Pepo13 [creativecommons license] via Wikimedia CommonsAnimal welfare science focuses on assessing and maximizing animals’ quality of life. In the research context, improving the welfare of laboratory animals is a high priority. To this end, objective measures of animal welfare are greatly needed. One way to evaluate welfare is to consider an animal’s affective state, which can be assessed indirectly by observing its influence on cognitive processes, such as those underlying the interpretation of ambiguous signals (or judgment bias). A negative affective state leads to an expectation of negative outcomes and thus a negative bias in the interpretation of ambiguous signals (a pessimistic outlook). In contrast, a positive affective state leads to an expectation of positive outcomes and a positive bias in the interpretation of ambiguous signals (an optimistic outlook). A recent report in PLoS One (9, e107794; 2014) describes the use of a portable, automated apparatus to train and test the judgment bias of dogs.