The effect of intruded events on peak time: the role of reinforcement history during the intruded event

Pigeons were studied in an extension of a study by Aum et al. [Aum, S., Brown, B.L., Hemmes, N.S. 2004. The effects of concurrent task and gap events on peak time in the peak procedure. Behav. Process. 65, 43-56] on timing behavior under a discrete-trial fixed-interval (FI) procedure during which 6-s intruded events were superimposed on peak-interval (PI) test trials. In Aum et al., one event consisted in termination of the timing cue (gap trial); the other was a stimulus in the presence of which subjects had been trained to respond under an independent random-interval (RI) schedule of reinforcement (concurrent task trial). Aum et al. found a disruption of timing on concurrent task trials that was greater than that on gap trials. The present study investigated history of reinforcement associated with intruded events as a possible explanation of this earlier finding. After training to peck a side key on a 30-s PI procedure, discrimination training was conducted on the center key in separate sessions; red or green 6-s stimuli were associated with RI 24s or EXT (extinction) schedules. During testing under the PI procedure, three types of intruded events were presented during probe trials--the stimulus associated with the RI (S+) or EXT (S-) schedule during discrimination training, or a gap (termination of the side-keylight). Intruded events occurred 3, 9, or 15s after PI trial onset. Effects of reinforcement history were revealed as substantial disruption of timing during the S+ event and relatively little disruption during the S- event. Intermediate effects were found for the gap event. Results indicate that postcue effects are at least partially responsible for the disruptive effects of the S+ event.     

Acquisition and transfer of visual Go/No-go discrimination by a chimpanzee

An adolescent female chimpanzee was trained to press a key in the presence of a computer-graphic geometric figure (“Go” stimulus) within 5 sec and not to press the key during 5-sec presentations of another figure (“No-go” stimulus) with food reinforcement. In the acquisition training, the accuracy of performance increased primarily as a result of learning to inhibit key presses in No-go trials. The chimpanzee acquired this “Go/No-go” visual discrimination task in 1,260 trials. She was then given 14 successive transfer problems. The results for these problems suggested that learning-set formation and repeated use of the same discriminative stimuli both influenced transfer to new problems.     

Time under tension and blood lactate response during four different resistance training methods

Mechanical stimuli have often been suggested to be the major determinant of resistance training adaptations; however, some studies suggested that metabolic changes also play an important role in the gains of muscle size and strength. Several resistance training methods (RTM) have been employed with the purpose of manipulating mechanical and metabolic stimuli; however, information about their physiological effects are scarce. The objective of this study was to compare the time under tension (TUT) and blood lactate responses among four different RTM reported in the literature. The four RTM were performed in a knee extension machine at 10 repetition maximum (RM) load by 12 recreationally trained young men. The RTM tested were: 10RM, super-slow (SL-subjects performed one 60-second repetition with 30 seconds for eccentric and 30 seconds for concentric phase), functional isometrics (FI-in each repetition, a five-second maximal isometric contraction was executed with the knees fully extended) and adapted vascular occlusion (VO-subjects performed a 20-second maximal isometric contraction with the knees fully extended and immediately proceeded to normal isoinertial lifts). According to the results, all RTM produced significant increases in blood lactate levels. However, blood lactate responses during FI (4.48+/-1.57 mM) and VO (4.23+/-1.66 mM) methods were higher than the SL method (3.41+/-1.14 mM). The TUT for SL (60 s), FI (56.33+/-6.46 s), and VO (53.08+/-4.76 s) methods were higher than TUT for 10RM (42.08+/-3.18 s). Additionally, TUT for the SL method was higher than TUT during the VO method. Therefore, the SL method may not be recommended if one wants to provide a high metabolic stimulus. The FI method appeared to be especially effective in promoting both type of stimuli.     

The effects of concurrent task and gap events on peak time in the peak procedure

The effect of a concurrent task on timing performance of pigeons was investigated with the peak interval procedure. Birds were trained to peck a side key on a discrete-trial schedule that included reinforced fixed-interval (FI) 30-s trials and nonreinforced extended probe trials. Then, in separate sessions, birds were trained to peck a 6-s center key for food. In a subsequent test phase, the FI procedure was in effect along with dual-task probe test trials. On those test trials, the 6-s center key (task cue) was presented at 3, 9, or 15s after probe trial onset. During another test phase, a 6-s gap (the FI keylight was extinguished) was presented at 3, 9, or 15s after probe trial onset. Peak time increased with center key time of onset, and was greater under task than gap conditions. Moreover, peak time under task conditions exceeded values predicted by stop and reset clock mechanisms. These results are at variance with current attentional accounts of timing behavior in dual-task conditions, and suggest a role of nontemporal factors in the control of timing behavior.     

