Prospective timing in pigeons: Isolating temporal perception in the time-left procedure

In the time-left procedure, a task used to study prospective timing, animals choose between two stimuli that signal different delays to reinforcement. Trials begin with one stimulus signaling C seconds to reinforcement and, at different moments since its onset, another stimulus, signaling S seconds to reinforcement, with C > S, is introduced. Optimal performance consists in choosing the stimulus signaling the shorter time to reinforcement. Animals have been found to perform in this optimal way. However, this procedure is complex and variables other than time may be responsible for the results. In two experiments with pigeons we sought to improve the time-left procedure to better isolate the effect of time in the animals’ behavior. We attempted to control for two confounding variables, the asymmetry in the time markers from training to testing and the cost of switching between the two response alternatives. We conclude that in the time-left task pigeons seem indeed to regulate their behavior based on time because, with our improved procedure, they still chose the stimulus associated with the shorter time to food. However, our version of the procedure created new interpretative difficulties, strengthening the idea that the time-left procedure may be too complex to study timing.     

Influence of escalating alternative reinforcer values on cigarette choice

The availability of alternative reinforcers reduces drug taking. Escalating alternative reinforcer values have been used to initiate and maintain abstinence from drug use. A reset in reinforcer value has been added to the schedule of alternative reinforcer presentation to discourage relapse. The purpose of this preliminary study was to test the influence of escalating and escalating and resetting alternative reinforcer value on cigarette choice in the human laboratory. Fourteen daily cigarette smokers completed this experiment, which required one practice and three experimental sessions. During each experimental session, subjects made six choices between smoking a cigarette and receiving money, available under Constant, Escalating or Escalating and Resetting conditions. The total number of cigarettes chosen and puffs taken, but not the maximum consecutive number of cigarettes choices, was decreased in the Escalating condition relative to the Constant condition. The maximum number of consecutive cigarettes chosen was decreased in the Escalating and Resetting condition relative to the Constant condition. The proportion of money earned was increased in the Escalating condition relative to the Constant and Escalating and Resetting conditions. These initial findings indicate that whereas an escalating alternative reinforcer schedule reduces cigarette smoking overall, an escalating and resetting alternative reinforcer schedule may reduce repeated cigarette smoking (i.e., relapse).     

Human performance on a two-alternative rapid-acquisition choice task

Davison and Baum [Davison, M., Baum, W. M., 2000. Choice in a variable environment: every reinforcer counts. Journal of the Experimental Analysis of Behavior 74, 1-24.] developed a concurrent-schedule procedure where, within each session, different reinforcer ratios were arranged across components separated by brief black-outs. Behaviour adapted quickly to the reinforcer ratios and reinforcers also had local effects on responding. This procedure has been used with pigeons and rats. In the present experiment, we adapted the Davison and Baum procedure to study the effects of reinforcement on human choice behaviour. Eighteen participants were presented with four different reinforcer ratios within a single 50-minute session. Mean sensitivity to the reinforcer ratios increased within components, and preference was greater for the just-reinforced response alternative immediately following reinforcer delivery, similar to the results from non-human experiments. Although there were limitations to the current procedure, the local time scale analyses are a novel way of examining human operant behaviour.     

Attention, the presolution period, and choice accuracy in pigeons

Six pigeons were trained first on a color then on a form discrimination; four other pigeons were trained first on form and then on color. One of two colors or one of two forms (sample stimuli) appeared in the center of a touch sensitive monitor for 5 pigeons and in the center and in 16 other locations for 5 other pigeons. A peck anywhere within the region in which the sample stimuli appeared produced two white disks (comparison stimuli), one on the left and one on the lower right corners of the screen. Correct left-right choices provided food. Although of no consequence, the location of pecks in presence of the sample was predictive of the pigeon's subsequent choice. Accuracy, choice of the correct comparison stimulus, was greater when the sample stimuli appeared in the center as well as 16 other locations than when it appeared only in the center. The presolution period, the period of chance accuracy prior to evidence of discrimination learning, was decreased on each task following training on the other task. This evidence of facilitation following an extra-dimensional shift was attributed to continued relevance of the conditions under which the first task was learned. The duration of the presolution period was inversely related to asymptotic accuracy-data accounted for by Heinemann's (1983) theory of information processing during the presolution period.     

