Abstract
Learning labels for surface features is a central component of regulating cognitive processing in early childhood. We used functional near-infrared spectroscopy (fNIRS) to examine changes in neural activation across bilateral frontal, temporal, and parietal cortices during production and comprehension of labels for surface features longitudinally from 2 to 4 years of age. During production tasks, children were shown a single item and asked to label the color or shape. During comprehension tasks, children were shown an array of 6 differently-colored and shaped objects and asked to touch an object based on the specified feature label. Canonical colors (red, blue, green, purple, orange, yellow) and shapes (square, circle, triangle, rectangle, star, heart) were used. Performance improved for comprehension (color: 59%, 71%; shape: 42%, 54%) and production (color: 94%, 97%; shape: 87%, 89%) from age 2 to 4, respectively. Across tasks, 2-year-olds activated the left superior temporal region, whereas 4-year-olds activated the left inferior frontal junction (IFJ). Additionally, we found a shift in right IFJ such that 2-year-olds showed activation during color tasks, but 4-year-olds showed activation during shape tasks. 2-year-olds, however, did show activation in the superior temporal regions during the shape tasks. Frontal activation increased as children gained expertise in comprehending and producing labels for surface features. 2-year-olds exhibited greater activation when performing color tasks possibly because color terms are typically the first dimension learned. 2-year-olds haven’t mastered color labels, but are exhibiting increasing proficiency with them. Color versions of this task may fall in a sweet-spot of complexity where the 2-year-old is familiar enough with the feature labels to complete the task, but still find it challenging. Thus, the frontal cortex is engaged due to a “Goldilocks” effect. Shape may be too difficult for 2-year-olds to engage the frontal cortex, but may reach the “Goldilocks” zone for four-year-olds.