Latency and frequency of responding under discrete-trial fixed-interval schedules of reinforcement

Pigeons' key pecking was studied under a number of discrete-trial fixed-interval schedules of food reinforcement. Discrete trials were presented by briefly illuminating the keylight repetitively throughout the interreinforcement interval. A response latency counterpart to the fixed-interval scallop was found, latency showing a gradual, negatively accelerated decrease across the interval. This latency pattern was largely invariant across changes in fixed-interval length, number of trials per interval, and maximum trial duration. Frequency of responding during early trials in the intervals varied, however, with different schedule parameters, being directly related to fixed-interval length, inversely related to number of trials, and complexly affected by conjoint variations of fixed-interval length and number of trials. Response latency thus was found to be simply related to elapsed time during the interval while response frequency was complexly determined by other factors as well.     

Stimulus control in a two-choice discrimination procedure

The relation between performance during discriminative training and subsequently obtained measures of stimulus control was investigated. Pigeons served as experimental subjects. In the discriminative training phase, a single peck on the center key, transilluminated by a bright or dim white light, resulted in the onset of the side keys, one red and one green. If the center key was brightly lighted, a response on the red side key was correct. A response on the green side key was correct if the center key was dimly lighted. Correct responses were reinforced on independently arranged variable-interval schedules. Following discriminative training, tests of stimulus control were administered during which white light of 11 intensities was projected on the center key and responses on the red and green side keys recorded. The proportion of correct responses in the presence of a bright or dim center-key stimulus decreased with decreases in the frequency of reinforcement of correct red or correct green responses, respectively. The slopes of the stimulus control gradients were related to the extent of response bias during training. The greater the bias to respond on the green key, the flatter the gradient showing the proportion of green-key responses to each stimulus and the steeper the corresponding gradient of red-key responses.     

Aging and individual differences in rapid two-choice decisions

The effects of aging on performance were examined in signal detection, letter discrimination, brightness discrimination, and recognition memory, with each subject tested on all four tasks. Ratcliff’s (1978) diffusion model was fit to the data for each subject for each task, and it provided a good account of accuracy and the distributions of correct and error response times. The model’s analysis of the components of processing showed that aging had three main effects: The nondecision components of processing were slower and the decision criteria were more conservative for 60- to 74-year-old and 75- to 85-year-old subjects than for college students, but the quality of the evidence on which decisions were based was as good for the older subjects as for college students on some of the tasks. Individual differences among subjects in components of processing tended to be preserved across the tasks, as was shown by strong correlations across the tasks in the parameters of the model that represent the components of processing. For example, if the evidence on which a subject’s decisions were based was good in one task, it tended to be good in all four tasks.     

Within-session changes in responding during concurrent schedules with different reinforcers in the components.

Rats and pigeons responded on several concurrent schedules that provided different reinforcers in the two components (food and water for rats, Experiment 1; wheat and mixed grain for pigeons, Experiment 2). The rate of responding and the time spent responding on each component usually changed within the session. The within-session changes in response rates and time spent responding usually followed different patterns for the two components of a concurrent schedule. For most subjects, the bias and sensitivity to reinforcement parameters of the generalized matching law, as well as the percentage of the variance accounted for, decreased within the session. Negative sensitivity parameters were sometimes found late in the session for the concurrent food-water schedules. These results imply that within-session changes in responding could cause problems for assessing the validity of quantitative theories of concurrent-schedule responding when the components provide different reinforcers. They question changes in a general motivational state, such as arousal, as a complete explanation for within-session changes in responding. The results are compatible with satiation for, or sensitization-habituation to, the reinforcers as explanations.     

Sequential effects in a two-choice serial reaction task

Twenty-four subjects performed a symbolic two-choice serial reaction task under four conditions. These were with a delay from previous response to onset of next stimulus of 100 millisec, 600 millisec., 2 sec., and a fourth condition of 2 sec. delay with verbal prediction of the next stimulus. A positive recency or repetition effect occurred at 100 millisec. delay where RTs to repeated stimuli were faster than RTs to alternate stimuli. At 600 millisec. this effect was still present, though much reduced. The 2 sec. delay gave a negative recency effect where RTs were slower to repeated than to alternate stimuli. This effect increased significantly with simultaneous prediction of the next stimulus. The verbal predictions themselves displayed negative recency. Run analysis of the four conditions revealed strking differences. These results emphasize the need for analysing the microstructure of choice RT situations and reveal deficiencies in present models.     

