Many languages have a phonological pattern of regressive voicing assimilation, according to which an obstruent is required to match a following obstruent in voicing (e.g. Russian, Sanskrit). This restriction on the distribution of categories has parallels in the phonetic fact that an obstruent has a longer interval of glottal pulsing when it occurs before a voiced sound than when it occurs before a voiceless sound. It is proposed that the phonological pattern arises diachronically through a reanalysis of the phonetic pattern, beginning with a tendency for listeners to identify an obstruent before another obstruent as matching the latter in voicing. This paper reports on two experiments designed to test premises of this account. A production study explores how obstruent voicing in English is affected by voicing in a following segment. A perception study explores how the identification of voicing categories is impacted by the acoustic effects of following segment context. It is found that listeners tend to identify a fricative as voiceless if it is drawn from the position before a voiceless obstruent, but that a following voiced segment has no significant effect on voicing class identification. Implications for the diachronic account of regressive voicing assimilation are discussed.