Biomedical subjects
M D Zeiler
Publications and source records attributed to M D Zeiler.
Temporal control in fixed-interval schedules.
The peak procedure was used to study temporal control in pigeons exposed to seven fixed-interval schedules ranging from 7.5 to 480 s. The focus was on behavior in individual intervals. Quantitative properties of temporal control depended on whether the aspect of behavior considered was initial pause duration, the point of maximum acceleration in responding, the point of maximum deceleration, the point at which responding stopped, or several different statistical derivations of a point of maximum responding. Each aspect produced different conclusions about the nature of temporal control, and none conformed to what was known previously about the way ongoing responding was controlled by time under conditions of differential reinforcement. Existing theory does not explain why Weber's law so rarely fit the results or why each type of behavior seemed unique. These data fit with others suggesting that principles of temporal control may depend on the role played by the particular aspect of behavior in particular situations.
To wait or to respond?
Emitting a certain response and waiting for a specified time without making that response had the same consequence. In Experiment 1, food-deprived pigeons were as likely to wait as to respond only if waiting provided food at a much higher frequency than did pecking. In Experiment 2, the consequence for humans was a brief light flash and tone. People were not biased for responding over waiting. Instead, their choices suggested crude payoff maximization. In Experiment 3, pigeons again obtained food, but they were not food deprived and could eat freely at each opportunity. Their behavior was more like that of the humans of Experiment 2 than that of food-deprived pigeons given small quantities of food at each feeding opportunity. The three experiments together showed that biases for responding over waiting were neither inherent characteristics of species nor inevitable outcomes of particular schedules. Choice between active search and waiting depended on ecological-motivational factors even when species and schedules were held constant.
On immediate function.
Behavior is a property of living organisms, not of inanimate matter. The problems of physical science are to understand how a phenomenon works; biological science adds the questions of what a phenomenon does and how something that does such things came to be. Exclusive dedication to cause-effect explanations ignores how behavior helps creatures cope with their internal and external environments. Laws of causation describe the precursors to behavior; laws of function describe the effects of behavior. The numerous instances of learning reflect the many ways that selective pressure for altering behavior on the basis of experience has been manifested. Little basis exists for assuming that the various forms of learning reflect either common functions or common processes. Instead, it seems that evolutionary processes have resulted in domain-specific learning. The rules of learning must be understood in terms of the function that the particular manifestation of learning serves for the organism. Evolutionary theory provides the framework for understanding function as well as relations between function and causal mechanisms.
Temporal reproduction.
A signal appeared for a certain time period. After the period elapsed, pigeons had to begin and complete a sequence of 15 responses in a time window ranging from the signal duration to 50% longer. Sessions involved as many as 10 different signal durations occurring in a random sequence. The times produced by pigeons often were in the same ranges as those that have been found with adult human subjects. The average times were described equally well as linear or power functions of signal duration. However, instead of the overestimation of durations usually found when animals have timed the duration of antecedent stimuli, the linear functions suggested that the pigeons underestimated the durations of their own behavior. The birds showing the strongest control when the conditions involved eight or 10 different duration requirements revealed the constant coefficients of variation that support Weber's law and scalar timing theory. Scalar timing in temporal differentiation appears to depend on non-ambiguous information about the duration required for reinforcement and on a high degree of sensitivity to the duration requirement.
Optimal temporal differentiation.
In order to illuminate a light signaling a correct response, adult humans had to space their button presses according to a range of time requirements. In some conditions, the spacing needed only to exceed a minimum duration; in others, it had to fall between lower and upper bounds. Mean interresponse times always exceeded the lower limit, and decreased the more stringent were the upper bounds. Variability of interresponse times increased with larger lower bounds, but was unaffected by the size of the upper bound. Feedback about the direction of errors in conditions involving both upper and lower bounds did not affect the means, but it did reduce variability. Predictions were derived from optimality theory, based on the assumption that the critical factor was minimization of the time between correct responses. Without upper bounds, the theory overestimated the mean interresponse times by about 10%; with upper bounds, the theoretical predictions corresponded closely to the actual data. The results did not appear to reflect a scalar timing process. Optimality theory, in contrast to Weber's law, correctly predicted the variety of curves relating sensitivity to duration requirements.
Two sides of behavior.
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Pure timing in temporal differentiation.
