The ability to learn abstract regularities from a limited set of particulars is a powerful cognitive tool that comes into play in tasks as disparate as recognizing objects (Ullman, 1996
), reasoning under uncertainty (Tenenbaum & Griffiths, 2001
), and learning the rules of language (Pinker, 1989
). Traditional empiricist views have long associated the time course of development with the stages of induction, assigning the gathering of information to infancy and the creation of more abstract knowledge to later childhood (Locke, 1964/1690
; Piaget, 1952
); however, more recent research has revealed evidence of abstraction away from perceptual particulars even in young infants (Kuhl, Williams, Lacerda, Stevens, & Lindblom, 1992
; Marcus, Vijayan, Bandi Rao, & Vishton, 1999
; Saffran, Pollak, Seibel, & Shkolnik, 2007
). A major goal of recent developmental research has been determining the sources of this abstraction, through investigations of the phylogenetic origins of these abilities (e.g., Ramus, Hauser, Miller, Morris, & Mehler, 2000
) and through research into the learning mechanisms available to young infants (e.g., Saffran, Aslin, & Newport, 1996
An explicit demonstration of infants’ early abstraction abilities was given by Marcus et al. (1999)
. They familiarized 7-month-old infants to two minutes of syllable strings like ga ti ga
or li na li
, where each string was of the form ABA (the first and last syllables were the same). At test, infants listened longer to strings instantiating a novel rule (ABB) than those instantiating the familiar rule, even though all strings were composed of syllables, such as wo fe wo
, that had not been used during the training phase of the experiment. Marcus et al. concluded that the infants had successfully learned an abstract rule that was unbound to the particulars of the training stimuli. As with other artificial language learning paradigms used with both adults and children (Mintz, 2002
; Saffran et al., 1996
; Saffran, Newport, & Aslin, 1996
; Smith, 1966
), the rule learning paradigm serves as an excellent test case for further investigation of the mechanisms underlying infants’ success in this type of task.
More recent research using this paradigm has focused on the perceptual and cognitive domains in which this type of mechanism can operate. Interest in the question of domain-specificity has largely been driven by the possibility of rule learning as a possible mechanism for language learning (Peña, Bonatti, Nespor, & Mehler, 2002
). However, even if the learning mechanisms responsible for successes in the Marcus et al. (1999)
study are domain general, characterizing how they operate will still be of interest in understanding the inductive tools available to young infants.
In fact, the picture that has emerged from a variety of recent studies is that infants are able to induce abstract rules from a variety of materials across domains and modalities, but that the difficulty of rule extraction varies widely across different stimuli. For example, Saffran et al. (2007)
reported that infants were successful in learning abstract rules in a visual stimulus set consisting of pictures of dogs presented simultaneously. Johnson et al. (2008) reported a more mixed series of results using looming visual shapes presented sequentially, as with the auditory materials in the original Marcus et al. (1999)
studies: 8-month-olds were able to learn and discriminate ABB rules from ABA but not AAB rules, while 11-month-olds were able to discriminate ABB from AAB as well. In contrast to the Marcus et al. studies, neither age group succeeded when they were trained on strings of the form ABA. These results suggest that acquiring rules instantiated in abstract visual shapes is more difficult than acquiring rules instantiated in speech, and that not all three-item identity rules are equally easy to learn. Finally, Marcus, Fernandes, & Johnson (2007)
showed that infants were not able to learn ABA or ABB rules when they were instantiated in (inherently sequential) auditory materials such as tones, timbres, and animal sounds, but succeeded when they were trained using speech rules and tested on materials in each of these domains.
In the context of these studies, we ask a separate but related question: can rule extraction be facilitated by training that uses multimodal stimuli? This issue is of interest for a number of reasons. First, multimodal information has been shown to be useful in a wide variety of perceptual and associative learning tasks (Bahrick, Flom, & Lickliter, 2002
; Bahrick & Lickliter, 2000
; Flom & Bahrick, 2007
; Gogate & Bahrick, 1998
; Kirkham, Slemmer, Richardson, & Johnson, 2007
) but it is not known whether multimodal information supports more complex tasks such as rule learning. Second, the presence of multiple, redundant cues often allows infants to succeed in particular learning tasks earlier than they might in the presence of unimodal information (Flom & Bahrick, 2007
; Gogate & Bahrick, 1998
; Kirkham et al., 2007
). Thus using multimodal stimuli might allow younger infants to succeed in this task, suggesting that the mechanisms responsible for rule learning are present earlier than had previously been documented. Finally, the role of multimodal information in facilitating rule learning may be of interest in determining the nature of the underlying mechanisms.
In the following studies we investigate these questions. We tested whether 5-month-olds are able to learn ABB and ABA rules from input consisting of coordinated strings of colored, looming shapes and speech syllables (Experiment 1). Then, in two control experiments, we tested whether input in either modality is uniquely responsible for infants’ success in learning the rules in Experiment 1. In Experiment 2, we tested visual stimuli separated from speech, and Experiment 3, we examined speech stimuli coordinated with an uninformative shape cue.