Trygg Engen

Odor memory: Review and analysis

We critically review the cognitive literature on olfactory memory and identify the similarities and differences between odor memory and visual-verbal memory. We then analyze this literature using criteria from a multiple memory systems approach to determine whether olfactory memory can be considered to be a separate memory system. We conclude that olfactory memory has a variety of important distinguishing characteristics, but that more data are needed to confer this distinction. We suggest methods for the study of olfactory memory that should make a resolution on the separate memory system hypothesis possible while simultaneously advancing a synthetic understanding of olfaction and cognition.

Individual psychophysical functions for 28 odorants

Individual scales of odor intensity were obtained for 28 different chemical compounds by the method of magnitude estimation. Eleven Ss participated in an experiment with 196 olfactory stimuli which differed in both quality and intensity. It was found (1) that power functions described the relationship between partial vapor pressure of the odorants and their subjective odor intensity for all Ss, (2) that all exponents were less than one but varied greatly between Ss, (3) that consistent intraindividual differences in the exponents of different odorants exist, and (4) that these are attributable to perceptual differences rather than to response bias.

PSYCHOPHYSICAL SCALING OF ODOR INTENSITY AND QUALITY

Psychophysical descriptions of sensation are usually derived from the variability of responses, for example, the energy difference an observer can detect on 50 per cent of the trials. This paper will summarize some experiments with the relatively new direct psychophysical scaling methods (Stevens, 1958). All of these methods instruct the observer to judge psychological or apparent magnitudes of stimuli directly on a numerical ratio scale. These methods are called direct because there is but a short step between the observer’s response and the final scale, namely, a simple averaging of his responses to each stimulus. The simplicity of these new methods makes them particularly useful in the study of olfaction, for scaling of odors with the classical indirect methods is a very slow and difficult process. This paper presents a summary of such direct scaling experiments. Groups of 10 or more men and women served as observers in these experiments; some of them served in more than one experiment. The observers were advanced undergraduate and graduate students in psychology, and all of them had some previous experience in psychophysical experiments. The experiments were performed in a ventilated room where the temperature was maintained at 20 to 22” C. and humidity, 50 to 60 per cent. Various odorants were used, but most of the research has been with amyl acetate, heptanal, and a series of homologous alcohols. Geometric dilution series were prepared by pipette with either benzyl benzoate or diethyl phthalate, such that the strongest stimulus contained 100 per cent of a particular odorant, the next strongest, 50 per cent of the odorant and 50 per cent of the dilutent, the next, 25 per cent odorant and 75 per cent dilutent, etc. This procedure provides a reasonably good psychological scale unit (Beck et al., 1954). One cc. of the mixture was kept in a 10 X 75 mm. test tube stopped with an aluminum-wrapped cork. The observers sniffed the solution from a little wad of cotton attached to a glass rod which was fastened to the cork inside the test tube. Sniffing odors from cotton seems to be relatively easy and “natural” for the observers, and comparison of data indicates that this procedure improves the reliability of judgments over sniffing the solutions from the test tubes themselves. Duplicate sets of stimuli were often used simultaneously in order to minimize identification of certain stimuli by incidental marks on the test tubes which might have been overlooked by the experimenter. All experiments started with detailed instructions to the observer about what attribute of the stimulus he should judge and how he should judge it, i.e., to sniff consistently, judge only intensity (or quality) and not pleasantness, and that he should make each judgment independent of previous judgments. This was followed by several practice trials. The observer was allowed to work at his own speed and could repeat observations but only after a rest period of at least one minute. There was a longer rest period after about 15 judgments. The stimuli were presented in irregular orders and standard procedures were followed in counterbalancing experimental conditions. Typically, two days elapsed between conditions for a n individual observer.

Perception of odor and irritation

Abstract Compared with visual and auditory perceptions, smells, which in the colloquial sense include both odor and irritation, are often difficult to identify by name and are therefore not well processed cognitively— and yet they persist as disquieting feelings of arousal. These two factors, the persistence and poor semantic identification, form the basis for the strong impact of environmental smells associated with environmental stimulation. The literature of experimental psychology, anatomy, physiology and epidemiology relevant to perception of odor, mediated by the olfactory nerve, and irritation, mediated by the trigeminal nerve is reviewed. It is proposed that the two perceptions are higly interelated and that while anatomically different structures are involved in such environmental stimulation, perceptions are not so readily categorized. In the most simple case, whether or not odor or irritation is experienced depends on the strength of the stimulus. But it is usually more complex than that because perception is affected by the environmental context, facilitation and inhibition by other stimulation, and the state of adaptation of the perceiver. In addition, there are three important differences between odor perception and irritation. One is that the reaction time to odor is shorter than that of irritation, but this observation is perhaps of limited application to practical field research. The second is that while odors persist, they do show adaptation after prolonged exposure and, in particular, habituation. By contrast, the distinguishing characteristic of irritation is that it shows neither habituation nor adaptation. The third, partly as a consequence of these two, is that while odor perception is more sensitive and functions to arouse explorative behavior, learning, and odor memory, irritation has a general and direct effect on behavior, involving respiration, cutaneous effects, and potential pathological consequences. Odor per se does not make one sick. Evidence of effects on behaviour beyond mere perception, reinforces the need for a broader approach to problems such as mental fatigue and other performances which appear to be affected by smell.

