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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Resistance to extinction of conditioned odor perceptions: Evaluative conditioning is not unique.

A tasteless odor will smell sweeter after being sampled by mouth with sucrose and will smell sourer after being sampled with citric acid. This tasty-smell effect was found in experiments that compared odor-taste and color-taste pairings. Using odors and colors with minimal taste (Experiment 1), the authors found that repeated experience of odor-taste mixtures produced conditioned changes in odor qualities that were unaffected by intermixed color-taste trials (Experiment 2). An extinction procedure, consisting of postconditioning presentations of the odor in water, had no detectable effect on the changed perception of an odor (Experiments 3 and 4). In contrast, this procedure altered judgments about the expected taste of colored solutions. Evaluative conditioning (conditioned changes in liking) is claimed to be resistant to extinction. However, these results suggest that resistance to extinction in odors is related to the way they are encoded rather than to their hedonic properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Children's Hedonic Judgments of Cigarette Smoke Odor: Effects of Parental Smoking and Maternal Mood.

Age-appropriate tasks were used to assess 3- to 8-year-old children's liking, identification, and preference for a variety of odors, including that of exhaled cigarette smoke. Children whose parents smoke took longer to decide whether they liked the cigarette odor and were significantly more likely to prefer the odor of cigarette to the neutral and unfamiliar odor of green tea compared with children of nonsmokers. Among children of smokers, relative preferences for the cigarette odor were related to maternal mood disturbance and depression scores. These findings suggest that some early learning about cigarette smoke odor is based on sensory experiences at home and anchors it to the emotional context in which their mothers smoke. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Effect of Verbal Context on Olfactory Perception.

Three experiments were conducted to examine how verbal context and sensory stimulation interact to influence odor hedonic perception. Eight common odors were presented in their natural and synthetic forms, and verbal labels designating name and source (natural, synthetic) information were either explicitly given, self-generated, falsely provided, or not provided. Results revealed that verbal information about source influenced hedonic ratings whether or not the odorant itself was also present. When odorants were presented without verbal labels, olfactory evaluations were based in sensation. Name and source information contributed different levels of meaning and influence to perceptual evaluations. The findings are discussed with reference to an experiential-collocation model for odor-label interactions and a dual-coding hypothesis for olfactory perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Separate signals for orthonasal vs. retronasal perception of food but not nonfood odors.

There is a controversy concerning whether smelling via the nose (ortho-nasally) or the mouth (retro-nasally) represent two routes to the same modality or two distinct submodalities. Since olfactory coding is dependent upon experience, and since food odors are experienced retro-nasally, the authors tested the hypothesis that whether an odor represents a food may influence whether sensation via the two routes leads to separable responses. The authors demonstrate that salivary response to food odors decrease with repeated presentation and show that this response rebounds upon presentation of a novel food odor via the same route and upon presentation of the same food odor via a novel route. This finding indicates that the novel odor and the novel route represent distinct sensory signals. This effect is specific, in that it does not depend on differences in odor intensity or pleasantness and is selective, in that it occurs for food odors but not for equally pleasant and intense nonfood odors. These results demonstrate that separable signals are generated for the same food odor depending upon route and support the existence of category-specific processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age-related changes in children's hedonic response to male body odor.

Male sweat smells disgusting to many adults, but it is unclear whether children find it so. In Experiment 1A, children (mean age=8.7 years) and adolescents (M=16.6 years) smelled male sweat and other odors, rated each for liking, and attempted their identification. Only female adolescents disliked male sweat and could identify it. Experiment 1B, using the same procedure, obtained this gender difference in adults (M=26.7 years). In Experiment 2, children (M=8.1 years) and adolescents (M=16.6 years) were cued about the identity of the same odors. Irrespective of gender, adolescents disliked male sweat more than did children. In sum, dislike for the odor of male sweat may be an acquired social response that is based on odor identification. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Affect and memory: Effects of pleasant and unpleasant odors on retrieval of happy and unhappy memories.

