Behavioural evidence based on speeded classification of centrally presented emotions suggests that the mental representation of affects is similar to number, with faster left-sided responses to negative emotions (anger) and faster right-sided responses for positive emotions (happiness), SNARC-Like Effect (SLE). However, it is not clear whether a similar effect would hold true using a One Interval Speed-Comparison Task (OIS-CT) between pairs of simultaneously displayed facial expressions (horizontally aligned), either fully-emotional (happy/angry) or half-emotional (neutral/happy-or-angry). In this case a Semantic Congruity Effect (SCE) might rise. Emotion comparison indeed requires judging greater or lesser, depending on whether the task involves detecting the happiest or the angriest face. The speed of comparative judgements should thus be faster when the target image is emotional rather neutral irrespective from the response side relative to average valence, and/or the spatial congruency of image-pairs with the left-to-right mental format. This would produce standard vs reversed SLE for spatially congruent (angriest-left/happiest-right) vs incongruent displays. In particular, for incongruent displays, a positive right-to-left speed advantage for half-emotional displays with negative rather than positive average valence should be observed: vice-versa for congruent displays. We found a strong SCE, not a SLE, in two Experiments involving the same OIS-CT with (self-terminating stimulus, n=40) vs without foveation (stimulus presentation time=[190, 200] ms, n=40). Individual average speeds were fully accounted for by a model formalizing SCE: a nlme-regression including the sum between global display and absolute target valence as the only covariate of speeds.
