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.     

Influence of auditory and audiovisual stimuli on the right–left prevalence effect

When auditory stimuli are used in two-dimensional spatial compatibility tasks, where the stimulus and response configurations vary along the horizontal and vertical dimensions simultaneously, a right–left prevalence effect occurs in which horizontal compatibility dominates over vertical compatibility. The right–left prevalence effects obtained with auditory stimuli are typically larger than that obtained with visual stimuli even though less attention should be demanded from the horizontal dimension in auditory processing. In the present study, we examined whether auditory or visual dominance occurs when the two-dimensional stimuli are audiovisual, as well as whether there will be cross-modal facilitation of response selection for the horizontal and vertical dimensions. We also examined whether there is an additional benefit of adding a pitch dimension to the auditory stimulus to facilitate vertical coding through use of the spatial-musical association of response codes (SMARC) effect, where pitch is coded in terms of height in space. In Experiment 1, we found a larger right–left prevalence effect for unimodal auditory than visual stimuli. Neutral, non-pitch coded, audiovisual stimuli did not result in cross-modal facilitation, but did show evidence of visual dominance. The right–left prevalence effect was eliminated in the presence of SMARC audiovisual stimuli, but the effect influenced horizontal rather than vertical coding. Experiment 2 showed that the influence of the pitch dimension was not in terms of influencing response selection on a trial-to-trial basis, but in terms of altering the salience of the task environment. Taken together, these findings indicate that in the absence of salient vertical cues, auditory and audiovisual stimuli tend to be coded along the horizontal dimension and vision tends to dominate audition in this two-dimensional spatial stimulus–response task.     

Agonistic sensory effects of airborne chemicals in mixtures: Odor, nasal pungency, and eye irritation

Threshold responses of odor, nasal pungency (irritation), and eye irritation were measured for single chemicals (1-propanol, 1-hexanol, ethyl acetate, heptyl acetate, 2-pentanone, 2-heptanone, toluene, ethyl benzene, and propyl benzene) and mixtures of them (two three-component mixtures, two sixcomponent mixtures, and one nine-component mixture). Nasal pungency was measured in subjects lacking a functional sense of smell (i.e., anosmics) to avoid interference from olfaction. Various degrees of stimulus agonism (additive effects) were observed for each of the three sensory channels when testing mixtures. As the number of components and the lipophilicity of such components in the mixtures increased, so did the degree of agonism. Synergistic stimulus agonism characterized the eyeirritation response for the most complex (the nine-component) and the most lipophilic (one of the sixcomponent) mixtures. Physicochemical properties play a large role in the determination of sensitivity to airborne chemicals, particularly to their ability to evoke irritation. While this has revealed itself previously with respect to single chemicals, it seems to have relevance to mixtures as well.     

Does taste or odor activate the same brain networks after retrieval of taste potentiated odor aversion?

When simultaneous presentation of odor and taste cues precedes illness, rats acquire robust aversion to both conditioned stimuli. Such a phenomenon referred to as taste-potentiated odor aversion (TPOA) requires information processing from two sensory modalities. Whether similar or different brain networks are activated when TPOA memory is retrieved by either the odor or the taste presentation remains an unsolved question. By means of Fos mapping, we investigated the neuronal substrate underlying TPOA retrieval elicited by either the odor or the taste conditioned stimulus. Whatever the sensory modality used to reactivate TPOA memory, a significant change in Fos expression was observed in the hippocampus, the basolateral nucleus of amygdala and the medial and the orbito-frontal cortices. Moreover, only the odor presentation elicited a significantly higher Fos immunoreactivity in the piriform cortex, the entorhinal cortex and the insular cortex. Lastly, according to the stimulus tested to induce TPOA retrieval, the BLA was differentially activated and a higher Fos expression was induced by the odor than by the taste in this nucleus. The present study indicates that even if they share some brain regions, the cerebral patterns induced by either the odor or the taste are different. Data are discussed in view of the relevance of each conditioned stimulus to reactivate TPOA memory and of the involvement of the different labeled brain areas in information processing and TPOA retrieval.     

Individual differences in right and left reaction time.

Experiments designed to check the absence of effects for hands and handedness in simple and two-choice reaction time found unexpected individual differences related to stimulus laterality. The majority of subjects responded faster to the stimulus on the left and a substantial minority responded faster to the stimulus on the right in any choice pair. The right index finger was slower than the left index or the middle fingers. Choices tended to be faster between fingers on different hands than on the same hand and same-hand choices were faster with the left hand than the right hand. There were no effects attributable to hand preference or sex.     

