Perception described

A strict definition of color includes (1) the object appearance that depends on light, object, and observer, and (2) the visual perception described with color names. Color is a primary attribute of appearance and it can be quantified. The measurement of color is known as colorimetry. The colorimetric principles associated with the response of the normal eye are important when reviewing color analysis. The eye-brain combination is sensitive, flexible. 

In the middle 1950s Aldous Huxley published his influential The Doors of Perception, describing an experience with mescaline and advocating it as a means of vitalizing the... 

Figure 19-1, however, shows a much more complex process than this clear perception of primary stimulus information, my own psychological observations have convinced me that this more complex process takes place all the time, and the straightforward, relatively clear perception described above is a rarity, especially for any prolonged period of time. So, let us look at this diagram of samsara in detail. 

Risk perception describes an individual s intuitive judgment of the risk. Risk perception is not often in agreement with the actual level of risk. 

Having defined the appropriate pharmacophore features, the expert must next derive the pharmacophore of interest. A prerequisite, in the absence of a protein structure, is a series of active molecules that are presumed to bind in the same way. The pharmacophore may then be derived from examining the disposition of pharmacophore features within the molecules to locate common distances and then generating a superposition of the molecules. The key elements of this process are pharmacophore feature perception, described above, conformational analysis to explore the conformational space of the ligands, and identification of the common features. 

The aroma of fmit, the taste of candy, and the texture of bread are examples of flavor perception. In each case, physical and chemical stmctures ia these foods stimulate receptors ia the nose and mouth. Impulses from these receptors are then processed iato perceptions of flavor by the brain. Attention, emotion, memory, cognition, and other brain functions combine with these perceptions to cause behavior, eg, a sense of pleasure, a memory, an idea, a fantasy, a purchase. These are psychological processes and as such have all the complexities of the human mind. Flavor characterization attempts to define what causes flavor and to determine if human response to flavor can be predicted. The ways ia which simple flavor active substances, flavorants, produce perceptions are described both ia terms of the physiology, ie, transduction, and psychophysics, ie, dose-response relationships, of flavor (1,2). Progress has been made ia understanding how perceptions of simple flavorants are processed iato hedonic behavior, ie, degree of liking, or concept formation, eg, crispy or umami (savory) (3,4). However, it is unclear how complex mixtures of flavorants are perceived or what behavior they cause. Flavor characterization involves the chemical measurement of iadividual flavorants and the use of sensory tests to determine their impact on behavior. 

Saturation is the concentration of a stimulus above which no increase in perception can be detected. It is tme that Weber-Stevens laws can predict the relationship between stimulus intensity and sensory response with some precision however, they do not describe the very common situation of stimuli at or near the threshold or point of saturation. 

A persistent idea is that there is a very small number of flavor quaUties or characteristics, called primaries, each detected by a different kind of receptor site in the sensory organ. It is thought that each of these primary sites can be excited independently but that some chemicals can react with more than one site producing the perception of several flavor quaUties simultaneously (12). Sweet, sour, salty, bitter, and umami quaUties are generally accepted as five of the primaries for taste sucrose, hydrochloric acid, sodium chloride, quinine, and glutamate, respectively, are compounds that have these primary tastes. Sucrose is only sweet, quinine is only bitter, etc saccharin, however, is slightly bitter as well as sweet and its Stevens law exponent is 0.8, between that for purely sweet (1.5) and purely bitter (0.6) compounds (34). There is evidence that all compounds with the same primary taste characteristic have the same psychophysical exponent even though they may have different threshold values (24). The flavor of a complex food can be described as a combination of a smaller number of flavor primaries, each with an associated intensity. A flavor may be described as a vector in which the primaries make up the coordinates of the flavor space. 

Several aspects affect the extent and character of taste and smell. People differ considerably in sensitivity and appreciation of smell and taste, and there is lack of a common language to describe smell and taste experiences. A hereditary or genetic factor may cause a variation between individual reactions, eg, phenylthiourea causes a bitter taste sensation which may not be perceptible to certain people whose general abiUty to distinguish other tastes is not noticeably impaired (17). The variation of pH in saUva, which acts as a buffer and the charge carrier for the depolarization of the taste cell, may influence the perception of acidity differently in people (15,18). Enzymes in saUva can cause rapid chemical changes in basic food ingredients, such as proteins and carbohydrates, with variable effects on the individual. 

Specific scales may be used to rate the perception of intensity of (/) the malodor, and (2) the malodor along with an odorous material designed to modify the malodor. Rating scales may consist of numerical assignments to words, eg, from 0 = no odor to 10 = very strong odor. These same type of scales maybe used to describe both the hedonic acceptabiUty of the net result, ie, from 0 = very unpleasant to 10 = extremely pleasant, and the degree of modification, ie, from 0 = does not modify to 10 = complete elimination or cover-up. 

