BACKGROUND: Studies have identified that object properties lead to adjustments to reaching. However, few have investigated the specific influence of object size and rigidity among young infants. OBJECTIVE: To verify whether four to six-month-old infants make proximal and distal adjustments when reaching for objects of different sizes and rigidity. METHOD: Nine healthy infants were seated on a chair inclined at 50°. Four objects were presented to them: one large rigid (LR), one small rigid (SR), one large malleable (LM) and one small malleable object (SM), each for a one-minute period. A total of 384 reaches were analyzed to verify proximal adjustments (single-hand and two-hand reaching) and distal adjustments (horizontal, vertical and oblique hand orientation; opened, closed and half-open hand), and the success in reaching the objects. RESULTS: The infants exhibited two-hand adjustments for the LR object and single-hand adjustments for the other objects. Oblique orientation was predominant for touching the objects, while vertical orientation was predominant for grasping them, particularly the LR object. Horizontal orientation was not observed for grasping the LR object. At the start of reaching for all objects, the hands were most frequently half-open, while the hands were predominantly open when touching the LR object. Success was greater when reaching for malleable objects (LM, SM) than for rigid objects (LR and SR). CONCLUSION: The young infants studied were capable of planning and adjusting their movements on the basis of their perceptions of the physical properties of the objects, which suggests that perception-action interaction was occurring.
physical properties of objects; reaching; grasping; perception; infant; affordances
