Very long-term memory for odors: retention of odor-name associations.

The ability to remember odor-name associations for recent odors (those associated with everyday products experienced within the past 2 years) and distant odors (those associated with children's toys not encountered for 3 years or more) was examined in two experiments. In recognition tasks, subjects attempted to match odor names to odors, or odors to odor names. In a recall task, subjects tried to identify odors by name. The results showed that although odor retention was better for recent than distant odors, significant retention remains for odors not experienced since childhood. These results are consistent with other studies that found very slow and gradual loss of odor information in memory. They extend that research by showing that odor information is still available over a much longer period of time.     

The influence of chemical complexity on the perception of multicomponent odor mixtures

The present study investigates the hypothesis that complexobject odors (odors that emanate from flowers, foods, sewage, etc.) that consist of dozens of odorants are processed and encoded as discrete entities, as if each was a single chemical odor. To test this hypothesis, the capacity of trained subjects to discriminate and identify the components of stimuli consisting of one to eight object odors was determined. The results indicated that subjects could only identify up to four object odors in a mixture, which is similar to earlier findings with mixtures that contained only single chemical odors. The limited capacity was also reflected in the number of odors selected, regardless of whether the choices were correct or incorrect, in confidence ratings, and in decision times. The identification of a limited number of object odors in every mixture that was presented suggests that both associative (synthetic) and dissociative (analytic) processes are involved in the perceptual analysis of odor mixtures.     

Novel odors evoke risk assessment and suppress appetitive behaviors in mice

The effects of four novel odors on risk assessment by mice (i. e., flat back approach, stretched attention, immobility) and the suppression of appetitive behaviors were examined in two experiments. When novel odors were presented in a straight runway, subjects spent significantly less time in the odor compartment, relative to controls, when it contained sheep wool, chocolate, or citronella (but not cat fur) odors. Risk assessment behaviors occurred at similar levels among all groups and appetitive behaviors were not suppressed by the novel odors. When odorants were scattered over one half of the subjects' home cage floor in Experiment 2, all novel odors increased the duration of at least on e risk assessment measure and/or suppressed appetitive behaviors (i. e., eating, grooming, rearing). The results clearly reveal that a reasonably wide range of novel odors evoke at least some level of risk assessment which presumably reflects increased fearfulness. The odors of sheep wool and cat fur induced a wider range of such responses than did chocolate or cinnamon suggesting that mammalian odors may be particularly effective stimuli. If so, however, it is clear that predator odors are not uniquely effective in this regard. Experiment 1 also underscores the importance of the testing environment in assessing the behavioral effects of novel odors in mice. © 1993 Wiley-Liss, Inc.     

Iranian Herbalists,But Not Cooks,Are Better at Naming Odors Than Laypeople

Odor naming is enhanced in communities where communication about odors is a central part of daily life (e.g., wine experts, flavorists, and some hunter‐gatherer groups). In this study, we investigated how expert knowledge and daily experience affect the ability to name odors in a group of experts that has not previously been investigated in this context—Iranian herbalists; also called attars—as well as cooks and laypeople. We assessed naming accuracy and consistency for 16 herb and spice odors, collected judgments of odor perception, and evaluated participants' odor meta‐awareness. Participants' responses were overall more consistent and accurate for more frequent and familiar odors. Moreover, attars were more accurate than both cooks and laypeople at naming odors, although cooks did not perform significantly better than laypeople. Attars' perceptual ratings of odors and their overall odor meta‐awareness suggest they are also more attuned to odors than the other two groups. To conclude, Iranian attars—but not cooks—are better odor namers than laypeople. They also have greater meta‐awareness and differential perceptual responses to odors. These findings further highlight the critical role that expertise and type of experience have on olfactory functions.     

