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PubMed1992

Spectral and temporal weights in spectral-shape discrimination.

The COSS analysis [B. G. Berg, J. Acoust. Soc. Am. 86, 1743-1746 (1989)] was used to estimate spectral and temporal weights of a three-component, amplitude-modulated stimulus in a spectral-shape discrimination task. In all experiments, the task of the observer was to detect an increment in the level of the center component. A spectral-temporal weight quantifies the relative influence of a spectral component on the decisions of an observer during a specified segment of the total stimulus duration. In the first two experiments, the signal was added to all three temporal segments of the center component. The ideal weights for each component should be the same across temporal segments. Spectral-temporal weights were obtained for four conditions with different stimulus durations. In general, the estimated weights for each component were not equal at different temporal segments. In the third experiment, the signal was added to only one of three segments of the center component. Ideally, weight patterns should have changed when the temporal position of the signal segment was altered. Two stimulus durations, 300 and 15 ms, were used. For the 300-ms condition, the signal was added to only the end segment, and for all three observers the weight patterns are different from that obtained in experiment 1 with the signal added to all segments. For the 15-ms conditions, altering the signal position changed the estimated weights for only one observer.

Adult↗
PubMed1979

Coding of incremental changes in skin temperature by single warm fibers in the monkey.

1. Experiments were designed to answer the question: how well does a single warm fiber innervating the glabrous skin of the monkey's hand resolve incremental changes in the intensity of near-rectangular warming pulses applied to the fiber's receptive field? 2. In these experiments the measure of the warm fiber's capacity to resolve incremental changes in the intensity of successive warming pulses was termed the discriminable stimulus increment (DSI). The DSI is defined as that incremental difference in the intensity of a pair of warming pulses that could be resolved correctly, with a probability of 0.75, by comparing the fiber's responses to these two stimuli. In the specified conditions of the experiment, DSI = 0.67 sigma delta tau/(dR/dI) where sigma delta tau is the standard deviation of the difference in responses of the fiber to pairs of stimuli, and dr/dI is the fiber's sensitivity to incremental stimulus change. (dr/dI) was experimentally determined as the mean rate of change of the fiber's responses to incremental changes in the intensity of the warming pulse. 3. The DSI, as defined above, assumes that the basis for differentiating the stimuli in each pair was that the larger response in the fiber was in each instance generated by the more intense stimulus. A more general form of the DSI was also developed and used to examine the effects on intensity resolution of different discrimination rules that the brain might use. 4. In the experimental analysis the response measure of each warm fiber was the cumulative impulse count over successively longer segments of the stimulus period. With short integration intervals the DSI was high (i.e., intensity resolution was poor), but typically the DSI fell to a plateau level within 2.0--2.5 s of the onset of the warming stimulus. 5. The DSI was measured on 23 warm fibers in Macaca nemestrina for warming pulses with intensities of 0, 2, 4, 6, and 8 degrees C, at T-base levels of 29, 34 (near normal temperature of palmar skin), and 39 degrees C. For most observations the intensity resolution possible from the responses of single warm fibers, measured over this wide variety of stimulus conditions, was less than is achieved by the human observer trained to differentiate comparable warming pulses applied to the skin of the thenar eminence.

Adaptation, Physiological↗
PubMed2001

Discriminative stimulus properties of the selective norepinephrine reuptake inhibitor, reboxetine, in rats.

