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At least 1,621 records · Page 90Linked to original sources
PubMed2005

Pigeons do not perceptually complete partly occluded photos of food: an ecological approach to the "pigeon problem".

Humans routinely complete partly occluded objects to recognize the whole objects. However, a number of studies using geometrical figures and even conspecific images have shown that pigeons fail to do so. In the present study, we tested whether pigeons complete partially occluded objects in a situation simulating a natural feeding context. In Experiment 1, we trained pigeons to peck at any photograph of food and not to peck at any containing a non-food object. At test, we presented both photos of food partly occluded by pigeon's feather and photos simply truncated at the same part. We predicted that if the pigeons perceptually completed the occluded portion, then they would discriminate the photos of occluded food better than the truncated photos. The result was that the pigeons pecked at the truncated photos earlier than the occluded photos. Placing the occluder next to all of the stimuli in Experiment 2 or substituting indented lozenge for the feather in Experiment 3 did not affect the results. Thus, even in a simulated ecologically significant situation, pigeons continued to not show evidence of perceptual completion.

Animals↗
PubMed2005

Avian detection and identification of perceptual organization in random noise.

Recent research has suggested that pigeons may have difficulty globally integrating visual information in hierarchically arranged stimuli. To isolate and understand the mechanisms responsible for processing emergent perceptual structure, three pigeons were tested in a two alternative choice task that required the global integration of organized local information. They were reinforced for localizing, on randomized distractor backgrounds of black and white square elements, different types of structured targets (e.g., stripes, squares, checkerboards) arranged from these same elements. These hierarchical stimuli were tested at four different levels of spatial granularity (i.e., different element sizes). Experiment 1 found rapid acquisition for the vertical and horizontal stripes or square targets and somewhat slower learning with the checkerboard pattern. Experiment 2 demonstrated successful transfer to a novel target types (alternating bars and "diagonal" stripes). In both experiments, displays with the greatest spatial granularity (smallest elements and most repetitive structure) monotonically supported the best discrimination. These results indicate pigeons can perceive and discriminate emergent visual structure under the right circumstances and suggest they do so with a generalized rule for detecting patterns of non-random perceptual structure.

Animals↗
PubMed2005

Spatial associative memory: a possible species difference in rats and pigeons.

Previous research has shown that pigeons can remember which of four spatially distinct responses was last reinforced, for at least 72 h. The present study sought to replicate this finding using rats. Rats were tested in an operant chamber containing four spatially distinct levers. In each session one lever was randomly selected to provide reinforcement for 15 min. This reinforced period was preceded by a non-reinforced period that was 30s long, on average. During the non-reinforced period the amount the rat pressed on the previously reinforced lever was compared to responding on the other three levers, and was taken as a measure of memory. Sessions were separated either by 17 min, 24 or 72 h. Unlike pigeons, rats responded at chance levels following each of these retention intervals. This finding adds to previous research suggesting differences in cognitive processes in rats and pigeons.

Animals↗
PubMed2005

Olfactory conditioning experiments in a food-searching passerine bird in semi-natural conditions.

Because passerine birds have a very small relative olfactory bulb size, they have been considered to have weak olfactory capacities for decades. Recent investigations however suggest that breeding female blue tits (Parus caeruleus) are sensitive to lavender odour in the reproductive context of building and maintaining the nest. Here, we present results of an olfactory conditioning experiment in blue tits held in semi-natural conditions during the breeding season. We show that captive male blue tits, trained to associate lavender odour with a food reward, are more attracted to an empty feeder box emitting lavender odour than an odourless empty feeder box. Females did not distinguish significantly between empty feeders with and without lavender odour during the test phase, although they responded positively at the end of the training phase. These results suggest that male blue tits can use olfaction in a context not related to nest building. Additional experiments will be required to better understand the observed sex differences in response to the experimental set up, and in what context free-ranging individuals use olfaction.

Animals↗
PubMed2005

Influence of seed size and seed nature on recruitment in the polymorphic harvester ant Messor barbarus.

In the polymorphic harvester ant Messor barbarus, the colony modulates response during foraging according to seed characteristics. The easiness of picking up small seeds (oat fragments or canary seeds) shortens the time lapse between food discovery and the return of scouts to the nest, favouring the onset of recruitment and higher mobilisation rates than bigger seeds (whole oat). However, size is not the only criterion, as canary seeds are preferred among small ones. A modulation of the trail laid by the first scouts also plays a role in the shaping of harvesting patterns and in the enhancement of recruitment towards small and/or preferred seed. This flexibility extends to the relative participation of the three worker sizes classes, which differs according to seed. Media are the most numerous at the foraging arena and largely responsible for trail-laying. Minor participate in seed harvesting and trail-laying, mostly when they can be efficient in carrying seeds, such as oat fragments. Major scarcely participate in harvesting and trail-laying, but are involved in the exploitation of bigger and/or preferred seed species. When faced with different seed species, M. barbarus seems thus to collectively adopt a "foraging time minimisation" rather than an "energetic gain per item harvested maximisation" strategy. Dynamics of foraging and division of labour between foragers of different sizes are related to both the workers' ability to carry seed items, and the transfer of information to nestmates by trail-laying, all parameters that vary according to seed characteristics.

