Dogs generally seem to be cheerful, happy-go-lucky characters, but according to a new study some pooches are distinctly more pessimistic than others. "This research is exciting because it measures positive and negative emotional states in dogs objectively and non-invasively," said Dr Melissa Starling, from the Faculty of Veterinary Science at the University of Sydney. "Finding out as accurately as possible whether a particular dog is optimistic or pessimistic is particularly helpful in the context of working and service dogs and has important implications for animal welfare," she added.