RATIONALE: Although drug discrimination procedures have proven difficult to apply to antidepressant agents, we recently characterized discriminative stimulus properties of the selective serotonin (5-HT) reuptake inhibitor, citalopram, in rats. However, discriminative stimulus properties of selective norepinephrine (NE) reuptake inhibitors remain to be evaluated. OBJECTIVE: We determined the potential discriminative stimulus properties of the highly selective NE reuptake inhibitor and antidepressant, reboxetine. METHODS: Employing a two-lever discrimination procedure, rats were trained to discriminate reboxetine (2.5 mg/kg, IP) from saline. In parallel, the influence of reboxetine (2.5 mg/kg) upon dialysate levels of monoamines in frontal cortex and dorsal hippocampus of freely moving rats was determined. RESULTS: After 54+/-10 training sessions, reboxetine elicited robust stimulus recognition, fully generalizing to itself with an ED50 of 1.2 mg/kg. Two further NE reuptake inhibitors, desipramine (5.3) and maprotiline (1.8), as well as the 5-HT/NE reuptake inhibitor, venlafaxine (1.0), likewise generalized. In contrast, the 5-HT reuptake inhibitors, paroxetine, citalopram and sertraline, and the DA reuptake inhibitors, GBR12935 and bupropion, did not show significant generalization. Reboxetine markedly increased dialysate levels of NE, but not 5-HT, in frontal cortex and hippocampus. Dopamine (DA) levels were also (though less markedly) enhanced in frontal cortex. CONCLUSION: In parallel with an elevation in extracellular levels of NE, the selective NE reuptake inhibitor, reboxetine, elicits a specific discriminative stimulus in rats.

Adrenergic Uptake Inhibitors↗
PubMed1995

[Unification of extreme levels of exposure to flight factors of different energy nature].

The factors of a various energetic nature the extreme levels of which both directly (via special receptors) and mediately influence and change the functions of nervous system are studied. Empirical data suggest conclusively that the general biological regularities of the effects of an "intensity-time" type is also valid on the organism level if the central nervous system is thought of as an irritable object. In all cases the initial cause of the disturbed cerebral activity is an external energetic irritative action. It is demonstrated that the character of human response to the extreme effects of some flight factors corresponds to general biological regularity of the reaction toward irritating stimulus. In this case the general mechanism of such reactions of the nervous system is an exhaustion of the energetic brain resources. There have been derived the equalities which define the quantitative relationships among the equivalent levels of extreme flight factor effects and the common unit of their measurement is introduced. On the basis of general biological regularities of the body response to irritating stimulus, the method for estimating and predicting useful consciousness time of the pilot in case of a combined effect of the flight factors under extreme conditions is suggested. For some flight factors (altitude, flight accelerations, noise, ionizing radiation) there have been obtained the qualitative indices enabling one to apply this method to solve the practical tasks. The set algorithm can be fed in personal computers and extended to other flight factors.

Acceleration↗
PubMed2003

Conditioning-specific reflex modification of the rabbit (Oryctolagus cuniculus) nictitating membrane response: US intensity effects.

Conditioning-specific reflex modification (CRM) of the rabbit's nictitating membrane response (NMR) describes changes in responding to an unconditioned stimulus (US) when the rabbit is tested in the absence of the conditioned stimulus. Specifically, after at least 3 days of tone-electrical stimulation pairings, responses to the US increase in size, especially at intensities weaker than the training intensity. CRM is similar to classical conditioning in that it is a function of the strength of conditioning, it can be extinguished, and it can be generalized from one stimulus to another. To compare CRM and classical conditioning further, we conducted three experiments to examine the effects of US intensity (1.0, 2.0, and 4.0 mA) on CRM. CRM was weak following conditioning with 1.0 mA and extremely strong following conditioning with 2.0 mA and 4.0 mA. The data suggest that CRM is a function of US intensity and have implications for posttraumatic stress disorder, a disorder potentially modeled by CRM.

Animals↗
PubMedDate not supplied

[Slow potentials and the impulse activity of cerebral cortex neurons following elaboration of internal inhibition].

The development of all studied kinds of internal inhibition in rabbits is accompanied by an enhanced phasic state, alternation of activation and inhibition in the responses of the visual area neurones, and enhanced late components of evoked potentials to flashes. During further intensification of inhibition, generalized polyrhythmic potential oscillations develop, which are in correspondence with chaotic or irregular group discharges of units in the visual and sensorimotor cortical areas, separated by inhibitory pauses. It has been concluded that enhanced hyperpolarization plays a considerable part in the development of internal inhibition; it may be local, predominantly in the conditioned stimulus analyser, or generalized in the case of a stronger inhibition comprising many brain structures.

