Figure 6.
Prediction accuracy within and across perceptual categories. Behavioral performance and prediction accuracy are shown for three observers that performed the simple categorization task based on spatial similarity for the A–B stimulus set, allowing us to evaluate perceptual differences between stimuli that were matched for their distances in the physical space. Note that data from the C–D stimulus set was not used in the analysis as the morphing steps used were not equidistant (20, 30, 40, 60, 70, and 80%); morphing steps in this set were selected to match performance between stimulus sets (A–B, C–D). A, Behavioral performance for categorization based on spatial similarity (proportion of trials in which observers assigned the stimuli to category 2) across spatial morphing steps is shown for each observer and averaged across observers. Performance was fitted with a logistic function to estimate the 50% categorization threshold for each observer. The average threshold across observers was 44.82 (thresholds for individual observers were very similar: s1, 44.87; s2, 44.97; s3, 44.62), placing the categorization boundary approximately at the morphing step of 45. B, We compared the mean prediction accuracy for small stimulus distances close to the boundary (morphing steps, 35 vs 45 and 45 vs 55) and small distances within category (morphing steps, 25 vs 35 and 55 vs 65). The Euclidean distances were very similar across these morphing steps (25–35 = 0.33; 35–45 = 0.34; 45–55 = 0.32; 55–65 = 0.35). A significant interaction between region of interest and classification (F(29,58) = 2.21; p < 0.01) was observed (for ROI definitions, see supplemental Table 1, available at www.jneurosci.org as supplemental material). C, We compared mean prediction accuracy between small distances within category (morphing steps, 55 vs 65 and 65 vs 75; Euclidean distances, 0.35 and 0.36) and a large distance within category (morphing steps, 55 vs 75; Euclidean distance, 0.51). A significant interaction between region of interest and classification (F(29,58) = 1.78; p < 0.05) was observed.