Effects of varying total adaptor energy in selective adaptation

Two experiments were designed to examine the effects of varying total adaptor energy in selective adaptation along a synthetic stop consonant continuum. Experiment I considered the effect of the number of adaptors presented in the adaptation sequence preceding each test sequence, with repetition rate held constant: Over the range from 8 to 32 adaptors, the magnitude of the phonetic boundary shift was found to be a linear function of the logarithm of the number of adaptors. Experiment II explored the effect of variations in the repetition rate (or density) of adaptors with the number held constant. A nonmonotonic relation was found between the phoneme boundary shift and the interadaptor interval: A greater shift was observed for a 750‐msec interval than for either a 250‐msec interval or a 1750‐msec interval. These low‐level stimulus energy variables (adaptor number and repetition rate) affect the magnitude of the phonetic boundary shift in what may be a trading relationship. [Work supported by NICHD to the Haskins Laboratories.]