Animals↗
PubMedDate not supplied

Remembering and forgetting as context discrimination.

In 1929, H.C. Blodgett reported the results of a seminal maze learning experiment using rats. In that experiment, hungry rats ran in a complex maze but were not rewarded on reaching the goal box. Not surprisingly, the performance of the hungry rats did not improve over trials. However, with the introduction of reward, the error scores of the rats suddenly dropped to the level of the control rats that were rewarded from the outset. This finding indicates that the experimental group had learned the maze despite the absence of reward but that the learning was latent rather than manifest. With Blodgett's findings, the distinction between learning and performance became firmly established, if not as widely appreciated as it might be. Blodgett's (1929) early experimental finding of latent learning could well serve as a paradigm for the approach taken here. That is, we have emphasized the principle that a lack of performance does not necessarily indicate a lack of either learning or memory. This principle is much more than an empty admonition: We have shown it can have a firm theoretical basis, one that has been confirmed repeatedly by experiments cited throughout this paper. That is, it has been shown numerous times that a failure to perform either in a Pavlovian or instrumental learning task or to remember in an animal or human memory task under one set of conditions could be alleviated under another set of conditions. Forgetting was viewed here as a failure of performance resulting from the cues at test retrieving a memory other than the target memory or retrieving no memory at all. According to this view, memory involves discrimination learning. Essentially, memories are stored in the presence of an elaborate set of interoceptive and exteroceptive stimuli, a context. Whether at test the target memory is retrieved depends on how well the cues at test discriminate between the target memory and other memories. This approach suggests that forgetting does not occur: There is only a failure to perform because of a difference between the stimulus conditions prevailing at encoding and at test. It was demonstrated that this approach is at least as reasonable as that which suggests that true forgetting occurs, but certainly more useful. At least three advantages adhere to our view that memory is a discrimination problem. First, in almost numberless cases, it has been shown that failure of performance under one set of stimulus conditions can be alleviated under some other set of stimulus conditions. Second, the proposition that altered stimulus conditions are responsible for forgetting is one of wide generality. Thus, the altered stimulus conditions approach can serve as an explanation not only for various human memory findings but also for various animal memory and learning findings. Finally, and perhaps most importantly, the present approach provides investigators with a powerful and proven working hypothesis. It tells us not to accept failures of performance as indicating an absence of learning or a loss of memory but rather to seek conditions favorable to improving performance, a strategy that should lead to a better fundamental understanding of memory and learning. This position is obviously a type of optimality theory, of which evolutionary theory is one of the more outstanding examples. In optimality theory, any deviation from some ideal state or condition prompts the investigator to seek the reasons for deviation. This approach may prove as successful when applied to learning and memory as it has to other areas of science.

Animals↗
PubMed1992

The discriminative stimulus properties of acute ethanol withdrawal (hangover) in rats.

Twenty male Sprague-Dawley rats were trained to discriminate pentylenetetrazole (PTZ, 15 mg/kg, intraperitoneally) from saline (SAL) under a drug discrimination procedure. Test sessions were conducted with 10 randomly selected subjects. Tests with various doses of PTZ resulted in a dose-dependent increase in the percentage of total session responses emitted on the PTZ-appropriate lever without a significant change in response rates across a wide range of test PTZ doses. Rats did not generalize the PTZ stimulus to ethanol (ETOH) up to ETOH test doses that completely suppressed responding. High acute ETOH doses (2, 3, and 4 g/kg) administered at various time points prior to discrimination test sessions engendered responding on the PTZ-appropriate level in a quantitative fashion, that was dose- and time-dependent. This acute ETOH delayed effect from these high doses replicates our previously published study using a Drug 1-Drug 2 discrimination task with Chlordiazepoxide and PTZ. More importantly, we suggest that the present behavioral assay may be a sensitive animal analogue of human "hangover" phenomena.

