Abstract

The importance of the haptic system (cutaneous and kinaesthetic processes) in development is widely acknowledged. Yet little is known about infants' haptic perceptual abilities during the first half-year of life. This is due, in part, to the view that haptic perceptual abilities are limited prior to the development of fine-motor exploratory skills and visual prehension. The methodology of existing studies (e.g., the visibility of stimuli and confounding properties, selection of stimuli, and fixed-trials habituation procedures) has also limited clear interpretations with respect to infants' haptic perception. The present research consisted of two studies designed to assess early haptic perceptual abilities by employing a stimulus property salient to this system, texture. Study 1 examined unimodal haptic perception at 3 and 6 months of age, just before and after gains in fine-motor and visual prehension are made. Vision was occluded by an opaque plastic cover and the textures were presented underneath the cover to infants' hands. An infant-controlled Habituation (HAB)-Novelty (NOV)-Return-to-Familiar (RFAM) procedure was employed. Following habituation, experimental group infants received a novel texture for 3 NOV test trials and the original texture for 3 RFAM test trials. Control group infants received the same HAB texture during all test trials. Study 2 was designed to assess the influence of vision on haptic perception of texture. Using the same textures as in Study 1 and presenting them under a transparent cover, infants were permitted both haptic and visual exploration during the HAB phase. However, the test phases were unimodal haptic. Results of infants' haptic manipulations indicated that both 3- and 6-month-olds habituated following similar amounts of haptic manipulation, and that levels of haptic manipulation to habituation did not differ across Studies 1 and 2. In addition, infants discriminated novel textures during NOV, and recognized the original texture during RFAM in both studies. These results suggest that haptic perception and discrimination of texture may not be dependent on visual guidance. However, infants in Study 2 haptically manipulated for shorter amounts of time during NOV and RFAM, relative to Study l, suggesting that the visual input during HAB may have facilitated discrimination and recognition of textures. Facilitation effects may reflect the integration of visual and haptic input during HAB and the detection of amodal relations across haptics and vision. Vision also suppressed the novelty responses observed in Study 1 on the measure of exploratory procedures (EPs). The EPs may have been suppressed by the lack of salient visual features, again suggesting that visual and haptic input was integrated. Suppression of EPs was less pronounced for the 6-, relative to 3-month-olds, who engaged in more EPs in response to the rough texture in both studies, suggesting that among infants with more developed fine-motor skills, the haptic features of stimuli may alone elicit exploration in this modality. Overall, the findings: (1) support haptic perception of texture during the first half-year of life; (2) suggest an important and unique role for haptics in early perceptual learning; and (3) contribute to the understanding of infants' haptic perception during bimodal exploration. The methodological contributions of the present studies in accessing infants' haptic abilities are discussed and future research directions are proposed.