Bait shyness: avoidance of the taste without escape from the illness in rats.

Thirsty rats habituated to drinking .12 M sodium chloride accepted .12 M lithium chloride for 5 min on the first trial but stopped short of their sodium baseline. With repeated trials they reduced consumption of the toxin by either (a) detecting subtle oral (conditioned stimulus, CS) differences, thus avoiding toxicosis (unconditioned stimulus, US) or (b) detecting earlier signs of malaise (US), thus escaping further distress. When both solutions were masked with saccharin, the discrimination was more difficult but still possible. When both solutions were mixed in a solution masking all four taste qualities, the discrimination was severely disrupted. When oral sensors were bypassed with nasopharyngeal tubes, intragastric pumping rats were unable to use postingestional cues to escape, even though such cues were proximal to the ultimate malaise. Oral cues at the distal end of the consummatory chain were extremely effective.