A slowing effect on visual search by advance information in pigeons (Columba livia): a comparison with humans (Homo sapiens)

A comparative study was conducted to investigate whether the search for a target letter was facilitated when the target and prime (preceding stimulus) letters were identical. Pigeons (Section 2) and human participants (Section 3) were first trained to search for “A” among “Y”s and “E” among “D”s in a condition in which a square shape appeared as the prime (Neutral condition). In subsequent testing, a prime was identical either to the corresponding target (Target-priming condition) or to the distractor (Distractor-priming condition). Humans and pigeons responded differently to the two priming conditions. On early trials, the Target prime facilitated search in humans, reducing reaction times (RTs) to targets. In pigeons, however, RTs were longer with Target primes, suggesting that pre-exposure to target letters may directly inhibit the search for targets in subsequent search displays. Furthermore, pre-exposure to the distractor letters may inhibit the processing of the distractor. On later trials, RTs of humans were faster in both priming conditions than in the Neutral condition, suggesting that expectation of a target facilitated search (“Y” predicted “A” and “D” predicted “E”). In contrast, the pigeons showed no evidence of expectation-based facilitation, with constant slowing effects of the Target prime extending across sessions. Possible mechanisms underlying such a slowing priming effect in pigeons were discussed.     

Maladaptive choice behaviour by pigeons: an animal analogue and possible mechanism for gambling (sub-optimal human decision-making behaviour)

Consistent with human gambling behaviour but contrary to optimal foraging theory, pigeons showed maladaptive choice behaviour in experiment 1 by choosing an alternative that provided on average two food pellets over an alternative that provided a certain three food pellets. On 20 per cent of the trials, choice of the two-pellet alternative resulted in a stimulus that always predicted ten food pellets; on the remaining 80 per cent of the trials, the two-pellet alternative resulted in a different stimulus that always predicted zero food pellets. Choice of the three-pellet alternative always resulted in three food pellets. This choice behaviour mimics human monetary gambling in which the infrequent occurrence of a stimulus signalling the winning event (10 pellets) is overemphasized and the more frequent occurrence of a stimulus signalling the losing event (zero pellets) is underemphasized, compared with the certain outcome associated with not gambling (the signal for three pellets). In experiment 2, choice of the two-pellet alternative resulted in ten pellets with a probability of 20 per cent following presentation of either stimulus. Choice of the three-pellet alternative continued to result in three food pellets. In this case, the pigeons reliably chose the alternative that provided a certain three pellets over the alternative that provided an average of two pellets. Thus, in experiment 1, the pigeons were responding to obtain the discriminative stimuli signalling reinforcement and the absence of reinforcement, rather than to obtain the variability in reinforcement.     

Matching-to-sample by pigeons: the dissociation of comparison choice frequency from the probability of reinforcement

It has been proposed that comparison choice in matching-to-sample should depend on two factors, the relative probability of reinforcement associated with each of the comparison stimuli and the conditional probability of each comparison stimulus being correct given presentation of one of the samples. DiGian and Zentall [DiGian, K.A., Zentall, T.R., 2007. Matching-to-sample in pigeons: in the absence of sample memory, sample frequency is a better predictor of comparison choice than the probability of reinforcement for comparison choice. Learn Behav. 35, 242-261] have shown that sample frequency together with the probability of choosing each of the comparison stimuli in training can influence comparison choice when delays are introduced, when the number of reinforcements associated with each of the comparison stimuli is equated. Furthermore, Zentall and Clement [Zentall, T.R., Clement, T.S., 2002. Memory mechanisms in pigeons: Evidence of base-rate neglect. J. Exp. Psych.: Anim. Behav. Proc. 28, 111-115] have found that sample frequency can affect comparison choice when delays are introduced independently of the number of choices of each of the comparison stimuli in training and the number of reinforcements associated with each of the comparison stimuli is equated. In the present experiment we found that the probability of choosing each of the comparison stimuli in training can affect comparison choice when delays are introduced, independently of sample frequency and when the number of reinforcements associated with each of the comparison stimuli is equated. Together, these experiments suggest that when the sample is not available, there is a partial dissociation between comparison choice and the probability of reinforcement associated with each of the comparison stimuli.     