Recall of odors: naming and autobiographical memories illustrate odor aftereffects

In the study phase, subjects had to encode either odors or the names there of by generating autobiographical memories, by judging the quality of the food source of the odors, or by labeling responses to odors. At the testing stage, explicit and implicit olfactory memory performance was assessed. With recognition testing, the provision of odors at study improved performance. Furthermore, recognition depended on elaborative encoding conditions with olfactory stimuli only. Implicit memory was measured by the correctness and speed of labeling responses at the testing stage. Old odors were named more correctly and faster than new ones, but only if subjects had encoded odors in the study phase. These results demonstrate that implicit memory in naming odors depends on olfactory stimulus processing and is not a purely verbal priming effect. As a further measure of implicit memory, the speed of autobiographical memory productions was assessed. We registered shorter reaction times for old versus new odors. But again, this effect of implicit memory was restricted to conditions of odor pre-experiences in the study phase. We conclude that olfactory memory is based on different types of memory traces. Implicit memory measures may prove to be useful in isolating sensory and other attributes of olfaction that seem to be interacting in making explicit memory judgments.     

Recognition of odors and identification of sources

The purpose of the present study was to investigate the accuracy of the memory for odors and for the location of odors. In Experiment 1, 5 unfamiliar odors were presented in each of 2 rooms. Twenty participants were instructed to remember only the odors (odor-only control group) and 20 were instructed to remember both the odors and the room where the odors were presented (odor place group). In Experiment 2, both the odor presentation room and the sex of the experimenters were manipulated to increase the uniqueness of the odor location. The results demonstrated that the memory for an odor is superior to the memory for the location of an odor. The results also indicated that the intention to learn the sources of an odor improves the memory for the source. These results are discussed in the context of the source monitoring framework.     

Verbal coding in olfactory versus nonolfactory cognition

Two paired-associate memory experiments were conducted to investigate verbal coding in olfactory versus nonolfactory cognition. Experiment 1 examined the effects of switching/not switching odors and visual items to words between encoding and test sessions. Experiment 2 examined switching/not switching perceptual odors and verbal-imagine versions of odors with each other. Experiment 1 showed that memory was impaired for odors but not visual cues when they were switched to their verbal form at test. Experiment 2 revealed that memory was impaired for both odors and verbal-imagine cues when they were switched in format at test and that odor sensory imagery was not accessed by the instruction to imagine a smell. Together, these findings suggest that olfaction is distinguished from other sensory systems by the degree of verbal coding involved in associated cognitive processing.     

Recognition of common odors,pictures, and simple shapes

Recognition of common odors and simple shapes decayed in a similar manner over the course of 4 months. Recognition of complex pictures was uniformly higher than recognition of the odors and simple figures, although the distractors for these stimuli were much less similar than for the odors or simple shapes. Recognition of these common odors was the same as recognition performance on single chemicals used in previous studies. These results suggest that simple chemicals and complex familiar odors are encoded or remembered in a similar fashion, and that visual stimuli exist which are encoded in a similar manner to odors, possibly as unitary images with few features.     

Do infusion-related tastes and odors facilitate the development of anticipatory nausea? A failure to support hypothesis

Distinctive tastes and odors have been identified as potent nausea-eliciting stimuli in cancer chemotherapy patients who develop anticipatory nausea or vomiting (ANV). Based on the experimental research on illness-aversion learning and based on previous clinical research with chemotherapy patients, it was hypothesized that the presence of tastes and odors during infusions should increase the likelihood that a patient will subsequently develop ANV. Seventy-eight new chemotherapy outpatients were interviewed immediately following each of their infusions with regard to the experience of infusion-related tastes, odors, and body sensations. Results failed to support the hypothesis. The subsequent development of ANV was unrelated to reports of tastes and odors both during patients' initial two chemotherapy infusions and during the two infusions preceding their initial report of ANV. Furthermore, reports of tastes and odors were surprisingly infrequent relative to previous research. Methodological and environmental explanations for this difference in taste and odor prevalence are considered. It is concluded that, when present, infusion-related tastes and odors may indeed increase the likelihood of subsequent development of ANV. However, future research should examine the extent to which the physical characteristics of chemotherapy clinics might affect the prevalence of infusion-related tastes and odors.     

