Figure 2. Stimuli.

The top row shows the two prototypes A and B used to create all intervening objects. The second and third rows represent the 15 training and test objects, respectively. Note that training and test sets differ, except for the prototypes, which were used in all sessions. The x-axis displays the proportion of B-features in each intermediate (morph) object, as a percentage. The bottom three rows show the MDS results for two object orientations (0° and 180°, see text for more details). The numbers in black (top row) indicate the relative positions of the physical stimuli in terms of the percentage of B features. The numbers in grey (bottom two rows) indicate the perceived differences between the test stimuli. Specifically, the horizontal position of each grey number along the morph line indicates the perceived position of the corresponding stimulus, as calculated by MDS. The perceptual MDS maps were linearly scaled to the same range as the physical stimuli, for easy comparison. It is clearly visible that participants perceive the morphed objects to span a roughly equally-spaced morph line independent of object orientation (10 participants were tested for each orientation). Note that the perceived ordering of the stimuli is preserved.