Posture support improves object individuation in infants.

One of the primary tasks of visual cognition is to track the identity of objects through discontinuities in space and time, allowing us to determine whether an object currently in view is the same object or a different object than one seen before. Given the importance of object individuation to human cognition, developmental scientists have invested a great deal of effort to identify the ontogeny of this capacity (Leslie & Kaldy, 2001; Tremoulet et al., 2001; Van de Walle, Carey, & Prevor, 2000; Wilcox, 1999; Wilcox & Baillargeon, 1998a,b; Woods & Wilcox, 2006, 2010; Xu, 1999; Xu & Carey, 1996). A number of studies have uncovered a hierarchical progression in infants’ sensitivity to featural information, with infants first demonstrating sensitivity to form features, such as shape or size, and then to surface features, such as pattern, color, or luminance, as the basis for individuating objects (Needham, 1999; Tremoulet et al., 2001; Wilcox, 1999; Woods & Wilcox, 2006, 2010). More recent research has focused on identifying the mechanisms that underlie infants’ later emerging ability to recognize surface features as relevant to object individuation. This research has revealed select experiences that can lead infants to attend to surface features at an age younger than they do so spontaneously (Wilcox & Chapa, 2004; Wilcox, Smith, & Woods, 2010; Wilcox, Woods, & Chapa, 2008; Wilcox, et al., 2007). One type of experience that is known to prime infants to use surface features to individuate objects is multisensory exploration. There is evidence that 11.5-month-olds, but not infants 10.5 months or younger, use color differences as the basis for individuating objects (Wilcox 1999; Wilcox et al., 2007; Woods & Wilcox, 2010). In one set of studies, Wilcox and her colleagues (Wilcox et al., 2007) presented 10.5-month-olds with a green ball and a red ball, successively, for 60 seconds each prior to an individuation task involving those same objects. The infants who engaged in multimodal exploration of the objects, examining each ball visually and tactilely during the pre-exposure trials, subsequently used the color information to individuate the objects a month earlier, at 10.5 months, than infants who did not. On the other hand, another group of infants who received visual-only experience with the objects prior to test failed to attend to color information to individuate the objects. These results suggest that infants needed multisensory experience, and not simply extra visual experience, with the objects for color priming to occur. Why does visual and tactile exploration, and not visual exploration alone, lead to greater sensitivity to color information? Visual and tactile exploration provides infants with the opportunity to experience the same information in more than one modality (e.g., shape encoded tactilely and visually) and to link information across modalities (e.g., link color encoded visually to shape encoded visually and tactilely). Some researchers have proposed that information available concurrently to two or more senses, because it is invariant and redundant, captures and focuses infants’ attention (Bahrick & Lickliter, 2002; Slater, Quinn, Brown, & Hayes, 1999; see Bahrick, 2004, for a review). Bahrick and her colleagues (Bahrick & Lickliter, 2000, 2002; Bahrick, Lickliter, & Flom, 2004; Bahrick & Pickens, 1994) have proposed a conceptual model of intermodal processing, the Intersensory Redundancy Hypothesis, that focuses on the importance of detecting amodal relations within the context of physical events. Two components of this model are most relevant here. First, amodal relations are detected prior to modality-specific relations. That is, when exploring and interacting with objects, infants attend first to information that is presented redundantly and in temporal synchrony across the senses and then to unimodal information. Second, the detection of amodal relations guides and constrains learning about modality-specific information. That is, the extent to which infants attend to modality-specific information depends on whether they have identified amodal object properties. When infants are provided object information via a single modality (i.e., vision), they have difficulty identifying amodal relations which, in turn, prevents integration of modality-specific information into their object representation. There are a number of studies that support this proposal and demonstrate that multisensory presentation of amodal information, such as shape, facilitates processing of modality-specific object information, such as color and pattern (Bahrick, 1992, 1994; Hernandez-Reif & Bahrick, 2001). What remain unspecified are details about the nature and development of multisensory priming in infants. For example, once young infants begin to engage in simultaneous visual and tactile exploration of objects do they demonstrate multisensory priming? What role do attentional and motor factors play in the priming process? Under what conditions is multisensory priming most effective? Can infants be primed to attend to other surface features, such as pattern, or is multisensory priming limited to color information? The purpose of the current research was to enhance our understanding of multisensory priming by addressing these questions. First, we investigated whether multisensory priming is specific to color or if infants can be primed to attend to another object surface feature, pattern. Second, we investigated the extent to which multisensory priming is observed in younger infants, who may be less skilled at multisensory exploration. Finally, we investigated the direct effect of motor development (i.e., postural control and object manipulation behaviors) on infants’ ability to benefit from multisensory priming. There is evidence that postural strength and sitting ability can influence both object exploration and object processing (Bertenthal & Von Hofsten, 1998; Fallang, Saugstad, & Hadders-Algra, 2000; Gabbard, Santos, & Goncalves, 2007; Out, van Soest, Savelsbergh, & Hopkins, 1998; Rochat, 1992; Rochat & Senders, 1991; Soska, Adolf, & Johnson, 2010; Thelen & Spencer, 1998). Given that infants begin the transition to self-supported sitting between 4 and 7 months of age, leaving the hands free for two-handed exploration of objects (Piper & Darrah, 1994), we might expect to see a relation between sitting ability, multisensory exploration, and object individuation during this time. In summary, the current research investigated the extent to which multisensory experiences could prime infants 4.5 to 6.5 months of age to attend to pattern differences in an object individuation task and the role that postural support plays in this process.