▁experiment ally ▁there ▁was ▁little ▁difference ▁in ▁learning ▁rates ▁between ▁the ▁two ▁groups . ▁However , ▁Rock ' s ▁work ▁did ▁not ▁sett le ▁the ▁controvers y ▁because ▁in ▁his ▁experiment ▁he ▁re arr anged ▁replaced ▁word ▁pairs ▁that ▁could ▁be ▁either ▁easier ▁or ▁harder ▁to ▁learn ▁than ▁the ▁original ▁words ▁in ▁the ▁word - ▁digit ▁pair . ▁In ▁further ▁experiments ▁that ▁addressed ▁the ▁question , ▁there ▁were ▁mixed ▁results . ▁The ▁increment al ▁learning ▁hypothesis ▁is ▁supported ▁by ▁the ▁notion ▁that ▁a while ▁after ▁A i - Bi ▁pairs ▁are ▁learned , ▁the ▁recall ▁time ▁to ▁recall ▁Bi ▁decre ases ▁with ▁continued ▁learning ▁tra ils . ▁ ▁Another ▁theory ▁that ▁can ▁be ▁tested ▁using ▁cu ed ▁recall ▁is ▁symmetry ▁of ▁forward ▁and ▁back ward ▁recall . ▁For ward ▁recall ▁is ▁generally ▁assumed ▁to ▁be ▁easier ▁than ▁back ward ▁recall , ▁i . e . ▁forward ▁recall ▁is ▁stronger ▁than ▁back ward ▁recall . ▁This ▁is ▁generally ▁true ▁for ▁long ▁sequences ▁of ▁word ▁or ▁letters ▁such ▁as ▁the ▁alphabet . ▁In ▁one ▁view , ▁the ▁independent ▁associations ▁hypothesis , ▁the ▁strength ▁of ▁forward ▁and ▁back ward ▁recall ▁are ▁hypoth es ized ▁to ▁be ▁independent ▁of ▁each ▁other . ▁To ▁confirm ▁this ▁hypothesis , ▁Dr . ▁George ▁Wol ford ▁tested ▁participants ' ▁forward ▁and ▁back ward ▁recall ▁and ▁found ▁that ▁forward ▁and ▁back ward ▁recall ▁are ▁independent ▁of ▁each ▁other . ▁The ▁probability ▁of ▁correct ▁forward ▁recall ▁was ▁. 4 7 ▁for ▁word ▁pair ▁associations ▁and ▁the ▁probability ▁of ▁correct ▁back ward ▁recall ▁of