No overall right-left prevalence for horizontal

The present study confirmed that there is no overall right—left prevalence effect for Simon tasks, in which stimulus location is irrelevant, when (1) the stimulus and response sets vary along both horizontal and vertical dimensions simultaneously, (2) the stimulus set varies along both dimensions, but the response set varies along only one dimension, and (3) the stimuli and responses vary in one of four possible locations and responses are made by a unimanual joystick movement. In all experiments, Simon effects of similar magnitude were evident for both the horizontal and the vertical dimensions. The findings suggest that the right—left prevalence effect observed with two-dimensional location-relevant tasks is not due to stronger overall automatic activation of horizontal codes but to different translation efficiencies in intentional response selection processes.     

Orthogonal cross-task compatibility: Abstract spatial coding in dual tasks

Spatially orthogonal stimulus and response sets can produce compatibility effects. To explore whether such effects cross the border of logically independent tasks, we combined a nonspeeded visual task requiring verbal report of a stimulus movement (up vs. down) with an auditory reaction time task that required a unimanual movement to the left or right. Two experiments demonstrated that up stimuli facilitate rightward responses and down stimuli facilitate leftward responses, relative to the opposite combinations, thus producing an orthogonal cross-task compatibility effect. This effect presumably arises from abstract coding with respect to the salient referents of a spatial dimension (i.e., up and right), so that coactivation of structurally similar codes leads to mutual priming even when the codes refer to different tasks. The present evidence for abstract spatial coding extends previously proposed coding principles from single-task settings to dual-task settings.     

Smelling what was there: Acquired olfactory percepts are resistant to further modification

Repeated exposure to a mixture of two odors can increase their perceived similarity to each other when presented separately. Experiment 1 failed to detect any reduction of this effect by an interference treatment consisting of separate exposures to the odors after they had first been presented as a mixture. Exposure to a mixture also results in participants mistakenly rating this mixture and its elements as having occurred with equal frequency (i.e., confusing the mixture and its elements). The interference treatment did not affect this either, whereas it did change judgments about the frequency of a color–odor mixture and its elements. The greater resistance to interference of odor–odor learning compared to color–odor learning may result from configural encoding of odor–odor mixtures. Experiment 2 found that separate exposures to two odors not previously mixed decreased their perceived similarity. This result was inconsistent with the possibility that the interference treatment in Experiment 1 had tended to increase the similarity of the two odors, for example, by a process of sensory adaptation. Rather it suggested a process akin to acquired distinctiveness.     

Olfactory discrimination, reversal learning, and stimulus control in rats.

Rats were trained to discriminate lights, tones, or odors and then given a series of discrimination reversals. Only rats trained with odors showed positive transfer on the first reversal and acquisition of a reversal set. Other experiments demonstrated that rats preferentially attend to odors when presented in compound with lights or tones; that odors exert more discriminative control than tones in tests using compound stimuli of competing sign; and that after pretraining on the positive stimulus, acquisition of an odor but not a light discrimination occurs with virtually no errors. These results demonstrate the importance of stimulus modality in the establishment of stimulus control and the need for more careful analysis of stimulus factors in cross-species comparisons of learning ability.     

Differential associative conditioning and olfactory discrimination in the spiny lobster Panulirus argus

A differential aversive associative conditioning paradigm was used to assess the ability of the spiny lobster Panulirus argus both to associatively learn not to respond to the odorant stimulus to which it was conditioned and to discriminate between odorants. The paradigm consisted of pairing an aversive stimulus (pseudopredator) with a conditioned chemical stimulus (shrimp mixture). Four artificial mixtures (crab, mullet, oyster, and shrimp), each at 0.05 and 0.5 mM, were presented to the animals prior to, during, and following conditioning to both concentrations of the shrimp mixture. Pre- vs postconditioning changes in three types of behavioral responses (and an index based on a composite of these three behaviors) were used as indicators of learned aversions. Olfactory discrimination abilities were determined by comparing the aversion to the conditioned mixture with the aversions to the three nonconditioned mixtures. A high degree of associative learning was attained after 10 pairings of the pseudopredator with the shrimp mixture over a period of 5 test days. According to the aversion index, animals conditioned to shrimp mixture perceived crab mixture as being more similar to shrimp mixture than were mullet and oyster mixtures, but all three nonconditioned mixtures were perceived as being significantly different from the shrimp mixture. These results are in concordance with results of a cluster analysis based on the mixture compositions, which indicates that shrimp and crab mixtures are compositionally similar, while mullet and oyster mixtures are compositionally distinct from the shrimp mixture.     