Interpretation of studies of induced mood and memory is complicated by the fact that mood induction procedures may elicit mood-related cognition in addition to mood per se. We used odors to produce positive and negative experiences with minimal cognitive involvement. College women recalled memories cued by neutral words while exposed to a pleasant odor, unpleasant odor, or no odor. Subjects then rated their memories as to how happy or unhappy the events recalled were at the time they occurred. Subjects in the pleasant odor condition produced a significantly greater percentage of happy memories than did subjects in the unpleasant odor condition. When subjects who did not find the odors at least moderately pleasant or unpleasant were removed from the analysis, more pronounced effects on memory were found. The results suggest that congruence between the general hedonic tone of current experience and that of material in long-term memory is sufficient to bias retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Similarity in the qualities of individual odors among kin and species in Turkish (Mesocricetus brandti) and golden (Mesocricetus auratus) hamsters.

In this investigation, the authors used habituation techniques to explore similarities and differences in the qualities of individual odors from hamsters. In Experiment 1, male Turkish hamsters (Mesocricetus brandti) treated flank-gland odors of 2 males from 1 litter as similar compared with the odor of a male from another litter, whether the odor donors were familiar or unfamiliar. At the same time, the Turkish hamsters discriminated between the subtle differences in the individual odors of their familiar brothers. In Experiment 2, male Turkish and golden hamsters (Mesocricetus auratus) treated the flank-gland odors of 2 unfamiliar, unrelated conspecifics as similar compared with the flank odor of a heterospecific individual. The results suggest that similarities in individual odors are related to genetic similarity of the odor donors. These similarities could provide a basis for different types of social recognition, including kin and species recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of cognitive and affective processing in a transgenic mouse model of cortical-limbic neuropotentiated compulsive behavior.

Obsessive compulsive disorder (OCD) may involve abnormal cortical-limbic processing or responsiveness. Mice with behaviors resembling the symptoms of OCD and related disorders were made by expression of a neuropotentiating cholera toxin (CT) transgene in cortical-limbic D1 receptor-expressing neurons. Because these D1CT mice express CT in the piriform cortex and amygdala (major cognitive and affective olfactory processing areas) it was tested whether abnormal odor perception, discrimination, or responsiveness facilitates their compulsion-like behavior. The mice exhibited normal olfactory discriminative capability. An anxiogenic odor potentiated their abnormal repetitive leaping, but novel or familiar nonthreatening odors did not. These data suggest that compulsions can be triggered not by impaired cortical-limbic processing but by increased cortical-limbic responsiveness, particularly to sensory or cognitive stimuli with affective properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Representations of odors in the rat orbitofrontal cortex change during and after learning.

Cells in the orbitofrontal cortex (OF) respond to odors and their associated rewards. To determine how these responses are acquired and maintained, the authors recorded single OF units in rats performing an odor discrimination task. Approximately 64% of all cells differentiated between rewarded and nonrewarded odors. These odor valence responses changed during learning in 26% of all cells, and these changes were positively correlated with improving performance, supporting the idea that the information provided by these cells is used in learning the task. However, changes in odor valence responses were also observed after learning, and included not only increases in odor discrimination, but also decreases or mixed increases and decreases. Thus, only some of the changes in firing reflected acquisition of the task. The results suggest that learning triggers a continuing reorganization of OF neural ensembles representing odors and their rewards. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Carbohydrate-conditioned odor preferences in rats.

The effectiveness of odor cues to support nutrient-conditioned flavor preferences in rats was studied. When the rats drank fluid, the CS+ odor was paired with intragastric (IG) infusions of Polycose, and the CS– odor with IG water. In Experiment 1, rats trained with almond and anise odors presented with plain drinking water failed to acquire a CS+ odor preference. In contrast, rats in Experiment 2 formed a strong aversion to anise (or almond) paired with lithium chloride, which indicated that the odors were distinguishable to the rats. Experiment 3 showed that providing unique tastes (bitter or sour) in combination with the odors during training potentiated odor conditioning. The rats displayed a strong preference for the odor?+?taste CS+ and for the odor component alone. Experiment 4 showed that with another pair of odors (peppermint and vanilla), CS+ preferences could be conditioned in the absence of taste cues during training. These results demonstrate that rats can acquire strong nutrient-conditioned odor preferences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interactions between conditioned and unconditioned flavor preferences.

