At which age does an infant hold its head steady when pulled to sit, without bobbing motion, and laugh and loud?

At 3 months, head lag is paially compensated but still present; the infant attains early head control with bobbing motion and sits with back rounded. At 4 months, there is no head lag when pulled to sit and the infant sits with full truncal suppo. Ref: Nelson textbook of pediatrics 21st edition Pgno: 132