A delivery system for olfactory stimuli

This paper describes the design of a new method for controlling and administering olfactory stimuli—namely, thehood system. The hood system involves a stream of vaporized odor (at known concentrations) mixed with odorless air and pumped (at a constant flow rate) into an oxygen therapy hood. It is designed to be used with odorants in solution, such as essential oils, as the olfactory stimulus. The use of oxygen therapy hoods allows for the precise control of a constant concentration of odorized air over time, while allowing subjects to breathe normally. The hood system provides a natural administration of olfactory stimuli and the exact determination of the stimulus concentration. The use of this system will allow experimental conditions to be completely defined and results and replication studies to be accurately interpreted. The hood system is portable, cost effective, and constructed from readily available components. It is proposed that the hood system could be adopted to suit a wide range of olfactory research, particularly that in which the effects of chronic exposure to olfactory stimuli on cognition are examined.     

A comparison of sniff bottle staircase and olfactometer-based threshold tests

Olfactometers have been gaining popularity as research tools, but they have yet to replace established testing procedures in a variety of laboratory and clinical settings, including absolute threshold tests. In this research, we designed and operated a simple olfactometer with which to assess threshold. To do this, we used a method-of-adjustment test that was compared to the three-alternative forced choice ascending sniff bottle staircase method, which is currently a standard threshold test procedure. We found that the olfactometer threshold test correlated highly with the staircase method, and that it possessed suitable test–retest reliability. The advantages of the olfactometer threshold test include faster test time and reduced cleaning and reassembly demands. Future use of the olfactometer in olfactory identification and/or detection thresholds amongst odors is also outlined.     

The construction of a programmable olfactometer

A new type of multichannel olfactometer is described, and the results are given for gas chromatographical standardization of this equipment. The olfactometer keeps 24 odorous substances available for presentation, consecutively, two per trial, or combinations of the two. It produces concentrations of odorous gas in the air between 1 × l0^?5 and 1 × 10^?11 molecules/liter. The principle of construction is gradual dilution of an odorous gas in streaming purified air. The design provides for electronic control of stimulus sequence and response registration via punched tapes.     

Methodological examination of the PEST (parametric estimation by sequential testing) procedure: II

Finite-state Markov sequences were constructed by a small digital computer, translated to interval-coded electrical pulse trains, and converted to sound. An adaptive stimulus programming procedure of variable step size, PEST, was employed to obtain interstate interval thresholds as a function of restrictions upon the internal structure of the sequences. These thresholds are not independent of the exit criterion for the adaptive procedure. An interactive approach is suggested for determining the exit criterion in order to protect the data against arbitrary decisions made by the E.     

Olfactory discrimination of estrous condition by the male golden hamster (Mesocricetus auratus)

After repeated exposure to receptive and nonreceptive females, male golden hamsters were tested for olfactory preferences in a four-choice olfactometer. Males discriminated between the odor of anesthetized females in different stages of their estrous cycle when the airstreams carrying the stimulus odors were diluted. Previous failures to demonstrate such an ability were probably due to ceiling effects resulting from laboratory testing. Males preferred the odor of females on the day before receptivity (a day coincident with maximal scent marking by the female) and least preferred the odor of females on diestrus-1 (the day on which females attacked and chased males during pretesting encounters). Detection and quick response to an impending estrus would be especially important for males of a solitary and promiscuous species in which there is a first male mating advantage.     

The influence of adaptation on absolute threshold measurements for olfactory stimuli

A group-test method of determining the mean absolute olfactory threshold to a test stimulus for a group of subjects is described. Probit analysis is employed to evaluate the results. This technique is utilized to measure the change in sensitivity to the test stimulus due to adaptation to the masking stimulus. When the values of the logarithm of the threshold concentration of the test stimulus are plotted against the logarithm of the concentration of the masking stimulus for a pair of odorous materials, a straight line is obtained. It is suggested that the gradient of this line may be used as a measure of the degree of community of odour-property between the pair of substances.     

