Abstract: Particle patterns formed on an inclined bottom surface of a reaction vessel are photoelectrically detected to produce a two-dimensional image signal. The signal is processed to judge or classify the particle patterns into an agglutinated pattern, a non-agglutinated pattern or an uncertain pattern with the aid of a neural network. An image signal representing a particle pattern is first extracted, then the image signal is decomposed into a series of light intensity areas due to different contours of the inclined bottom surface. The integrated light intensities of each area are presented to a neural network. The neural network operates in a training mode and a classification mode. In the training mode the neural network is presented with numerous samples of decomposed images as well as their respective classification. In the classification mode the neural network will judge a decomposed image based on a generalization made during the training mode.