A direct effect of competition on food choice by pigeons

Previous research on food choice of pigeons foraging alone and in competition showed an indirect response to the competitor, mediated by the resource depletion associated with the competitor. This experiment showed, in addition, that pigeons can adjust their food choice in direct response to the competitor itself. Pigeons foraged for large, preferred grains of maize and smaller, unpreferred grains of wheat presented in bowls covered with sawdust. In a within-subject design, pigeons were tested alone or in competition with another pigeon. In competition, a higher choice proportion of the wheat grains was observed on the first two choices out of 48 items, and this effect increased with time in the experiment. This result underscores the role of learning in group foraging behaviour. It also suggests a possible ecological implication: that individuals that learn faster may enjoy a competitive advantage in terms of reduced delay in responding to the presence of a conspecific.     

Absolute and relational control of a sequential auditory discrimination by pigeons (Columba livia)

Recent evidence indicates that pigeons can readily learn visual discriminations based on both absolute and relational stimulus factors. To examine how these two types of control function in their non-dominant auditory modality, we tested four pigeons in a go/no-go sequential auditory discrimination in which both absolute and relational cues were redundantly available. In this task, sequences of different sounds created from one set of pitches were reinforced, while different sequences created from another set of pitches and any same sequences made from either set of pitches were not. Across three experiments, we independently varied the relative discriminability of the absolute and relational components. The pigeons were consistently and primarily controlled by the absolute fundamental pitch of our notes in all of the experiments, although this was influenced by the range and arrangement of the pitches used in each set. A majority of the pigeons also demonstrated relational control when this component was made more salient. The more robust control exhibited by absolute factors is consistent with the comparative hypothesis that birds in general may have a well-developed aptitude for processing absolute pitch in many auditory settings. The relational control is consistent with our recent evidence of same/different auditory learning by pigeons.     

Role of stimulus-stimulus pairing in matching-to-sample procedure: cross-species comparison of humans and pigeons

The present experiment examined whether, in a matching-to-sample (MTS) procedure, a relation between two stimuli, a sample and a comparison, could be established as a result of just stimulus–stimulus pairing, even if back up reinforcers were never provided for the conditional relation between the sample and comparison stimuli, but rather only for the comparison stimulus. A procedure called “pseudo matching-to-sample” was used in which, when S1 was presented as a sample stimulus, two comparison stimuli (C1 and C2) were presented, and only responses to C1 were reinforced. Conversely, when S2 was presented, only responses to C3 (and not C4) were reinforced. In other words, organisms experiencing this procedure could discriminate C1 from C2, and C3 from C4, by simple discrimination without regard to the conditional sample stimuli. In order to examine cross-species differences, responding by humans in this procedure was compared to that by pigeons. Although the humans developed a discriminative function for the sample stimuli, that is, the humans’ responding was affected by both the sample stimuli and the reinforcers, responding by the pigeons was affected solely by the reinforcers. These data suggest that, in this procedure, humans (but not pigeons) are able to learn relations among stimuli simply as a result of stimulus–stimulus pairing.     

