‘Interest’ and ‘Pleasure’: Two Determinants of a Monkey's Visual Preferences

When given a choice between two visual stimuli (plain fields of light of different colour, photographs, cine films, etc.) monkeys show strong and consistent preferences. The strength and direction of the preferences is determined by two independent factors: the monkey's relative ‘interest’ in the stimuli (determined largely by their information content) and his relative ‘pleasure’ (determined by qualities such as colour and brightness). With an unchanging stimulus ‘interest’ rapidly fades but ‘pleasure’ (or ‘unpleasure’) remains stable. If the two factors are set against each other, as when a red-coloured cine film is paired with a plain white field (the pictorial content of the film being interesting, its colour unpleasant), interest over-rides pleasure in determining the observed preference. A quantitative model based on these principles predicts the behaviour in a variety of situations with great accuracy.