Table 2.

Reach development and learning targets.

Age (months)	Observed behavior	Robot targets
Pre-natal	Arm babbling in the womb De Vries et al., 1984	Proprioceptive-motor mapping of general movements
1	Hand-mouth movements Rochat, 1993	Learning of home position through tactile feedback
1	Directed (to the hemifield in which a target appears), but unsuccessful, hand movements von Hofsten and Rönnqvist, 1993; Ennouri and Bloch, 1996	Initial mapping of general movements to vision
1	Initial reaching is goal directed, and triggered by a visual stimulus, but visual feedback is not used to correct movements mid-reach Bremner, 1994, p. 38	Visual stimuli trigger general reach movements
3	Infants often move their hand to a pre-reaching position near the head before starting a reach Berthier et al., 1999, which then follows the line of sight Bruner, 1968, p. 44	Reaches conducted from “home” position
3	Infants engaged in early reaching maintained a constant hand-body distance by locking the elbow, and instead used torso movements to alter the distance to targets Berthier et al., 1999	Constraints on elbow movements reduce learning space
3	Successful reaching appears around 3–4 months after birth Shirley, 1933; Fiorentino, 1981; Berthier et al., 1999; Berthier and Keen, 2006	Primitive hand-eye mapping
3	Gaze still focused on the target and not the hand Clifton et al., 1993; Butterworth and Harris, 1994; Clifton et al., 1994; Berthier and Carrico, 2010	Reaches are visually elicited, but without continuous feedback
4	From 4 months, infants begin to use visual feedback to refine the movement of the hand White et al., 1964	Begin to map joint-visual changes and use visual feedback to correct reaches
4	As infants age their reaching becomes straighter, with the hand following the shortest path Carvalho et al., 2007	Refined reaching with smooth and direct movements