The dynamic spatial and temporal relationships between the phalanx-forming region and the interdigits determine digit identity in the chick limb autopod.

The digital rays are naïve during the initial stages of their development, at which time digit identity is not determined. To determine digit identity, each PFR cell shows a unidirectional response to obtain positional information specifically from the IDs located posterior to the PFR, regardless of the signal strength from the anteriorly located IDs.