Temporal control appears to depend on whether the critical durations are those of stimuli or those of responses. Stimulus timing (temporal discrimination) supports Weber's law, whereas response timing (temporal differentiation) indicates decreasing relative sensitivity with longer time intervals. The two types of procedure also yield different conclusions in scaling experiments designed to study the functional midpoint of two or more durations (temporal bisection procedures). In addition, the fractional-exponent power relation between emitted and required duration usually found with animals in differentiation experiments conflicts with deductions from formal analyses. The experiment reported here derived from considering differentiation arrangements as schedules of reinforcement. When analyzed from this perspective, the procedures are tandem schedules involving a required pause followed by a response, and it is the pause alone that involves temporal control. A choice procedure separated timing from responding, and enabled observations of pause timing in isolation. Pure temporal control in differentiation consisted of linear overestimation of the standard duration, and Weber's law described sensitivity. These results indicate that the two problems, the fractional-exponent power relations and the apparently different nature of sensitivity in differentiation and discrimination, disappear when temporal control is observed alone in differentiation.
The sleeping giant: Reinforcement schedules.
Schedule research has been the core of operant conditioning, but it is no longer an active area, at least with respect to its traditional focus of describing and explaining moment-to-moment behavior. Yet schedules are central in psychology: Not only do they establish lawful behavior, but they also play a major role in determining the effects of other variables. The reason for the decline appears to be primarily theoretical, in that the work seems not to have led to meaningful integration. The search for controlling variables brought into play by schedule specification has proven unsuccessful, and a catalog of all possible schedule effects is of limited interest. The paper reviews the reasons for the contemporary state of affairs. One prediction about future developments is that instead of revealing component variables and their modes of interaction, schedule effects will be treated as basic empirical laws. Theory will take the form of abstract statements that integrate these separate laws by reference to higher-order principles rather than by reduction to supposedly simpler component variables.
Choice between response units: The rate constancy model.
In a conjoint schedule, reinforcement is available simultaneously on two or more schedules for the same response. The present experiments provided food for key pecking on both a random-interval and a differential-reinforcement-of-low-rate (DRL) schedule. Experiment 1 involved ordinary DRL schedules; Experiment 2 added an external stimulus to indicate when the required interresponse time had elapsed. In both experiments, the potential reinforcer frequency from each component was varied by means of a second-order fixed-ratio schedule, and the DRL time parameter was changed as well. Response rates were described by a model stating that time allocation to each component matches the relative frequency of reinforcement for that component. When spending time in a given component, the subject is assumed to respond at the rate characteristic of baseline performance. This model appeared preferable to the absolute-rate version of the matching law. The model was shown to be applicable to multiple-response concurrent schedules as well as to conjoint schedules, and it described some of the necessary conditions for response matching, undermatching, and bias. In addition, the pigeons did not optimize reinforcer frequency.
Responses and pauses: discrimination and a choice catastrophe.
Pigeons produced a stimulus change either by responding or by not responding for a specified time period (by pausing). They then had to choose between two responses to obtain food. One choice was correct if the first component had been completed by a response; the other was correct if the component had been completed by a pause. The pigeons usually chose correctly, thereby indicating that they used their own prior behavior as a discriminative stimulus. Fixed pause requirements did not produce equal first component completions by a response and by a pause. To obtain equality, the pause requirement was titrated as a function of current performance. Titration resulted in equal completions and also produced accurate discrimination. In addition to showing that pigeons discriminated whether they had responded or paused, the data displayed and discontinuous functions predicted by catastrophe theory. Another procedure used forced choice rather than titration to produce equal completions by pausing and responding and also showed accurate discrimination of behavior.
Psychophysics of key-peck duration in the pigeon.
The duration of the pigeon's key peck was differentially reinforced in either a trials or a free-operant procedure. Mean emitted peck duration was a power function of the duration required for food delivery to occur. The exponents of the power function differed considerably from those observed in earlier research involving longer duration responses in pigeons and other species. The coefficients of variation also did not correspond with those of the earlier research on other responses, nor did consideration of the durations actually reinforced resolve the differences. Duration was neither a function of response rate nor of intermittency of reinforcement. Key-peck duration was changed in an orderly way by differential reinforcement. However, it appeared to be more strongly determined by its duration in the absence of differential reinforcement than were longer duration responses.
Reinforcing the absence of fixed-ratio performance.
