Vertebrate and invertebrate, experimental and theoretical, recent and old research in sensory processing are compared. The titles indicate the lines of reasoning: single neurons, neuron populations, processing in parallel channels and memory formation. From this introductory review new models for two invertebrate systems emerge. Histological and electrophysiological results indicated a prey capture model for stomatopod vision. Ethological results and the recent literature showed that this model was not auto-sufficient. The new model considers also identification of the prey, besides location determination, and is based on parallel processing and correlation between the neuronal subsets. A model for bee magnetoperception proposes interacting neuron populations in the ganglion and in the brain. In neuron population synapses are modified for multimodal, associative learning.