Examples of the most typical misclassification of objects in the mock test sample. The first row shows QSO-l classified as galaxies, the second row shows galaxies classified as QSO-l, the third row shows QSO-h classified as QSO-l, and the fourth row shows stars classified as QSO-l. From left to right, the objects are fainter. In each panel, we indicate the AB magnitude in the r band, the redshift (top left), and the probabilities yielded by the ANN₁ classifier for each one of the classes (top right). The SDSS spectra from which the test sample is generated are shown in the background in grey.