Rats’ novel object interaction as a measure of environmental familiarity

Environmental familiarization is a learning phenomenon embedded within most tasks used to study learning and motivation. Given its prevalence there is surprisingly little systematic behavioral research on factors affecting familiarization. The six experiments reported in the present report used rats’ tendency to interact more with a novel object in a familiar than in a novel environment as a measure of environmental familiarization. We found that 3 min of exposure to the environment was sufficient to increase object interaction above unfamiliar controls even when testing occurred up to 48 h after initial exposure to the environment; 1 or 1.5 min of exposure was not sufficient. Also, in the brief 2 min test, 10 min of environment exposure did not appear to increase object interaction above the 3-min condition. The 3-min of environment exposure was sufficient for familiarization whether environment exposure occurred in one 3 min placement or two 1.5 min placements. Environmental familiarization as measured by object interaction was also sensitive to ‘interference’ manipulations. That is, a distinct object present during initial exposure to the environment produced a level of object interaction in testing comparable to an unfamiliar control. Similarly, exposure to a second distinct alternate environment immediately after, but not before, initial exposure to the test environment partially disrupted environmental familiarization. In sum, object interaction might serve as a useful measure for studying processes mediating environmental familiarity.