Odor detection, theory

The experiments with H. M. employed a battery of tests. One set of experiments measured his sensitivity by means of a technique derived from signal detection theory (Corbit Engen, 1971), in which I asked H. M. to sniff 20 presentations of dilute odorant solution randomly interspersed with 20 presentations of odorless blank. The odor was so faint as to make it hard to tell it apart from blank. Figure 1 compares some of the data for H. M. with a male normosmic (P. D.) matched for age and race. After each presentation I asked H. M. whether he could smell an odor. His pattern of responding was the same as that of normosmics sometimes he gave affirmative responses to blanks (false alarms, symbolized by open symbols in fig. 14.1), but he did not always respond affirmatively to the dilute sample (correct affirmatives are symbolized by solid symbols in fig. 14.1). 

Figure 8 The decision space for signal detection theory, which has received support both in general [33,34,41] and in the detection of odors [55,135]. According to one common version of the theory, both blank and odorant give rise to Gaussian distributions of sensory strength with equal variance. The subject responds yes if an observed value of sensory strength exceeds some criterion (dashed vertical line), and no otherwise. The area under each distribution to the right of criterion corresponds to the probability the observer will respond yes to a given stimulus correct responses hits ) for odorants and incorrect responses false alarms) for blanks. Empirical estimates of these probabilities allow one to calculate the distance between the means of the two distributions in units of their common standard deviation, termed d d (which equals 2 in this case) remains constant as criterion changes (see Ref. [41] for an excellent overview).

A bottle of vanilla extract was left uncovered in a cabinet overnight. When the cabinet door was opened, a strong odor of vanilla was detected. Explain this observation using the kinetic theory of matter. 

One theory of lesser importance is the radiation theory, first postulated by Aristotle in the fourth century bc. This theory proposes that odorous substances emit radiation, which is detected by the... 

Most, perhaps all of the odor theories advanced so far made the assumption that the transcription of structureil information encoded in the stimulant molecule into an odor information pattern is an integral process One odorivector (AMOORE, 2) interacts with one receptor site and this interaction resvilts in transcription of all structural components simviltaneously into their corresponding informational modalities. However, observation tells us that olfactory information is inherently complex Ambergris for instance is described (OHLOFF, 3) by six distinctly different notes. This would imply that in an integral process of the periphersil molecular interaction one single neuron has to detect at least six different profiles with six different receptor sites and project the informational modalities intact to the higher centers. 

Flavor is a combination of taste, sensation, and odor transmitted by receptors in the mouth (taste buds) and nose (olfactory receptors). The stereochemical theory of odor is discussed in the essay that precedes Experiment 16. The four basic tastes (sweet, sour, salty, and bitter) are perceived in specific areas of the tongue. The sides of the tongue perceive sour and salty tastes, the tip is most sensitive to sweet tastes, and the back of the tongue detects bitter tastes. The perception of flavor, however, is not so simple. If it were, it would require only the formulation of various combinations of four basic substances—a bitter substance (a base), a sour substance (an acid), a salty substance (sodium chloride), and a sweet substance (sugar)—to duplicate any flavor In fact, we cannot duplicate flavors in this way. The human possesses 9,000 taste buds. The combined response of these taste buds is what allows perception of a particular flavor. 

Although our modern understanding of the detection of odor has evolved to become a more highly detailed theory than the one proposed by Lucretius, it would appear that his fundamental hypothesis was correct and has even withstood the scrutiny of modern science. 

The odors of both natural and synthetic organic chemicals surround us in our everyday life. Some, like the smells of fruits and many spices, are pleasant, whereas others, like those of decaying meat and rancid butter, can be rather unpleasant. We detect these odors because many organic chemicals are volatile, and in this chapter we explore the theory and practice of distillation, a technique that depends on our ability to coax these chemicals into the gas phase. 

Deet is the most widely used mosquito repellent. It was codeveloped by the U.S. military and the USDA as an insect repellent in 1946 and later introduced for public use. Despite several research studies and the wide use of deet for more than five decades, the precise mechanism of repellent action of deet is still being researched, although there are several theories. It seans possible that natural insect repellents act in a similar way, and several hypotheses have recently been reviewed." Curiosity about the mechanism of repellency has resnlted in major advances in nnderstanding how insects perceive odors. This topic has recently been reviewed." Several human-specific kairomones have been hypothesized to attract mosquitoes. Potential kairomones include carbon dioxide, lactic acid, and l-octen-S-ol." The pioneering studies performed by Davis and Sokolove on the mechanism of deet repellency reported that deet blocks the detection of human kairomones. Specifically, Davis and Sokolove showed that carbon dioxide works independently of lactic acid and deet inhibits lactic acid-sensitive neurons. Further studies suggested that there may be several mechanisms of action for deet and other repellents. These studies were supported by behavioral assays that were performed later. 

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