Piaget argued that movement from one stage to the next occurs when an individual reaches an appropriate level of physical maturation and is exposed to relevant experiences

When a psychologist asked groups of participants to listen to three different speakers presenting different lists of letters, he came across evidence for the existence of echoic memory. What was the evidence that supported the existence of echoic memory?

a) The participants had difficulty repeating the letters from all three participants, but if asked immediately for one of the lists, they could repeat it. b) After listening to the lists for a while, the letters became mixed into a single list as they seemed to bounce around the participants' minds like ping pong balls. c) The participants were able to repeat letters from all three speakers, although they could not do the same when presented with the letters in visual format. d) The lists were recalled quite efficiently because our memory for auditory memory goes directly to storage rather than for further detailed processing.

By about ________ months of age, a child can typically solve invisible displacement problems

A) 3 B) 6 C) 24 D) 18