The influence of chemical complexity on the perception of multicomponent odor mixtures

The present study investigates the hypothesis that complexobject odors (odors that emanate from flowers, foods, sewage, etc.) that consist of dozens of odorants are processed and encoded as discrete entities, as if each was a single chemical odor. To test this hypothesis, the capacity of trained subjects to discriminate and identify the components of stimuli consisting of one to eight object odors was determined. The results indicated that subjects could only identify up to four object odors in a mixture, which is similar to earlier findings with mixtures that contained only single chemical odors. The limited capacity was also reflected in the number of odors selected, regardless of whether the choices were correct or incorrect, in confidence ratings, and in decision times. The identification of a limited number of object odors in every mixture that was presented suggests that both associative (synthetic) and dissociative (analytic) processes are involved in the perceptual analysis of odor mixtures.     

Implicit and explicit tests of odor memory reveal different outcomes following interference

Experiencing two odors as a mixture can later increase their perceived similarity when presented separately. Such an increase in similarity can be used as an implicit measure of how well participants remember the mixture. Three experiments tested the resistance to interference of this effect by first giving participants exposure to two 2-odor mixtures and then presenting each odor from one mixture (interfered pair) separately many times. After the latter interference phase, participants rated the similarity of the two odors in each pair. The experiments varied in terms of the number of initial exposures to the mixtures, the number of odor presentations in the interference phase, and the control conditions employed. No difference in similarity ratings for the interfered and non-interfered pair was found in any experiment. In contrast to the lack of interference with this implicit measure, an explicit measure of memory based on participants’ ratings of odor frequency revealed that they could recall to some degree that the interfered odors had been presented alone in the second phase. These results suggest that implicit memory for odor mixtures is highly resistant to interference and is consistent with a configural encoding account of this effect.     

Perceptual learning with odors: implications for psychological accounts of odor quality perception

After two odors have been experienced in a mixture, the pair are subsequently rated as sharing more qualities and smelling more alike than equally exposed controls. These effects may result from the retrieval of a common mixture memory when either component is sniffed alone. If correct, odor pairs experienced together in a mixture should also be less discriminable than those experienced an equal number of times but in different mixtures. This was tested here by exposing participants to two odor mixtures (either AX, BY or AY, BX) and then testing their ability to discriminate between the components. As predicted, odors previously experienced together as a mixture were less discriminable than controls. These and related findings noted above suggest that learning and memory play an important role in odor quality perception.     

Display-control arrangement correspondence and logical recoding in the Hedge and Marsh reversal of the Simon effect

When left and right keypresses are made to stimuli in left and right locations, and stimulus location is irrelevant to the task, responses are typically faster when stimulus location corresponds with response location than when it does not (the Simon effect). This effect reverses when the relevant stimulus-response mapping is incompatible, with responses being slower when stimulus and response locations correspond (the Hedge and Marsh reversal). Simon et al. (Acta Psychol. 47 (1981) 63) reported an exception to the Hedge and Marsh reversal for a situation in which the relevant stimulus dimension was the color of a centered visual stimulus and the irrelevant location information was left or right tone location. In contrast, similar experiments have found a reversal of the Simon effect for tone location when relevant visual locations were mapped incompatibly to responses. We conducted four experiments to investigate this discrepancy. Both results were replicated. With an incompatible mapping, irrelevant tone location showed a small reverse Simon effect when the relevant visual dimension was physical location but not when the color of a centered stimulus or the direction in which an arrow pointed conveyed the visual location information. The reversal occurred in a more standard Hedge and Marsh task in which the irrelevant dimension was location of the colored stimulus, but only when the response keys were visibly labeled. Several of the results suggest that display-control arrangement correspondence is the primary cause of the Hedge and Marsh reversal, with logical recoding playing only a secondary role.     

Stimulus-set location does not affect orthogonal stimulus-response compatibility

In two-choice tasks for which stimuli and responses vary along orthogonal dimensions, one stimulus-response mapping typically yields better performance than another. For unimanual movement responses, the hand used to respond, hand posture (prone or supine), and response eccentricity influence this orthogonal stimulus-response compatibility (SRC) effect. All accounts of these phenomena attribute them to response-related processes. Two experiments examined whether manipulation of stimulus-set position along the dimension on which the stimuli varied influences orthogonal SRC in a manner similar to the way that response location does. The experiments differed in whether the stimulus dimension was vertical and the response dimension horizontal, or vice versa. In both experiments, an advantage of mapping up with right and down with left was evident for several response modes, and stimulus-set position had no influence on the orthogonal SRC effect. The lack of effect of stimulus-set position is in agreement with the emphasis that present accounts place on response-related processes. We favor a multiple asymmetric codes account, for which the present findings imply that the polarity of stimulus codes does not vary across task contexts although the polarity of response codes does.     

