Biomedical subjects

C P Shimp

Publications and source records attributed to C P Shimp.

14 recordsLinked to original sources

PubMed1994

Molar function depends on molecular structure of behavior.

Pigeons chose between green side keys, then waited a shorter or longer time before pecking a center key, and finally chose between red side keys. Two successive left choices (to green and then red) with a shorter wait intervening, or 2 successive right choices with a longer wait intervening, were intermittently reinforced with food. The 2 required waiting times and the relative frequency of reinforcement for the shorter reinforced pattern were varied. Molar preference, defined in terms of coherent responses that satisfied the molecular reinforcement contingency, conformed to the highly adaptive matching level, but molar preference, defined in terms of incoherent responses, did not. The molar matching result therefore generalizes to responses with complex molecular structures provided that analyses distinguish between coherent and incoherent responses. The results are compatible with the idea that awareness can facilitate adaptation.

Animals↗

PubMed1993

Behavioral and computational models of spatial attention.

Pigeons pecked for food in a spatially cued choice reaction time (RT) task. A brief (50-ms) white light appeared on a left or right key and probabilistically predicted the location (on either the left or right key) of a subsequent target stimulus. The time between cue and target onset (stimulus onset asynchrony), the base rate of left cues, and the probability that the cue correctly predicted the target (cue validity) were experimentally varied. The mean RT to respond to the target key was faster on correctly cued trials (defining a validity effect), decreased for both valid and invalid trials as stimulus onset asynchrony increased (defining an alerting effect), showed a variety of base-rate effects, and did not depend on cue validity. It is shown with a computational-processing model that dynamic interactions of short-term and associative memory processes are sufficient to produce these attentionlike empirical phenomena.

Animals↗

PubMed1992

Computational behavior dynamics: an alternative description of Nevin (1969).

A computational processing behavior-dynamic model was instantiated in the form of a computer program that "behaved" on the task developed by Nevin (1969). In this classic discrete-trials experiment, the relative frequency of choosing a response alternative matched the relative frequency of reinforcement for that alternative, the local structure of responding was opposite that predicted by momentary maximizing (i.e., the probability of a changeover decreased with run length), and absolute and relative response rates varied independently. The behavior-dynamic model developed here qualitatively reproduced these three results (but not in quantitative and specific detail) and also generated some interesting, as-yet-untested predictions about performance in Nevin's task. The model was discussed as an example of a stochastic behavior-dynamic alternative to algebraic behavior theory.

Animals↗

PubMed1990

Local patterns in human operant behavior and a behaving model to interrelate animal and human performances.

College students pressed buttons for points delivered according to molecular concurrent reinforcement contingencies similar to those used in previous experiments with animal subjects. Relative frequency of reinforcement and the relative and absolute durations of two reinforced patterns of button pressing were experimentally varied. Qualitative effects of all three variables resembled those obtained previously with animals. Computer simulation of a cognitive processing model described these qualitative effects. A similar model was used previously to describe corresponding behavior in pigeons. Therefore, similar cognitive processing may underlie the local temporal patterning of animal and human operant behavior maintained by this concurrent reinforcement contingency.

Adult↗

PubMed1990

Preference as a function of absolute response durations.

The durations of 2 responses, 2 categories of reinforced nondiscriminated interresponse times, were varied while their relative durations were held approximately constant, with the longer about 2 1/2 times longer than the shorter. Three pigeons pecked for food. Reinforcers for the shorter and longer responses were arranged by a concurrent variable-interval, variable-interval schedule. Preference for the shorter response increased when both were lengthened. These results, taken together with previous results for discriminated interresponse times, show that preference for the shorter of 2 responses depends on their absolute durations, whether they are discriminated or not and regardless of autoshaped key pecks that may occur in the discriminated case. Time-allocation-matching was not generally obtained. The results qualitatively agree with an associative learner, a computational processing model derived from a molecular analysis of behavior.

Animals↗

PubMed1989

Preference for starting and finishing behavior patterns.

Pigeon's key pecking was reinforced with food in two experiments in which the correspondence between preference for starting one of two reinforced behavior patterns and the likelihood of finishing it subsequently was examined. Reinforcers were scheduled according to concurrent schedules for two classes of interresponse times, modified such that reinforcers followed a center-key peck terminating either a shorter interresponse time started by a left-key peck or a longer interresponse time started by a right-key peck. In Experiment 1, the times when reinforcers potentially were available were not discriminated, whereas in Experiment 2 they were. Absolute reinforced pattern durations were varied. The relative frequency of starting a particular pattern was highly correlated with relative frequency of that completed pattern in both experiments. Other relations between starting and finishing a pattern depended on whether reinforced interresponse times were discriminated. For instance, preference for starting a pattern sometimes correlated negatively with the likelihood of subsequently completing it. The present experiments are described as capturing part of the ordinary language meaning of "intention," according to which an organism's behavior at one moment sets the occasion for an observer to say that the organism "intends" in the future to engage in one behavior rather than another.

