Latency and accuracy of discriminations of odor quality between binary mixtures and their components

Subjects made timed, same-different discriminations of odor quality, with the following principal findings: (i) latency reflected accuracy, with difficult discriminations, i.e. those between 50-50 mixtures and their components, requiring more time than less difficult discriminations, i.e. those between unmixed chemicals. This finding demonstrated the face validity of latency as a measure of qualitative similarity. (ii) Latency provided better resolution among pairs of odors than did errors of discrimination. This finding demonstrated the utility of collecting response times. (iii) Latency-based similarities among odors tested previously predicted similarities among pairs not yet tested. This finding demonstrated internal/predictive validity. (iv) A signal detection model assuming a differencing strategy best described the pattern of errors. Subjects appeared to make relative judgements regarding quality. (v) Finally, latency-based similarities between mixtures and their components demonstrated additivity. This finding suggested that binary mixtures fall on straight lines connecting their components in 'odor-space'.     

Perceptual interactions in odour mixtures: odour quality in binary mixtures of woody and fruity wine odorants

The qualitative perceptual interactions in three binary mixtures of wine odorants were studied: isoamyl acetate (fruity note)/whisky lactone (woody note), ethyl butyrate (fruity note)/whisky lactone (woody note) and ethyl butyrate (fruity note)/guaiacol (woody note). For each binary mixture, the perceived quality and intensity of 24 stimuli (four supra-threshold concentration levels of each of the two compounds and their 16 possible combinations) were evaluated in five replications by a trained panel of 13 subjects. The application of the Olsson predictive model for odour intensity and quality perception gave quite a good estimation of the evolution of single component identification in the mixture when the intensity proportion of unmixed components varied. However, this model was unable to account for the odour quality dominance in mixtures of iso-intense components. An alternative linear logistic model was proposed to study the qualitative dominance of the woody note in the three mixtures when the perceived intensities of each unmixed compound were equal.     

Qualitative and aqualitative intensity components of odour mixtures

The perception of the intensity of components of odorous mixturesis related to the overall mixture intensity in a complex mannerwhich has not so far been adequately modelled. Hypoadditivity,where the total perceived intensity of a mixture is less thanthe sum of the component intensities which arise when the substancesare presented in pure form at equivalent chemical concentrations,has been known for many years. An experiment on series of 56mixtures of amyl butyrate and bergamot at supra-threshold concentrationsfound that the total qualitatively unspecified intensity ofsuch mixtures can be greater than the sum of the identifiedcomponent intensities as judged in the context of the mixture.To reconcile an apparent contradiction, and to bring into onepsychophysical framework results from diverse procedures, amodel of mixed qualitative and aqualitative odour intensityis advanced, incorporating some evidence on the difference betweendetection and recognition processes. Each component in a mixturemay, in this theory, both partially mask the qualitative intensityof the other, and simultaneously convert some part of the other'sintensity into an aqualitative form.     

Effect of repeated presentation on sweetness intensity of binary and ternary mixtures of sweeteners

The purpose of the present study was to determine the effect of repeated presentation of the same sweet stimulus on sweetness intensity ratings. The sweet stimuli tested in this study were binary and ternary blends of 14 sweeteners that varied widely in chemical structure. A trained panel evaluated the sweetness intensity over four sips of a given mixture presented at 30 s intervals. The individual components in the binary sweetener combinations were intensity-anchored with 5% sucrose, while the individual sweeteners in the ternary mixtures were intensity-anchored with 3% sucrose (according to formulae developed previously). Each self-mixture was also evaluated (e.g. acesulfame-K-acesulfame-K). The main finding of this study was that mixtures consisting of two or three different sweeteners exhibited less reduction in sweetness intensity over four repeated sips than a single sweetener at an equivalent sweetness level. Furthermore, ternary combinations tended to be slightly more effective than binary combinations at lessening the effect of repeated exposure to a given sweet stimulus. These findings suggest that the decline in sweetness intensity experienced over repeated exposure to a sweet stimulus could be reduced by the blending of sweeteners.     

Behavioral chemoattractants for the shrimp, Palaemonetes pugio: identification of active components in food extracts and evidence of synergistic mixture interactions

We are studying chemoattractants for the shrimp, Palaemonetespugio, to identify the active components of stimulatory foodextracts, and to determine whether the mixtures of substancesoccurring in extracts express themselves in an additive or aninteractive manner. The results of quantitative analyses ofthe specific amino acids, quaternary ammonium compounds, organicacids, nucleotides and related substances in extracts of fourorganisms (crab, shrimp, oyster, mullet) were used to formulateartificial mixtures based on the composition of each organism.Quantitative behavioral bioassays with P. pugio showed thatthe artificial mixtures based on the composition of the craband shrimp extracts were virtually as effective as the respectivenatural extracts, whereas artificial mixtures based on the compositionof the oyster and mullet extracts were far less effective. Sincethe same types of substances were included in all of the mixtures,it is apparent that the substances serving as chemoattractantsin different extracts are not constant but can vary dependingupon the source of the extract. To examine for interactionsamong the components of the four artificial mixtures, responsesto the mixtures and to their individual components were analyzedusing the additive methods of stimulus summation and responsesummation. Synergistic interactions were evident since eachmixture was markedly more effective than predicted on the basisof these additive models. The degree of synergism varied withthe composition of the mixture.     

