An "Oblique Effect" in infants' haptic perception of spatial orientations.

The present research addresses the question of the "oblique effect" (better discrimination of the vertical orientation than of an oblique orientation) in manual haptic perception of orientations (without visual control) by 5-month-old infants. A familiarization/reaction to novelty procedure was used. The results revealed the occurrence of a haptic oblique effect. These findings are similar to those obtained in infant visual perception. We suggest that 5-month-old infants predominately use vertical orientation as a reference norm to perceive haptically spatial orientations. We discuss the implications of these results for both orientation processing and anatomofunctional level contributing specifically to the haptic oblique effect.