Domain: Healthcare — Human Physiology
Target concept: Grasp Reflex (Human Infant)

Video generation prompt: An adult gently inserts their index finger horizontally into an infant's open palm, touching the center of the palm, and observes the infant's hand movements.

Evaluation guide:
(i) Target concept: Palmar grasp reflex as an innate, subcortical motor response in neonates and young infants.
Minimum mechanism: Tactile stimulation of mechanoreceptors in the central palm must directly trigger spinal/brainstem-mediated flexor motor neuron activation, requiring intact peripheral nerves, dorsal root ganglia, spinal cord segments C6–T1, and corticospinal tract independence.
(ii)Storyline: [Phase 1: Baseline] Infant hand fully open, relaxed, stationary, no active movement. [Phase 2: Stimulus Delivery] Adult index finger enters frame horizontally, moves continuously toward palm center without deviation, and makes unambiguous contact. [Phase 3: Response Onset] Within same motion continuity, digits begin symmetric flexion; thumb initiates adduction across palm, fingers curl inward, grip tightens. [Phase 4: Sustained Response] Grasp remains firm and closed for duration; no voluntary correction, release, or co-contraction. [Perspective constraint: Fixed frontal view showing full palm surface, finger alignment, and thumb-palm opposition; no occlusion of critical contact zone.]

Manual:
Experimental Procedure
1. Position infant supine or seated with arm relaxed and unsupported, hand fully open.
2. Adult extends index finger horizontally and gently inserts it into the center of the infant's palm.
3. Maintain stillness for the observation period (≤10 s).
Observation of Experimental Phenomena
Infant's fingers curl inward symmetrically and thumb adducts across the palm surface, forming a firm grip around the inserted finger — occurring only after contact and persisting without voluntary release.
Summary of Experimental Principles
Grasp Reflex is an involuntary palmar response mediated by spinal and brainstem circuits; triggered by tactile stimulation of the palm, resulting in flexion of all digits and opposition of the thumb.

Prompt Grounding rubric:
level_1: No adult hand or finger appears in frame; no infant is visible; the index finger is never inserted into an open palm; none of the posted_prompt's core elements (adult finger, infant hand, insertion action) show up at any point in the clip.
level_2: Only fragments of the setup appear (for instance an adult hand is visible, or an infant is visible, or an open palm is shown), but the finger is never actually inserted horizontally into the center of the palm, or the sequence of events is too unclear to tell an insertion happened.
level_3: The adult's index finger is oriented horizontally and makes contact with the infant's open palm; the infant's hand is visibly open and at rest just before contact; the adult's finger, the infant's palm, and the infant's body all appear together in the same shot; the events proceed in the order approach-then-contact, with no reversal (e.g., finger pulling back before touching) and no skipped step.
level_4: Everything described at the 3-point level holds, and in addition: the finger enters specifically the center of the palm rather than the fingers, wrist, or the outer edge of the hand; the palm is still fully open immediately before contact, with no partial pre-closure; the infant's arm is visibly relaxed and unsupported by any hand, strap, or prop; and the camera holds one fixed framing that keeps the approaching finger and the whole palm surface in view at the same time.
level_5: Everything described at the 4-point level holds, and in addition: the finger's path into the palm is a single continuous motion with no jump cuts or freeze-frames; the finger stays fully extended and horizontal from entry through contact; the palm and forearm are never blocked from view by the adult's other hand, clothing, or any object before, during, or after contact; and in the baseline moments before contact, the infant's hand shows no voluntary movement of its own (no pre-emptive clenching, waving, or pulling away); it simply stays open and still until touched.

Scientific and Causal Correctness rubric:
level_1: No palmar grasp response occurs: the infant's fingers stay open the whole time, or they close at a moment that has no clear relationship to the finger touching the palm, for example closing before contact happens, or while the adult's finger is nowhere near the palm.
level_2: The hand does eventually close, but the timing doesn't fit a reflex: closure clearly starts before contact, or begins so long after contact (well over a second) that it reads as a voluntary movement rather than the fast palmar grasp reflex; or the closure is incomplete or lopsided, such as only two or three fingers curling while the rest stay open.
level_3: After the finger touches the palm, the infant's fingers curl inward and the thumb adducts across the palm; all five digits take part; the curling starts within roughly the same continuous motion as the contact itself, without an obvious pause between the touch and the first sign of finger flexion.
level_4: Everything described at the 3-point level holds, and in addition: the grasp holds rather than springing back open right after closing; the thumb presses against the palm instead of hovering above it or sliding off to the side; all the fingers close together at roughly the same time, with no single digit lagging noticeably behind the others; and the infant does not simultaneously yank the arm away or startle in response to the touch.
level_5: Everything described at the 4-point level holds, and in addition: the grasp looks complete and firm; the fingertips visibly press into the palm with no visible gaps between the curled fingers and the skin; the thumb overlaps the palm beneath the inserted finger; there is no visible tremor, hesitation, or partial loosening while the grip is held; and the closing motion reads as one smooth continuous sweep from fully open to fully closed rather than a series of jerky, stepped closures.

Spatiotemporal Consistency rubric:
level_1: Severe continuity breaks: the infant's body or the adult's hand instantly appears in a different position or pose between consecutive frames; the room's overall brightness switches abruptly (for instance bright daylight cutting straight to near-darkness) with no fade between them; the palm's shape warps impossibly, such as fingers bending backward or the palm stretching like rubber; or the adult's finger disappears partway through its approach and reappears somewhere else.
level_2: Noticeable but less extreme problems: the finger's approach freezes in place or skips forward for a stretch of the clip instead of moving smoothly; the palm appears to twist to a different angle with no visible in-between motion; the shadow cast on the palm suddenly switches direction or vanishes outright; or the infant's arm resets to an earlier position partway through the clip with no visible transition to explain it.
level_3: The finger travels toward the palm along one consistent path and angle from start to contact; the palm stays in the same orientation and location in frame throughout the approach and the contact itself; any movement of the infant's arm beyond the reflex response itself looks like small natural settling rather than a sudden correction; the direction and softness of the shadows on the hand and finger look the same at the end of the clip as they did at the start.
level_4: Everything described at the 3-point level holds, and in addition: the finger's motion toward and into the palm is unbroken from start to finish, with no visible stutter or skip; the skin and palm surface keep a consistent texture and shading as the hand moves, without flickering or warping; and the infant's body, the surface beneath the arm, and the adult's arm keep the same relative arrangement to one another throughout, with nothing sliding into or out of place unexpectedly.
level_5: Everything described at the 4-point level holds, and in addition: the finger and the background share the same level of sharpness and motion blur, so the finger is never crisp while the background looks like it's moving at a different speed (or vice versa); the finger and palm never abruptly swap which one appears in front of the other without a matching change in hand angle; and the palm's proportions (its width relative to its length) stay the same from the first frame to the last, with no stretching or squashing as the fingers curl.