In agreement with previous findings, there was a difference in category boundary between the two groups.
Little is known about individual differences in the position of the category boundary, nor whether the category boundaries differ across stimulus continua.
In a between-subject design, infants were tested on their ability to discriminate faces that were between-category (across the category boundary) or within-category (within emotion category).
Within its architecture it has two components that could reasonably lead to a difference in race category boundary, these being evidence accumulation rate and a priori bias.
The category boundary was set at 50%.
As a result, stimuli that were near opposite sides of a category boundary, though visually similar, belonged to different categories.
Even for morph ratios near the category boundary (55:45 morphs), performance exceeded 80% at the end of training.
As expected, for category training we obtained a significant effect of the category boundary (Figure 3, c and d): Subjects were much more likely to rate bird pairs to be the same when they belonged to the same side of the category boundary than equal distance bird pairs belonging to different sides of the category boundary [F 1,11) = 115.86, p<.0001].
Responses were more accurate for bird exemplars with higher morph levels (close to the prototype) than for bird exemplars with lower morph levels (close to the category boundary).
Our behavioural data showed that responses were more accurate and faster for birds at higher morph levels, reflecting that birds close to the prototype are more distinctive than birds close to the category boundary.
The presence of a category boundary was investigated by comparing the proportion of 'same' responses for bird pairs with an equal morph distance for cases in which the birds were from the same or from a different category.
