Ehri, L. C. (1977). Do adjectives and functors interfere as much as nouns in naming pictures? Child Development, 48, 697-701.

Third- and sixth-grade readers were asked to label sets of pictures printed with distracting words (either nouns, adjectives, or functors) and nonsense syllables. Picture-naming latencies were significantly longer with nouns than with adjectives and functors, indicating that noun interference stems from semantic-conceptual rather than phonological sources. Latency patterns among the words were similar for younger and older readers, suggesting that both groups are equally susceptible to semantic sources of interference. Adjectives but not functors yielded substantially longer latencies than nonsense syllables. However, interpretation is difficult because of the inadequacy of nonsense syllables as a control for phonological interference.