A sliding two-alternative forced-choice paradigm for pitch discrimination.

Studies that measure frequency discrimination often use 2, 3, or 4 tones per trial. This paper shows an investigation of a two-alternative forced choice (2AFC) task in which each tone of a series is judged relative to the previous tone ("sliding 2AFC"). Potential advantages are a greater yield (number of responses per unit time), and a more uniform history of stimulation for the study of context effects, or to relate time-varying performance to cortical activity. The new task was evaluated relative to a classic 2-tone-per-trial 2AFC task with similar stimulus parameters. For each task, conditions with different stimulus parameters were compared. The main results were as follows: (1) thresholds did not differ significantly between tasks when similar parameters were used. (2) Thresholds did differ between conditions for the new task, showing a deleterious effect of inserting relatively large steps in the frequency sequence. (3) Thresholds also differed between conditions for the classic task, showing an advantage for a fixed frequency standard. There was no indication that results were more variable with either task, and no reason was found not to use the new sliding 2AFC task in lieu of the classic 2-tone-per-trial 2AFC task.