Associative symmetry and stimulus-class formation by pigeons: The role of non-reinforced baseline relations

Two experiments tested the assumption of Urcuioli's (2008) theory of pigeons’ equivalence-class formation that consistent non-reinforcement of certain stimulus combinations in successive matching juxtaposed with consistent reinforcement of other combinations generates stimulus classes containing the elements of the reinforced combinations. In Experiment 1, pigeons were concurrently trained on symbolic (AB) and two identity (AA and BB) successive tasks in which half of all identity trials ended in non-reinforcement but all AB trials were reinforced, contingent upon either responding or not responding to the comparisons. Subsequent symmetry (BA) probe trials showed evidence of symmetry in one of four pigeons. In Experiment 2, pigeons learned three pair-comparison tasks in which left versus right spatial choices were reinforced after the various sample-comparison combinations comprising AB, AA, and BB conditional discriminations. Non-differentially reinforced BA probe trials following acquisition showed some indication of symmetrical choice responding. The overall results contradict the theoretical predictions derived from Urcuioli (2008) and those from Experiment 2 challenge other stimulus-class analyses as well.     

Effects of thyrotropin-releasing hormone (TRH) and MK-771 on schedule-controlled behavior of squirrel monkeys, rabbits and pigeons

The effects of TRH (0.001-10.0 mg/kg) and a more potent TRH analog, MK-771 (0.001-5.6 mg/kg), were studied on comparable schedule-controlled performances of squirrel monkeys, rabbits and pigeons. Responding was maintained in the presence of different stimuli by a multiple fixed-ratio (FR), fixed-interval (FI) schedule of food presentation (monkeys and pigeons) or 0.25% saccharin solution (rabbits). Generally, TRH and MK-771 produced decreases in responding under both schedules and in all three species. TRH and MK-771 were roughly equipotent in the squirrel monkey, whereas in the pigeon and rabbit MK-771 was approximately 20 times more potent than TRH in decreasing responding to 50 percent of control levels. The duration of action of doses of TRH and MK-771 that reduced responding to 50 percent of control was approximately 3 hr in the squirrel monkey; recovery of performance occurred twice as fast under the FR schedules. With the pigeon, TRH effects that produced 50 percent decreases in responding lasted over 6 hours, whereas behaviorally comparable doses of MK-771 lasted about 4 hours. With few exceptions, TRH and MK-771 appear to produce similar effects of schedule-controlled behavioral performances of the squirrel monkey, rabbit and pigeon. Compared to the effects of other behaviorally-active substances under these procedures, TRH and MK-771 exert a distinctive array of effects.     

Attention to uninformative features expressed by pigeons in a duration matching-to-sample task

Pigeons were trained on a matching-to-sample task in which they had to respond to a different choice stimulus following the same durations (2 or 10 s) of two different signals. The duration signals consisted of a white light presented from the ceiling and a red light presented from the front wall. Subsequent test performance indicated that matching accuracy declined (1) when the set of choice stimuli following a duration signal differed from the set presented during training, and (2) when the color or location of the duration signal was changed from values used during training. These results are discussed in terms of attention to uninformative features of a visual stimulus.     

Reinforcer devaluation by extinction depends on the food restriction protocol

A common feature of reinforcer devaluation studies is that new learning induces the devaluation. The present study used extinction to induce new learning about the conditioned reinforcer in a heterogeneous chain schedule. Rats pressed a lever in a heterogeneous chain schedule to produce a conditioned reinforcer (light) associated with the opportunity to obtain an unconditioned reinforcer (food) by pulling a chain. The density of food reinforcement correlated with the conditioned reinforcer was varied in a comparison of continuous and variable-ratio reinforcement schedules of chain pulling; this had no noticeable effect on conditioned reinforcer devaluation produced by extinction of chain pulling. In contrast, how rats were deprived appeared to matter very much. Restricting meal duration to 1h daily produced more lever pressing during baseline training and a greater reductive effect of devaluation on lever pressing than restricting body weight to 80% of a control rat's weight, which eliminated the devaluation effect. Further analysis suggested that meal-duration restriction may have produced devaluation effects because it was more effective than weight restriction in reducing rats' body weights. Our results exposed an important limitation on the devaluation of conditioned reinforcers: slight differences in food restriction, using two commonly employed food-restriction procedures, can produce completely different interpretations of reinforcer devaluation while leaving reinforcer-based learning intact.     

