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 betw een 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 ad ults as reported in the literature. This result suggests that the diff iculties are not solely due to memory problems. Experiment 2 tested th e hypothesis that these difficulties were caused by a problem in inhib iting the incorrect responses from a set of possible responses. Subjec ts completed a multiple response task in which the correct response wa s presented along with three distracters. The level of interference be tween the correct response and the distracters was varied by manipulat ing the nature of the distracters (Null Interference, NI: numbers that did not belong to the multiplication table; Weak Interference, WI: nu mbers belonging to other tables than those of a and b; Strong Interfer ence, SI: numbers belonging to the tables of either a or b). The SI co ndition resulted in a higher level of errors than the NI and WI condit ions and there was no difference between these latter two conditions. This result suggests that the main difficulty encountered by LD subjec ts is associated with inefficient inhibition of incorrect responses. T hus, the mobilisation of inhibitory processes seems to be an important stage in the development of multiplication skills.