Fish-zooplankton interactions and their effects on water quality of a tropical Brazilian reservoir

The influence of zooplanktivorous fishes on the plankton community and water quality of Americana Reservoir, Brazil was studied experimentally in 4 floating enclosures during the dry seasons (July–September) of 1982 and 1983. Two enclosures were stocked with adult fish (Astyanax bimaculatus in 1982;A. fasciatus in 1983) at near maximal densities measured in the reservoir upper surface waters (35 m^–2) and two were fish-free during each experiment lasting about one month. Marked differences were evident between the fish and fish-free enclosures after a 2–3 week period in each experiment, particularly with respect to water transparency, phytoplankton biomass, and zooplankton abundance as well as species and size composition. By the end of each experiment water transparencies were lower and phytoplankton biomass higher in the fish enclosures compared to those without fish. Also at that time Rotifera were the prominent zooplankters in the fish enclosures and Cladocera in the fish-free ones. Larger or more conspicuous species of Cladocera asDaphnia gessneri, D. ambigua, andMoina micrura were present in the fish-free enclosures but not in the fish enclosures. The interactions between fish predation, zooplankton grazing, phytoplankton biomass and water quality conditions are discussed in relation to eutrophication of a tropical aquatic ecosystem.     

Crowding effects in binary mixtures of rod-like and spherical particles

Crowding effects relevant to the phase stability of binary mixtures of rod-like and spherical particles are investigated by means of Monte Carlo simulations in the isobaric NPT ensemble. The two types of particles are represented, respectively, by freely rotating hard spherocylinders of a moderate aspect ratio (L/sigma = 5) and hard spheres of the same diameter sigma. Molar fractions of spheres ranging xHS = 0.00-0.37 are considered with the aim of characterizing the crowding effects on the liquid crystal phases of the hard spherocylinder fluid induced by the spherical component as depleting agent. We find that the addition of the spherical crowder is beneficial for the stabilization of the layers of the rod-like particles characteristic of the smectic phase. On the contrary, the addition of spheres has a negative impact upon the stability of the nematic phase, where the rod-like particles tend to align collectively parallel to each other. Interestingly, the spheres tend to arrange forming rod-like clusters in the nematic phase and lamellar structures in the smectic phase, which is compensated by the entropy gained by the spherocylinder particles in each phase. The main results are in qualitative agreement with recent experimental and theoretical studies and serve to test the prediction of current equations of state for these types of binary mixtures.     

Influence of stimulus intensity on odour discrimination by olfactory bulb neurons as compared with receptor cells

Previously reported electrophysiological responses recordedfrom individual neurons in the olfactory bulb of frogs stimulatedwith odorous compounds were further analyzed using statisticalmethods. Five of the odorants were delivered at two concentrations.The pattern of discrimination among these odorants was investigatedwith the aid of the Pearson's correlation test and Benzecri's‘analyse des correspondances’. Special attentionwas paid to the incidence of odour concentration on this discriminationpattern. The results were compared with those of a similar studyperformed on receptor cells in the same experimental conditions.The comparison indicated that the information processing inthe olfactory bulb seems to improve discrimination between chemicallydifferent stimuli, especially those poorly discriminated byreceptor cell responses, whereas it protects this discriminationagainst a massive influence of the intensity of the stimuli.     

Sublethal effects of chronic exposure to chlorpyrifos or imidacloprid insecticides or their binary mixtures on Culex pipiens mosquitoes

Mosquitoes represent one of the most significant threats to human and veterinary health throughout the world. Consequently, improving strategies for the control of mosquitoes is essential. In the present study, juvenile Culex pipiens (Diptera: Culicidae), the common house mosquito, are chronically exposed to sublethal concentrations of chlorpyrifos (20% of LC₅₀) and imidacloprid (5% of LC₅₀), both separately and as a mixture. Developmental time, the emergence rate of adults and the expression of five selected genes involved in detoxification and resistance to pesticides are assessed. To assess the effects on oviposition choice, gravid females are forced to oviposit into cups containing water with added chlorpyrifos, imidacloprid or a mixture of both. The time required for the development of second‐ and third‐instar larvae is observed to differ significantly between treatments. Adults of C. pipiens fail to emerge from larvae hatched in both imidacloprid and the binary mixture. The expression of the four quantified detoxification genes differs significantly in third‐larval instars exposed to chlorpyrifos and/or imidacloprid compared with controls. Gravid females also fail to lay eggs on water to which either of the insecticides or the binary mixture is added, although they do lay eggs in cups containing water only. Chronic exposure to sublethal concentrations of chlorpyrifos or imidacloprid has significant adverse effects on development and thus the reproductive fitness of C. pipiens and, accordingly, could be used in the population control of these mosquitoes.     