Self-regulation of slow cortical potentials in psychiatric patients: Schizophrenia

Slow cortical potentials (SCPs) are considered to reflect the regulation of attention resources and cortical excitability in cortical neuronal networks. Impaired attentional functioning, as found in patients with schizophrenic disorders, may covary with impaired SCP regulation. This hypothesis was tested using a self-regulation paradigm. Twelve medicated male schizophrenic inpatients and 12 healthy male controls received continuous feedback of their SCPs, during intervals of 8 s each, by means of a visual stimulus (a stylized rocket) moving horizontally across a TV screen. The position of the feedback stimulus was a linear function of the integrated SCP at each point in time during the feedback interval. Subjects were required to increase or reduce negative SCPs (referred to pretrial baseline) depending on the presentation of a discriminative stimulus. The correct response was indicated by the amount of forward movement of the feedback stimulus and by monetary rewards. Schizophrenics participated in 20 sessions (each comprising 110 trials), while controls participated in 5 sessions. Compared with the healthy controls, schizophrenics showed no significant differentiation between negativity increase and negativity suppression during the first sessions. However, in the last 3 sessions, patients achieved differentiation similar to controls, demonstrating the acquisition of SCP control after extensive training.     

Self-regulation of slow cortical potentials in psychiatric patients: schizophrenia.

Slow cortical potentials (SCPs) are considered to reflect the regulation of attention resources and cortical excitability in cortical neuronal networks. Impaired attentional functioning, as found in patients with schizophrenic disorders, may covary with impaired SCP regulation. This hypothesis was tested using a self-regulation paradigm. Twelve medicated male schizophrenic inpatients and 12 healthy male controls received continuous feedback of their SCPs, during intervals of 8 s each, by means of a visual stimulus (a stylized rocket) moving horizontally across a TV screen. The position of the feedback stimulus was a linear function of the integrated SCP at each point in time during the feedback interval. Subjects were required to increase or reduce negative SCPs (referred to pretrial baseline) depending on the presentation of a discriminative stimulus. The correct response was indicated by the amount of forward movement of the feedback stimulus and by monetary rewards. Schizophrenics participated in 20 sessions (each comprising 110 trials), while controls participated in 5 sessions. Compared with the healthy controls, schizophrenics showed no significant differentiation between negativity increase and negativity suppression during the first sessions. However, in the last 3 sessions, patients achieved differentiation similar to controls, demonstrating the acquisition of SCP control after extensive training.     

Oscillations following periodic reinforcement

Three experiments examined behavior in extinction following periodic reinforcement. During the first phase of Experiment 1, four groups of pigeons were exposed to fixed interval (FI 16 s or FI 48 s) or variable interval (VI 16 s or VI 48 s) reinforcement schedules. Next, during the second phase, each session started with reinforcement trials and ended with an extinction segment. Experiment 2 was similar except that the extinction segment was considerably longer. Experiment 3 replaced the FI schedules with a peak procedure, with FI trials interspersed with non-food peak interval (PI) trials that were four times longer. One group of pigeons was exposed to FI 20 s PI 80 s trials, and another to FI 40 s PI 160 s trials. Results showed that, during the extinction segment, most pigeons trained with FI schedules, but not with VI schedules, displayed pause-peck oscillations with a period close to, but slightly greater than the FI parameter. These oscillations did not start immediately after the onset of extinction. Comparing the oscillations from Experiments 1 and 2 suggested that the alternation of reconditioning and re-extinction increases the reliability and earlier onset of the oscillations. In Experiment 3 the pigeons exhibited well-defined pause-peck cycles since the onset of extinction. These cycles had periods close to twice the value of the FI and lasted for long intervals of time. We discuss some hypotheses concerning the processes underlying behavioral oscillations following periodic reinforcement.     