Trigeminal sensitivity to contact chemical stimulation: A new method and some results

Acquisition of knowledge about the chemical senses might be hastened if chemicals or techniques that permitted stimulation of either the common chemical sense, mediated by the trigeminal nerve, or the sense of smell, mediated by the olfactory nerve without concomitant stimulation of the other sense, were used. Flowing the nonodorized output of an olfactometer into one naris of subjects while velopharyngeal closure was maintained produced effluent flow from the contralateral naris. To prevent odorous molecules from reaching the olfactory epithelium, the contralateral naris was stimulated by applying diluted and undiluted chemical solutions directly to the septal squamous epithelium downstream from the olfactory mucosa. A series of five geometric dilutions of three chemicals and one saturated solution of a fourth were used. The weakest dilution of each chemical was an adequate olfactory stimulus. Two were known trigeminal stimulants (acetic acid and butanol), and two were rated low in trigeminal stimulatory capacity (phenethyl alcohol and vanillin). The results showed that this method was useful in determining the trigeminal threshold for some chemicals. When this method was used, saturated aqueous solutions of vanillin and phenethyl alcohol were clearly not detectable by the trigeminal receptors. The application of the undiluted vanillin and phenethyl alcohol yielded a clear sensation. This result may imply that there are no pure olfactory stimuli.     

Further experiments on the olfactory thresholds of pure chemical substances, using the “Sniff-Bottle method”

“Sniff-Bottle” method of determining olfactory thresholds under conditions of adaptation to a second olfactory stimulus, as described by Cheesman and Mayne (1953), has been further developed. Their study was limited to the mutual adaptation effects of three substances. The original matrix of nine quantities, described as degrees of community of odour property, has been revised and extended to include a fourth stimulus-substance. It is suggested that the matrix now obtained shows a definite pattern characteristic of consistent mutual relationships between the substances. A number of shortcomings in the original technique are discussed, and the appropriate emendations described.     

The design and operation of an improved olfactometer for behavioral and physiological investigation1

An improved olfactometer is described, and its range of application for the study of the olfaction in man is discussed. The apparatus is based on air dilution; an odorant is diluted in a constant-flowing stream of air. The odor-containing air flows to S, who is seated in an enclosed partition with his head in a Plexiglas hood. A visual signal system allows communication between E and S. Precision flowmeters, solenoid valves, one-way floats, and an automated control system permit E to select rapidly a large range of stimuli, stimulus concentrations, and trial lengths. The apparatus has been used in a variety of situations ranging from absolute threshold detection to adaptation and recovery.     

Evidence for multiple strategies in off-beat tapping with anisochronous stimuli

There is a large body of evidence relating to the ways that people tap in time with sounds, and perform error correction in order to do this. However, off-beat tapping is less well investigated than on-beat tapping. The current study involves coordinating with a stimulus sequence with underlying isochrony and systematic deviations from this isochrony that increase or decrease in magnitude to look at people’s capacity to error-correct when performing off-beat synchronisation with a set of sounds. Participants were instructed to ‘tap between the tones’ but ‘try to maintain regularity’. While analysis using typical methods suggested a form of error correction was occurring, a series of more complex analyses demonstrated that participants’ performance during each trial can be classified according to one of four different strategies: maintaining a regular pulse, error correction, phase resetting, and negative error correction. While maintaining a regular pulse was the preferred strategy in conditions with increasingly isochronous stimuli, the majority of trials are best explained by other strategies, suggesting that participants were generally influenced by variability in the stimuli.     

Olfactory stimulation induces filial preferences for huddling in rat pups.

Rat pups of all ages huddle with conspecifics, but the senosory control of contact behavior changes ontogenetically. Thermal cues control huddling until about Day 15, at which time species' odors become the dominant stimulus. The present experiments indicate that the filial response to conspecifics is dependent on olfactory experience. A synthetic chemical scent was added to the smells of the dam from Day 1 to Day 20 postpartum. Standardized videographic tests were used to assess the development of huddling preference. Preferences for nest-typical smells emerged by Day 15 in pups from both scented and nonscented litters. Pups from scented nests preferred to huddle with a scented stimulus rat, whereas control pups preferred a nonadulterated rat stimulus. Additional testing indicated that the affiliative preferences were specific to rearing odor and were not based on decreased aversion to test scents, or on disrupted olfactory discrimination. The ontogeny of species-typical contact behavior is discussed in terms of the induction of a perceptual preference that is based on early odor stimulation.     

