Response rates track the history of reinforcement times

When conditioning involves a consistent temporal relationship between the conditioned stimulus (CS) and unconditioned stimulus (US), the expression of conditioned responses within a trial peaks at the usual time of the US relative to the CS. Here we examine the temporal profile of responses during conditioning with variable CS-US intervals. We conditioned stimuli with either uniformly distributed or exponentially distributed random CS-US intervals. In the former case, the frequency of each CS-US interval within a specified range is uniform but the momentary probability of the US (the hazard function) increases as time elapses during the trial; with the latter distribution, short CS-US intervals are more frequent than longer intervals, but the momentary probability of the US is constant across time within the trial. We report that, in a magazine approach paradigm, rats' response rates remained stable as time elapses during the CS when the CS-US intervals were uniformly distributed, whereas their response rates declined when the CS-US intervals were exponentially distributed. In other words, the profile of responding during the CS matched the frequency distribution of the US times, not the momentary probability of the US during the CS. These results are inconsistent with real-time associative models, which predict that associative strength tracks the momentary probability of the US, but may provide support for timing models of conditioning in which conditioned responding is tied to remembered times of reinforcement.     

Studying reaction time with nonaging intervals: An effective procedure

The nonaging-intervals procedure, in which momentary probability of stimulus occurrence remains constant, is preferable in principle to varied or constant intervals for double-stimulation experiments on reaction time (RT). However, elevation of RT has uniformly been found at short waiting intervals on single-stimulation baseline tasks. Effects attributable to the first stimulus on double-stimulation tasks would thus be confounded. The required level baselines were obtained for both simple and choice reactions by combining the transit-signal method with nonaging intervals. Possible reasons for this success were the elimination of timekeeping error and psychological refractoriness. Results with precued full response information show the expected decline of RT with increase of precue-to-stimulus interval. Suggestions are given for the use of nonaging intervals for studying the attentional demands of movements and the influence of level of momentary probability on basic RT effects.     

Simple reaction time with very small imperative- stimulus probabilities

The simple reaction time was studied as a function of the probability of the delivery of the imperative stimulus which was or was not (randomly) delivered 1 sec after the warning signal. The probability of the imperative stimulus was varied much more extensively than in any of the previous studies; thus, the response speed with very small probabilities was of especial interest. The results obtained with five subjects suggested a quadratic relationship between the probability and the reaction time so that the latter appeared to be relatively independent of the former with very small probabilities.     

Expectancy and stimulus frequency: a comparative analysis in rats and humans.

We examined whether expectancy, one of several factors influencing attention, is similarly affected in rats and humans by manipulation of relative stimulus frequency. A two-choice reaction time (RT) task was developed for rats, and an analogous task was used for humans. Errors, RTs, discriminability, and response bias were measured. Both rats and humans shifted their response bias to the more frequent stimulus, with no change in overall discriminability. As stimulus probability or stimulus repetition increased, RTs and errors decreased. These results illustrate the similarity of expectancy in rats and humans. This two-choice RT task for rats can be used in future studies to examine the neuronal mechanisms of expectancy and attention.     

Expectancy and stimulus frequency: A comparative analysis in rats and humans

We examined whether expectancy, one of several factors influencing attention, is similarly affected in rats and humans by manipulation of relative stimulus frequency, A two-choice reaction time (RT) task was developed for rats, and an analogous task was used for humans. Errors, RTs, discriminability, and response bias were measured. Both rats and humans shifted their response bias to the more frequent stimulus, with no change in overall discriminability. As stimulus probability or stimulus repetition increased, RTs and errors decreased. These results illustrate the similarity of expectancy in rats and humans. This two-choice RT task for rats can be used in future studies to examine the neuronal mechanisms of expectancy and attention.     

Sequential dependencies in free-responding

Three pigeons pecked for food in an experiment in which reinforcements were arranged for responses terminating sequences of interresponse times. Each reinforced interresponse time belonged to a class extending either from 1.0 to 2.0 sec (class A) or from 3.0 to 4.5 sec (class B). Reinforcements were arranged by a single variable-interval schedule and a random device that assigned each reinforcement to one of four sequences of two successive interresponse times: AA, AB, BA, or BB. Throughout the experiment, half of the reinforcements were delivered for interresponse times in class A and half for those in class B. Over conditions, the interresponse time preceding a reinforced interresponse time always, half of the time, or never, belonged to class A. The duration of the interresponse time preceding a reinforced one had a pronounced effect on response patterning. It also had a pronounced effect on the overall response probability, which was highest, intermediate, and lowest, when the interresponse time preceding a reinforced interresponse time always, half of the time, or never, belonged to class A, respectively. In no case were successive interresponse times independent, so that overall response probability was not representative of momentary response probabilities.     