Effects of two high-intensity intermittent training programs interspaced by detraining on human skeletal muscle and performance

The purpose of this study was to investigate the effects of repeated high-intensity intermittent training programs interspaced by detraining on human skeletal muscle and performances. First, nineteen subjects were submitted to a 15-week cycle ergometer training program which involved both continuous and high-intensity interval work patterns. Among these 19 subjects, six participated in a second 15-week training program after 7 weeks of detraining. Subjects were tested before and after each training program for maximal aerobic power and maximal short-term ergocycle performances of 10 and 90s. Muscle biopsy from the vastus lateralis before and after both training programs served for the determination of creatine kinase (CK), hexokinase, phosphofructokinase (PFK), lactate dehydrogenase (LDH), malate dehydrogenase, 3-hydroxyacyl-CoA dehydrogenase (HADH) and oxoglutarate dehydrogenase (OGDH) activities. The first training program induced significant increases in all performances and enzyme activities but not in CK. Seven weeks of detraining provoked significant decreases in maximal aerobic power and maximal 90s ergocycle performance. While the interruption of training had no effect on glycolytic enzyme markers (PFK and LDH), oxidative enzyme activities (HADH and OGDH) declined. These results suggest that a fairly long interruption in training has negligeable effects on glycolytic enzymes while a persistent training stimulus is required to maintain high oxidative enzyme levels in human skeletal muscle. The degree of adaptation observed after the second training program confirms that the magnitude of the adaptive response to exercise-training is limited.     

Rats can discriminate illuminance,but not magnetic fields,as a stimulus for learning a two-choice discrimination

In each of the two experiments, nine rats were trained for 64 trials (eight trials per day) to determine if they could acquire a two-choice discrimination based on a specified discriminative stimulus (S(D)). In one experiment, the S(D) was a change in ambient illumination, while in the second experiment the S(D) was a change in the combination of sinusoidal 60 Hz and static magnetic field (MF) and any cues attendant to energizing the coils that produced the MF exposure. The rats that had a change in illuminance as the S(D) learned the two-choice task easily, P <.001, whereas the rats having a change in MFs as the S(D) did not.     

Undesirable Choice Biases with Small Differences in the Spatial Structure of Chance Stimulus Sequences

In two-alternative discrimination tasks, experimenters usually randomize the location of the rewarded stimulus so that systematic behavior with respect to irrelevant stimuli can only produce chance performance on the learning curves. One way to achieve this is to use random numbers derived from a discrete binomial distribution to create a ''full random training schedule'' (FRS). When using FRS, however, sporadic but long laterally-biased training sequences occur by chance and such ''input biases'' are thought to promote the generation of laterally-biased choices (i.e., ''output biases''). As an alternative, a ''Gellerman-like training schedule'' (GLS) can be used. It removes most input biases by prohibiting the reward from appearing on the same location for more than three consecutive trials. The sequence of past rewards obtained from choosing a particular discriminative stimulus influences the probability of choosing that same stimulus on subsequent trials. Assuming that the long-term average ratio of choices matches the long-term average ratio of reinforcers, we hypothesized that a reduced amount of input biases in GLS compared to FRS should lead to a reduced production of output biases. We compared the choice patterns produced by a ''Rational Decision Maker'' (RDM) in response to computer-generated FRS and GLS training sequences. To create a virtual RDM, we implemented an algorithm that generated choices based on past rewards. Our simulations revealed that, although the GLS presented fewer input biases than the FRS, the virtual RDM produced more output biases with GLS than with FRS under a variety of test conditions. Our results reveal that the statistical and temporal properties of training sequences interacted with the RDM to influence the production of output biases. Thus, discrete changes in the training paradigms did not translate linearly into modifications in the pattern of choices generated by a RDM. Virtual RDMs could be further employed to guide the selection of proper training schedules for perceptual decision-making studies.     

The effects of cue competition on timing in pigeons

We studied the effects of cue competition on timing in both overshadowing and blocking operant procedures with pigeons. A white center key delivered reward when pecked 30 s after a red or green sidekey was presented and 10 s after presentation of the alternate color on the other sidekey. In Experiment 1, key presentations were concurrent during training trials for overshadow-condition pigeons, while side key presentations were separated across training trials for control birds. In Experiment 2, half of the birds (Blocking group) were given pre-exposure trials to either the 10-s or 30-s sidekey condition. Both blocking-condition and control birds were then given trials of concurrent side key presentations. Peak time curves were compared between experimental and control conditions. The results showed blocking of timing accuracy of a long (30-s) stimulus by a short (10-s) stimulus, but no evidence for overshadowing of timing accuracy.     

