The answer is: Fergus Craik and Robert Lockhart
Both of them realized that some people often experienced a delayed response after receiving some information that is hart to deal with. This led to the conclusion that to levels of processing exist when we try to encode a certain information. (this can explain why the delay happened)
For example, When a mother heard that her son has died in an accident, that woman would not directly cried the second she heard the news.
She would most likely stunned for a while and unable to make proper response for other people. This because she experienced a difficult process to pass all the levels of processing needed to receive the information.
