Domain: Healthcare — Human Physiology
Target concept: Babinski reflex (infant)

Video generation prompt: Place the infant in a supine position and ensure relaxation. Using a blunt reflex hammer or stick, slowly and firmly stroke from the heel along the lateral side of the foot toward the toes, then horizontally across the anterior part of the foot. Observe the response of the foot.

Evaluation guide:
(i) Target concept: Cortically mediated inhibition of spinal reflex arcs is absent in infants, resulting in dorsiflexion and fanning upon lateral plantar stimulation.
Minimum mechanism: Intact peripheral sensation (tactile input), functional L4–S2 spinal cord segments, and uninhibited corticospinal tract development.
(ii)Storyline: 1. Infant placed supine → full lateral foot exposure → tool contacts heel (static start state); 2. Stroke initiates at heel and progresses uninterrupted up lateral side → visible tension-free skin glide; 3. At toe base, motion redirects smoothly into horizontal sweep across forefoot → simultaneous onset of big toe dorsiflexion + toe abduction + ankle dorsiflexion + foot eversion; 4. All responses cease immediately when stroke ends → no after-movement; 5. Camera maintains fixed frontal-lateral viewpoint capturing full foot, tool path, and toe kinematics without occlusion or angle shift.

Manual:
Experimental Procedure
1. Place infant supine on flat surface, limbs relaxed.
2. Expose lateral side of one foot.
3. Using blunt reflex hammer or stick, stroke firmly from heel → along lateral side → to base of toes → then horizontally across anterior foot.
Observation of Experimental Phenomena
Big toe extends upward (dorsiflexion), other toes fan outward (abduction), ankle dorsiflexes, foot everts — all occurring synchronously during horizontal stroke.
Summary of Experimental Principles
Babinski reflex is a primitive reflex in infants <2 years; stroking lateral foot triggers extensor response due to immature corticospinal inhibition.

Prompt Grounding rubric:
level_1: No infant is shown; the infant is not lying on its back; no foot is visible; no stroking action takes place; no reflex hammer, blunt stick, or similar tool ever appears.
level_2: An infant is present but not lying supine; or a foot is visible but its lateral edge is never shown to the camera; or a stroking tool appears but never actually touches the foot; or the stroke runs vertically/upward instead of heel-to-toe along the lateral edge; several of these core elements are missing at once.
level_3: The infant lies supine; the foot is fully visible with its lateral edge facing the camera; a blunt tool is present and touches the heel; the stroke moves from the heel along the lateral edge toward the toes, but the sequence ends there without ever sweeping horizontally across the ball of the foot; the procedure is only partly completed.
level_4: The infant lies supine; the whole foot is visible in the correct lateral orientation; the blunt tool touches the heel and moves continuously (heel, up the lateral edge, to the base of the toes, then across the ball of the foot), with every required element present and in the right order; only minor blemishes appear (e.g., the hand briefly covers the tool's tip, or the foot's edge briefly leaves frame).
level_5: The infant lies supine with visibly relaxed limbs; the entire lateral foot surface stays visible throughout; the blunt tool stays clearly visible and unobstructed, keeping continuous, unbroken contact from heel, up the lateral edge, to the base of the toes, then sweeping across the ball of the foot with no lifting or pausing; nothing is misidentified, no step of the stroke is skipped, and the tool's path is never ambiguous.

Scientific and Causal Correctness rubric:
level_1: No toe or foot movement follows the stroke at all; or the movement goes the wrong way entirely (the foot curls or plantar-flexes instead of extending); or any toe/foot movement happens before the stroke ever reaches the foot, unrelated to the stimulus.
level_2: The foot moves, but not consistent with a Babinski response, e.g., only the ankle rotates with no toe movement at all; the big toe flexes downward instead of extending upward; the other toes fan out without the big toe ever extending; or an otherwise correct-looking movement only appears well after the stroke has ended, with a delay too long to plausibly be a reflex to that stroke.
level_3: The big toe extends upward (dorsiflexion) clearly in response to the stroke, while the other toes stay neutral or barely move and the ankle/foot show no notable dorsiflexion or eversion; the toe's extension is clearly timed to the stroke, not to something else.
level_4: The big toe extends upward AND the other toes fan outward (abduction) together in response to the stroke, but ankle dorsiflexion and foot eversion are absent or only minimal; both toe movements are clearly timed to the stroke, with no contradictory movement such as curling or withdrawal.
level_5: All four classic components appear together and only during the horizontal stroke across the ball of the foot: the big toe extends fully upward, the other toes fan outward, the ankle dorsiflexes, and the foot everts slightly, with no movement lingering after the stroke ends and no unrelated leg movement (e.g., hip or knee flexion) accompanying it.

Spatiotemporal Consistency rubric:
level_1: The infant's position jumps between shots with no transition; the foot vanishes and reappears; the tool's position jumps discontinuously along what should be one continuous stroke; the lighting on the scene changes abruptly partway through the stroke; the foot appears rotated by more than a quarter turn with no visible motion causing it; the foot's shadow becomes detached from the foot or the tool.
level_2: The infant's posture shifts partway through (e.g., appears to roll off its back); the foot rotates by more than roughly 45 degrees without a smooth transition; the tool lifts off the foot and touches down again somewhere unexpected; the stroke path shows visible gaps or jump cuts; the lighting flickers or the shadow on the foot changes erratically.
level_3: The infant stays on its back with a stable head and limb position; the foot stays fixed in its lateral orientation; the tool keeps contact with the foot as it moves from the lateral stroke into the horizontal stroke, redirecting smoothly rather than lifting away and repositioning; the stroke path looks continuous along the lateral edge and then cleanly redirects into the horizontal sweep; the foot's shadow keeps a steady direction and softness through the sequence.
level_4: The infant's posture and foot orientation stay completely stable; the tool keeps continuous, unbroken contact from heel to toes and redirects smoothly into the horizontal stroke without lifting or pausing, tracing a smooth arc with no jitter; the horizontal stroke picks up right where the lateral stroke ended; shadows and highlights on the foot and tool stay spatially matched and don't flicker between frames.
level_5: There is no spatial discontinuity anywhere: the infant's body, the foot, and the tool keep a coherent, physically consistent arrangement relative to one another throughout the stroke; contact runs unbroken from heel to lateral edge to toes to horizontal sweep, with no unexplained lifts, pauses, or repositioning; the motion looks fluid and anatomically plausible; the lighting, shadow, and camera perspective all stay steady across the whole clip, with no warping, stretching, or morphing of the foot, leg, or tool.