Bimodal Stimuli Do Not Always Facilitate Infants' Rule Learning

Seven-month-old infants possess the ability to extract and generalize abstract rules from unimodal sequences of auditory syllables such as ABA and ABB whereas five-month-old infants are facilitated in their learning of these rules by bimodal sequences. In the current study, we investigated whether bimodal stimuli could also help infants acquire what we consider a more difficult abstract rule: AAB. Nineteen 8- to 9-month-old infants were habituated to the AAB rule with simultaneous visual shapes and speech sounds. They were later tested on their ability to discriminate this sequence from ABA and ABB with their looking times measured after each stimulus presentation at test periods. There was no significant difference in looking times amongst the different sequences, suggesting infants were not able to formulate an AAB rule different from those for ABA and ABB. Older infants' inability to utilize extra sensory information to acquire an abstract rule in which younger ones were ready to learn from unimodal stimulus (speech) was unexpected. It is unclear what leads to the failure of rule learning from bimodal stimuli, but possible explanations including perceptual narrowing in the inter-sensory integration and the difference in sensory representation of abstract rules with different difficulties are discussed.