Pigeons received food for key pecking according to a fixed-ratio schedule, while, at the same time, food also was available for not pecking for a specified time. With a fixed ratio of 60, responding was not affected by not-pecking times of 80 or 40 seconds, and was eliminated completely at 10 seconds. With ratios of 180, pecking stopped with not-pecking times of 80 seconds or less; with ratios of 300, it stopped at 120 seconds or less. Not-responding schedules produced steady-state performance immediately following contact with the schedule. With return to the fixed-ratio schedule alone, response rate sometimes was elevated temporarily. When response-independent food presentations replaced the not-pecking schedule, response rate often was enhanced, and the ratio pattern was lost. Only the highest densities of food delivery eliminated responding, even with a fixed ratio of 300. In general, the effects corresponded to those of punishment, except that contrast had appeared both during and after punishment, and now appeared only after the response elimination procedure was suspended.
Response requirements as constraints on output.
Two experiments studied how added response requirements affected fixed-interval schedule performance. Experiment 1 involved tandem fixed-interval fixed-ratio schedules, and Experiment 2 studied conjunctive fixed-interval fixed-ratio schedules. In both, pigeons' output, defined as overall response rate or as responses during the interval, first increased and then decreased as the ratio was raised. With small ratio requirements, the frequency of reinforcement in time either did not change or decreased slightly. With progressively larger ratios, reinforcement frequency decreased consistently. Alternative explanations were discussed. The first, a reinforcement theory account, was that response strength is an increasing monotonic function of both the response requirement and reinforcement frequency, and the bitonic output function represents interacting effects. Increases in the response requirement accompanied by small changes in reinforcement frequency enhance output, but further increases result in large enough decrements in reinforcement frequency so that output is lowered. The second explanation does not view reinforcement as a basic process but, instead, derives from concepts of economics and conservation. Organisms allocate their behavior among alternatives so as to maximize value, where value is a function of the responses that can occur in a given situation under the set of restrictions imposed by particular schedules. One form of this theory explicitly predicts that output is a bitonic function of ratio requirements in simple ratio schedules. However, it was not clear that this model could explain the present effects involving joint ratio and interval schedule restrictions.
Clustering in the output of behavior.
Pigeons exposed to fixed-interval schedules of 3, 5, 15, 40, and 120 minutes all maintained considerable variability in daily response rates for as many as 104 sessions. However, variations did not occur at random. Instead, rate in a session appeared dependent on those occurring previously. The series displayed a wave-like form arising because a group of high rates was followed by a group of low rates and vice versa. These sequential relations produced a curve having irregular periodicity, sometimes superimposed on a declining or rising linear trend. Whether grouping of response rates stemmed from experimental or extra-experimental sources was not determined. If the phenomenon was either totally or partially produced by the schedule itself, it suggests that response rate is determined by a combination of positive and negative feedback. Control by factors extrinisic to the experiment itself implies that response rate may be influenced by some rhythmic physiological process.
Elimination of reinforced behavior: intermittent schedules of not-responding.
Pigeons' key pecking resulted in food according to either a variable-ratio or a variable-interval schedule. At the same time, food was available for not pecking for a specified time. The required time of not-pecking was segmented into not-responding units, and these units were followed by food according to a fixed-ratio schedule. Both unit duration and the number required were varied. In general, the shorter the time unit or the smaller the ratio, the lower was response rate. When total required not-responding time was constant, but changes in unit duration and the number required altered how the total was achieved, shorter units produced lower rates. Other conditions involved substitution of food delivered independent of responding for the not-responding schedule. With low and moderate total times to food presentation, the not-responding schedule produced lower rates; with the longest times, the response-independent schedule generated less responding. When considered in terms of relative frequency of food presentation available from a source other than pecking, the not-responding schedule reduced rate more effectively than did the response-independent schedule. Comparisons with other research suggested that food presented dependent on not responding compared favorably with punishment as a procedure for reducing response rate. Transient effects differed. Although punishment temporarily depresses rate when first imposed and temporarily enhances it when first removed, food given for not responding quickly generated steady-state rates.
Time limits for completing fixed ratios. IV. Components of the ratio.
Pigeons received food after completing a fixed ratio if the temporal properties of responding exceeded minimum duration requirements. In one set of conditions, a minimum time had to elapse before the first response of the ratio (the initial pause). In another set, the minimum duration was the time between the first and last response of the ratio. Obtained times increased as a power function of required times in both conditions. The power function resembled that occurring in experiments involving temporal differentiation of individual responses, interresponse times, latencies, and entire fixed-ratio sequences. Moreover, in all of these experiments individual performances could be described as a function of the base duration (the duration occurring in the absence of temporal requirements) and the specific time requirement. Control conditions indicated that the effects resulted from temporal requirements and not from reinforcer intermittency.