STIMULUS VARIABILITY AND SPOKEN WORD RECOGNITION .1. EFFECTS OF VARIABILITY IN SPEAKING RATE AND OVERALL AMPLITUDE

The present experiments investigated how several different sources of stimulus variability within speech signals affect spoken-word recognit ion. The effects of varying talker characteristics, speaking rate, and overall amplitude on identification performance were assessed by comp aring spoken-word recognition scores for contexts with and without var iability along a specified stimulus dimension. Identification scores f or word lists produced by single talkers were significantly better tha n for the identical items produced in multiple-talker contexts. Simila rly, recognition scores for words produced at a single speaking rate w ere significantly better than for the corresponding mixed-rate conditi on. Simultaneous variations in both speaking rate and talker character istics produced greater reductions in perceptual identification scores than variability along either dimension alone. In contrast, variabili ty in the overall amplitude of test items over a 30-dB range did not s ignificantly aler spoken-word recognition scores. The results provide evidence for one or more resource-demanding normalization process whic h function to maintain perceptual constancy by compensating for acoust ic-phonetic variability in speech signals that can affect phonetic ide ntification.