Jst. Evans et al., ON THE MENTAL REPRESENTATION OF CONDITIONAL SENTENCES, The Quarterly journal of experimental psychology. A, Human experimental psychology, 49(4), 1996, pp. 1086-1114
Four experiments are reported which attempt to externalize subjects' m
ental representation of conditional sentences, using novel research me
thods. In Experiment 1, subjects were shown arrays of coloured shapes
and asked to rate the degree to which they appeared to be true of cond
itional statements such as ''If the figure is green then it is a trian
gle''. The arrays contained different distributions of the four logica
lly possible cases in which the antecedent or consequent is true or fa
lse: TT, TF, FT, and FF. For example, a blue triangle would be FT for
the conditional quoted above. In Experiments 2 to 4, subjects were abl
e to construct their own arrays to make conditionals either true or fa
lse with any distribution of the four cases they wished to choose. The
presence and absence of negative components was varied, as was the fa
rm of the conditional, being either ''if then'' as above or ''only if'
': ''The figure is green only if it is a triangle''. The first finding
was that subjects represent conditionals in fuzzy way: conditionals t
hat include some counter-example TF cases (Experiment 1) may be rated
as true, and such cases are often included when subjects construct an
array to make the rule true (Experiments 2 to 4). Other findings inclu
ded a strong tendency to include psychologically irrelevant FT and FF
cases in constructed arrays, presumably to show that conditional state
ments only apply some of the time. A tendency to construct cases in li
ne with the ''matching bias'' reported on analogous tasks in the liter
ature was found, but only in Experiment 4, where the number of symbols
available to construct each case was controlled. The findings are dis
cussed in relation to the major contemporary theories of conditional r
easoning based upon inference rules and mental models, neither of whic
h can account for all the results.