Animal Communication↗
PubMed2005

Interval duration effects on blocking in appetitive conditioning.

Three experiments examined absolute (Experiment 1) and relative (Experiments 2a and 2b) duration effects on blocking. In Experiment 1, rats were pretrained with a short or long conditioned stimulus (CS1) followed by food, after which they were given reinforced short-short or long-long CS1-CS2 simultaneous compounds. Compared to overshadowing control groups, both pretrained groups displayed blocking, and there was no clear effect of absolute stimulus duration on the magnitude of blocking. In Experiments 2a and 2b, the rats received partially overlapping short-long CS1-CS2 compounds. In both experiments, a long CS1 blocked a short CS2, but not vice versa. This was the case when the long CS1 was nine times (Experiment 2a) or only 1.5 times (Experiment 2b) the duration of the short CS2. The pattern of results is most consistent with a real-time model of conditioning, such as the Sutton and Barto [Sutton, R.S., Barto, A.G., 1990. Time derivative models of Pavlovian reinforcement. In: Gabriel, M.R., Moore, J.W. (Eds.), Learning and Computational Neuroscience: Foundations of Adaptive Networks. MIT Press, Cambridge, MA, 497-537] temporal difference model.

Animals↗
PubMed2006

Effects of partial reinforcement and time between reinforced trials on terminal response rate in pigeon autoshaping.

Partial reinforcement often leads to asymptotically higher rates of responding and number of trials with a response than does continuous reinforcement in pigeon autoshaping. However, comparisons typically involve a partial reinforcement schedule that differs from the continuous reinforcement schedule in both time between reinforced trials and probability of reinforcement. Two experiments examined the relative contributions of these two manipulations to asymptotic response rate. Results suggest that the greater responding previously seen with partial reinforcement is primarily due to differential probability of reinforcement and not differential time between reinforced trials. Further, once established, differences in responding are resistant to a change in stimulus and contingency. Secondary response theories of autoshaped responding (theories that posit additional response-augmenting or response-attenuating mechanisms specific to partial or continuous reinforcement) cannot fully accommodate the current body of data. It is suggested that researchers who study pigeon autoshaping train animals on a common task prior to training them under different conditions.

Animals↗
PubMed2006

Long-term effects of suppressing the preratio pause.

The preratio pause is a characteristic feature of performances under fixed-ratio schedules of reinforcement, even though the pause is not required by the schedule and it reduces the reinforcement rate. To investigate the reduction of pausing, five rats trained on fixed-ratio schedules were exposed to timeout punishment of pauses that exceeded a specified duration. After a series of 30 punishment sessions, most of the longest pauses were eliminated. For some subjects punishment was withdrawn abruptly, whereas for others a fading procedure was employed. Postpunishment observations then were continued for an additional 60 sessions. The reduced pausing was accompanied by reductions in the positive skew of the baseline distribution of pause durations, and by substantial increases in reinforcement rates. However, the results did not indicate differences as a function of the method of withdrawing the punishment contingency. Although postpunishment performances indicated some degree of recovery in the number of long pauses, performances had stabilized below prepunishment levels when the experiment ended. The results suggest the possibility that reduced pause durations can be self-maintained by the resulting increase in reinforcement rates.

Animals↗
PubMed2006

Appetitive latent inhibition in rats: preexposure performance does not predict conditioned performance.

Nonreinforced preexposure to a conditioned stimulus impairs subsequent conditioning with that stimulus. The goal of these studies was to assess the extent to which acquisition performance could be predicted from preexposure performance using a correlational approach. For both preexposure and autoshaping, four measures of performance were computed, including overall average lever pressing, lever pressing in the initial session, percentage change in lever pressing, and slopes. These measures were correlated in a large sample of rats trained in an autoshaping situation. None of the three measures of autoshaping performance was consistently predicted by any of the three measures of preexposure performance. These results are consistent with the view that latent inhibition is not reducible to long-term habituation.

Animals↗
PubMed2006

Intertrial interval as a contextual stimulus.

