ase ▁Trans itions ▁(' Switch es ') ▁ ▁The ▁H KB ▁model ▁diff ers ▁from ▁other ▁motor ▁coord ination ▁models ▁with ▁the ▁addition ▁of ▁phase ▁trans itions ▁( ‘ switch es ’ ). ▁ ▁Kel so ▁initially ▁observed ▁this ▁phenomen on ▁while ▁conduct ing ▁an ▁experiment ▁looking ▁at ▁subjects ’ ▁finger ▁movements . ▁Sub ject s ▁oscill ated ▁their ▁fingers ▁rh ythm ically ▁in ▁the ▁trans verse ▁plane ▁( i . e ., ▁ab du ction - ad du ction ) ▁in ▁one ▁of ▁two ▁patterns , ▁parallel ▁or ▁anti - parallel . ▁In ▁the ▁parallel ▁pattern , ▁the ▁finger ▁mus cles ▁contract ▁in ▁an ▁altern ating ▁fashion ; ▁in ▁the ▁anti - parallel ▁pattern , ▁the ▁hom olog ous ▁finger ▁mus cles ▁contract ▁simultaneously . ▁Kel so ' s ▁study ▁observed ▁that ▁when ▁the ▁subject ▁begins ▁in ▁the ▁parallel ▁mode ▁and ▁increases ▁the ▁speed ▁of ▁movement , ▁a ▁sp ont aneous ▁switch ▁to ▁symmet rical , ▁anti - parallel ▁movement ▁occurs . ▁This ▁transition ▁happens ▁swift ly ▁at ▁a ▁certain ▁critical ▁frequency . ▁Sur pr ising ly , ▁after ▁the ▁switch ▁has ▁occurred ▁and ▁the ▁movement ▁rate ▁decre ases , ▁Kel so ' s ▁subjects ▁remain ▁in ▁the ▁symmet rical ▁model ▁( did ▁not ▁switch ▁back ). ▁Kel so ' s ▁study ▁indicates ▁that ▁while ▁humans ▁are ▁able ▁to ▁produce ▁two ▁patterns ▁at ▁low ▁frequency ▁values , ▁only ▁one — the ▁symmet rical , ▁anti - parallel ▁mode ▁remains ▁stable ▁as ▁frequency ▁is ▁scale d ▁beyond ▁a ▁critical ▁value . ▁ ▁Pred