“Preference for Familiar versus Novel Stimuli As a Function of the Familiarity of the Environment”, 1969 (; similar):
[biographical background] The effect of high and low levels of environmental novelty on the direction of response to novel stimuli was tested by placing rats in a strange environment where they had the choice of approaching a source of familiar stimulation or a comparable novel one.
On first exposure, subjects statistically-significantly preferred the familiar stimulus, but after habituation to the environment, subjects changed to a statistically-significant preference for novel stimuli. A subsequent increase in novel stimulation tended to change preference back to familiar stimuli.
These findings support the previously untested optimal-level hypothesis of novelty response.