Taste and Smell
Taste and smell are separate senses with their own receptor organs, these cells send signals to specific areas of the brain, which make us. Grain of Salt Popular understanding of the brain holds that it consists of centers for each type of stimuli. There are definitely areas associated with certain types of . But her mother hadn't lived long enough to meet Joe. thought, remembering how he would taste and smell if she buried her nose in the spot just under his ear .
Investigators have documented age-related olfactory impairment through a variety of psychophysical measures, including odor detection, quality discrimination, identification, recognition, estimation of magnitude and estimation of similarity Schemper et al. While compromise of olfactory perception in the elderly is evident in virtually all these measures, odor detection, as reflected in absolute threshold, provides the most fundamental and interpretable index of deficit Stevens and Dadarwala, Even if threshold does not directly measure ability to perceive concentrated stimuli, it does set a framework to evaluate changes in suprathreshold functioning.
In olfactory percep tion studies, a substantial elevation in threshold accompanies diminished perceptual abilities throughout the suprathreshold range [see Stevens and Cain, for a review]. Thus, if the odor threshold in older adults is substantially above that of young adults, then perceived intensity of concentrated odorants would be diminished as well. These studies have varied in methodology number of subjects, psychophysical technique, mode of stimulus delivery, odorant as well as in the characteristics of the subjects age, ethnicity, general health, dental health, geographic residence, place of work.
All of these factors may influence the stability of the olfactory threshold [see Doty, for a review], especially for the elderly Stevens and Dadarwala, Some of these variables were held constant in studies of threshold to 1-butanol with subjects from New Haven, CT. From these studies, threshold differences between young and elderly ranged from fold to fold Cain et al.
A question of interest concerns whether thresholds for olfactory flavor fall within the range found for odors. Delivered in the vapor phase, retronasal olfactory thresholds can exceed orthonasal thresholds Voirol and Daget, The elderly show poor performance in identification of the presence or absence of olfactory flavorings in foods Schiffman, ; Murphy, ; Cain et al. This study proposes a way to measure olfactory flavor thresholds to examine both differences between young and elderly subjects and predictors of threshold level in elderly subjects.
The olfactory flavor threshold test was designed to mimic perceptual experiences of food and be suitable for laboratoryor field-testing. In a simple task, subjects orally palpated a sweetened gelatin with an orange flavoring that varied from subthreshold to threshold concentrations. The first of two studies verified that aging subjects perform substantially below young subjects; the second employed the task in a field study of healthy elderly women to examine predictors of olfactory flavor sensitivity a clinical measure of orthonasal perception, age, and denture status.
The subjects were recruited in New Haven, the young with posters and the elderly through presentations at senior centers.
All subjects professed average or better health for their age. Young subjects were tested in the laboratory and the elderly at their senior centers. The investigation was approved by the University of Connecticut Human Subjects Committee; subjects gave informed consent and received compensation for participation.
Materials The stimulus consisted of a full-strength, water-soluble, blended natural and artificial orange flavoring ProductCultor Food Science, Ardsely, NYwhich was dissolved in a sweetened gelatin base. This flavoring is used commercially to flavor beverages. Subsequent dilutions halved the concentration of flavoring 11 times to produce a series of 12 concentrations weakest member: Pilot testing showed that step 12, a dilution of fold from stock, lay safely under the threshold for most young subjects and step 1 lay above the threshold for most elderly subjects.
By design, the sweet background, 0. The combination of orange and sweet gave the product a more natural character than its unsweetened version would have. The cubes were chilled to 4. The cubes did not present a masticatory challenge, yet felt like food. The addition of the olfactory flavoring did not modify the visual characteristics of the gelatin sample. In order to establish whether discrimination depended on sensory cues other than those from olfaction, two anosmic subjects participated in the entire threshold procedure see below.
These subjects were not able to obtain four correct answers in the discrimination between blanks and flavor stimuli, even at the highest concentration of flavoring. Procedure A two-alternative forced-choice 2AFC version of the ascending method of limits, common in chemosensory testing, served to measure threshold Cain et al.
At testing, the experimenter read the following instructions to the subject: Both are made with gelatin, table sugar and water. However, one has an orange flavor in addition to the sweet taste. I would like you to tell me which sample has the orange flavor. The subject rinsed with water before sampling again and expectorated the rinse.