Five experiments investigated how rats' conditioned preferences or aversions for aqueous odors paired with sucrose or salt are affected by their unconditioned response to those tastes. Rats preferred an odor paired with 30% sucrose over an odor paired with 5% sucrose when both were presented in 5% sucrose, but they showed no preference or, if thirsty, showed the reverse preference, when the odors were presented in 30% sucrose. These changes in conditioned preference corresponded to changes in the rats' unconditioned preference for the accompanying sucrose solution. Rats' conditioned aversions for odors paired with salt showed a similar dependence on their reaction to the accompanying salt solution. The results were interpreted as showing that conditioned and unconditioned flavor preferences combine additively, as if mediated by the same sensory representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A honeybee's ability to learn, recognize, and discriminate odors depends upon odor sampling time and concentration.

Animals sample sensory stimuli for longer periods when they must perform difficult discrimination tasks, implying that the brain's ability to represent stimuli improves as a function of time. Although it is true in other senses, few studies have examined whether increasing sampling time improves olfactory discrimination. In the experiments reported here, odor sampling time was controlled with the goal of testing whether odor concentration affected a honeybee's ability to learn, recognize, and discriminate odors. Increasing sampling time during conditioning and testing improved a honeybee's ability to learn, recognize, and differentiate low-concentration (0.0002 M) odors. For intermediate-concentration (0.02 M) odors, both acquisition and recognition improved when stimulus duration was longer, but discrimination was unaffected. Having longer to sample a high-concentration (2.0 M) stimulus also improved acquisition, but it did not affect the ability to recognize or differentiate odors. Differences in time to respond to the conditioned and novel odors during the test period depended on the difficulty of the discrimination task. The results suggest that the sensory coding of molecular identity takes longer for low-concentration odors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention and habituation: Odor preferences, long-term memory, and multiple sensory cues of novel stimuli.

Investigation of and habituation to novel stimuli are part of exploratory behavior of rodents. They are necessary for assessing the environment in seeking food and sexual partners and in avoiding predators. Six experiments tested male and female Mongolian gerbils (Meriones unguiculatus) in a stimulus-elicited investigation paradigm. Findings indicate that (1) Ss initially showed preference for odors of strange male bedding and for odors of home cage bedding and then habituated. There was no preference between these 2 odors, although they could be discriminated. The complex odor stimulus elicited more response than any of the components tested. (2) Memory of an object or odor was demonstrated up to 4 wks later. (3) Sensory deprivation by blinding, anosmizing, or removing somatosensation of the upper snout made only small differences in investigation. The removal of any 2 of these sensory inputs produced more interference with the response, but all Ss investigated the stimulus. It is concluded that attention to novelty and habituation after repeated exposure are very robust behaviors and are mediated through multiple sensory channels. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of the hippocampus in memory for the temporal order of a sequence of odors.

Memory for the temporal order of a sequence of odors was assessed in rats. A sequence of 5 odors mixed in sand was presented in digging cups, 1 at a time, to each rat in a sequence that varied on each trial. A reward was buried in each cup. After the 5th odor, 2 of the previous 5 odors were presented simultaneously; to receive a reward, the rat had to choose the odor that occurred earliest in the sequence. Temporal separations of 1, 2, or 3 represented the number of odors that occurred between the 2 odors in the sequence. Once a preoperative criterion was reached, each rat received a hippocampal (HIP) or cortical control lesion and was retested on the task. On postoperative trials, the HIP group was impaired relative to controls. However, the HEP group could discriminate between the odors. The data suggest that the hippocampus is involved in separating sensory events in time so that 1 event can be remembered separately from another event. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual learning in olfaction: professional wine tasters versus controls

By having professional wine tasters and controls perform olfactory tasks of absolute detection (1-butanol), discrimination (lemon and cloves), and identification (common household odors), the present two experiments studied (a) if perceptual odor learning takes place from odor experience acquired under nonlaboratory conditions, (b) if this learning generalizes to odors for which experience is limited, and (c) if generalized learning can be referred to increased general interest for odors that increases attention to odorous features. The results showed that whereas wine tasters were not better than controls on detection, they were superior to controls on discrimination and identification, the latter due to only a few odors. Ratings of experience with certain odors during professional evaluation suggest that generalized perceptual learning may take place in discrimination but not in identification. Wine tasters did not show more general interest for odorous features than did controls. The nonsuperiority in detection may be explained by the fact wine tasters have no professional experience of a detection task per se, implying that perceptual odor learning does not generalize from the olfactory tasks of discrimination and identification to detection.     

