Each primitive reflex is present at birth and disappears ("integrates") on its own developmental schedule as the maturing cortex increasingly inhibits brainstem-level reflex circuits. The response strength shown here follows a logistic decay in age a (months), the standard curve shape for a threshold that fades gradually rather than switching off instantly:
strength(a) = 1 / (1 + exp((a − a50) / k))
where a50 is the reflex's typical integration age (the age at which strength has fallen to 50%) and k sets how gradual the fade is. The five reflexes here use published typical windows: Moro (~5 mo), rooting (~4 mo), palmar grasp (~5.5 mo), tonic neck (~6 mo) and Babinski (~18 mo, the slowest to fade — it stays physiologically normal well into the second year). Drag the age slider forward and the animated response visibly weakens and eventually flattens out, exactly as it would during a real newborn neuro exam.
- Stimulus intensity — scales how firmly the trigger is applied; it modulates the response amplitude independently of age.
- Status — Present (≥70% strength), Fading (30–70%) or Integrated (<30%), matching how a pediatric exam would characterize the same reading.