Three-stimulus procedures in olfactory psychophysics: An experimental comparison of Thurstone-Ura and three-alternative forced-choice models of signal detection theory

The experimental differences between the triangular method and three-alternative forcedchoice (3-AFC) signal detection theory procedure are briefly reviewed, and the conditions to be met for a valid application of the respective procedures under the Thurstone-Ura and 3-AFC models are described. The assumptions of both of these unidimensional probabilistic models are given, and the functions relating the probability of a correct response to d, a parameter of sensory stimulus distance, are specified. Since the two models both contain d, the hypothesis of invariability of this parameter with the triangular method and the 3-AFC procedure was tested using olfactory stimuli. This hypothesis was strongly confirmed, since the functions relating d to the logarithm of the ratio of the physical stimulus values were virtually identical for the two methods and their concomitant models. The results are important not only for the field of olfactory psychophysics; they also have wider methodological and psychophysical interest. The bias against the middle stimulus of a triangle in the triangular method observed when olfactory stimuli are used can be explained as the resultant of sensory adaptation. Finally, some practical implications of the present results for application of the triangular method are discussed.     

The effect of irrelevant spatial correspondences on two-choice response-time.

Simon and his associates have demonstrated a general effect in two-choice reaction- time tasks involving laterally disposed responses, and a succession of stimuli presented unpredictably at either of two laterally disposed positions, the stimulus positions being irrelevant in deciding the response. Reaction times are found to be faster for trials in which the spatial loci of stimulus and response correspond than for trials in which they counter-correspond. The present experiment investigated the dependence of this effect upon spatial orientation and upon the logical character of the task. The effect was found not only for laterally disposed pairs of stimulus positions and responses but also for vertical dispositions. The effect was found to be critically dependent upon the logical character of the task, such that it could readily be produced in a reversed form. The results could be well described by considering the logical characters of the recodings of the relevant and irrelevant attributes of stimulus and response. The special status formerly attributed to the processing of spatial information is questioned.     

Measurement of olfactory signal detectability using an air-dilution olfactometer

The Cheesman air dilution olfactometer, although designed for group threshold measurements, was modified to allow individual testing of subjects. However, adaptation effects of olfactory stimuli precluded use of interstimulus intervals of less than 30 sec. so that 3-hr. testing sessions were necessary to obtain a single measurement of sensitivity. Four subjects were tested intensively with isopropyl alcohol (CH3CH(OH)CH3) at concentration levels determined by previous group threshold studies. In the first condition, one concentration only was presented in testing sessions, while in the second condition, six concentrations were presented and the limits of concentrations adjusted to allow subthreshold presentations. Signal detectability indices (dc') were calculated more frequently and more reliably in the second condition than in the first.     

An inexpensive and automated method for presenting olfactory or tactile stimuli to rats in a two-choice discrimination task

An inexpensive and automated method for presentation of olfactory or tactile stimuli in a two-choice task for rats was implemented with the use of a computer-controlled bidirectional motor. The motor rotated a disk that presented two stimuli of different texture for tactile discrimination, or different odor for olfactory discrimination. Because the solid olfactory stimuli were placed outside the chamber in metal pods with a mesh at front for odor sampling, "washout" of odors between trials was not necessary. To avoid differential auditory cues from motor rotation, the stimuli were arranged such that on each trial the motor always rotated exactly one quarter revolution (in 1 s), left or right, to present the next stimulus at trial start. To illustrate the use of the equipment, 2 rats were trained on tactile discrimination and 2 rats on olfactory discrimination. The rats sampled the stimulus on the disk through a port on the back wall by sniffing at it (olfactory) or touching it (tactile). The task was a go-left/go-right discrimination with the stimulus on the disk being discriminative for which lever provided reinforcement. The rats reached a stable level above 90% correct after 21 and 32 training sessions for tactile and olfactory discrimination, respectively. The article outlines how the equipment was constructed from low-cost components. Inputs from and outputs to the equipment were implemented through the parallel port of a personal computer without the use of a commercial interface board. The method of automated and low-cost presentation of olfactory or tactile stimuli should be of use for a variety of experimental situations such as matching-to-sample and cross-modal discrimination.     

