DECODING A DECEPTIVE INSTRUCTION

Abstract

Equivalent forms of instruction for a task requiring response to one of two equal classes of items were investigated. The class of items requiring response was defined positively (by inclusion) in one form of instruction and negatively (by exclusion) in the other. It was hypothesized that preference for positive rather than negatively defined classes would lead subjects to transform (decode) the exclusion form of instruction into the equivalent inclusion form. Performance of subjects first given the ‘exclusion’ instruction and afterwards transferred to the ‘inclusion’ form was compared with a control group, using the latter form throughout. Less than half the subjects decoded the ‘exclusion’ instruction, and the remainder performed the task at a significantly slower speed both before and after transfer. The error pattern of these subjects indicated that an instruction of the form ‘Respond to all items except x and y ’ generates a spurious set to make a response to the items x and y . The implicit nature of the negative in the qualifier ‘except’ appeared to be a contributing factor to the deceptive effect of this type of instruction.