Testing began with the lowest concentration and progressed in steps to higher levels upon incorrect choices. Concentration remained the same after correct choices. A minute elapsed between trials. Testing ceased when the subject made four successive correct choices, and this concentration was designated as the threshold. Replicate sessions occurred about 1 week later.
Results Compared with the young, elderly subjects needed 49 times the concentration of olfactory flavoring for consistent detection. Average threshold, expressed as dilution step, equaled 2. Means may actually underestimate the difference because some elderly subjects failed to detect the maximum available concentration and were therefore assigned a threshold one step above the maximum.
When assessed for the combined sample of young and elderly subjects, test—retest reliability r equaled 0. When assessed separately, reliability equaled 0. Discussion The task discriminated olfactory flavor thresholds of elderly and young with high resolution, to almost two and one-half standard deviations i. The use of chilled gelatin allowed samples to pass into the mouth with minimal orthonasal olfactory cues and eliminated the need for encumbrances, such as nose clips. The task would therefore seem reasonable for demonstrating the amount of olfactory flavor a person might extract from food under somewhat unchallenging circumstances of eating.
Eating can present an array of challenges to the extraction of flavor, from assessment of olfactory subtleties too fine for instruments to detect to gross distinctions between edible and inedible substances.
Perhaps no task or index will capture all of these ranges, but our method appears to be on task for the measurement of threshold. If the olfactory flavor threshold test is a reasonable assessment of olfactory perception, an individual who performs poorly on an orthonasal measure should perform poorly on the olfactory flavor threshold task.
However, the olfactory flavor threshold might provide additional information that is relevant to olfactory experiences that accompany eating.
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Persons who perform below a criterion level on this test—which combines a threshold with a task of identification—are deemed impaired, not only because of their relative infrequency in the population, but also because those who perform below that level often complain to physicians about loss.
Elderly persons perform less well on the CCCRC test than the young and more often score below the criterion for impairment set for nonelderly persons. It appears, however, that few elderly approach physicians about their loss, either because they fail to notice the slow accumulation of deficit or because they accept it as normal Stevens, Since incremental loss of smell begins in middle age, net loss in old age may readily escape notice Eskenazi et al.
Persons who seek medical attention for olfactory loss tend to report rapid changes. Also of interest was the question of whether conditions in the mouth influenced olfactory flavor perception.
In experiment 1, many elderly subjects wore dentures 20 of Thus, we may have revealed a difference in olfactory flavor threshold between elderly with dentures and young subjects. Dentures may handicap masticatory functioning and mouth movements and, as a result, alter perception of olfactory food flavor Zarb, The interactions between the palate and the tongue appear critical during both the voluntary and involuntary stages of swallowing to create the changes in the intraoral pressure sufficient to pump volatiles retronasally to the olfactory receptors Burdach and Doty, We hypothesized that the average olfactory flavor threshold would be higher in those with palatal covering dentures than in those who were dentate or had minimal partial dentures.
The independent and combined influences of denture status, orthonasal olfactory functioning as measured by the CCCRC test and age on olfactory flavor threshold were examined through multiple regression analysis. The women were independent-living in separate apartments and were primarily Caucasian.
- Smell and the brain
- From tongue to brainstem
For study participation, each had to meet and additional criteria for functional status. The first author was certified to administer and score this questionnaire by the Center for the Study of Aging and Human Development, Duke University. Taste and smell are separate senses with their own receptor organs, yet they are intimately entwined. Tastants, chemicals in foods, are detected by taste buds, which consist of special sensory cells.
When stimulated, these cells send signals to specific areas of the brain, which make us conscious of the perception of taste. Similarly, specialized cells in the nose pick up odorants, airborne odor molecules.
Odorants stimulate receptor proteins found on hairlike cilia at the tips of the sensory cells, a process that initiates a neural response. Ultimately, messages about taste and smell converge, allowing us to detect the flavors of food. Illustration by Lydia V.
Taste and Smell
Just as sound is the perception of changes in air pressure and sight the perception of lighttastes and smells are the perception of chemicals in the air or in our food. Separate senses with their own receptor organs, taste and smell are nonetheless intimately entwined.
This close relationship is most apparent in how we perceive the flavors of food. Actually, what is really being affected is the flavor of the food, or the combination of taste and smell. However, interactions between the senses of taste and smell enhance our perceptions of the foods we eat.
Tastants, chemicals in foods, are detected by taste budsspecial structures embedded within small protuberances on the tongue called papillae.