Three experiments were conducted to investigate the effects of age and hearing loss on the ability to maintain perceptual constancy in spoken word recognition. Specifically, the studies examined how variations in talker characteristics, speaking rate, and overall amplitude affected perceptual identification in normal-hearing young (NHY), normal-hearing elderly (NHE), and hearing-impaired elderly (HIE) listeners. The three dimensions were selected because variations in voice characteristics and speaking rate affect features of speech signals that are important for word recognition while overall amplitude changes do not have direct effects on phonetic identification. Thus, both phonetically-relevant and irrelevant sources of variability were investigated. Age differences, as indicated by greater effects of variability for the NHE compared with the NHY listeners, were observed for conditions with trial-to-trial variations in talker characteristics and overall amplitude. Effects of hearing impairment, as indicated by reduced scores for the HIE compared with the NHE group, were observed for conditions with variations in either speaking rate or talker characteristics. Considered together, the findings suggest that age-related changes in perceptual normalization, selective attention, and absolute sensitivity may all contribute to the reduced speech understanding often reported for older adults. Several possible mechanisms for the age- and hearing-related deficits are discussed.