Alcoholic Intoxication↗
PubMed2004

Variation in complex olfactory stimuli and its influence on odour recognition.

Natural olfactory stimuli are often complex and highly variable. The olfactory systems of animals are likely to have evolved to use specific features of olfactory stimuli for identification and discrimination. Here, we train honeybees to learn chemically defined odorant mixtures that systematically vary from trial to trial and then examine how they generalize to each odorant present in the mixture. An odorant that was present at a constant concentration in a mixture becomes more representative of the mixture than other variable odorants. We also show that both variation and intensity of a complex olfactory stimulus affect the rate of generalization by honeybees to subsequent olfactory stimuli. These results have implications for the way that all animals perceive and attend to features of olfactory stimuli.

Animals↗
PubMed1997

Discriminative stimulus properties of amphetamine in a conditioned taste aversion paradigm.

It has been proposed that the conditioned taste aversion paradigm may be used to achieve rapid training of subjects in drug discrimination studies. We report here that amphetamine (1.0 mg/kg) may acquire discriminative control over the preference of rats for a distinctive flavour when its administration precedes access to a saccharin solution (0.15% w/v), versus the occasions when the injection of saline precedes no toxicosis after access to the same flavour. Other doses of amphetamine (0.18-1.0 mg/kg) or apomorphine (0.1-1.0 mg/kg) produced a dose-dependent generalization to the stimulus cue of amphetamine (1.0 mg/kg), and haloperidol (0.01-0.1 mg/kg) was able to prevent the stimulus control exerted by amphetamine. No stimulus control was seen in a control group where no distinctive outcomes followed the administration of either amphetamine or saline before the subjects had access to the saccharin-flavoured solution. In the experimental group only, changes in the preference for saccharin were observed, with no changes in the total amount of water and saccharin ingested. Taken together, the present results suggest the usefulness of the conditioned taste aversion procedure to train subjects in drug discrimination.

Amphetamine↗
PubMed1975

Inhibitory stimulus control following errorless discrimination learning.

Three generalization procedures were used to investigate inhibitory stimulus control following discrimination learning with few errors. Three groups of pigeons acquired a discrimination between a green stimulus (the positive stimulus) and a vertical or horizontal line (the negative stimulus) through differential autoshaping followed by multiple schedule presentation of the two stimuli with gradually increasing stimulus durations. Genereralization testing was along a line-tilt continuum. For one group, the test involved a resistance-to-reinforcement procedure in which responses to all line tilts were reinforced on a variable-interval schedule. For a second group, also tested with the resistance-to-reinforcement procedure, the lines were superimposed on the green field that formerly served as the positive stimulus. A third group was tested in extinction with the combined stimuli. Control groups had no discrimination training but responding to green was nondifferentially reinforced. The control subjects responded more to all line tilts during testing than did the comparable experimental subjects, indicating that the negative stimulus had become an inhibitory stimulus. Both resistance-to-reinforcement groups revealed inhibitory gradients around the negative stimulus, but the gradient for the extinction group was relatively flat. These data are consistent with others that modify Terrace's early conclusion concerning the failure of inhibition to develop during errorless training.

Journal Article↗
PubMed1981

Plasma concentrations of oxytocin and intramammary pressure in goats during manual stimulation of the udder and hand-milking.

The concentration of oxytocin in the jugular venous plasma of goats was studied by radioimmunoassay and the intramammary pressure measured upon manual stimulation of the udder and hand-milking. Before stimulation the concentrations of oxytocin were close to the limit of detection, about 3 pg/ml. Manual stimulation of the udder resulted in a short-lasting increase in plasma oxytocin in 11 out of 18 experiments carried out on nine goats. There were large variations between and within individuals in the magnitude of the oxytocin increase. Hand-milking was in general as efficient stimulus for oxytocin release. In experiments in which manual stimulation had led to a large increase in plasma oxytocin, the ensuing hand-milking did not lead to a further increase. In three experiments neither manual stimulation of the udder not hand-milking resulted in any significant increase in plasma oxytocin. The intramammary pressure increased upon manual stimulation of the udder and/or hand-milking in four out of six experiments. There was, in general, a close time-relationship between changes in intramammary pressure and plasma oxytocin.