Effects of prior agonistic experience on risk assessment and approach behavior evoked by familiar or unfamiliar conspecific odors

Risk assessment and appetitive behaviors in response to familiar and unfamiliar conspecific odors were measured in mice rendered dominant or subordinate by a series of resident-intruder encounters. Subordinate mice showed elevated levels of risk assessment in response to the odors of both familiar dominant and unfamiliar males. These behaviors were almost totally absent among dominant males exposed to familiar subordinate or unfamiliar male odors. Subordinate mice showed a marginally significant elevation in latencies to approach familiar, but not unfamiliar, dominant odors. Dominant and subordinate mice spent comparable amounts of time in the cage area containing familiar antagonist odors, however, and the durations of subordinates were mildly elevated, rather than decreased, when unfamiliar conspecific odors were present. There were no group differences in any of the appetitive behaviors. These findings suggest that apparent preferences for conspecific odors may arise from quantitatively and/or qualitatively differing emotional states. The inclusion of risk assessment measures is suggested to be a useful adjunct for studies of olfactory preference/rejection. © 1994 Wiley-Liss, Inc.     

Olfactory Information Processing and Temporal Lobe Epilepsy

It has been suggested that olfactory information processing is impaired in patients with temporal lobe epilepsy. However, the existing evidence is not wholly in accordance with this notion. Patients with epileptogenic foci in the left temporal lobe, the right temporal lobe, or other brain regions were compared with normal control subjects in the identification and retention of common odors. All three patient groups were substantially and equally impaired in verbally labelling the odors in question. The patients with epilepsy associated with the left temporal lobe or with nontemporal regions showed no sign of any impairment on a test of immediate recognition memory for common odors. However, the patients with epilepsy associated with the right temporal lobe showed a specific disturbance in their retention of nameable odors. It is suggested that the latter patients were selectively impaired in their retrieval of the episodic memories which provide the context for the encoding of distinctive odors.     

Responses of dominant and subordinate male rats to the odors of male and female conspecifics

The resident-intruder paradigm was used to examine the effects of social dominance and individual recognition on odor preferences and urine-marking in male rats. Resident males were significantly more aggressive than intruders and spent more time investigating the odors of familiar intruders. Resident males urine-marked most over the odors of females and familiar intruders while intruders marked least over the odor of the familiar resident. Intruders did not avoid investigating nor marking over the odors of familiar resident males or other conspecifics. These results suggest that individual odors of male rats may be more salient than a general odor of dominance, and that the dominant males increase their investigation and marking over the odors of familiar subordinates but not unfamiliar subordinates. The importance of olfactory learning during aggressive interactions is discussed.     

Responses to olfactory stimuli in spotted hyenas (Crocuta crocuta): I. Investigation of environmental odors and the function of rolling

Olfaction is crucial to spotted hyenas (Crocuta crocuta), yet there are no controlled studies of their reactions to odors. In Experiment 1, the authors examined responses of captive hyenas to various environmental (prey, nonprey animal, and plant) odors. Subjects approached and sniffed all odors equally but preferentially licked prey odors, scent marked next to odors, and rolled in animal-based odors. In Experiment 2, the authors examined the function of rolling by applying odors to the pelts of captive hyenas. When hyenas wore carrion, they gained positive social attention (increased investigation and allogrooming) from pen mates, but when they wore camphor, the normal social greeting ceremony was curtailed. Thus, olfactory stimuli elicit specific responses, influence where behavior is directed, and can be used to affect social interaction.     

Effects of novel odors on intermale attack behavior in mice

Offensive, defensive, and nonagonistic social behaviors of resident male mice toward unfamiliar intruders were examined during exposure to the novel odors of chocolate or sheep's wool. Both novel odors reduced lateral attacks and boxing when compared to familiar sawdust odor. Chocolate, but not sheep's wool, also reliably increased flight behavior by residents. Neither social behaviors nor self-grooming were affected by these odors. The novel odors had no effect upon, or actually decreased, the defensive responses of intruders towards residents. The equivalent effectiveness of both predator and nonpredator odors in elevating risk assessment and suppressing attack during firsttime exposure, and the decreased potency of cat odors following repeated exposure, suggests that novelty contributes to the enhanced defensiveness seen among subjects during initial exposure to predator odors. © 1995 Wiley-Liss, Inc.     