Reaction times of pigeons on a wavelength discrimination task

After extensive pretraining, three pigeons were exposed in 2-second trials to a random series of 14 light wavelengths, ranging in one nanometer (nm) steps from 575 nanometers to 589 nanometers. Responses to one of the wavelengths, 582 nanometers, were intermittently reinforced. The relative frequency of response approached 1.0 at 582 nanometers, and decreased with progressively higher and lower wavelengths. Reaction times shorter than about 0.2 second occurred with a low frequency that was largely independent of wavelength. Wavelength controlled the frequency of longer reaction times, but did not affect the distribution of these reaction times. Consequently, receiver-operating characteristic curves constructed by using reaction time as a rating measure did not conform to the signal-detection model, in contrast to such conformity when response rate is used in a similar way. The data suggest that stimulus onset as such triggers early response emission with some small probability; the probability of responses with longer latency is controlled by wavelength, but their time of emission is controlled by some independent process.     

刻板印象激活效应对社会分类的影响

采用改进的flanker范式,探讨了刻板印象激活效应对社会分类的影响,并考察了匹配刺激出现概率对刻板印象激活效应影响社会分类的调节作用。实验一发现,性别刻板印象激活后,按性别分类时,匹配刺激中和不匹配刺激中面孔分类反应时之间的差异是显著的,但按年龄分类时,二者间的差异不显著。实验二表明,匹配刺激出现概率为80%时和50%时,匹配刺激中和不匹配刺激中面孔分类反应时之间的差异是显著的;但当匹配刺激出现概率为20%时,二者间的差异不显著。结果表明,刻板印象激活效应对与该刻板印象对应的社会分类有显著的影响,对与该刻板印象无关社会分类不会产生影响。刻板印象激活效应对社会分类的影响受匹配刺激出现概率的调节。     

Contrast as seen in visual search reaction times.

Three pigeons searched arrays of alphabetic letters displayed on computer monitors. On each trial, either an A or an E appeared, and the reaction time and accuracy with which the bird pecked at this target were measured. In each block of trials, each target (A or E) was displayed alone, or together with a number of distractor letters (2 or 18) that varied in their similarity to the target. During a baseline series of sessions, responses to the A and to the E each yielded food reinforcement on 10% of the trials. In the next series of sessions, reinforcement continued at 10% for A, but rose to 30% for E. In a final series, these reinforcement conditions were reversed. As expected, reaction times increased with target-distractor similarity and (for similar distractors) with the number of distractors. Increased reinforcement of E had no effect on reaction times to E, but produced a very consistent increase in reaction times to A; the average increase was constant across the various display conditions. Reversal of the differential reinforcement conditions reversed this contrast effect. Analysis of the reaction time distributions indicated that increased reinforcement to E decreased the momentary probability of response to A by a constant amount, regardless of display conditions. These results are discussed in relation to theories of contrast, memory, and of the search image.     

Response latencies of rats during behavioral thermoregulation

The cutaneous thermal stimulation that elicits behavioral thermoregulatory behavior was investigated in these experiments. In Experiment I, rats were placed in a cool environment and allowed to barpress for 3-sec bursts of radiant heat reinforcement. In various phases of the study, rats could earn different intensities of anterior, posterior, or whole-body radiation. Identical response rates were exhibited at each intensity for all exposure conditions; this information, when considered with existing literature on behavioral and neurophysiological studies, suggests that the rat’s thermoregulatory behavior depends on information carried by nonmyelinated fibers that supply thermoreceptors in the skin. Experiment II investigated the hypothesis that cooling of the skin is the stimulus that elicits each thermoregulatory response. Time series measures of skin temperature fluctuations and reaction times (RTs) were obtained. Tails of the RT distributions were shown to conform to exponential probability density functions, and mean RT varied linearly over the domain of reinforcement intensities used. A computer simulation model that describes temperature gradients across layers of skin was employed to estimate temperature fluctuations at the level of the cool receptors. Comparison of simulated skin temperatures with obtained RTs suggests that momentary thermoregulatory behavior is controlled mainly by cooling skin temperature.     

