemptively—only when animation is imminent (`:hover`, `.animating`). For scroll-triggered animations, use Intersection Observer instead of scroll events; unobserve after animating once. Create motion tokens for consistency (durations, easings, common transitions).

dist/codex/AGENTS.frontend-design.md

@@ -340,6 +340,22 @@ This is not optional. Vestibular disorders affect ~35% of adults over 40.
 
 **What to preserve**: Functional animations like progress bars, loading spinners (slowed down), and focus indicators should still work—just without spatial movement.
 
+## Perceived Performance
+
+**Nobody cares how fast your site is—just how fast it feels.** Perception can be as effective as actual performance.
+
+**The 80ms threshold**: Our brains buffer sensory input for ~80ms to synchronize perception. Anything under 80ms feels instant and simultaneous. This is your target for micro-interactions.
+
+**Active vs passive time**: Passive waiting (staring at a spinner) feels longer than active engagement. Strategies to shift the balance:
+
+- **Preemptive start**: Begin transitions immediately while loading (iOS app zoom, skeleton UI). Users perceive work happening.
+- **Early completion**: Show content progressively—don't wait for everything. Video buffering, progressive images, streaming HTML.
+- **Optimistic UI**: Update the interface immediately, handle failures gracefully. Instagram likes work offline—the UI updates instantly, syncs later. Use for low-stakes actions; avoid for payments or destructive operations.
+
+**Easing affects perceived duration**: Ease-in (accelerating toward completion) makes tasks feel shorter because the peak-end effect weights final moments heavily. Ease-out feels satisfying for entrances, but ease-in toward a task's end compresses perceived time.
+
+**Caution**: Too-fast responses can decrease perceived value. Users may distrust instant results for complex operations (search, analysis). Sometimes a brief delay signals "real work" is happening.
+
 ## Performance
 
 Don't use `will-change` preemptively—only when animation is imminent (`:hover`, `.animating`). For scroll-triggered animations, use Intersection Observer instead of scroll events; unobserve after animating once. Create motion tokens for consistency (durations, easings, common transitions).

dist/cursor/.cursor/rules/frontend-design.md

@@ -340,6 +340,22 @@ This is not optional. Vestibular disorders affect ~35% of adults over 40.
 
 **What to preserve**: Functional animations like progress bars, loading spinners (slowed down), and focus indicators should still work—just without spatial movement.
 
+## Perceived Performance
+
+**Nobody cares how fast your site is—just how fast it feels.** Perception can be as effective as actual performance.
+
+**The 80ms threshold**: Our brains buffer sensory input for ~80ms to synchronize perception. Anything under 80ms feels instant and simultaneous. This is your target for micro-interactions.
+
+**Active vs passive time**: Passive waiting (staring at a spinner) feels longer than active engagement. Strategies to shift the balance:
+
+- **Preemptive start**: Begin transitions immediately while loading (iOS app zoom, skeleton UI). Users perceive work happening.
+- **Early completion**: Show content progressively—don't wait for everything. Video buffering, progressive images, streaming HTML.
+- **Optimistic UI**: Update the interface immediately, handle failures gracefully. Instagram likes work offline—the UI updates instantly, syncs later. Use for low-stakes actions; avoid for payments or destructive operations.
+
+**Easing affects perceived duration**: Ease-in (accelerating toward completion) makes tasks feel shorter because the peak-end effect weights final moments heavily. Ease-out feels satisfying for entrances, but ease-in toward a task's end compresses perceived time.
+
+**Caution**: Too-fast responses can decrease perceived value. Users may distrust instant results for complex operations (search, analysis). Sometimes a brief delay signals "real work" is happening.
+
 ## Performance
 
 Don't use `will-change` preemptively—only when animation is imminent (`:hover`, `.animating`). For scroll-triggered animations, use Intersection Observer instead of scroll events; unobserve after animating once. Create motion tokens for consistency (durations, easings, common transitions).

dist/gemini/GEMINI.frontend-design.md

@@ -340,6 +340,22 @@ This is not optional. Vestibular disorders affect ~35% of adults over 40.
 
 **What to preserve**: Functional animations like progress bars, loading spinners (slowed down), and focus indicators should still work—just without spatial movement.
 
+## Perceived Performance
+
+**Nobody cares how fast your site is—just how fast it feels.** Perception can be as effective as actual performance.
+
+**The 80ms threshold**: Our brains buffer sensory input for ~80ms to synchronize perception. Anything under 80ms feels instant and simultaneous. This is your target for micro-interactions.
+
+**Active vs passive time**: Passive waiting (staring at a spinner) feels longer than active engagement. Strategies to shift the balance:
+
+- **Preemptive start**: Begin transitions immediately while loading (iOS app zoom, skeleton UI). Users perceive work happening.
+- **Early completion**: Show content progressively—don't wait for everything. Video buffering, progressive images, streaming HTML.
+- **Optimistic UI**: Update the interface immediately, handle failures gracefully. Instagram likes work offline—the UI updates instantly, syncs later. Use for low-stakes actions; avoid for payments or destructive operations.
+
+**Easing affects perceived duration**: Ease-in (accelerating toward completion) makes tasks feel shorter because the peak-end effect weights final moments heavily. Ease-out feels satisfying for entrances, but ease-in toward a task's end compresses perceived time.
+
+**Caution**: Too-fast responses can decrease perceived value. Users may distrust instant results for complex operations (search, analysis). Sometimes a brief delay signals "real work" is happening.
+
 ## Performance
 
 Don't use `will-change` preemptively—only when animation is imminent (`:hover`, `.animating`). For scroll-triggered animations, use Intersection Observer instead of scroll events; unobserve after animating once. Create motion tokens for consistency (durations, easings, common transitions).

source/skills/frontend-design/reference/motion-design.md

@@ -74,6 +74,22 @@ This is not optional. Vestibular disorders affect ~35% of adults over 40.
 
 **What to preserve**: Functional animations like progress bars, loading spinners (slowed down), and focus indicators should still work—just without spatial movement.
 
+## Perceived Performance
+
+**Nobody cares how fast your site is—just how fast it feels.** Perception can be as effective as actual performance.
+
+**The 80ms threshold**: Our brains buffer sensory input for ~80ms to synchronize perception. Anything under 80ms feels instant and simultaneous. This is your target for micro-interactions.
+
+**Active vs passive time**: Passive waiting (staring at a spinner) feels longer than active engagement. Strategies to shift the balance:
+
+- **Preemptive start**: Begin transitions immediately while loading (iOS app zoom, skeleton UI). Users perceive work happening.
+- **Early completion**: Show content progressively—don't wait for everything. Video buffering, progressive images, streaming HTML.
+- **Optimistic UI**: Update the interface immediately, handle failures gracefully. Instagram likes work offline—the UI updates instantly, syncs later. Use for low-stakes actions; avoid for payments or destructive operations.
+
+**Easing affects perceived duration**: Ease-in (accelerating toward completion) makes tasks feel shorter because the peak-end effect weights final moments heavily. Ease-out feels satisfying for entrances, but ease-in toward a task's end compresses perceived time.
+
+**Caution**: Too-fast responses can decrease perceived value. Users may distrust instant results for complex operations (search, analysis). Sometimes a brief delay signals "real work" is happening.
+
 ## Performance
 
 Don't use `will-change` preemptively—only when animation is imminent (`:hover`, `.animating`). For scroll-triggered animations, use Intersection Observer instead of scroll events; unobserve after animating once. Create motion tokens for consistency (durations, easings, common transitions).