Effects of the stimulus and chamber size on unlearned fear across development

▶ Adolescent and adult rats freeze more during exposure to cat fur compared to control odor. ▶ Infant and juvenile rats freeze more during exposure to cat fur and cat urine compared to control odor. ▶ Younger animals freeze more to cat odor cues than older animals, but risk-assessment levels do not change. ▶ Chamber size had no effect on unconditioned fear behavior.