The effects of practice with one positive set in a memory scanning task can be completely transferred to a different positive set

Recognition tasks in which the items have been assigned to one and only to one response category throughout an experiment typically reveal that the functions relating reaction time and positive set size are negatively accelerated and have slopes which decrease significantly with practice. The present experiments were designed to determine whether this practice effect is specific to the individual items practiced or if it depends, at least partially, on relations built up among the positive set items. The results permit rejection of both alternatives. In the extreme case tested, it was found that, after prolonged practice with the same items composing nested positive sets, these items could be replaced with unpracticed ones without producingany significant change in the effect of set size, reaction times, or error levels. Absence of change in overall reaction times in combination with stability of slope values leads to the conclusion that not only do those practice effects which are related to the set-size effect transfer exceedingly well to unpracticed items, but practice effects on all other stages involved in item recognition also show almost total transfer to unpracticed items. It is concluded that, under the conditions of these experiments, the gain (through practice) in efficiency in processing the stimulus is independent of the stimulus.     

Some sequential aspects of IRTs emitted during Sidman-avoidance behavior in the white rat,

This study investigated some of the serial patterns among interresponse times during Sidman avoidance. It was found that the momentary probability of a response was determined by the length of exposure to the avoidance procedure during a session, by the time since the last shock, and by the duration of the preceding IRT.     

Rehearsal,generative processes,and the activation of underlying stimulus representations

Previous research found that subjects engaged in mental rehearsal could reduce stimulus encoding time in classification and identification tasks by generating an appropriate representation of the probe stimulus prior to its presentation. The present experiment examined the types of representational codes activated by generative processes in character classification. Numerical stimuli were employed which could differ visually, yet have the same name and meaning (e.g., TWO, 2, II, &.). The results indicate that generative processes may activate visual and nonvisual memory codes prior to the encoding of an external stimulus. Effects of generative processes were discussed in terms of an activation model which defines the function of rehearsal in perceptual processing. Attention, through rehearsal, activates stimulus representations which are described by distributions of activation which change continuously over time. The momentary state of each distribution determines the rate of stimulus encoding.     

Stimulus-response compatibility and response preparation: effects on motor component of information processing for upper and lower limb responses

The effects of stimulus-response compatibility and response preparation on the motor component of the information processing system were investigated by analyzing the fractionated reaction time for the upper and lower limbs. The reaction time was divided into two periods with respect to the onset of electromyographic activity, premotor and motor times. The response preparation was manipulated by the probability that the locations of the precue and subsequent imperative stimulus corresponded. On a stimulus-response compatible task, subjects were required to release a key on the same side as an imperative stimulus, irrespective of the precued side. On an incompatible task, subjects were required to act in the reverse manner. The upper and lower limb responses were measured during both tasks. A repeated-measures design was used with 12 male university students. Analysis of the reaction and premotor times indicated that the stimulus-response compatibility effect became larger as response preparation decreased. The analysis of motor time yielded significant interactions between stimulus-response compatibility and limb and between response preparation and limb. These findings indicated that the motor component of information processing for the lower limb response is affected by both stimulus-response compatibility and response preparation.     

Neuromagnetic evidence for the timing of lexical activation: an MEG component sensitive to phonotactic probability but not to neighborhood density

Evidence from electrophysiological measures such as ERPs (event-related potentials) and MEG (magnetoencephalography) suggest that the first evoked brain response component sensitive to stimulus properties affecting reaction times in word recognition tasks occurs at 300-400 ms. The present study used the stimulus manipulation of Vitevich and Luce (1999) to investigate whether the M350, an MEG response component peaking at 300-400 ms, reflects lexical or postlexical processing. Stimuli were simultaneously varied in phonotactic probability, which facilitates lexical activation, and in phonological neighborhood density, which inhibits the lexical decision process. The present results indicate that the M350 shows facilitation by phonotactic probability rather than inhibition by neighborhood density. Thus the M350 cannot be a postlexical component.     

Probability effects on stimulus evaluation and response processes.

This study investigated the effects of probability information on response preparation and stimulus evaluation. Eight subjects responded with one hand to the target letter H and with the other to the target letter S. The target letter was surrounded by noise letters that were either the same as or different from the target letter. In 2 conditions, the targets were preceded by a warning stimulus unrelated to the target letter. In 2 other conditions, a warning letter predicted that the same letter or the opposite letter would appear as the imperative stimulus with .80 probability. Correct reaction times were faster and error rates were lower when imperative stimuli confirmed the predictions of the warning stimulus. Probability information affected (a) the preparation of motor responses during the foreperiod, (b) the development of expectancies for a particular target letter, and (c) a process sensitive to the identities of letter stimuli but not to their locations.     

