Conditioned taste aversions induced by ionizing radiation and LiCl were compared in both forward (CS-US, conditioned stimulus-unconditioned stimulus) and backward (US-CS) conditioning paradigms. Taste aversions were produced when a saccharin CS preceded or followed a 100-r. radiation US by as much as 6 hr., but a 2% of body weight, .15 M LiCl US was effective only in CS-US pairings. It was argued that the ineffectiveness of a LiCl stimulus in US-CS pairings was not attributable to differences in the "strength" of the respective LiCl and radiation doses in that these doses yielded comparable aversions in forward pairings. These results were related to inadequacies of a "sickness" model of taste aversion conditioning.Several recent articles have pointed out the difficulties which taste aversion conditioning presents for traditional learning theory (e.g., Revusky & Garcia, 1970;Rozin & Kalat, 1971;Seligman, 1970). In these articles the phenomenon of radiation-induced taste aversions was discussed along with the drug-induced conditioned aversions which comprise the bait-shyness literature.The rationale for equating these 2 phenomena appears to have been provided in a series of papers in which the toxic effects of injections of cyclophosphamide, apomorphine, and lithium chloride were compared to ionizing radiation (Garcia & Ervin, 1968;Garcia, Ervin, & Koelling, 1967;. Although the specific mode of action of these various unconditioned stimuli was presumed to differ, speculated that "... these agents probably all produce a general malaise or illness [p. 246]" and that in conditioning taste aversion these stimuli "... have similar mechanisms of learning [Garcia & Ervin, 1968, p. 395]".

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Memory formation for the absolute intensity of taste and smell was investigated in a series of experiments. In Experiment I, 336 subjects tasted 10 ml of 15% sucrose and were asked to remember the strength of the solution. They were retested with 5%, 10%, 15%, or 20% sucrose, at one of four delay intervals (1, 5, or 15 min, or 72 h). They compared the second stimulus with the first stimulus and reported whether the second was "less sweet," "the same," or "sweeter." Subjects reliably reported that 5% sucrose was less sweet and that 20% sucrose was sweeter. However, when the second stimulus was 15% sucrose (Le., was equal to the standard), approximately 60% of the subjects reported that it was sweeter, regardless of the delay interval between the two stimuli. About 2/3 of those tasting 10% sucrose reported that it was as sweet as or sweeter than the 15% standard. A similar finding from a procedure using magnitude estimation was reported in Experiment 2. The same pattern of results was also found for an olfactory memory test (Experiment 3). When asked to match either a 1.33-or a 5.0-ppm pyridine olfactory stimulus, subjects consistently picked a concentration weaker than the standard. Apparently, olfactory and taste stimuli are remembered as being substantially weaker as soon as the memory for these stimuli can be tested. A memory model that posits a sensory store within which a taste or smell stimulus of a given intensity rapidly fades to a lower level of intensity is suggested. The new memory is then relatively unchanged for at least 3 days.Most research into human memory formation has been concerned with the fate of information coming through the auditory and visual senses. From these experiments human information processing models of the formation of auditory and visual memory have been developed (e.g., Atkinson & Shiffrin, 1968). Although these models do not specifically exclude the chemical senses (Barker, 1982), most research in human memory has been concerned with the ultimate fate of words, numbers, lists, etc. There is little research into how humans process information on taste and smell.Most models of memory posit three stages: for example, a "sensory store" (the first stage of sensing), primary memory (short term), and secondary memory (long term). Evidence of sensory stores has been reported for vision (Sperling, 1960) and audition (Treisman, 1964). Following the transduction process, visual and auditory information persists for a brief period of time «1.0 and 2-4 sec, respectively) before rapidly becoming inaccessible to the attentive processes of primary memory (Crowder, 1972).In the present paper, we offer evidence for a sensory store in the chemical senses. The results of the experiments reported here have allowed us to monitor the fate and time course of memory formation for a taste stimulus (l5% sucrose solution) and for olfactory stimuli (1.33-and 5.0-ppm pyridine solutions). Subjects inThe authors' mailing address is: Department of Psychology, Baylor University, Waco, Texas 76798. several expe...

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Conditioned taste aversion was demonstrated to result from a US-CS, or "backward," conditioning procedure using a 75-mg/kg cyclophosphamide injection as the US. The magnitude and resistance to extinction of the conditioned taste aversion was found to decrease monotonically when the US·CS lSI was systematically varied from 1.0 min to 4 h. In this respect and in the inconclusive nature of the signs of sickness following US administration, cyclophosphamide appears to act similarly to ionizing radiation in conditioning taste aversions. It was argued that these results reflect truly associative, not pseudoconditioned, avoidance responses.