Why did scientists once think perceptual learning was limited to early childhood?

Scientists once assumed that perceptual learning was restricted to early childhood because of the significant neural tuning and reorganization that occurs during that developmental period. It was traditionally believed that once this critical period passed, the neural mechanisms responsible for the earliest stages of information processing lost their plasticity and could no longer be modified by experience.1

Furthermore, regarding improvements in adult perceptual performance, it was generally assumed that these changes were driven by high-level cognitive processes, such as decision making, rather than by modifications to the sensory systems themselves.1

These assumptions were challenged in the latter part of the 20th century, when researchers demonstrated that adult perceptual systems are highly mutable. This discovery revealed that low-level cognitive processes—involving the areas of the brain that first receive sensory information—can indeed be reshaped by experience, a concept now understood through the study of neuroplasticity.1