Hierarchical diffusion models for two-choice response times

Two-choice response times are a common type of data, and much research has been devoted to the development of process models for such data. However, the practical application of these models is notoriously complicated, and flexible methods are largely nonexistent. We combine a popular model for choice response times-the Wiener diffusion process-with techniques from psychometrics in order to construct a hierarchical diffusion model. Chief among these techniques is the application of random effects, with which we allow for unexplained variability among participants, items, or other experimental units. These techniques lead to a modeling framework that is highly flexible and easy to work with. Among the many novel models this statistical framework provides are a multilevel diffusion model, regression diffusion models, and a large family of explanatory diffusion models. We provide examples and the necessary computer code.     

Selective responding to the components of multiple visual cues by autistic children

Fifteen autistic and 15 normal Ss were trained to respond to a card containing two visual cues. After this training disctimination was established, the children were tested on the single cues in order to assess whether one or both stimuli had acquired control over their responding. The autistic children (12 of 15) gave evidence for stimulus overselectivity in that they responded correctly to only one of the two component cues. On the other hand, the normal children (12 of 15) showed clear evidence of control by both component cues of the training card. These results were consistent with previous studies, where autistics showed overselectivity when presented with multiple sensory input in several modalities. However, now autistic children appear to have difficulty responding to multiple cues even when both cues are in the same modality. These results were discussed in relation to the experimental literature on selective attention in normally functioning organisms.     

Interhemispheric transmission time in an auditory two-choice reaction task

An unimanual auditory choice reaction task was performed by 16 right-handed male subjects. Upon release of a central ready button subjects pressed a target button on their right or left side depending on the ear in which they heard a tone. A significant 'Ear' x 'Hand' interaction effect appeared on both reaction time (RT) and the first component of movement (MT₁), showing that uncrossed conditions give rise to faster responses than crossed conditions. Interhemispheric transmission time (IHTT) was estimated from the difference of response latency in the two types of conditions. No asymmetry in the speed of information transfer between the hemispheres was found. IHTT was 16 ms in the case of RT, which supported previous research with visual reaction tasks, and IHTT for MT₁ was 13 ms, which has not been reported before.     

Differential effects of omission contingencies on various components of Pavlovian appetitive conditioned responding in rats

Five experiments with rat subjects investigated the effects of omission and partial reinforcement contingencies on five individual behaviors evoked by visual and auditory conditioned stimuli paired with a food unconditioned stimulus. The effects of omission depended on the behavior on which that contingency was placed: One behavior was eliminated, one was unaffected, and three were reduced relative to the performance of yoked controls. Partial reinforcement resulted in lower frequencies of three behaviors and higher frequencies of two behaviors, compared with performance under consistent reinforcement. A partial reinforcement extinction effect was noted with one behavior but not with the others. These results are related to the possible role of instrumental conditioning contingencies in generating conditioned behavior in this appetitive conditioning preparation and to the independence of individual components of a complex conditioned response.     

Multiple Visual Latency

It has long been known that a dark visual stimulus is seen later than a bright one, with a delay up to several 10s of milliseconds. Systematic studies of various phenomena demonstrating this delay have revealed that the perceptual latency decreases monotonically as the stimulus intensity increases. Because latencies measured by psychological methods and cortical evoked responses are very similar to electroretinogram latencies, it has become a common belief that there is little in the intensity-dependent latency function that cannot be explained by retinal processes. In this study, we report evidence that there is no one absolute visual delay common to the whole visual system, but rather that the delay varies considerably in different perceptual subsystems. The relative visual latency was found to be considerably shorter in the task involving detecting the direction of movement than in other perceptual tasks that presume visual awareness of the beginning or temporal order of visual events.     

Individual differences,aging, and IQ in two-choice tasks

The effects of aging and IQ on performance were examined in three two-choice tasks: numerosity discrimination, recognition memory, and lexical decision. The experimental data, accuracy, correct and error response times, and response time distributions, were well explained by Ratcliff’s (1978) diffusion model. The components of processing identified by the model were compared across levels of IQ (ranging from 83 to 146) and age (college students, 60–74, and 75–90 year olds). Declines in performance with age were not significantly different for low compared to high IQ subjects. IQ but not age had large effects on the quality of the evidence that was obtained from a stimulus or memory, that is, the evidence upon which decisions were based. Applying the model to individual subjects, the components of processing identified by the model for individuals correlated across tasks. In addition, the model’s predictions and the data were examined for the “worst performance rule”, the finding that age and IQ have larger effects on slower responses than faster responses.