Gustatory intensity discrimination in rat NTS: a tool for the evaluation of neural coding theories

Summary The neural coding of taste quality in vertebrates currently is addressed by the labeledline and the across-fiber pattern theory. Experimental tests that have tried to distinguish between these theories by manipulating taste quality have been problematic in that both are fairly successful. However, the two theories maintain that different numbers of neurons participate in coding the presence of a substance. In the labeled-line theory, only those neurons labeled by that substance are supposed to be involved, whereas in the across-fiber pattern theory, all neurons responding to the substance are taken into account. We therefore expected that the theories might predict different intensity discriminating abilities among the four classical taste stimuli, which could provide a less equivocal test between the theories.A previous paper (Maes 1984) described a model for the neural basis of intensity discrimination, based on signal-detection theory. In the present paper, experimental data obtained from single neurons in the nucleus of the solitary tract of rat are analyzed in terms of this model. Whole-mouth stimulation with the four classical taste substances was used. For both theories, predictions of the intensity discriminating acuity for the four substances were derived, using different response analysis intervals, and including two plausible non-linearities in neural processing.The acuity profile across the four stimuli (consisting of the reciprocals of the four differential thresholds) turned out to be sensitive to the choice of coding theory and non-linearity. The interval chosen for response analysis had a strong effect. The predicted profiles should be checked against behavioral data on intensity discrimination in rat, but since such data are not yet available, a comparison was made with human psychophysical data, for illustrative purposes. It appeared that a unique combination of variables (tonic part of the response, across-fiber pattern coding with a contrast enhancement type of non-linearity) could be selected to match the psychophysical profile.In the Discussion, special attention is paid to the fundamental differences between the two coding theories, to the relevance of whole-mouth stimulation, and to the informational significance of various parts of the phasic/tonic response.Abbreviations AFP across-fiber pattern - CT chorda tympani - DA discrimination acuity - DT differential threshold - H sour - LL labeled line - N salty - NTS nucleus tractus solitarius - PTA pontine taste area - Q bitter - S sweet     

Asymmetric suppression of components in binary aldehyde mixtures: behavioral studies in the laboratory rat

The aim of the present study was to assess component interaction in the perception of the 2 aldehydes butanal and heptanal when presented in binary mixtures to rats. A further aim was to develop a behavioral paradigm for testing suppression of components in mixtures using rodent subjects. Thirsty rats were initially trained to discriminate between the 2 aldehydes butanal and heptanal in an olfactometer using a go/no-go discrimination task. This involved rats learning to place their noses in a sniff port where odors were presented and to lick a tube for water reward when one of the aldehydes was presented (S+) while withholding licking at the tube to the other, unrewarded, aldehyde (S-). A mixture condition was then introduced into the task, whereby a proportion of trials involved presentation of a combination of the 2 aldehydes as an additional unrewarded condition. Rats readily learned to withhold licking on trials when the mixture was presented. The concentration of the nonrewarded (S-) aldehyde in the mixture was then systematically decreased, whereas the concentration of the S+ component was held constant. This eventually caused the S+ component in the mixture to suppress detection of the S-, as shown by an increasing number of lick responses (false alarms) on trials when the mixture was presented. These suppressing effects occurred well above the detection threshold for the S- aldehyde presented alone. Results showed asymmetric suppression in the mixture condition such that butanal suppressed detection of heptanal at much lower concentrations than vice versa. A second experiment showed that when both butanal and heptanal were present in a binary mixture at the same concentration (10(-6) volume %), then rats responded to the mixture as if only butanal was present. These findings are discussed in terms of butanal having higher mobility and being able to compete more effectively than heptanal for occupation of shared receptor sites.     

Correct and logical inference on efficacy in subgroups and their mixture for binary outcomes

Targeted therapies are becoming more common. In targeted therapy development, suppose its companion diagnostic test divides patients into a marker‐positive subgroup and its complementary marker‐negative subgroup. To find the right patient population for the therapy to target, inference on efficacy in the marker‐positive and marker‐negative subgroups as well as efficacy in the overall mixture population are all of interest. Depending on the type of clinical endpoints, inference on mixture population can be nontrivial and commonly used efficacy measures may not be suitable for a mixture population. Correlations among estimates of efficacy in the marker‐positive, marker‐negative, and overall mixture population play a crucial role in using an earlier phase study to inform on the design of a confirmatory study (e.g., determination of sample size). This article first shows that when the clinical endpoint is binary (such as respond or not), odds ratio is inappropriate as an efficacy measure in this setting, but relative response (RR) is appropriate. We show a safe way of calculating estimated correlations is to consider mixing subgroup response probabilities within each treatment arm first, and then derive the joint distribution of RR estimates. We also show, if one calculates RR within each subgroup first, how wrong the correlations can be if the Delta method derivation fails to take randomness of estimating the mixing coefficient into account.     