Odor preferences of female house mice (Mus domesticus) in seminatural enclosures.

Preferences for male odors by female house mice (Mus domesticus) were examined with respect to age, dominance status, and spatial relationships. Mice were free living in 6 field enclosures. Estrous or nonestrous females were placed in an aquarium with soiled bedding from live traps as the odor source. Females were tested for preferences between (1) adult and juvenile male odors, (2) dominant and subordinate male odors, and (3) "near" and "far" male odors. In dominance odor tests, estrous females preferred odors from dominant males; nonestrous females exhibited no significant preferences. In adult juvenile and spatial odor tests, there were no significant differences between odor preferences of estrous and nonestrous females. However, most females preferred odors from adult and "near" males. Male dominance status appears to be the strongest influence on female odor preference in these seminatural enclosures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enrichment to odors improves olfactory discrimination in adult rats.

The authors tested how prior odor enrichment affects the spontaneous discrimination of both preexposed and novel odors. Experimental rats were exposed to single odors or to pairs of similar or dissimilar odors for 1-hr periods twice daily over 20 days. Spontaneous discriminations between pairs of similar odors were tested before and after the odor exposure period using an olfactory habituation task. The authors found that (a) experimental rats did not spontaneously discriminate similar odor pairs before the exposure period, whereas they spontaneously discriminated them after the enrichment period, and (b) the improvement of performance was not selective for the odors used during enrichment. These results show that odor experience changes perception in the manner predicted based on other groups' electrophysiological experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential unfolding of novelty and pleasantness appraisals of odors: Evidence from facial electromyography and autonomic reactions.

We investigated the effects of odors on appraisal processes and consequent emotional responses. The main goal was to test whether an odor is detected as novel or familiar before it is evaluated as pleasant or unpleasant. Participants performed a recognition task in which they were presented with pairs of unpleasant or pleasant odors (sample and target odors). Within a pair, the sample and target were either identical or different to assess participants’ novelty detection; unpleasant and pleasant target odors were contrasted to examine participants’ appraisal of intrinsic pleasantness. We measured facial expressions using electromyography and physiological reactions using electrocardiogram and electrodermal activity in response to odors. The earliest effects on facial muscles and heart rate occurred in response to novelty detection. Later effects on facial muscles and heart rate were related to pleasantness evaluation. This study is the first to demonstrate the existence of a sequence of appraisal checks for odors eliciting emotional reaction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chemical dependencies of learning in the rabbit olfactory bulb: Acquisition of the transient spatial pattern change depends on norepinephrine.

Intracerebral cannulas were implanted in both olfactory bulbs of 6 New Zealand albino rabbits. A surface electrode array was implanted epidurally on the lateral surface of the left bulb. Each S was conditioned to respond to sniffing to an odor paired with cutaneous shock while receiving continuous intrabulbar infusion of propranolol (100 μM at 1 μl/hr) or vehicle. After 2 training sessions to the original odor, a response to a new odor was conditioned under the influence of the alternate infusate. EEG activity was sampled on inspirations before and during odor presentations. During vehicle infusion a transient alteration in the pattern of activity was acquired that occurred during the 2nd and 3rd inspirations following presentation of the reinforced odor. The acquisition did not occur when propranolol was infused. No significant pattern changes occurred with unreinforced odors in either condition. Intrabulbar norepinephrine injection (100 μM) resulted in an amplitude increase of the bulbar 40–80 Hz EEG and a potentiation of the transient spatial pattern change to a novel odor, when compared with those observed during vehicle infusion. It is concluded that norepinephrine released under centrifugal control may act to prevent or delay habituation that otherwise occurs rapidly to unreinforced odors. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)