Observed infant behaviour in response to four stimuli.
Recorded infant behaviour through real-time videotapes.
Independent observers judged the videos, not knowing the infant's response.
Noted instances of infant tongue protrusions and head movements.
Behavioural categories included mouth opening, termination of mouth opening, tongue protrusion, and termination of tongue protrusion.
Each observer scored the tapes twice for intra-observer and inter-observer reliability.
All scores were greater than .92.