Animals↗
PubMed1987

A comparison of testing procedures on the discriminative morphine stimulus.

The study investigated the effects of reinforcement and non-reinforcement during test sessions, and the effects of duration of generalization test sessions on the generalization of a morphine-induced discriminative stimulus. Rats were trained to discriminate 3 mg/kg morphine from saline in a two-lever drug discrimination task and were then tested for generalization of 0, 1, 2, 3, 4, and 5 mg/kg morphine with the training drug under both reinforced and non-reinforced contingencies during 4-min test periods. The percentage of drug-appropriate responses and response rates were recorded for the first 2 min and the second 2 min of each test session. A higher proportion of drug-appropriate responding occurred with an intermediate dose of morphine when reinforcement was available during test sessions. The frequency of responding was higher during the last 2 min than during the first 2 min of reinforced test sessions. The changes in response rate observed between the first 2 min and the last 2 min of the test sessions also depended on the reinforcement contingency available and the dose of morphine administered presession. The testing parameters thus altered the degree of generalization and the shape of the generalization curve of the morphine discrimination.

Animals↗
PubMed1990

Quantification and Comparison of Cell Properties in Cat's Striate Cortex Determined by Different Types of Stimuli.

Direction and orientation tuning elicited by moving bars, flashing bars and a moving noise field were compared in cells in area 17 of the cat. Fourier analysis of tuning curves (SDO-analysis) was applied to quantify the general sensitivity (S) to visual stimulation, tuning strength to direction(D) and orientation (O), as well as the preferred direction (PD) and orientation (PO). Results from SDO-analysis were compared with the commonly used direction index and half-width-at-half-height orientational tuning parameter and it is demonstrated that the commonly used parameters can be replaced and are superseded by the results from SDO-analysis. The comparison of the responses elicited by the different types of stimuli showed that a linear correlation between D (or O) components was mainly found in simple cells, while in most cases no correlation was obtained for complex cells. Since several of the simple cells also showed no linear relationship, a direct mutual prediction of the S, D and O components can only be achieved for approximately 50% of the cortical cells applying commonly used stimulus types. The general responsiveness (S) shows that flashing bar stimuli are at least as effective as moving bars, whereas moving noise stimulates cortical cells more weakly. A moving bar tends to increase the orientation tuning (O) in most cells and with a moving noise stimulus predominantly the directional tuning (D) of complex cells is strongly enhanced. In conclusion, Fourier analysis of tuning curves (SDO-analysis) provides a valuable and simple tool for the quantification of direction and orientation specificity. Motion enhances the cortical response specificity which indicates the involvement of facilitation or inhibition exclusively induced by movement.

Journal Article↗
PubMed2006

Lack of generalization of object discrimination between spatial contexts by a bat.

Discrimination and generalization are important elements of cognition in the daily lives of animals. Nectar-feeding bats detect flowers by olfaction and probably vision, but also use echolocation and echo-perception of flowers in immediate target surroundings. The echo received from an interference-rich flower corolla is a function of a bat's own relative position in space. This raises the question how easily a free-flying bat will generalize an echo stimulus from a learning situation to a new spatial context where differences in relative flight approach trajectories may lead to an unfamiliar spectral composition of the self-generated echoes. We trained free-flying Glossophaga soricina in echoacoustic discrimination in a two-alternative forced-choice (2-AFC) paradigm at location A. We then tested at location B for spontaneous transfer of discrimination ability. Bats did not spontaneously transfer the discrimination ability acquired at A to location B. This lack of spontaneous generalization may have been caused by factors of the underlying learning mechanisms. 2-AFC tasks may not be representative of the natural foraging behaviour of flower-visiting bats. In contrast to insect-eating bats that constantly evaluate the environment to detect unpredictable prey, the spatial stability of flowers may allow flower visitors to rely on spatial memory to guide foraging. The 2-AFC task requires the disregard (learned irrelevance) of salient spatial location cues that are different at each new location. In Glossophaga, a conjunction between spatial context and 2-AFC discrimination learning may have inhibited the transfer of learned irrelevance of spatial location in the 2-AFC task to new spatial locations. Alternatively, the bats may have learnt the second discrimination task completely anew, and were faster only because of an acquired learning set. We suggest a dissociation between 2-AFC task acquisition and novel object discrimination learning to resolve the issue.

