Abstract

When an anticipated food reward is unexpectedly
reduced in quality or quantity, many mammals show a
successive negative contrast (SNC) effect, i.e. a reduction
in instrumental or consummatory responses below the level
shown by control animals that have only ever received the
lower-value reward. SNC effects are believed to reflect an
aversive emotional state, caused by the discrepancy
between the expected and the actual reward. Furthermore,
how animals respond to such discrepancy has been suggested
to be a sign of animals’ background mood state.
However, the occurrence and interpretation of SNC effects
are not unequivocal, and there is a relative lack of studies
conducted outside of laboratory conditions. Here, we tested
two populations of domestic dogs (24 owned pet dogs and
21 dogs from rescue kennels) in a SNC paradigm following
the methodology by Bentosela et al. (J Comp Psychol
123:125–130, 2009), using a design that allowed a within-,
as well as a between-, subjects analysis. We found no
evidence of a SNC effect in either population using a
within- or between-subjects design. Indeed, the withinsubjects
analysis revealed a reverse SNC effect, with subjects
in the shifted condition showing a significantly higher
level of response, even after they received an unexpected
reduction in reward quality. Using a within-, rather than a
between-, subjects design may be beneficial in studies of
SNC due to higher sensitivity and statistical power; however,
order effects on subject performance need to be
considered. These results suggest that this particular SNC
paradigm may not be sufficiently robust to replicate easily
in a range of environmental contexts and populations.