Sequential Learning by Touch, Vision, and Audition

Sequential Learning by Touch, Vision, and Audition Christopher M. Conway (cmc82@cornell.edu) Morten H. Christiansen (mhc27@cornell.edu) Department of Psychology Cornell University Ithaca, NY 14853, USA Abstract We investigated the extent to which touch, vision, and audition are similar in the ways they mediate the processing of statistical regularities within sequential input. While previous research has examined statistical/sequential learning in the visual and auditory domains, few researchers have conducted rigorous comparisons across sensory modalities; in particular, the sense of touch has been virtually ignored in such research. Our data reveal commonalities between the ways in which these three modalities afford the learning of sequential information. However, the data also suggest that in terms of sequential learning, audition is superior to the other two senses. We discuss these findings in terms of whether statistical/sequential learning is likely to consist of a single, unitary mechanism or multiple, modality-constrained ones. Introduction The acquisition of statistical/sequential information from the environment appears to be involved in many learning situations, ranging from speech segmentation (Saffran, Newport, & Aslin, 1996), to learning orthographic regularities of written words (Pacton, Perruchet, Fayol, & Cleeremans, 2001) to processing visual scenes (Fiser & Aslin, 2002). However, previous research, focusing exclusively on visual and auditory domains, has failed to investigate whether such learning can occur via touch. Perhaps more importantly, few studies have attempted directly to compare sequential learning as it occurs across the various sensory modalities. There are important reasons to pursue such avenues of study. First, a common assumption is that statistical/sequential learning is a broad, domain- general ability (e.g., Kirkham, Slemmer, & Johnson, 2002). But in order to adequately assess this hypothesis, systematic experimentation across the modalities is necessary. If differences exist between sequential learning in the various senses, it may reflect the operation of multiple mechanisms, rather than a single process. Second, in regards to the touch modality in particular, prior research has generally focused on low- level perception; discovering that the sense of touch can accommodate complex sequential learning may have important implications for tactile communication systems. This paper describes three experiments conducted with the aim to assess sequential learning in three sensory modalities: touch, vision, and audition. Experiment 1 provides the first direct evidence for a fairly complex tactile sequential learning capability. Experiment 2 provides a visual analogue of Experiment 1 and suggests commonalities between visual and tactile sequential learning. Finally, Experiment 3 assesses the auditory domain, revealing an auditory advantage for sequential processing. We conclude by discussing these results in relation to basic issues of cognitive and neural organization—namely, to what extent sequential learning consists of a single or multiple mechanisms. Sequential Learning We define sequential learning as an ability to encode and represent the order of discrete elements occurring in a sequence (Conway & Christiansen, 2001). Importantly, we consider a crucial aspect of sequential learning to be the acquisition of statistical regularities occurring among sequence elements. Artificial grammar learning (AGL; Reber, 1967) is a widely used paradigm for studying such sequential learning 1 . AGL experiments typically use finite-state grammars to generate the stimuli; in such grammars, a transition from one state to the next produces an element of the sequence. For example, in the grammar of Figure 1, the path begins at the left-most node, labeled S1. The next transition can lead to either S 2 or S3. Every time a number is encountered in the transition between states, it is added as the next element of the sequence, producing a sequence corresponding to the rules of the grammar. For example, by passing through the nodes S1, S2, S2, S4, S3, S5, the “legal” sequence 4-1-3-5-2 is generated. During a training phase, participants typically are exposed to a subset of legal sequences—often under the guise of a “memory experiment” or some other such task—with the intent that they will incidentally encode structural aspects of the stimuli. Next, they are tested on whether they can classify novel sequences as In the typical AGL task, the stimulus elements are presented simultaneously (e.g., letter strings)—rather than sequentially (i.e., one element at a time). We consider even the former case to be a sequential learning task because scanning strings of letters generally occurs in a left-to-right, sequential manner. However, our aim here is to create a truly sequential learning environment using temporally-distributed input.