Figure 2.

Morphed images were created by gradually morphing one distinct image into another distinct image across a 100-step series. Test I, illustrated here, was constructed using the 30 images from steps 31–45 and 56–70. The numbers below each image indicate its position in the morph series. The materials for faces and for test II were created using a similar method. For testing with the material illustrated here, images 31 and 70 appeared at the top of the screen and one of the intermediate images appeared at the bottom. How close the bottom image was to image 31 or 70 determined whether the judgment was easy, medium, or difficult.