Auditory successive conditional discrimination and auditory stimulus equivalence classes.

Six adults listened to nonsense syllables in a sound booth. They learned to pick the correct second sound after hearing a first sound.

Each trial played two sounds in a row. The task was a successive conditional discrimination — no pictures, no text, just audio.

All six adults mastered the sound-to-sound matches. Most then showed new sound pairs they had never heard — three- or four-member auditory equivalence classes.

The classes formed even though the sounds meant nothing and never appeared together before.

Saunders et al. (1988) did the same thing five years earlier and built even bigger classes — eight sounds each. The 1993 study simply shows the effect still holds with smaller sets.

Murphy et al. (2014) later pushed the method further. They kept the same successive-auditory format but added extra trials. Overtraining lifted success to 85%, proving repetition helps more than meaning.

Guerrero et al. (2021) swapped pure sounds for sound-plus-picture pairs. They found the early audio-visual mix made later visual-only tests easier. The 1993 paper is the baseline: it proves auditory-only training is enough.

If you teach conditional discriminations with spoken words, songs, or audio cues, this study says you can build full equivalence classes without ever showing a picture. That opens the door for learners who are blind, have poor vision, or simply respond better to sounds. Try running a few extra auditory-only trials — the data say the classes will still emerge.