视觉刺激探测的警觉性注意特征初探

采用"预警提示-目标探测"范式,对视觉刺激探测的警觉性注意特征进行初步探索。实验一表明,随着预备到目标刺激的时间间隔(interstimulus interval,ISI)变化,固定位置上探测目标刺激的速度也随之变化,并且对大概率刺激的探测更快,表现出了警觉性注意的稳定性和选择性特征。实验二进一步考察了目标刺激在不同ISI和不同空间位置的情况,除发现与实验一相似的结果以外,被试探测目标刺激的速度随注意视角增大而下降,表现出了警觉性注意的集中性特征。     

Concurrent schedules: Maximization versus reinforcement of changeover behaviour

Pigeons responded on concurrent variable-interval 180-sec variable-interval 36-sec schedules during Conditions 1 and 3 of Experiment 1. Condition 2 arranged variable-interval 60-sec schedules for both response alternatives. The schedule assigned to the alternative that was associated with the variable-interval 36-sec schedule in Conditions 1 and 3 operated only when the subject responded on that alternative. The proportion of time spent responding on the alternative with the conventional variable-interval 60-sec schedule increased during Condition 2, but exclusive choice of that alternative did not develop. This result is inconsistent with maximization of the overall reinforcement rate and with maximization of the momentary probability of reinforcement (momentary maximizing). Increasing time proportions were also found in Experiment 2, which arranged similar conditions, except that reinforcement was provided on a variable-time basis. The time proportions were close to the momentary maximizing prediction in Experiment 2. The results of both experiments can be explained if it is assumed that time allocation is controlled by delayed reinforcement of changeovers between alternatives.     

Psychophysiologic chronometry: detection of facilitating and inhibiting processes in information processing using electroencephalographic and electromyographic data]

The objective of the present research was to tally the potential usefulness of psychophysiological measures in the systematic analysis of human information processing. Different context conditions were established in two cued choice-reaction time experiments. The context could either facilitate or inhibit the processing of an imperative stimulus. Event-related brain potentials (EEG-ERP) and event-related electromyograms (EMG-ERP) were recorded and from these biosignals latencies and duration times for different aspects of stimulus evaluation and movement execution were derived. The EEG-ERP provided measures for the time of primary stimulus categorization (N2), the time necessary to test actual stimulus information against stimulus expectancies (P3b), and the time necessary to check the decision about the stimulus-response mapping (pSW). From the EMG-ERP, processing times were derived which are related to the initiation of a motor program and to distinct sections of the movement trajectory. Results show that these latency measures react differently to different context manipulations. EEG-ERP measures, for example, reflected differences during stimulus evaluation which were not detectable in response- or EMG-derived movement times. The parallel analysis of EEG-ERPs and EMG-ERPs allowed delineation of processing modules which are responsible for particular context-dependent facilitation and inhibition effects. Moreover, the data revealed substantial overlap of evaluation times and movement times. This finding seems to be more compatible with a parallel processing model than with a strictly sequential model.     

IRT-stimulus contingencies in chained schedules: implications for the concept of conditioned reinforcement

Two experiments with pigeons investigated the effects of contingencies between interresponse times (IRTs) and the transitions between the components of 2- and 4-component chained schedules (Experiments 1 and 2, respectively). The probability of component transitions varied directly with the most recent (Lag 0) IRT in some experimental conditions and with the 4th (Lag 4) IRT preceding the most recent one in others. Mean component durations were constant across conditions, so the reinforcing effect of stimulus change was dissociated from that of delay to food. IRTs were longer in the Lag-0 than in the Lag-4 conditions of both experiments, thus demonstrating that stimulus change functioned as a reinforcer. In the Lag-0 conditions of Experiment 2, the Component-1 IRTs increased more than the Component-2 IRTs, which in turn increased more than the Component-3 IRTs. This finding runs counter to the conditioned-positive-reinforcement account of chained-schedule responding, which holds that the reinforcing effect of stimulus change should vary in strength as an inverse function of the delay to the unconditioned reinforcer at the end of the chain because conditioned reinforcement is due to first- or higher-order classical conditioning. Therefore, we present other possible explanations for this effect.