Knowing a word affects the fundamental perception of the sounds within it

Understanding spoken language is an exceptional computational achievement o f the human cognitive apparatus. Theories of how humans recognize spoken wo rds fall into two categories: Some theories assume a fully bottom-up flow o f information, in which successively more abstract representations are comp uted. Other theories, in contrast, assert that activation of a more abstrac t representation (e.g., a word) can affect the activation of smaller units (e.g., phonemes or syllables). The two experimental conditions reported her e demonstrate the top-down influence of word representations on the activat ion of smaller perceptual units. The results show that perceptual processes are not strictly bottom-up: Computations at logically lower levels of proc essing are affected by computations at logically more abstract levels. Thes e results constrain and inform theories of the architecture of human percep tual processing of speech.