Four experiments with rats investigated whether the time between appetitive conditioning trials can serve as a discriminative cue for responding during the next conditional stimulus (CS). In Experiment 1, rats that received extinction trials with a 4-min intertrial interval (ITI) showed spontaneous recovery after a retention interval of 16 min, whereas rats that received extinction with a 16-min ITI did not. Experiments 2 and 3 investigated more explicit discriminations between the 4- and 16-min ITIs. When a 16-min ITI signaled that the CS would be reinforced and a 4-min ITI signaled that it would not, the ITIs modulated responding to the CS. But when the 4-min ITI signaled reinforcement and the 16-min ITI did not, there was less evidence of modulation by the ITIs. This asymmetry was due at least partly to a difficulty in performance rather than learning. Experiment 4 investigated similar discriminations with 1- and 4-min ITIs. Here the results took a different form: time in the reinforced ITI elicited responding directly, but did not modulate responding to the CS. ITI can function as a contextual cue, and the results suggest new similarities between the processes behind interval timing and associative learning.

Animals↗
PubMed2006

Passage of time leaves response-outcome associations intact.

The effect of the passage of time on the association between an instrumental response and its outcome was examined in three experiments with rats using outcome devaluation. In Experiments 1 and 2, rats were initially trained to make one pair of instrumental responses for different outcomes (e.g., lever press-->pellets and chain pull-->sucrose). Then, after a delay of several weeks, a second pair of responses for those different outcomes (e.g., nose poke-->pellets and handle pull-->sucrose) was trained in Experiment 1 but not in Experiment 2. One of the outcomes was then devalued and the responses were tested in extinction. There was no evidence that the passage of time eliminated the sensitivity of a response to a change in the value of its outcome. Experiment 3 used the same design as Experiment 1 to examine the effect of the passage of time on extinguished instrumental responses. First, one pair of responses was trained with different outcomes and then extinguished prior to the training and subsequent extinction of a second pair of responses. After retraining both pairs of responses with a polycose outcome, one of the original outcomes was devalued. Each pair of responses was then tested in extinction. The results of the extinction tests revealed no evidence that the passage of time removed the sensitivity of an extinguished response to devaluation of its original outcome. These findings are consistent with other reports that the response-outcome association survives various response elimination techniques.

Animals↗
PubMed2006

Effect of stimulus orderability and reinforcement history on transitive responding in pigeons.

Transitive responding in humans and non-human animals has attracted considerable attention because of its presumably inferential nature. In an attempt to replicate our earlier study with crows [Lazareva, O.F., Smirnova, A.A., Bagozkaja, M.S., Zorina, Z.A., Rayevsky, V.V., Wasserman, E.A., 2004. Transitive responding in hooded crows requires linearly ordered stimuli. J. Exp. Anal. Behav. 82, 1-19], we trained pigeons to discriminate overlapping pairs of colored squares (A+ B-, B+ C-, C+ D-, and D+ E-). For some birds, the colored squares, or primary stimuli, were followed by a circle of the same color (feedback stimuli) whose diameter decreased from A to E (Ordered Feedback group); these circles were made available to help order the stimuli along a physical dimension. For other birds, all of the feedback stimuli had the same diameter (Constant Feedback group). In later testing, novel choice pairs were presented, including the critical BD pair. The pigeons' reinforcement history with Stimuli B and D was controlled, so that the birds should not have chosen Stimulus B during the BD test. Unlike the crows, the pigeons selected Stimulus B over Stimulus D in both ordered and Constant Feedback groups, suggesting that the orderability of the post-choice feedback stimuli did not affect pigeons' transitive responding. Post hoc simulations showed that associative models [Wynne, C.D.L., 1995. Reinforcement accounts for transitive inference (TI) performance. Anim. Learn. Behav. 23, 207-217; Siemann, M., Delius, J.D., 1998. Algebraic learning and neural network models for transitive and non-transitive responding. Eur. J. Cogn. Psychol. 10, 307-334] failed to predict pigeons' responding in the BD test.

Animals↗
PubMed2006

Long-interval timing is based on a self-sustaining endogenous oscillator.

The mechanism of anticipating long-intervals (16-21 h) was investigated. Rats earned food by interrupting a photobeam in a food trough during 3- or 4-h meals. Intermeal intervals were 16, 21, and 24 h (offset to offset) for independent groups of rats (n=8 per group). After approximately a month of experience with the intermeal intervals, the meals were discontinued. The rate of visiting the food trough increased as a function of time before the meal. When meals were discontinued, visits continued to be periodic. The periodicity was approximately 21 h after 16- and 21-h intermeal intervals and approximately 28 h after 24-h intermeal intervals. These data suggest that long-interval timing is based on a self-sustaining, endogenous oscillator.

Animals↗
PubMed2005

Honeybees foraging response in genetically diversified opium poppy.