Right or wrong, familiar or novel in pictorial list discrimination learning

The interaction between nonassociative learning (presentation frequencies) and associative learning (reinforcement rates) in stimulus discrimination performance was investigated. Subjects were taught to discriminate lists of visual pattern pairs. When they chose the stimulus designated as right they were symbolically rewarded and when they chose the stimulus designated as wrong they were symbolically penalised. Subjects first learned one list and then another list. For a "right" group the pairs of the second list consisted of right stimuli from the first list and of novel wrong stimuli. For a "wrong" group it was the other way round. The right group transferred some discriminatory performance from the first to the second list while the control and wrong groups initially only performed near chance with the second list. When the first list involved wrong stimuli presented twice as frequently as right stimuli, the wrong group exhibited a better transfer than the right group. In a final experiment subjects learned lists which consisted of frequent right stimuli paired with scarce wrong stimuli and frequent wrong stimuli paired with scarce right stimuli. In later test trials these stimuli were shown in new combinations and additionally combined with novel stimuli. Subjects preferred to choose the most rewarded stimuli and to avoid the most penalised stimuli when the test pairs included at least one frequent stimulus. With scarce/scarce or scarce/novel stimulus combinations they performed less well or even chose randomly. A simple mathematical model that ascribes stimulus choices to a Cartesian combination of stimulus frequency and stimulus value succeeds in matching all these results with satisfactory precision.     

Influences of multiple spatial stimulus and response codes on orthogonal stimulus-response compatibility

When up-down stimuli are mapped to left-right responses, an up-right/down-left mapping advantage is found that is modified by response eccentricity and hand posture. These effects can be attributed to correspondence of asymmetric stimulus and response codes formed relative to multiple reference frames. We examined the influence of stimulus-set location on these orthogonal stimulus-response compatibility (SRC) effects. In Experiment 1, the stimulus set appeared in the upper or lower display positions. A spatial code for stimulus-set location was formed, producing Simon-type response eccentricity and hand posture effects, but this code had no influence on the coding of the relevant stimuli. In Experiment 2, the stimulus set appeared in the left, center, or right positions relative to the response location, which also varied, to dissociate the effects of response location, relative to the stimulus display and body midline. The former factor influenced the orthogonal SRC effect for both unimanual switch movements and bimanual keypresses, and the latter factor influenced the effect for only unimanual switch movements. Stimulus-set location causes orthogonal Simon-type effects when varied along the stimulus dimension and provides a referent for response coding when varied along the response dimension.     

Influences of multiple spatial stimulus and response codes on orthogonal stimulus—response compatibility

When up-down stimuli are mapped to left-right responses, an up-right/down-left mapping advantage is found that is modified by response eccentricity and hand posture. These effects can be attributed to correspondence of asymmetric stimulus and response codes formed relative to multiple reference frames. We examined the influence of stimulus-set location on these orthogonal stimulus-response compatibility (SRC) effects. In Experiment 1, the stimulus set appeared in the upper or lower display positions. A spatial code for stimulus-set location was formed, producing Simon-type response eccentricity and hand posture effects, but this code had no influence on the coding of the relevant stimuli. In Experiment 2, the stimulus set appeared in the left, center, or right positions relative to the response location, which also varied, to dissociate the effects of response location, relative to the stimulus display and body midline. The former factor influenced the orthogonal SRC effect for both unimanual switch movements and bimanual keypresses, and the latter factor influenced the effect for only unimanual switch movements. Stimulus-set location causes orthogonal Simon-type effects when varied along the stimulus dimension and provides a referent for response coding when varied along the response dimension.     

The Formation of Left‐Right Identification: Pathways and Correlates of Parental Influence

Given the significance of the left‐right dimension as one of the most frequently employed capping term of ideological thought in most western democracies, the question arises as to how people come to identify themselves along this continuum. Drawing on a set of parent‐child pairs located in Catalonia, we seek to determine whether the processes found elsewhere with respect to the intergenerational transmission of partisanship and issue stances also apply to left‐right ideology, in a novel context characterized by the presence of a distinctive, partially cross‐cutting dimension based on center‐periphery loyalties. Results provide strong support for the principles of the direct transmission model as derived from social learning theory, while also showing the significant role of parents' place identities in conditioning the passing on of left‐right orientations.     

AUDITORY PITCH AS A PERCEPTUAL ANALOGUE TO ODOR QUALITY

Abstract— Experiments in cross-modal matching suggest that smells can be arranged by odor qualify along the color dimensions of hue and lightness. Here we report that subjects readily adjust the loudness-equalized pitch of on auditory tone to match a stimulus odor. The results allow odors to be arranged in sequence by their pitch-equivalents. The tone matches appear to be based on perceptual feature of olfaction other than stimulus intensity or pleasantness. The results suggest that features of odor quality may be more accessible and structured than previously acknowledged.