The book Babyhood, by Penelope Leach, states: “Many studies have been made of the sights which interest an infant most, the sounds which attract and hold his attention, the sensations he most clearly seeks to repeat.
Psiholoģe Penelope Līča savā grāmatā Babyhood (Mazbērna vecums) raksta: ” Daudz ir pētīts, kuras ainas zīdainim raisa vislielāko interesi, kuras skaņas piesaista un notur viņa uzmanību, kuras sajūtas viņš nepārprotami cenšas izjust vēlreiz.