Rig ht or Wrong , Fa mil ia r or Novel in Pictorial List Discri m i nation Lea

The interaction between nonassociative learning (presentation frequencies) and associative learning (reinforcement rates) in stimulus discrimination performance was investigated. Subjects were taught to discriminate lists of visual pattern pairs. When they chose the stimulus designated as right they were symbolically rewarded and when they chose the stimulus designated as wrong they were symbolically penalised. Subjects first learned one list and then another list. For a 'tight" group the pairs of the second list consisted of right stimuli from the first list and of novel wrong stimuli. For a 'wrong" group it was the other way round. The right group transferred some discriminatory performance from the first to the second list while the control and wrong groups initially only performed near chance with the second list. When the first list involved wrong stimuli presented twice as frequently as right stimuli, the wrong group exhibited a better transfer than the right group. In a final experiment subjects learned lists which consisted of frequent right stimuli paired with scarce wrong stimuli and frequent wrong stimuli paired with scarce right stimuli. In later test trials these stimuli were shown in new combinations and additionally combined with novel stimuli. Spbjects preferred to choose the most rewarded stimuli and to avoid the most penalised stimuli when the test pairs included at least one frequent stimulus. With scarce/scarce or scarce/novel stimulus combinations they performed less well or even chose randomly. A simple mathematical model that ascribes stimulus choices to a Cartesian combination of stimulus frequency and stimulus value succeeds in matching all these results with satisfactory precision.