Animals↗

PubMed1985

An infrared system for the detection of a pigeon's pecks at alphanumeric characters on a TV screen: the dependency of letter detection on the predictability of one letter by another.

Three pigeons pecked at letters of the alphabet and at the symbol "?" displayed on a computer-driven cathode ray screen. A 4 by 4 matrix of infrared emitting and detecting diodes and associated circuitry identified the location of a pigeon's responses to the screen. Responses at the target letter T were probabilistically reinforced with food whenever T appeared in a string of three letters in the middle of the screen. Responses at the symbol "?" appearing below this string were probabilistically reinforced whenever T did not appear. The letter F anywhere in the three-character string either strongly predicted the occurrence of the target letter T, in two conditions, or predicted its nonoccurrence, in a third. This manipulation of the frequency with which the familiar letter F predicted T was shown to change the function relating probability of a correct peck at the symbol "?" to the number of Fs in the string. This effect may be interpreted as an instance of the phenomenon where an organism's acquired knowledge changes what it sees.

Animals↗

PubMed1984

Timing, learning, and forgetting.

A computer-simulation model (AL) was developed for molecular and molar operant conditioning data. AL assumes a simple forgetting rule and all-or-nothing associations between memory representations of responses and reinforcers. AL describes acquisition and steady-state behavior in both concurrent interresponse time (IRT) schedules and in ordinary concurrent schedules. It describes functions relating the relative frequency of an IRT to IRT duration and to reinforcement frequency. AL accurately predicts for ordinary concurrent variable-interval schedules that the log ratio of responses to the two alternatives is a linear function of the log ratio of the reinforcers they deliver, and that the slope of this straight line approximates the degree of undermatching that characterizes the behavior of real animals. In addition, AL successfully describes the fact that in real data of Nevin, Heyman, and others, the probability of a changeover from one response to the other is roughly independent of the number of consecutive responses to the same alternative preceding the changeover. A previous version of AL assimilated data on temporal psychophysics, such as that animals bisect two temporal intervals at the geometric mean, and that the Weber fraction in DRL schedules is approximately constant. AL therefore describes transient and steady-state molecular and molar performances as well as data on temporal psychophysics.

Animals↗

PubMed1983

The local organization of behavior: dissociations between a pigeon's behavior and self-reports of that behavior.

The purpose of the experiment was to study the relation between what an organism does in a setting that demands temporal patterning of behavior and what it reports it has done. More specifically, a pigeon produced two classes, shorter and longer, of temporal patterns of key pecks (interresponse times) on a center key. Occasionally, a symbolic matching-to-sample probe arranged on side keys asked the pigeon whether its most recent pattern was a shorter or longer one. The longer reinforced pattern was always three times as long as the shorter one and the two patterns were reinforced equally often. Absolute duration of reinforced patterns was varied. In some conditions, interresponse-time distributions on the center key were bimodal, indicating a clear behavioral adaptation to the contingency, yet a bird did not report very well by appropriate side-key responding what its most recent interresponse time had been. In other conditions, the interresponse-time distributions were less clearly bimodal, yet a bird reported more accurately its previous interresponse time as shorter or longer. Thus, there was a dissociation between how well behavior on the center key conformed to the schedule requirement and how well a bird reported what it was doing on the center key. In addition, as absolute duration of the reinforced patterns was increased, a bird categorized its most recent pattern less well even as its preference for the shorter pattern increased dramatically. These results were interpreted as an example of the phenomenon of dissociation between tacit knowledge and knowledge.

Color Perception↗

PubMed1981

The local organization of behavior: discrimination of and memory for simple behavioral patterns.