Interruption of pacemaker signals is mediated by GABAergic inhibition of the pacemaker nucleus in the African electric fish <Emphasis Type="Italic">Gymnarchus niloticus</Emphasis>

The wave-type African weakly electric fish Gymnarchus niloticus produces electric organ discharges (EODs) from an electric organ in the tail that is driven by a pacemaker complex in the medulla, which consists of a pacemaker nucleus, two lateral relay nuclei and a medial relay nucleus. The prepacemaker nucleus (PPn) in the area of the dorsal posterior nucleus of the thalamus projects exclusively to the pacemaker nucleus and is responsible for EOD interruption behavior. The goal of the present study is to test the existence of inhibition of the pacemaker nucleus by the PPn. Immunohistochemical results showed clear anti-GABA immunoreactive labeling of fibers and terminals in the pacemaker nucleus, but no apparent anti-glycine immunoreactivity anywhere in the pacemaker complex. GABA injection into the pacemaker nucleus could induce EOD interruptions that are comparable to the interruptions induced by glutamate injection into the PPn. Application of the GABA_A receptor blocker bicuculline methiodide reversibly eliminated the effects of stimulation of the PPn. Thus the EOD interruption behavior in Gymnarchus is mediated through GABAergic inhibition of the pacemaker nucleus by the PPn.     

Choice in humans: Functional properties of reinforcers established by instruction

Adult human subjects chose between schedules containing stimuli (indicator lights) that the subjects were instructed to consider pleasurable. The schedules differed in amount of reinforcement (period of illumination) or delay (interval between a choice response and light onset). Although subjects preferred large to small amounts of reinforcement, they were essentially indifferent between immediate and delayed reinforcement. In contrast, previous data on video game reinforcement demonstrated preferences for both immediate and large amounts of reinforcement. The instructed reinforcer was thus partially effective in controlling choice but was not equivalent to a reinforcer that presumably had intrinsic value.     

Vaginocervical stimulation induces Fos in glutamate neurons in the ventromedial hypothalamus: Attenuation by estrogen and progesterone

Vaginocervical stimulation (VCS) induces the immediate-early gene product Fos in the ventromedial hypothalamus (VMH) of female rats. However, this induction is lower in ovariectomized rats that receive estradiol benzoate (EB) and progesterone (P) relative to an oil vehicle. We have observed that a substantial proportion of cells activated in the VMH by VCS stain for glutamate, and infusions of glutamate or its selective receptor agonists to the VMH inhibit both appetitive and consummatory sexual behaviors in females. This raises the possibility that VCS activates an inhibitory glutamate system in the VMH, and that ovarian steroids blunt the activation, although it is not known whether EB or P, alone or in combination, lead to this effect. The present experiment examined the ability of VCS to induce Fos in glutamate neurons in the VMH of ovariectomized rats under 4 hormonal regimens: oil, EB alone, P alone, or EB + P, following 1 or 50 distributed VCSs administered with a lubricated glass rod over the course of 1 h. Treatment with EB or P alone significantly reduced the number of glutamate neurons activated by 1 VCS, with P being more effective than EB. Treatment with EB + P also produced a significant reduction, but not to the extent of EB or P alone. Although EB and P work in synergy to activate sexual behavior in female rats, actions of EB or P alone are sufficient to blunt the ability of VCS to activate glutamate neurons in the VMH. It thus appears that ovarian steroids may “disinhibit” sexual responding, in part, by dampening the ability of VCS to activate glutamate neurons in the VMH. In turn, this may allow females to receive a sufficient number of intromissions for the activation of sexual reward and the facilitation of pregnancy.     