The influence of rate of temperature change and peak stimulus duration on pain intensity and quality

An important aspect of experimental pain research is that the assessment methods can investigate the different aspects of pain perception. The aim of the present study was to investigate the influence of rate of temperature change and peak stimulus duration on heat evoked pain intensity and quality. All stimuli were applied within the medial aspect of the anterior forearm. The rate of temperature change was varied from 1 to 16 C/s without any effect on the pain threshold. The pain threshold decreased with an increasing peak stimulus duration from 0.1 to 2 s, but not from 2 to 3 s. The pain intensity for suprathreshold stimuli (46 C, 48 C, 50 C) increased for decreasing rates and increasing duration. The pain intensity was highly correlated with the energy of the stimulus. When the rates of temperature change (1-16 C/s) are varied, no differences between pricking and burning pain were present at either low stimulus intensity (46 C) or high stimulus intensity (50 C). At low stimulus intensity (46 C), the pricking pain was not influenced by the duration (0.1-3 s), but the burning pain was intensified when the duration was increased from 1.5 to 3 s. At high intensity stimuli (50 C), the pricking pain intensified with an increased duration, whereas burning pain did not. The heat pain threshold is influenced by the peak stimulus duration, and not by the rate of temperature change. If suprathreshold stimuli are used, both the rate of temperature change and the peak stimulus duration can strongly affect the pain intensity and the pain quality. Therefore, the same stimulus modality can be used to assess the modulation of different pain intensities and of the pricking and burning pain qualities simply by varying the stimulus configuration.     

Behavioral determination of stimulus pair discrimination of auditory acoustic and electrical stimuli using a classical conditioning and heart-rate approach

Acute animal preparations have been used in research prospectively investigating electrode designs and stimulation techniques for integration into neural auditory prostheses, such as auditory brainstem implants and auditory midbrain implants. While acute experiments can give initial insight to the effectiveness of the implant, testing the chronically implanted and awake animals provides the advantage of examining the psychophysical properties of the sensations induced using implanted devices. Several techniques such as reward-based operant conditioning, conditioned avoidance, or classical fear conditioning have been used to provide behavioral confirmation of detection of a relevant stimulus attribute. Selection of a technique involves balancing aspects including time efficiency (often poor in reward-based approaches), the ability to test a plurality of stimulus attributes simultaneously (limited in conditioned avoidance), and measure reliability of repeated stimuli (a potential constraint when physiological measures are employed). Here, a classical fear conditioning behavioral method is presented which may be used to simultaneously test both detection of a stimulus, and discrimination between two stimuli. Heart-rate is used as a measure of fear response, which reduces or eliminates the requirement for time-consuming video coding for freeze behaviour or other such measures (although such measures could be included to provide convergent evidence). Animals were conditioned using these techniques in three 2-hour conditioning sessions, each providing 48 stimulus trials. Subsequent 48-trial testing sessions were then used to test for detection of each stimulus in presented pairs, and test discrimination between the member stimuli of each pair. This behavioral method is presented in the context of its utilisation in auditory prosthetic research. The implantation of electrocardiogram telemetry devices is shown. Subsequent implantation of brain electrodes into the Cochlear Nucleus, guided by the monitoring of neural responses to acoustic stimuli, and the fixation of the electrode into place for chronic use is likewise shown.     

Response of olfactory receptor neurons in honeybees to odorants and their binary mixtures

Recordings were made from single sensilla placodea of the worker honeybee (Apis mellifera). The sensilla were stimulated with one of two sets of four compounds and their binary mixtures, at two dosage levels. Aromatic compounds comprised one set, and saturated n-octane derivatives comprised the other set. Correlation, principal component, and cluster analyses indicate that responses to binary mixtures are not linear combinations of responses to the component compounds. The first principal component indicated that neuronal units had either more excitatory or more inhibitory responses to all odorants than would be expected from a model where inhibitory and excitatory responses are randomly distributed among the neuronal units. When compared to the responses to the component odorants, synergistic responses to binary odors occurred more often than would be expected by chance. Clear inhibitory responses to binary odors were less prevalent. This study agrees with an earlier study employing aromatic odorants in that most of the aromatic odorants each had groups of receptor neurons that were relatively selective for it, and each odorant had a distinctly different number of receptor neurons selective for it. Among the octane derivatives, receptor neurons were selective for the level of oxidation of the functional group or its site of attachment, rather than specific compounds.