Pigeons are well known for their visual capabilities as well as their ability to categorize visual stimuli at both
the basic and superordinate level. We adopt a reverse engineering approach to study categorization
learning: Instead of training pigeons on predefined categories, we simply present stimuli and analyze
neural output in search of categorical clustering on a solely neural level. We presented artificial stimuli,
pictorial and grating stimuli, to pigeons without the need of any differential behavioral responding
while recording from the nidopallium frontolaterale (NFL), a higher visual area in the avian brain. The
pictorial stimuli differed in color and shape; the gratings differed in spatial frequency and amplitude. We
computed representational dissimilarity matrices to reveal categorical clustering based on both neural
data and pecking behavior. Based on neural output of the NFL, pictorial and grating stimuli were
differentially represented in the brain. Pecking behavior showed a similar pattern, but to a lesser extent.
A further subclustering within pictorial stimuli according to color and shape, and within gratings
according to frequency and amplitude, was not present. Our study gives proof-of-concept that this reverse
engineering approach—namely reading out categorical information from neural data—can be quite
helpful in understanding the neural underpinnings of categorization learning.