Early exposure to certain stimuli in rats can affect their ability to learn later on. When rats were exposed to lights or tones paired with footshocks at a young age, they had trouble learning to associate those same lights or tones with the footshocks later on. This early conditioning also affected their ability to learn in a different sensory modality. However, exposure to the individual stimuli or context alone did not have the same negative impact on learning. This suggests that early experiences can interfere with later learning, possibly due to competition between different senses during development.