Fading on the S+, the S-, both, or neither.

Mentally retarded adults were presented with size and number discriminations using four stimulus conditions. In Condition 1, the S+ circles faded from large (Size 10) to smaller (Size 6) while the S- circles remained at Size 5 and number of circles varied randomly. In Condition 2, the S- squares faded in number from 1 to 5 while the S+ squares remained at Number 6, and size varied randomly. In Condition 3, simultaneous fading of the S+ and S- triangles occurred on size for 6 subjects and on number for the other 6. In Condition 4, fading did not occur on the S+ or S- hexagons. Each of the fading procedures (Conditions 1, 2, and 3) produced fewer errors on all 80 trials than did the no-fading control condition but did not differ significantly among themselves. These same results generally occurred for fading and test trials. Although fading has been used successfully to teach a variety of skills, systematic analyses of fading procedures clearly delineating component stimulus operations have been neglected.