Alterations in evertor/invertor muscle activation and center of pressure trajectory in participants with functional ankle instability

Participants with ankle instability demonstrate more foot inversion during the stance phase of gait than able-bodied subjects. Invertor excitation, coupled with evertor inhibition may contribute to this potentially injurious position. The purpose of this experiment was to examine evertor/invertor muscle activation and foot COP trajectory during walking in participants with functional ankle instability (FI). Twelve subjects were identified with FI and matched to healthy controls. Tibialis anterior (TA) and peroneus longus (PL) electromyography (EMG), as well as COP, were recorded during walking. Functional analyses were used to detect differences between FI and control subjects with respect to normalized EMG and COP trajectory during walking. Relative to matched controls, COP trajectory was more laterally deviated in the FI group from 20% to 90% of the stance phase. TA activation was greater in the FI group from 15% to 30% and 45% to 70% of stance. PL activation was greater in the FI group at initial heel contact and toe off and trended lower from 20% to 40% of stance in the FI group. Altered motor strategies appear to contribute to COP deviations in FI participants and may increase the susceptibility to repeated ankle inversion injury.     

Effect of protein source in diets fed during gestation and lactation on food intake regulation in male offspring of Wistar rats

We hypothesized that protein source in the nutritionally adequate AIN-93G diets fed during gestation, lactation, and weaning influences food intake (FI) regulation in male offspring of Wistar rats. Pregnant rats were fed the recommended casein-based (C) or soy protein-based (S) diet during gestation (experiment 1) or during gestation and lactation (experiment 2). Pups (n = 12 per group) weaned to C or S diets were followed for 9 wk (experiment 1) or 14 wk (experiment 2). At termination, body weight was 5.4% and 9.4% higher, respectively, in offspring of dams fed the S diet. Altered FI regulation was shown by failure of devazepide (a CCK-A receptor blocker) to block FI reduction after protein preloads in offspring of S diet-fed dams, whereas it had a strong effect on offspring of C diet-fed dams (P < 0.005). Similarly, naloxone (an opioid receptor blocker) blocked FI reduction more after casein than after soy protein preloads (P < 0.01). In experiment 2, offspring of dams fed the S diet had higher hypothalamic gene expression of agouti related protein at weaning (P < 0.05), and higher FI was found throughout postweaning (P < 0.0001). FI reduction after protein preloads at week 7 and after glucose preloads at week 13 was greater in offspring of C diet-fed dams (P < 0.05). Plasma insulin at weaning and insulin, ghrelin, and glucagon-like peptide-1 at week 15 were higher in offspring of S diet-fed dams (all P < 0.05). In conclusion, nutritionally complete C and S diets consumed during gestation and lactation differ in their effects on body weight and FI regulation in the offspring. Extending the diet from gestation alone to throughout gestation and lactation exaggerated the adverse effects of the S diet. However, the diet consumed postweaning had little effect on the outcome.     

Relationships between maximal muscle oxidative capacity and blood lactate removal after supramaximal exercise and fatigue indexes in humans.

The present study investigated whether blood lactate removal after supramaximal exercise and fatigue indexes measured during continuous and intermittent supramaximal exercises are related to the maximal muscle oxidative capacity in humans with different training status. Lactate recovery curves were obtained after a 1-min all-out exercise. A biexponential time function was then used to determine the velocity constant of the slow phase (gamma(2)), which denoted the blood lactate removal ability. Fatigue indexes were calculated during all-out (FI(AO)) and repeated 10-s cycling sprints (FI(Sprint)). Biopsies were taken from the vastus lateralis muscle, and maximal ADP-stimulated mitochondrial respiration (V(max)) was evaluated in an oxygraph cell on saponin-permeabilized muscle fibers with pyruvate + malate and glutamate + malate as substrates. Significant relationships were found between gamma(2) and pyruvate + malate V(max) (r = 0.60, P < 0.05), gamma(2) and glutamate + malate V(max) (r = 0.66, P < 0.01), and gamma(2) and citrate synthase activity (r = 0.76, P < 0.01). In addition, gamma(2), glutamate + malate V(max), and pyruvate + malate V(max) were related to FI(AO) (gamma(2) - FI(AO): r = 0.85; P < 0.01; glutamate + malate V(max) - FI(AO): r = 0.70, P < 0.01; and pyruvate + malate V(max) - FI(AO): r = 0.63, P < 0.01) and FI(Sprint) (gamma(2) - FI(Sprint): r = 0.74, P < 0.01; glutamate + malate V(max) - FI(Sprint): r = 0.64, P < 0.01; and pyruvate + malate V(max) - FI(Sprint): r = 0.46, P < 0.01). In conclusion, these results suggested that the maximal muscle oxidative capacity was related to blood lactate removal ability after a 1-min all-out test. Moreover, maximal muscle oxidative capacity and blood lactate removal ability were associated with the delay in the fatigue observed during continuous and intermittent supramaximal exercises in well-trained subjects.     

