The responses of human observers while tracking 75%‐correct thresholds using a block up‐and‐down adaptive procedure has been examined. Three signals (wide‐band noise, narrow band noise, and a 2000‐Hz sinusoid) were used with a continuous or a gated wide‐band masking noise at various levels. A strong bias in favor of the “2” response in the two‐interval paradigm and the “NO” response in theYES NOparadigm was consistently observed. Subjects also tended to follow correct responses with correct responses and vice versa. These data suggest that, although the subjects were supposedly performing a two‐interval task, they were actually attending to only one interval, most frequently the first, on each trial.