Perceptual Judgments of Logical Propositions

Aims: This study is part of a series aiming to evaluate the computational complexity used by the human brain while perceptually judging a logic proposition.

Methods: In the present article we report a psychophysical study in which the hypothesis that efficiency and efficacy of these perceptual decisions depend on the proposition but not on the validating sensory stimuli was tested. Subjects had to judge whether a color stimulus verifies a proposition under a go/no-go protocol. Different protocols were used for the evaluation of the relative weight of proposition connectors on the latency, accuracy and precision of the responses.

Results and Discussion: Errors and latencies increase with the minimum description length of the proposition, but the relative weight of absences was double than the weight of presences (even when brief and single color stimuli ruled out visual search). However, values predicted by this rule are smaller than those found for conditionals and larger than those found for biconditionals and exclusive disjunctions. We postulate that the brain uses a “one and only one is valid” operator (which is equivalent to exclusive disjunction in dyadic statements) to deal with these propositions.

Conclusions: Decision difficulty (including within this term time and accuracy) depends on proposition structure. We provide a heuristic rule that predicts evaluation time better than previously proposed hypotheses.