Improved low-cost,MR-compatible olfactometer to deliver tobacco smoke odor

We describe a low-cost, MRI-compatible olfactometer that delivers fresh cigarette smoke odor, a challenging odorant to present, as well as other odorants. This new olfactometer retains all of the advantages of an earlier design that was capable of only delivering volatile odors (Lowen & Lukas, Behavior Research Methods, 38, 307–313, 2006). The new system incorporates a novel switching mechanism that allows it to deliver fresh smoke generated from a burning cigarette during a stimulus presentation paradigm that might be employed in a cue-reactivity experiment. An evaluation study established that the olfactometer reliably delivered smoke to the participants and that tobacco smoke was discriminated from other odorants; there were no adverse reactions to the device.     

Causal judgments about empirical information in an interrupted time series design

Empirical information available for causal judgment in everyday life tends to take the form of quasi-experimental designs, lacking control groups, more than the form of contingency information that is usually presented in experiments. Stimuli were presented in which values of an outcome variable for a single individual were recorded over six time periods, and an intervention was introduced between the fifth and sixth time periods. Participants judged whether and how much the intervention affected the outcome. With numerical stimulus information, judgments were higher for a pre-intervention profile in which all values were the same than for pre-intervention profiles with any other kind of trend. With graphical stimulus information, judgments were more sensitive to trends, tending to be higher when an increase after the intervention was preceded by a decreasing series than when it was preceded by an increasing series ending on the same value at the fifth time period. It is suggested that a feature-analytic model, in which the salience of different features of information varies between presentation formats, may provide the best prospect of explaining the results.     

Context-dependent olfactory learning monitored by activities of salivary neurons in cockroaches

Context-dependent discrimination learning, a sophisticated form of nonelemental associative learning, has been found in many animals, including insects. The major purpose of this research is to establish a method for monitoring this form of nonelemental learning in rigidly restrained insects for investigation of underlying neural mechanisms. We report context-dependent olfactory learning (occasion-setting problem solving) of salivation, which can be monitored as activity changes of salivary neurons in immobilized cockroaches, Periplaneta americana. A group of cockroaches was trained to associate peppermint odor (conditioned stimulus, CS) with sucrose solution reward (unconditioned stimulus, US) while vanilla odor was presented alone without pairing with the US under a flickering light condition (1.0 Hz) and also trained to associate vanilla odor with sucrose reward while peppermint odor was presented alone under a steady light condition. After training, the responses of salivary neurons to the rewarded peppermint odor were significantly greater than those to the unrewarded vanilla odor under steady illumination and those to the rewarded vanilla odor was significantly greater than those to the unrewarded peppermint odor in the presence of flickering light. Similar context-dependent responses were observed in another group of cockroaches trained with the opposite stimulus arrangement. This study demonstrates context-dependent olfactory learning of salivation for the first time in any vertebrate and invertebrate species, which can be monitored by activity changes of salivary neurons in restrained cockroaches.     

Sustained perceptual invisibility of solid shapes following contour adaptation to partial outlines

Contour adaptation (CA) is a recently described paradigm that renders otherwise salient visual stimuli temporarily perceptually invisible. Here we investigate whether this illusion can be exploited to study visual awareness. We found that CA can induce seconds of sustained invisibility following similarly long periods of uninterrupted adaptation. Furthermore, even fragmented adaptors are capable of producing CA, with the strength of CA increasing monotonically as the adaptors encompass a greater fraction of the stimulus outline. However, different types of adaptor patterns, such as distinctive shapes or illusory contours, produce equivalent levels of CA suggesting that the main determinants of CA are low-level stimulus characteristics, with minimal modulation by higher-order visual processes. Taken together, our results indicate that CA has desirable properties for studying visual awareness, including the production of prolonged periods of perceptual dissociation from stimulation as well as parametric dependencies of that dissociation on a host of stimulus parameters.