Influence of visual contextual cues on haptic discrimination of orientations in 5-month-old infants

The influence of intersensory discrepancy on visuo-haptic integration is similar in 6-year-old children and adults

When participants are given the opportunity to simultaneously feel an object and see it through a magnifying or reducing lens, adults estimate object size to be in-between visual and haptic size. Studies with young children, however, seem to demonstrate that their estimates are dominated by a single sense. In the present study, we examined whether this age difference observed in previous studies, can be accounted for by the large discrepancy between felt and seen size in the stimuli used in those studies. In addition, we studied the processes involved in combining the visual and haptic inputs. Adults and 6-year-old children judged objects that were presented to vision, haptics or simultaneously to both senses. The seen object length was reduced or magnified by different lenses. In the condition inducing large intersensory discrepancies, children's judgments in visuo-haptic conditions were almost dominated by vision, whereas adults weighted vision just by ~40%. Neither the adults' nor the children's discrimination thresholds were predicted by models of visuo-haptic integration. With smaller discrepancies, the children's visual weight approximated that of the adults and both the children's and adults' discrimination thresholds were well predicted by an integration model, which assumes that both visual and haptic inputs contribute to each single judgment. We conclude that children integrate seemingly corresponding multisensory information in similar ways as adults do, but focus on a single sense, when information from different senses is strongly discrepant.

Factors Influencing Manual Discrimination of Orientations in 5-Month-Old Infants

Factors affecting manual discrimination of spatial orientations and orientation preferences in 5-month-old infants have been investigated by using a familiarisation/reaction to novelty procedure. In the first experiment we explored whether the ‘vertical preference’ observed by Gentaz and Streri (2004 Journal of Cognitive Neuroscience16 1–7) and Kerzerho et al (2005 NeuroReport16 1833–1837) is an intrinsic preference or whether it is due to familiarisation. In the second experiment we examined whether the magnitude of angular deviation to the vertical influences the direction of preference. Results showed that when both gravitational vertical and body axes were aligned, the intrinsic ‘vertical preference’ exists when the angular difference between the two orientations was 10°. When the angular deviation from the vertical was greater than 10°, the novel orientation was preferred. This modification of orientation preference in the manual discrimination of orientation by 5-month-old infants is discussed in relation to the magnitude of the angular deviation to the gravitational vertical and the spatial reference cues available in each condition.