Animals↗
PubMed1997

Differential effects of mu-, delta- and kappa-opioid receptor agonists on the discriminative stimulus properties of cocaine in rats.

The effects of selective mu-, delta- and kappa-opioid receptor agonists on the discriminative stimulus properties of cocaine were examined in rats trained to discriminate between cocaine (10 mg/kg) and saline. Cocaine produced a dose-related increase in cocaine-appropriate responses in all of the rats. In generalization tests, neither morphine (mu-opioid receptor agonist) nor N-methyl-N-7-(1-pyrrolidinyl)-1-oxaspiro[4,5]dec-8-11-4-benzofu ranacetamide (U50,488H: kappa-opioid receptor agonist) generalized to the discriminative stimulus properties of cocaine. On the other hand, the newly synthesized non-peptide selective delta-opioid receptor agonist 2-methyl-4a alpha-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a alpha-octahydro-quinolino(2,3,3,-g)isoquinoline (TAN-67) partially generalized (56.7% cocaine-appropriate responses) to the discriminative stimulus properties of cocaine. Intracerebroventricular (i.c.v.) administration of [D-Ala2]deltorphin II (peptide delta 2-opioid receptor agonist) completely generalized, while neither [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAMGO: mu-opioid receptor agonist) nor [D-Pen2,D-Pen5]enkephalin (DPDPE; delta 1-opioid receptor agonist) generalized to the discriminative stimulus properties of cocaine. These results suggest that the discriminative stimulus properties of cocaine may be partially mediated by delta-opioid (especially delta 2-opioid) receptors. In combination tests, pretreatment with morphine (3.0 mg/kg) and TAN-67 (3.0 and 10 mg/kg) significantly potentiated the discriminative stimulus properties cocaine. In contrast, pretreatment with U50,488H (2.0 and 4.0 mg/kg) scarcely shifted the discriminative stimulus properties of cocaine. Furthermore, the potentiating effect of 3.0 mg/kg morphine on the discriminative stimulus properties of cocaine was attenuated by 2.0 mg/kg U50,488H. In contrast, the potentiating effect of 10 mg/kg TAN-67 on the discriminative stimulus properties of cocaine was not reversed by either 2.0 or 4.0 mg/kg U50,488H. These results suggest that mu-, delta- and kappa-opioid receptor agonists modulate the discriminative stimulus properties of cocaine through different mechanisms, perhaps through different effects on the dopaminergic system.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1968

Some effects of discriminative training with equated frequency of reinforcement.

Pigeons were exposed to a multiple schedule which provided equally frequent reinforcement in the presence of two stimuli but which produced markedly different rates of key-pecking. Generalization gradients were displaced away from the stimulus associated with the lower rate of key-pecking. Another group of pigeons had similar training, except that a low rate of key-pecking was established in a stimulus with a much higher frequency of food reinforcement. In this case, the generalization gradients were not affected by the training on the schedule producing a low response rate.

Animals↗
PubMed2000

Further evaluation of low-ranked items in stimulus-choice preference assessments.

The generality of the findings reported by DeLeon, Iwata, and Roscoe (1997) was examined by conducting two stimulus-choice preference assessments, the second of which evaluated low-ranked items from the initial assessment. Results for the 2 participants suggested that supplementary assessments of low-ranked items may be useful for identifying a wider variety of reinforcing stimuli.

Adolescent↗