Stimulus sequence effects on human express saccades described by a Markov model

Express saccades predominantly occur in experiments employing the gap paradigm where the target onset is separated from the fixation point offset by a blank period. Their relative frequency is distinctly influenced by catch trials (i.e. trials without a saccadic target) mixed into the stream of regular target trials. Generalizing this concept for other stimulus uncertainties (direction, amplitude), we found that the preparation time of a saccade depends on both the type of uncertainty used and the sequence of trial type (e.g., target vs catch, left vs right) in the experiment. This stimulus sequence effect is most prominent for catch trials. A similar but less pronounced effect can still be observed in the case of direction uncertainty but not in that of amplitude uncertainty. A two-state Markov process model is proposed which is based on the dichotomy of express and regular saccades in the gap paradigm. According to this model the actual state of the saccadic system, which determines the type of saccade just in preparation, depends on the "trial history". The implications for models of saccade programming are discussed. Received: 14 April 1993/Accepted in revised form: 2 July 1993     

Factors that influence negative summation in a spatial-search task with pigeons

A variant of the standard conditioned inhibition procedure was used to evaluate landmark-based spatial search in a touchscreen preparation. Pigeons were given compound trials with one landmark (A) positioned in a consistent spatial relationship to a hidden goal and another landmark (B) positioned randomly with respect to A and the hidden goal (AB+). On half of the non-reinforced inhibitory trials, A was paired with landmark X (AX-) and on the remaining trials B was paired with Y (BY-). All subjects were also given reinforced trials with a transfer excitor (T+). During conditioned inhibition training, subjects showed no change in overall responding during AX- trials but did show a decrease in the number of pecks to the goal location signaled by A. During non-reinforced summation tests with landmark T, X had a greater suppressive effect than did Y on overall responding but the percentage of pecks at the goal did not differ unless X was positioned near the expected goal signaled by T. These data demonstrate that the effectiveness of a stimulus trained as an inhibitor is dependent on the strength of the association between its training excitor (A) and the US, as well as, the spatial arrangement of stimuli during testing.     

Influence of the reinforcement magnitude on omission effects

Reinforcement Omission Effects (ROEs), indicated by higher rate of responses after nonreinforced trials in a partial reinforcement schedule, have been interpreted as behavioral transient facilitation after nonreinforcement induced by primary frustration, and/or behavioral transient inhibition after reinforcement induced by demotivation or temporal control. The size of the ROEs should depend directly on the reinforcement magnitude. The present experiment aimed to clarify the relationship between reinforcement magnitude and the omission effects manipulating the magnitude linked to discriminative stimuli in a partial reinforcement FI schedule. The results showed that response rates were higher after omission than after reinforcement delivery. Besides, response rates were highest immediately after the reinforcement omission of a larger magnitude than of a smaller magnitude. These data are interpreted in terms of ROEs multiple process behavioral facilitation after nonreinforcement, and behavioral transient inhibition after reinforcement.     

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.     

慢性动脉血压监测模型在惊恐条件反射中的应用

目的：探索一种新的、可靠的模型,用于惊恐条件反射的相关研究。方法：通过使用条件刺激(声音)和非条件刺激(足部电击)相结合的方法,可使动物对条件刺激产生惊恐反应。同时对动脉血压进行长期监测并测定利多卡因阻断杏仁基底外侧核群前后的血压变化。结果：该惊恐条件反射建立后(需经4d训练),单独给予动物条件刺激即可引起血压明显升高。我们将它作为条件反射已形成的标志。此时,用利多卡因阻断杏仁基底外侧核群的作用,单独给予动物条件刺激不再引起血压明显升高。结论：慢性动脉血压监测模型在惊恐条件反射的研究中是一种可靠的动物模型。