Most but not all bottom-up interactions between signal properties improve categorization

The massive acoustic redundancy of minimally contrasting speech sounds, cou pled with the auditory integration of psychoacoustically similar acoustic p roperties produces a highly invariant percept, which cannot be improved by top-down feedback from the lexicon. Contextual effects are also bottom-up b ut not all entirely auditory and may thus differ in whether they affect sen sitivity or only response bias.