Odor data for the various amyl alcohols is limited. The lowest perceptible limit for 1-pentanol and / fZ-amyl alcohol are 10 and 0.04 ppm, respectively (135). tert-Axa[. alcohol has a threshold value of 2.3 ppm (and a 100% recognition level of 0.23 ppm) 3-methyl-1-butanol has an odor threshold of 7.0 ppm. The odor of 1-pentanol has been described as sweet and pleasant whereas that of 3-methyl-2-butanol is sour (135). 

Local air motion is another thermal nonuniformity that can cause a local cooling of the skin and the feeling of a draft. Draft discomfort from local air motion increases as the air temperature decreases below skin temperature. Fluctuations in the local air motion increase the perception of drafts and should be avoided. The unsteadiness of air motion is often described in terms of its turbulence intensity (Tu) ... 

The links between levels of exposure and inconvenience caused by ventilation noise are described in an investigation carried out on office workers.- Technical measurements and analyses of the ventilation noise at 155 typical office workplaces were in this study combined with assessments by the office workers of the level of disturbance that they experienced, the effect on working performance, fatigue, stress-related pain, and headaches. The average noise level was about 40 dB(A) at two of the workplaces, while it was about 35 dB(A) at two others. It emerged from rhe narrow-band analyses that the sound pressure levels of rhe infrasound were not in any event of an order that this type of sound frequencies (below 20 Hz) could contribute to any disturbance effects. Any steps taken to counter the sound frequencies of the ventilation noise under 50 Hz, i.e., the point of btersection between the threshold curve of auditory perception and the spectral level distribution curve of... 

As described earlier, in the first stage of perception, information is acquired via the senses from a number of sources. These may include gauges and chart recorders, VDU screens in a control room, verbal communication with individuals on the plant, or direct observation of process variables. In the short term, this information provides feedback with regard to specific control actions. 

The classification structure for PIFs used in this chapter is based on the model of human error as arising from a mismatch between demands and resources which was described in Chapter 1, Section 1.6 (Figure 1.6). In this model demands were seen as requirements for human performance which arise from the characteristics of the process environment (e.g., the need to monitor a panel or to be able to fix a seal in a flange) and the nature of the human capabilities to satisfy these demands (e.g., skills of perception, thinking, and physical action). These demands are met by the individual and group resources of personnel and the extent to which the design of the task allows these resources to be effectively deployed. Where demands exceeded resources, errors could be expected to occur. 

The disulfide is dissolved by aqueous potassium hydroxide, yielding a greenish-yellow solution. At low temperatures no perceptible evolution of gas takes place. Since the disulfide in many respects behaves as a pseudo-halogen, Brown et al. have supposed that the reaction described by Eq. (8) takes place, i.e. a reaction analogous to the formation of halide and halite ions from a halogen and alkali. 

The present chapter, therefore, will present certain topics based on a selection of references, mainly in view of providing a perception of the current developments and great potential of chitin today. The reader is referred to books and reviews [1-17] where basic information and specific subjects are treated in a more systematic way. These polysaccharides are described not only in encyclopaedias, handbooks, monographs and articles, but also in the American Standard Testing Materials standard guides and in the Pharmacopoeias of various coimtries [10,16,17]. 

An abstinence syndrome after long-term, low-dose treatment has also been described (Busto et al. 1986a Covi et al. 1973 Petursson and Lader 1981b Tyrer et al. 1981). Reported symptoms include muscle twitching, abnormal perception of movement, depersonalization or derealization, anxiety, headache, insomnia, diaphoresis, difficulty concentrating, tremor, fear, fatigue, lowered threshold to perception of sensory stimuh, and dysphoria. 

Basic biologic processes like photosynthesis and vision are fairly well understood. However, the perception of fight by individuals is not easy to describe in physical terms because the fight receptors differ considerably among species and... 

There have also been attempts to describe the temporal aspects of perception from first principles, the model including the effects of adaptation and integration of perceived stimuli. The parameters in the specific analytical model derived were estimated using non-linear regression [14]. Another recent development is to describe each individual TI-curve,/j(r), i = 1, 2,..., n, as derived from a prototype curve, S t). Each individual Tl-curve can be obtained from the prototype curve by shrinking or stretching the (horizontal) time axis and the (vertical) intensity axis, i.e. fff) = a, 5(b, t). The least squares fit is found in an iterative procedure, alternately adapting the parameter sets (a, Zi, for 1=1,2,..., n and the shape of the prototype curve [15],... 

The observations of fine motor problems in infants born to heroin addicts has also been described by Wilson et al., in 1973. She notes the discrepancy between the gross motor skills of the infants and fine motor abilities during the first year. Furthermore, in 1979, Wilson et al, described the development of preschool children between 3 and 6 years of age, born to heroin-addicted mothers. They performed poorer on measures of visual, tactile, and auditory perception, were more active, and had... 

---