Proboscis conditioning (also known as olfactory conditioning or proboscis extension reflex conditioning ) is an invertebrate classical conditioning technique in which an olfactory stimulus (CS) is paired with a sucrose feeding (US). After several CS-US pairings, extension of the proboscis-a tube through which liquids are sucked into the mouth- is evoked by the CS, which at the outset of training is ineffective. The primary data consists of the presence or absence of a proboscis extension following presentation of the relevant stimuli. By employing video technology or physiological recording, fine-grain analysis of the proboscis response can readily be achieved. First developed by Frings (1944) to determine sensory thresholds in blow flies, the proboscis technique has become the most popular technique for classical conditioning in the bee.
The technique permits excellent control of intertrial interval, CS-US interval, stimulus intensity, and stimulus duration. The importance of these and other training variables is easily investigated. It is also possible to compare directly the performance of free-flying foragers-trained using some variant on the von Frisch technique- with those trained under restrained conditions. This is the only invertebrate in which such a comparison is possible. In addition to behavioral experiments, the proboscis technique is well suited also for quantitative physiological and biochemical analysis of the learning process.