Phenomenal and access consciousness in olfaction

Contemporary literature on consciousness, with some exceptions, rarely considers the olfactory system. In this article the characteristics of olfactory consciousness, viewed from the standpoint of the phenomenal (P)/access (A) distinction, are examined relative to the major senses. The review details several qualitative differences in both olfactory P consciousness (shifts in the felt location, universal synesthesia-like and affect-rich experiences, and misperceptions) and A consciousness (recovery from habituation, capacity for conscious processing, access to semantic and episodic memory, learning, attention, and in the serial-unitary nature of olfactory percepts). The basis for these differences is argued to arise from the functions that the olfactory system performs and from the unique neural architecture needed to instantiate them. These data suggest, at a minimum, that P and A consciousness are uniquely configured in olfaction and an argument can be made that the P and A distinction may not hold for this sensory system.     

Differential luminance sensitivity of the human visual system

In this paper the differential sensitivity of the visual system is investigated by means of two simultaneously presented stimuli in a yes-no procedure. The sensitivity measure σ_I appears to be proportional to stimulus intensity (i.e., Weber’s law). The curve displaying Weber’s law is little affected by variation of the background intensity or of the adaptation level. An increment threshold experiment using only one stimulus yields a proportionality of σ_I with the square root of the background intensity. An additional experiment shows that the sensitivity measure σ_I for two flashes decreases first, from dark up to a particular background intensity, and increases when the background tends to mask the flashes. So, in general, two background levels exist with the same differential sensitivity. The results cannot easily be explained by the simple quantum fluctuation concept. A model based partially on electrophysiological data from the literature is proposed which encounters a particular adaptation mechanism, a transducer with a limited dynamical range, and a range setting mechanism.     

Identification of self through olfaction

To study olfactory communication in humans, 100 undergraduates ranging from age 18 to 45 yr. wore freshly washed, identical T-shirts continuously for 24 hr. During this time, the participants did not bathe or shower or apply any scent producing substance to their bodies, i.e., deodorants, perfumes. Upon retrieval, each shirt was placed in an identical brown bag. In groups of 10, each participant attempted to identify the T-shirt he had worn the previous 24 hr. The task was administered separately for each individual so that no participants knew the choice by a previous colleague. Analysis shows that the participants were able to identify correctly their own shirts on the first try three-quarters of the time. Furthermore, sex, age, smoking habit of the participant, and menstrual cycle phase in the women were factors in successful outcomes.     

A factorial analysis of olfaction

Twenty-one reagents were rated on a pleasantness scale by 182 subjects. The tetrachoric correlation coefficients were determined for the variables. The correlation matrix thus obtained was subjected to a Thurstone analysis which gave rise to a 6-dimensional structure. Two of these were not clear-cut, and the last one appeared to be a residual factor. One factor, the benzene-ketone, revealed the chemical property of unsaturation and the physiological quality of possible trigeminal stimulation. The other two factors were marked by the presence of oxygen and nitrogen, respectively, and were tentatively labelled as a plant factor and an animal factor accordingly. The intercorrelations of the primaries are high.The author wishes to express his gratitude to Professor L. L. Thurstone for his kindness in providing facilities which made this study possible and for his guidance on the factorial problem; to Doctor T. G. Andrews for his many invaluable assistances and technical advice on the experimental aspect of this problem; to Miss Florence Brown for her editorial assistance; and to Mrs. Virginia Brown for her generous assistance on the computational procedures.     

Cognition and olfaction: a review

Examines research in cognitive psychology, which has in the past paid little attention to the olfactory modality. But there is now a significant body of literature on the role of the olfactory system in memory and cognition. Human beings possess an excellent ability to detect and discriminate odors, but they typically have great difficulty in identifying particular odorants. This results partly from the use of an improverished and idiosyncratic language to describe olfactory experiences, which are normally encoded either in a rudimentary sensory form or as part of a complex but highly specific biographical episode. Consequently, linguistic processes play only a very limited role in olfactory processing, whereas hedonic factors seem to be of considerable importance.     

On the consistency of intramodal intensity matching in olfaction

Magnitude matchings of odor intensity were obtained for three chemical compounds (hydrogen sulfide, pyridine, and dimethyl disulfide) in four experiments. An equal-sensation function in the form of a power function described the data well. This equation can be written neglecting the multiplicative constant, Ф_i = Ф_k ^b _ik, where i and k represent two different odorants. The exponent b_ik, where the first index stands for matching continuum and the second index for reference continuum, was fairly well predicted according to the formulae, (ie, 264, 2) where i, j, and k are three different odorants. The results validate the equal-sensation function and indicate implicitly that intensity matchings between different intramodal continua are approximately transitive and symmetric with respect to odor.     

Sex differences in human olfaction: Between evidence and enigma

The sex of individuals plays an important part in determining their olfactory abilities, with females generally being superior to males. The present review examines the way in which sex differences influence sensitivity, identification, familiarity, and recognition of odours. It also examines whether sex differences are more pronounced with some odours than others, and how sex differences are affected by the manner of testing. Two different explanations for the superiority of females over males in olfaction are evaluated.     

