The effects on speeded classification of implicit and explicit instructions regarding redundant dimensions

Two experiments were run in which speed of sorting decks of stimulus cards was measured. Stimuli were constructed from two dichotomous dimensions, used either alone or perfectly correlated. The lack of evidence for a selective serial processing (SSP) strategy (in which S sorts by his most preferred dimension whenever the dimensions are correlated) in a similar study by Garner and Felfoldy (1970) was thought to be due to Ss’ failure to notice that the dimensions were correlated, and thus that SSP would be effective. Ss in the present experiment therefore received either implicit instructions concerning the existence of the correlated deck (by seeing only decks in which there were just two different stimuli), or explicit instructions that on some trials the two dimensions would be correlated and S could sort by any means he preferred. When dimensions of size of circle and angle of diameter were of unequal discriminability, implicit instructions produced partial use of the SSP strategy, while explicit instructions produced nearly total use of SSP by all Ss. When the Munsell dimensions of value and chroma were varied in two separate color chips and were equally discriminable on the average, evidence for a small amount of SSP was found in both the implicit and explicit conditions. With neither pair of dimensions did implicit or explicit instructions regarding the correlated task produce integration of information.