Selecting between competitors in multiplication tasks: An explanation of the errors produced by adolescents with learning difficulties

Two experiments were conducted in order to determine the nature of the difficulties encountered by learning disabled (LD) adolescents in the resolution of multiplication problems (a x b, where a and b vary between 2 and 9). A response production task (Experiment 1) revealed that the incorrect responses generally belonged to the table of one of the two operands, and that the order of difficulty of the problems was the same for the LDs as for normal children, adolescents, and educated adults as reported in the literature. This result suggests that the difficulties are not solely due to memory problems. Experiment 2 tested the hypothesis that these difficulties were caused by a problem in inhibiting the incorrect responses from a set of possible responses. Subjects completed a multiple response task in which the correct response was presented along with three distracters. The level of interference between the correct response and the distracters was varied by manipulating the nature of the distracters (Null Interference, NI: numbers that did not belong to the multiplication table; Weak Interference, WI: numbers belonging to other tables than those of a and b; Strong Interference, SI: numbers belonging to the tables of either a or b). The SI condition resulted in a higher level of errors than the NI and WI conditions and there was no difference between these latter two conditions. This result suggests that the main difficulty encountered by LD subjects is associated with inefficient inhibition of incorrect responses. Thus, the mobilisation of inhibitory processes seems to be an important stage in the development of multiplication skills.