Human perception

Human perception creates difficulty ia the characterization of flavor people often, if not always, perceive flavors differently due to both psychological and physiological factors. For example, certain aryl thiocarbamates, eg, phenylthiocarbamide, taste exceedingly bitter to some people and are almost tasteless to others (5). This difference is genetically determined, and the frequency of its occurrence differs from one population to another 40% of U.S. Caucasians are nontasters, whereas only 3% of the Korean population caimot perceive the strong bitter taste of the aryl thiocarbamates (6). Similar differences were found ia the sense of smell for compounds such as menthol, carvone, and ethyl butyrate (7). 

The sensory technique used for assessing human perception of odors is called olfactometry. The basic technique is to present odorants at different concentrations to a panel of subjects and assess their response. The process favored by the U.S. National Academy of Sciences is dynamic olfactometry (16). This technique involves a sample dilution method in which a flow of clean, nonodorous air is mixed with the odorant under dynamic or constant... 

Regional Haze Visibility Impairment any humanly perceptible change in visibility (light extinction, visual range, contrast, coloration) from that which would have existed under natural conditions, caused predominantly by a combination of many sources from, and occurring over, a wide geographic area. 

Physical constants reflect nature s algorithms. They reflect an ordering of physical systems or events. The human perception of that natural order is reflected in how much constants are expressed mathematically. 

Human perception is. .. inferred from fragmentary and often hardly relevant data signalled by the eyes, so requiring inferences from knowledge of the world to make sense of the sensory signal. 

To serve as an indicator of appropriate food sources (mainly for animals) and to assess food quality (mainly human perceptions)... 

In the preceding section, we presented principles of spectroscopy over the entire electromagnetic spectrum. The most important spectroscopic methods are those in the visible spectral region where food colorants can be perceived by the human eye. Human perception and the physical analysis of food colorants operate differently. The human perception with which we shall deal in Section 1.5 is difficult to normalize. However, the intention to standardize human color perception based on the abilities of most individuals led to a variety of protocols that regulate in detail how, with physical methods, human color perception can be simulated. In any case, a sophisticated instrumental set up is required. We present certain details related to optical spectroscopy here. For practical purposes, one must discriminate between measurements in the absorbance mode and those in the reflection mode. The latter mode is more important for direct measurement of colorants in food samples. To characterize pure or extracted food colorants the absorption mode should be used. 

Any color signal received from the snbject will be rated by the spectral sensitivity of the eye. The physiological bases for this are three types of cone-shaped receptors on the human retina that are sensitive to red, green, and bine. The color measurement techniques have been established on this tri-colorimetric system. They simulate human perception by the relative extent to which the observer estimates the relative share of which of these three components contributes to his color impression from an object. 

Omiir-Ozbek, P. and Dietrich, A.M. Determination of temperature-dependent Henry s law constants of odorous contaminants and their application to human perception, Environ. Sci. Technol, 39(ll) 3957-3963, 2005. 

Pattern recognition methods have been used for the description of air pollution in the industrialized region at the estuary of the river Rhine near Rotterdam. A selection of about eight chemical and physical-meteorological features offers a possibility for a description that accounts for out 70% of the information that is ccmprised in these features with two parameters only. Prediction of noxious air situations scmetimes succeeds for a period of at most four hours in advance. Seme-times, hewever, no prediction can be made. Investigations pertaining to the correlation between air conpo-sition and complaints on bad smell by inhabitants of the area show that, apart frem physical and chemical descriptors, other features are also involved that depend on human perception and bdiaviour. 

And although om natural and personal detector, the retina, shows us a tranquil sky, with a light scatter of stars across it, striking only by its steadfast inaction, the new sky revealed by telescopes and satellites sensitive to invisible emissions is one of tempest. It is animated by the birth of clouds, the creative explosion of stars and the transition of the Universe from opacity to transparence. Human perception now contemplates regions once forbidden to it. 

Exploratorium. Available online. URL http //www.exploratorium.edu/. Accessed May 28, 2009. The Exploratorium, a museum of science, art, and human perception in San Francisco, has a fantastic Web site full of virtual exhibits, articles, and animations, including much of interest to chemists and chemists-to-be. 

If we were able to extend our current senses in range and intensity, we could glimpse alien sense-domains. Think about bees. Bees can see into the ultraviolet range of the spectrum, although they do not see as far as we do into the red range. When we look at a violet flower, we do not see the same thing that bees see. In fact, many flowers have beautiful patterns that only bees can see to guide them to the flower. These attractive and intricate patterns are totally hidden to human perception. 

Household Hazardous Waste (HHW) is defined by the U.S. EPA as solid wastes, discarded from homes or similar sources, that are either hazardous wastes or wastes that exhibit any of the following characteristics ignitabiUty, corrosivity, reactivity, or toxicity. A significant fraction of HHW is generated by home mechanics who use such products as motor oil, cleaners and solvents, refrigerants, and batteries. The results indicate that most of the survey respondents perceive automotive products to pose significant health and environmental risks, and they tend to dispose of these wastes in an environmentally conscious manner. There is qnite often a discrepancy between human perception and scientific reality (see table 8.2) (Shorten et al., 1995). 

Human perception of flavor occurs from the combined sensory responses elicited by the proteins, lipids, carbohydrates, and Maillard reaction products in the food. Proteins Chapters 6, 10, 11, 12) and their constituents and sugars Chapter 12) are the primary effects of taste, whereas the lipids Chapters 5, 9) and Maillard products Chapter 4) effect primarily the sense of smell (olfaction). Therefore, when studying a particular food or when designing a new food, it is important to understand the structure-activity relationship of all the variables in the food. To this end, several powerful multivariate statistical techniques have been developed such as factor analysis Chapter 6) and partial least squares regression analysis Chapter 7), to relate a set of independent or "causative" variables to a set of dependent or "effect" variables. Statistical results obtained via these methods are valuable, since they will permit the food... 

Figure Gl.7.lisa comparison of chromatograms from a solid-phase microextraction (SPME) from a beverage in a sealed container and from the same beverage in a mouth simulator. This comparison demonstrates that a very different volatile ratio is produced from the same food under different sampling conditions. Due to these differences, it is important to use a sampling method that simulates mouth conditions when studying flavor compositions that produce a human perception. Most methods intended to increase headspace volatile concentration, such as adding salt for salting out, do not uniformly affect volatility. For some compounds,...

An alternative approach to the system characterization, valid for any system, is the perceptual approach. In the context of this chapter a perceptual approach is defined as an approach in which aspects of human perception are modelled in order to make measurements on audio signals that have a high correlation with the subjectively perceived quality of these signals and that can be applied to any signal, that is, speech, music and test signals. 

For human perception of the depth of three-dimensional molecular structures, it is important to provide depth cues [44]. Movement is the strongest depth cue, so it is very important to render the image quickly enough to provide smooth movements of the object on the screen. Lighting is used to provide a better impression of the shapes of objects, and also additional depth. Finally, objects that are further away appear as if seen through fog, which improves the impression of three-dimensional space. 

Observations are the heart of the scientific method, but human perception is faulty when it comes to observing absolutes. That is, one may be able to say that this liquid is hotter than that liquid, but not by how much, nor... 

Banks, W. P., Clark, H. H., and Lucy, P. (1975). The locus of the semantic con-gruity effect in comparative judgments. Journal of Experimental Psychology Human Perception and Performance, 1, 35-47. 

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