Potentiation of the behavioral effects of pentobarbital, chlordiazepoxide and ethanol by thyrotropin-releasing hormone

Effects of pentobarbital, chlordiazepoxide and ethanol were studied alone and in combination with thyrotropin-releasing hormone (TRH), IM, on punished behavior. Key-peck responses of pigeons were maintained by food presentation under a fixed-interval 3-min schedule in which every 30th response produced shock. Moderate doses of pentobarbital, chlordiazepoxide and ethanol increased punished responding to 150-200% of control values while the higher doses of these drugs almost completely eliminated responding. TRH (0.01-1 mg/kg) had little effect on punished responding and 3 mg/kg produced 50% decreases. Although the lower doses of TRH were without effect when given alone, doses of 0.03 mg/kg and greater markedly potentiated the rate-increasing effects of pentobarbital, chlordiazepoxide and ethanol. Increases in punished responding of 350% were obtained with combinations of TRH and these drugs. The rate-decreasing effects of the sedative-hypnotic and anxiolytic compounds were not reversed by TRH. Potentiation of the behavioral effects of sedative-hypnotic and anxiolytic drugs by TRH suggests that TRH may play an important role in modulating the behavioral effects of these compounds and that combinations of neuroactive peptides with certain psychotherapeutic agents may be of some therapeutic value.     

Nitrogen-fixers <Emphasis Type="Italic">Alnus</Emphasis> and <Emphasis Type="Italic">Lupinus</Emphasis> influence soil characteristics but not colonization by later successional species in primary succession on Mount St. Helens

Changes to the primary successional environment caused by colonizing plants that present symbiotic associations with nitrogen-fixing bacteria were investigated at two areas on Mount St. Helens. One area was occupied by alder (Alnus viridis) thickets and old lupine (Lupinus lepidus) patches and the other area by young lupine patches and pumice barrens. Alder thicket soils had higher levels for a few soil nutrients and had greater cover by other pioneer species as compared to old lupine patches. Many soil nutrients, including nitrogen and soil organic matter, were below detection limits in old lupine patches but not in alder thicket soils. Young lupine patch soils were generally not different from barren site soils but had greater cover by other pioneer species. Below detection nitrogen and soil organic matter levels also occurred in many barren soil samples but not in young lupine patch soils. Barren soils were moister than were the other sites. The apparent increase in soil fertility has not led to invasion by later successional species, perhaps due to dry conditions or to other inhibitory factors. Seedbanks, composed of early successional species, appear to be developing in these areas.     

Effects of thyrotropin-releasing hormone (TRH) and MK-771 on behavior of squirrel monkeys controlled by noxious stimuli

The effects of TRH (0.1-30 mg/kg) and an enzyme-resistant analogue, MK-771 (0.1-10 mg/kg), were characterized in squirrel monkeys on responding maintained in the presence of different visual stimuli by a multiple 3-min fixed-interval (FI), 30-response fixed-ratio (FR) schedule of stimulus-shock termination or by a multiple 5-min FI schedule of food or shock presentation. Under the termination schedule, the first response at the end of 3 min in the FI component or the completion of the 30-response requirement in the FR component terminated the visual stimulus in the presence of which shocks occurred (escape schedule). Under the schedule of food or shock presentation, the first response at the end of the 5-min FI produced food in the presence of red stimulus lights or shock in the presence of white lights. TRH and MK-771 produced large, dose-related increases in responding maintained under the FR stimulus-shock termination schedule whereas these peptides produced smaller increases or did not affect responding under the FI schedule. TRH and MK-771 also produced marked increases in responding maintained by shock presentation at doses that did not alter or decreased food-maintained responding in the same subject. Thus, performances maintained by noxious stimuli are uniquely sensitive to the rate-increasing effects of TRH and MK-771. These findings suggest that the behavioral effects of the neuropeptides, TRH and MK-771, can depend on the specific consequences of behavior and, as such, the effects of these substances are determined by many of the same variables that determine the effects of other behaviorally-active drugs.