Differential sensitivity of recent vs. remote memory traces to extinction in a water-maze task in rats

Extinction has mostly been studied in conditioning paradigms, more sparsely in spatial tasks, and never as a function of the age of a spatial memory. Using rats, we compared the time-course of extinction of a recent (5 days) vs. remote (25 days) spatial memory in a water maze, over three probe trials. When the trials were set 24h apart, performance in the remote memory group was significantly worse on the first probe trial and significantly better on the third probe trial, as compared to the recent memory group, thereby showing differences between cognitive operations underlying recent vs. remote memory extinction. In contrast, when trials were given consecutively, both groups showed a similar profile of extinction. Furthermore, in a room with overly-salient cues providing a strong remote memory trace, no difference between groups was observed when the spaced extinction paradigm was used. These results might be related to a balance between reconsolidation and extinction processes occurring after a first retrieval experience, of which the outcome may depend on the extinction protocol, and on the age and strength of a memory.     

A role for olfaction in object recognition by normal and hippocampal-damaged rats

To examine how olfactory and visual factors affect object discriminations in rats with and without hippocampus damage, the authors trained Long-Evans rats on simple object discriminations. They then examined how these discriminations were affected by rotations of the objects, by coating the objects in a transparent acrylic coating, or by both rotating and coating the objects in acrylic. The rats displayed no impairments when the objects were only sprayed in acrylic, and they displayed minor impairments when the objects were rotated. However, when the objects were both rotated and acrylic coated, the rats displayed severe impairments. This suggests that the rats are solving the rotated-only phase based on surface features of the objects (probably odor) and not based on the visual information. Such species' biases for obtaining object information are important factors to consider when designing and interpreting visual memory experiments across species. There was no difference in performance between the rats with hippocampus damage and the sham rats, and this is consistent with the literature on similar tasks.     

A symmetric and an asymmetric model for the equal-sensation function in olfaction

Data from various intramodel matching experiments in olfaction were analyzed with regard to a symmetric and an asymmetric model for the equal-sensation function. The asymmetric model was discussed in relation to the symmetric model. In all, 11 equal-sensation functions were investigated, and of these 9 were with different pairs of odorants. The following odorants were investigated: hydrogen sulfide, pyridine, dimethyl disulfide, and five odorants obtained by different combustion procedures of animal manure. It was found that the equal-sensation function can be written in the following asymmetric form: $$\varphi _i = b_{ik} \lambda \cdot \varphi _k ^{b_{ik} } ,\psi _i = \psi _k $$ or symmetric form: $$\varphi _i = C^{I - b_{ik} } \cdot \varphi _k ^{b_{ik} } ,\psi _i = \psi _k ,$$ where ?_i and ?_k are stimuli expressed in multiples of respective absolute thresholds, λ and C are general constants invariant of experimental matching method and matched attribute (perceived unpleasantness or intensity). The constants λ and C were calculated both for group data and individual data. The asymmetric form of the equal-sensation function was interpreted in terms of relativity and the symmetric form in terms of measurement.     

A possible confound and the role of olfaction in mouse aggressive interactions

In investigating the olfactory modulation of aggression in mice, a urine-coating technique frequently has been used. Fighters typically have been tested against castrated animals coated with either urine or water. Then, if the fighters are more aggressive toward urine-coated castrates than toward water-coated castrates, it is concluded that olfaction plays a role in this discriminatory response. However, it is possible that the fighers might react to behavioral differences between these two groups of castrates caused by the different experimental treatment. Three experiments were conducted to study this possible confound and the role of olfaction in the control of agonistic encounters. The results indicated that 1) the confound is not likely to operate; 2) even if the confound is allowed to operate, it is not an effective discriminatory cue; and 3) anosmic fighters do not exhibit differential attacks toward castrates treated with different chemo-signals. Therefore, the emission and perception of olfactory cues do play an important role in mouse agonistic interactions.     

A computer-controlled olfactometer for fMRI and electrophysiological studies of olfaction

A design for an inexpensive and reliable olfactometer is presented. The design has several advantages for fMRI and electrophysiology investigators. These advantages include relatively rapid odorant rise times, computer control, multiple odor administration, and no ferrous materials near the subjects. In addition, the device is contamination resistant, and, because the air is neither warmed nor humidified, it is unlikely to become an incubator for bacteria. The olfactometer is constructed of off-the-shelf chromatography parts that require little modification.     

Neuroimaging of multisensory processing in vision,audition, touch,and olfaction

The development of neuroimaging methods has had a significant impact on the study of the human brain. Functional MRI, with its high spatial resolution, provides investigators with a method to localize the neuronal correlates of many sensory and cognitive processes. Magneto- and electroencephalography, in turn, offer excellent temporal resolution allowing the exact time course of neuronal processes to be investigated. Applying these methods to multisensory processing, many research laboratories have been successful in describing cross-sensory interactions and their spatio-temporal dynamics in the human brain. Here, we review data from selected neuroimaging investigations showing how vision can influence and interact with other senses, namely audition, touch, and olfaction. We highlight some of the similarities and differences in the cross-processing of the different sensory modalities and discuss how different neuroimaging methods can be applied to answer specific questions about multisensory processing.Edited by: Marie-Hélène Giard and Mark Wallace