The effect of adaptation on odor detection

The sensitivity of human Ss to a weak odor (hydrogen sulphide) following prior exposure to it varying in both duration (0–5 min) and concentration (4.05 × 10−7 to 24.40 × 10−7 mg/liter) was studied with a yes-no detection method and a specially designed olfactometer. The effect of adaptation was demonstrated, because the proportion of hits was lower the higher the concentration of the adaptation stimulus, when the response criterion, as measured by the proportion of false alarms, was fairly constant. By contrast, the proportion of hits was apparently independent of the duration of the exposure to the adaptation concentration. This finding suggests that the sense of smell is more stable than is usually believed. The paper ends with a discussion of the importance of considering adaptation in contemporary detection theory.

Facilitation of olfactory detection

Olfactory sensitivity to n-aliphatic alcohols was determined by use of a yes-no signal detection procedure. The values of d’ for these compounds indicated higher sensitivity and less variability than has been shown previously by classical threshold methods. Self- and cross-adaptation studies demonstrated the usual decrement in sensitivity to one stimulus, following exposure to another stimulus, and in addition, cross-facilitation with certain stimulus pairings. The facilitating effects of one odorant upon the detection of another may be related to the differences in water solubilities of the odorants.

THE POTENTIAL USEFULNESS OF SENSATIONS OF ODOR AND TASTE IN KEEPING CHILDREN AWAY FROM HARMFUL SUBSTANCES

The purpose of the present study was to evaluate the possibility of using odor and taste aversions to inhibit oral manipulation and ingestion of harmful substances by young children. Previous research ir. olfactionl. * had indicated that children show a high degree of tolerance for unpleasant odors, and that differential responses to hedonic attributes associated with the sense of smell seem to be learned rather than inborn. The first experiment reported here extended the selection of odorants used to include some with definite trigeminal effects, with the possibility in mind of using the trigeminal system to elicit inherent defense mechanisms. In the second experiment, measurements of taste preferences were made on the general assumption that taste may be inherently more important for survival than odor and less influenced by age and experience. For example, it seems to be generally assumed that bitter is distasteful to a child regardless of age. In addition, the results of self-selection experiments are often quoted as evidence that the body somehow knows what it needs and knows how to select a diet to satisfy those needs.3.4 Such studies, however, have not tested harmful or even distasteful substances. Children ranging in age from three to six participated in the experiments with approval of their parents, who had complete information about the nature and purpose of the experiments. All children appeared normal, although medical screening was not feasible at the time and place they were observed.

A Comparison of Self-Adaptation and Cross-Adaptation to Odorants Presented Singly and in Mixtures

Fifteen subjects made 450 judgments each by the method of magnitude estimation of dimethyl disulfide and hydrogen sulfide after prior exposure to various mixtures of them. Exposure to the same odorant clearly affected the perceived intensity of it (self-adaptation). By contrast, exposure to the other odorant showed at best a small effect (cross-adaptation). Consistent with this, adaptation to a mixture of the test odorant and another odorant is proportional to the amount of the test odorant in the mixture, and does not exceed that of self-adaptation. These results indicate that olfactory adaptation is specific and that the sense of smell is more robust than generally assumed.

Discrimination of Intonation by Hearing-Impaired Children.

Earlier research has shown that sentence intonation involves frequencies of 500 Hz or less. The present research verified the hypothesis that most hearing-impaired children whose auditory input is limited to those low frequencies do perceive differences in intonation. Their performance was influenced by their response tendencies but was clearly evident across three different acoustic listening conditions and two psychophysical tests. The educational implications of this are discussed briefly.

The human newborn's sucking behavior for sweet fluids as a function of birthweight and maternal weight*

The paper presents previously unpublished data related to the study of Engen, Lipsitt, and Peck (1974) . It assesses the effects of infant birthweight and mothers pregnant weight on a newborns responsiveness to sweet fluids. Heavy mothers tended to give birth to heavy infants, but even when this correlation was partialed out, it was observed that heavy babies sucked at faster rates for a sugar solution than did light babies.