Watson + Rayner (1920)

to demonstrate that simple emotional responses such a fear can be acquired through a process of classical conditioning

Little Albert
9 months old at the start of the study, 11 months when conditioning began
mother was a nurse - grew up in a hospital environment

tested alberts baseline emotional responses to a arange of objects, one at a time (white rat, rabbit, dog, monkey, various masks, cotton wool + wooden blocks)
session 1 - white rat presented, when little albert reached for the rat, the bar was struck loudly behind his head
session 2 - a week later, albert was exposed 5 times to the rat paired with the loud noise + tested with wooden blocks (showing he wasn't just more scared generally)
session 3 - 5 days later, assessed alberts responses to the 7 stimuli
session 4 - 5 days later, new environment - lecture room with 4 ppl present . placed on table and assessed for responses
session 5 - tested again one month later (when he was 12 months)

basline testing: no fear displayed, did respond to loud noise (startled + lip trembled)
session 1: cried after noise
session 2: more cautious towards rat, not reaching out + pulling away when rat nuzzled him, after further conditioning he began to cry and tried to rapidly crawl away
session 3: reacted to the white furry objects (rat + rabbit) with fear (crying)
session 4+5: fear reactions remained but became less extreme when he was in a different environment and after time

it is relatively easy to condition an emotional response to a neutral stimulus
just 2 sessions pairing a US and NS was enough to produce a fear response towards rats and other objects - stimulus generalisation

weakness
only one participant- the inidividual studied may not be representative of the population
Little Albert was only 11 months old at the start of conditioning - this is not reflective of how adults would respond as children are not fully developed and lack the complex cognitive functioning adults have
therefore, the results may be ungeneralisable to adults