Studies were carried out on honeybees foraging on plant flowers. Results showed significantly higher foraging response of honeybees (Apis mellifera) in genetically divergent narcotic plant opium poppy (Papaver somniferum). Of the 18 mutants and two locally adapted cultivars of diverse genotypes screened, eight revealed significantly greater foraging response manifesting honeybee's preference towards specific plant morphotypes. The number of flower bloom did not correspond to number of foraging bees in both mutant and cultivar plant types of opium poppy. The genotype specific foraging response of honeybees could be attributed to physico-chemical properties of opium poppy flowers. This could have implications for the development of opium alkaloid fortified honeys for novel pharmaceuticals and isolation of natural spray compounds to attract honeybee pollinators for promoting crossing and sustainable hybridity in crops.

Animals↗
PubMed2004

Extracellular level of basolateral amygdalar dopamine responding to reversal of appetitive-conditioned discrimination in young and old rats.

Young and old rats, aged 3 and 24 months old, respectively, were conditioned to press a lever under lamp-on conditions for reward acquisition and lamp-off for no reward using a variable interval reinforcement schedule that averaged 15 s; i.e., the minimal requirement was 4 responses/min. Over a 30-day period, young and old groups showed increased response to lamp-on from 22 to 35/min and from 10 to 23/min, respectively, and shortened response to lamp-off after initial training. Response to lamp-on as a percentage of total response to lamp-on and -off (the discrimination ratio) was over 80%. For the next 30 days, reversal learning was imposed to reinforce discrimination of the lamp-off state. Young rats showed a steadily increasing discrimination ratio from 40% to 70%, and old rats from 30% to 60%. In comparison with the initial training, young rats showed a total response increase from 50% to 60%, while old rats showed an approximately 5% decrease without loss of reward-obtaining efficiency. In vivo microdialysis during reversal revealed that young rats had higher dopamine transmission in the basolateral amygdala than old rats. The dopamine level was positively correlated with the number of responses to state of reward in young rats and negatively with the numbers of both NRF and RF responses to lamp-on and -off states in old rats. These results suggest that in reversal discrimination, basolateral amygdalar dopamine efflux correlates with the manner of age-related conditioned response rather than the ability to learn.

Age Factors↗
PubMed2005

Brief access to sweets protect against relapse to cocaine-seeking.

The availability of alternative rewards can reduce acquisition and maintenance of cocaine self-administration in rats and humans. Once acquired, however, addiction is an intractable disease where relapse is elicited by exposure to drug-associated cues, the drug itself, or stress. The present study shows that both cocaine-seeking and drug-induced relapse are significantly reduced when drug-experienced, but abstinent, rats are given just 5 min daily prior access to a palatable glucose + saccharin mixture. The results suggest that presentation of an alternative reward may be useful as a therapeutic intervention for cocaine seeking and relapse.

Animals↗
PubMed2004

A novel method for induction of salt appetite in rats.

A number of procedures exist for the experimental induction of sodium appetite. With the exception of a low sodium diet, nearly all of these methods are invasive, requiring injections, surgery, or both. In addition to stimulating intake of concentrated salt, some of them produce substantial side-effects like reduced food intake and weight gain. The present experiment was designed to evaluate the efficacy of a novel non-invasive method to induce a salt appetite. We investigated the effects of ingesting 100 microM amiloride, a diuretic and natriuretic compound, on urine quantity, electrolyte balance, 0.5 1M sodium chloride (NaCl) intake, water intake, and Na(+)-free chow intake, and weight gain in rats. A water ingestion only group served as control. Consumption of amiloride in mixture with water produced greater loss of urinary Na(+) and intake of 0.51 M NaCl compared with controls. This treatment was without effect on food intake and only modestly influenced weight gain. These results demonstrate a rapid and non-invasive method for the induction of salt appetite free of unwanted side-effects.

Amiloride↗
PubMed2006

Colour-coded pellets increase the sensitivity of the staircase test to differentiate skilled forelimb performances of control and 6-hydroxydopamine lesioned rats.

The Montoya staircase test has previously been used to study the skilled forelimb performance of mice and rats following lesions and cell implants in different parts of the central nervous system. Here we describe a modification of the original test design which introduces differently coloured food pellets for each step, and present the results of the new and modified method. In this study unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats and healthy control rats were used. The new evaluation of reaching and grasping movements takes into consideration the various levels of reaching difficulty. The coloured food pellets code for different steps of the staircase. The comparison between the original versus the modified test methods revealed significant differences most prominently on the lower steps. It is important to notice that the pattern of grasping movements in the hemiparkinsonian rats changes from precise reaching (prior to lesion) to shuffling and unsuccessfully trying to reach pellets. The observation of this change in behaviour would not have been obtained through the evaluation of the original staircase test. In summary, the modified staircase test introduces a colour-coded pellet system which obviously increases the test sensitivity and discloses new insights into the skilled forelimb use in a rat model of Parkinson's disease. It may therefore become a valuable tool in future studies related to plasticity-induced changes in skilled forelimb reaching and grasping movements.

Analysis of Variance↗