The role of the dorsal CA1 and ventral CA1 in memory for the temporal order of a sequence of odors

Memory for the temporal order of a sequence of odors was assessed in male rats. A sequence of five odors mixed in sand was presented in digging cups one at a time to each rat in a sequence that varied on each trial. A reward was buried in each cup. Following the fifth odor, two of the previous five odors were presented simultaneously and the rat needed to choose the odor that occurred earliest in the sequence to receive a reward. Temporal separations of 1, 2, or 3 were used which represented the number of odors that occurred between the two odors in the sequence. Once pre-operative criterion was reached, rats received a control, dorsal CA1 (dCA1), or ventral CA1 (vCA1) lesion and were retested on the task. On post-operative trials, only the vCA1 group was impaired relative to both control and dCA1 groups. All groups of rats could discriminate between the odors. The data suggest that the vCA1, but not dorsal CA1, is involved in separating sensory events (odors) in time so that one odor can be remembered separate from another odor.     

Implicit and explicit memory for odors: Hemispheric differences

In two experiments, implicit and explicit tests were used to investigate the lateralization of odor memory. Odors were at all times presented monorhinically. At test, odors were presented to either the ipsi- or the contralateral side of the nostril used for inspection. In Experiment 1, participants were first primed to a set of odors. At test, response latencies for odor identification were measured. The results were that priming odors tested via the left but not the right nostril were identified faster than control odors. In Experiment 2, a similar design probed episodic recognition memory. Memory performance did not differ between the left and right nostrils, but the measures of response latency favored the right side. The study demonstrates that it is possible to tap differences in memory performance between the cerebral hemispheres through monorhinic presentation of odors in healthy persons, and that these differences depend on the test nostril rather than the inspection nostril.     

Hedonic and sensory characteristics of odors conditioned by pairing with tastants in humans

Animals readily acquire positive odor-taste hedonic associations, but evidence for this in humans remains weak and was explored further. Retronasal pairing of odors with sucrose or salty stimuli (Experiment 1) increased the rated sweetness of sucrose-paired odors without altering liking, although changes in odor pleasantness correlated with sucrose liking. Experience of odors with sucrose or quinine by sweet likers (Experiment 2) found increased pleasantness and sweetness for sucrose-paired odors, whereas quinine-paired odors became less liked and more bitter. Odor-sucrose pairings in sweet likers and dislikers (Experiment 3) found increased sweetness in both groups but increased odor liking only in likers. These data suggest that evaluative and sensory learning are dissociable and that evaluative changes are sensitive to individual differences in sweet liking.     

Behavioral modulation induced by food odor aversive conditioning and its influence on the olfactory responses of an oscillatory brain network in the slug Limax marginatus

We compared behaviorally and physiologically the olfactory responses of slugs (Limax marginatus) that had been subjected to aversive, appetitive, or unpaired training with food odors (carrot or cucumber). In the aversive training, the slugs were exposed to the food odor as a conditioned stimulus (CS), and then quinidine sulfate solution as an unconditioned stimulus (UCS) was immediately applied to the lip of the slugs. This training caused a decrease in preference level for the CS. The unpaired training, in which the CS and the UCS were presented to the slugs with a 5-min interval, induced no change in the preference level for the CS. In the appetitive training, the slugs were allowed to eat the CS odor source without UCS application. When we used nonstarved slugs, it was found that the preference level for the CS increased upon the appetitive training. These results indicate that each training changed the preference for the odors in a characteristic manner. In the physiological experiments, we used brain-inferior tentacular nose preparations isolated from slugs and investigated the olfactory responses of the oscillations in the local field potential (LFP) of the procerebral (PC) lobe. We found that odor presentation induced various types of changes in the LFP oscillation frequency, although the rate of occurrence of the frequency modulation differed between odors used in the aversive and the unpaired training (aversive-conditioned and unpaired odors). The aversive-conditioned odors induced a decrease in the oscillatory frequency. Unpaired odors did not change it. Moreover, odors used in the appetitive training (appetitive-conditioned odors) induced an increase in the frequency. Thus, it was considered that those modulations of PC lobe oscillatory activity were independent of odor and reflected learned preference for odors.