A procedure was developed to enable nonverbal organisms to report what they remember of the temporal organization of their recent behavior. A baseline behavior with known temporal structure was established by a concurrent variable-interval variable-interval schedule for two temporal patterns of behavior (two different classes of reinforced inter-response times). The five pigeon subjects emitted these two temporal patterns on a center key and were occasionally given a short-term memory probe for their most-recently-emitted pattern. The probes consisted of symbolic delayed matching-to-sample tests, in which a response on a green side key was reinforced if the most recent pattern belonged to the shorter reinforced class, and a response to a red side key was reinforced if the most recent pattern belonged to the longer reinforced class. All subjects could report with over ninety percent accuracy what their most recently emitted behavioral pattern was when a retention interval separating the pattern from the memory probe was only .1 seconds. The retention interval was then manipulated, and it was found that recall for a pattern was frequently above chance after a delay of as much as eight seconds. Thus, pigeons can remember their most recent interresponse time not only right after it is emitted, but for several seconds thereafter. In other conditions, the patterns themselves were manipulated. It was found that as the patterns became more similar, discrimination became poorer. These results agree with the view that reinforcement tends to organize and integrate the local structure of behavior to the extent to which that structure is remembered.

Animals↗

PubMed1977

Short-term memory in the pigeon: delayed-pair-comparison procedures and some results.

A discrete-trials, delayed-pair-comparison procedure was developed to study visual short-term memory for tilted lines. In four experiments, pigeons' responses on left or right keys were reinforced with food depending on whether a comparison stimulus was or was not the same as a standard stimulus presented earlier in the same trial. In Experimental I, recall was an increasing function of the exposure time of the to-be-remembered stimulus and was a decreasing function of the retention interval. In Experiment II, retroactive interference was investigated: recall was poorer after a retention interval during which was presented either a tilted line or contextual stimuli in the form of the illuminated experimental chamber. In Experiment III, a subject was required to engage, throughout the retention interval, in one or the other of two different behaviors, depending on which of two stimuli a subject was to remember. This mnemonic strategy vastly improved recall after 15- and 20-second retention intervals. In Experiment IV, the opposite end of the performance continuum was studied: by combining the effects of a larger stimulus set and the effects of what presumably was an increased memory load, performance was reduced to approximately chance levels after retention intervals shorter than 1 second.

Animals↗

PubMed1968

Magnitude and frequency of reinforcement and frequencies of interresponse times.

The relative magnitude and relative frequency of reinforcement for two concurrent interresponse times (1.5 to 2.5 sec and 3.5 to 4.5 sec) were simultaneously varied in an experiment in which pigeons obtained grain by pecking on a single key. Visual discriminative stimuli accompanied the two time intervals in which reinforcements were arranged by a one-minute variable-interval schedule. The resulting interresponse times of each of three pigeons fell into two groups; "short" (1.0 to 2.5 sec) and "long" (3.0 to 4.5 sec). Steady-state relative frequencies of these interresponse times were orderly functions of both reinforcement variables. The combined effects of both independent variables were well summarized by a linear function of one variable, relative access to food. Unlike corresponding two-key concurrent variable-interval schedules, the present schedule did not produce an equality between the relative frequency of an operant and either the relative magnitude or the relative frequency of reinforcement of that operant. A tentative account is provided for this difference between one-key and two-key functions.

Animals↗

PubMed1967

The reinforcement of short interresponse times.

Five contingencies were superimposed successively on a variable-interval schedule of reinforcement. In each of the resulting conditions, a different short, interresponse time was reinforced and an interresponse-time distribution was obtained from each of three pigeons. The lower bound of the reinforced interresponse times ranged from 0.3 to 2.4 sec. The resulting distributions were combined, according to a rationale based upon concurrent operants, induction, and a property of variable-interval schedules, to describe the interresponse-time distributions from a variable-interval schedule.

Animals↗

PubMed1966

Probabilistically reinforced choice behavior in pigeons.

A single principle, "momentary maximizing", may account for much of a pigeon's steady-state behavior in both probability learning and concurrent variable interval experiments. The principle states that a pigeon tends to choose the alternative that momentarily has the higher probability of reinforcement. A successive discrimination procedure, which produced matching in an earlier experiment, produced here a tendency to maximize if training were adequately extended. Maximizing was produced also by other procedures, in which no reinforcing event was presented on some trials: one procedure did and two did not provide a bird with information about the availability of reinforcement on a key after an unreinforced response on the other key. The latter two procedures were analogous to concurrent variable interval schedules in two respects: the reinforcement probability on one key increased while a bird responded on the other key; and they produced matching. But sequential statistics suggested that matching resulted from momentary maximizing. Depending on the procedure, the tendency to maximize produced different relative frequencies of pecking a key for a fixed relative frequency of reinforcement. Computer simulation of maximizing behavior in several concurrent variable interval schedules produced matching and sequential statistics similar to those produced by a real bird.

Animals↗