Nancy S. Hemmes

Time Estimation of Fear Cues in Human Observers

Previous research suggests that time judgments are a function of the affective properties of to-be-timed stimuli and that time judgments are longer for stimuli that are fear-inducing (e.g., Hare, 1963; Watts and Sharrock, 1984). The goals of the present study were twofold: to replicate the effect of a fear cue on time estimation, and to evaluate the mechanism underlying the effect. Seven stimulus durations in two different duration ranges (short: 250-1000 ms; long: 400-1600 ms) were employed in the bisection procedure. Adult human participants were exposed to two successive sessions, one each with the short and long range. Images from the International Affective Picture System (IAPS; Lang et al., 2008) that were rated on three scales including arousal and fear were presented as temporal stimuli. Three images that were rated high on fear and three rated low served as fear cues and neutral control images, respectively. Results indicated that for both ranges, judgments were longer for fear cues than for neutral images, and that the magnitude of the effect did not differ between ranges as measured by the bisection point. Application of scalar expectancy theory (SET; Gibbon, 1977; Church, 1984) to these results suggests that the fear effects were mediated by switch latency of an internal clock, rather than by clock speed.

Internal Clock and Memory Processes in Animal Timing

Temporal control of behavior was investigated within the framework of an internal clock model. Pigeons were exposed to signaled fixed-interval 30-s trials mixed with extended unreinforced (baseline) trials. On unreinforced break trials, the signal was interrupted for a period of time after trial onset. In Experiment 1, comparisons between the peak time obtained on baseline and on break trials produced peak time shifts that were longer than those expected if the clock had stopped during the break but shorter than if the clock had reset. In Experiment 2, systematic manipulations of duration and location of breaks produced peak time shifts that were nonlinear functions of break duration and that varied linearly with break location. The obtained peak times were more consistent with a continuous memory decay model than with the stop-retain or the reset hypotheses.

THE EFFECTS OF SCHEDULES OF REINFORCEMENT ON INSTRUCTION FOLLOWING

The present study is a mixed design that examines instruction following, with the accuracy of instructions varied across phases within subjects and the schedule of reinforcement varied across six groups. A choice experiment was conducted in which subjects were provided with instructions that varied systematically in their accuracy. Across phases, the accuracy of instructions (expressed in percentages) was either 0-50-100-50-0 or 100-50-0-50-100. Across groups, the schedule of reinforcement was one of the following: continuous, Fixed Ratio 2, or Fixed Ratio 3. With continuous reinforcement, subjects showed collateral consequence control and either followed or disobeyed instructions, in keeping with the predictions of reinforcement theory. When the schedule of reinforcement was leaned, however, insensitivity was observed. The implications of the results for the controversies regarding the concept of rule-governed behavior are discussed.

Specification of the stimulus-reinforcer relation in multiple schedules: Delay and probability of reinforcement

Control of pigeons’ keypecking by a stimulus-reinforcer contingency was investigated in the context of a four-component multiple schedule. In each of three experiments, pigeons were exposed to a schedule consisting of two two-component sequences. Discriminative stimuli identifying each sequence were present only in Component 1, which was 4, 6, or 8 sec in duration, while reinforcers could be earned only in Component 2 (30 sec in duration). Control by a stimulus-reinforcer contingency was sought during Component 1 by arranging a differential relation between Component 1 cues and schedule of reinforcement in Component 2. In Experiment 1, rate of keypecking during Component 1 varied with the presence and absence of a stimulus-reinforcer contingency. When a contingency was introduced, rate of keypecking increased during the Component 1 cue associated with the availability of reinforcement in Component 2. In Experiment 2, the stimulus-reinforcer contingency was manipulated parametrically by varying the correlation between Component 1 cues and Component 2 schedules of reinforcement. Responding in Component 1 varied as a function of strength of the stimulus-reinforcer contingency. The relatively high rates of Component 1 responding observed in Experiments 1 and 2 pose difficulties for conceptions of stimulus-reinforcer control based on probability of reinforcement. In these two experiments, the stimulus-associated probabilities of reinforcement in Component 1 were invariant at zero. An alternate dimension of stimulus-reinforcer control was explored in Experiment 3, in which Component 1 cues were differentially associated with delay to reinforcement in Component 2, while probability of reinforcement was held constant across components. When the stimulus-reinforcer contingency was in force, rate of responding in Component 1 varied inversely with delay to reinforcement in Component 2. In a quantitative analysis of data from Experiments 2 and 3, relative rate of responding during Component 1 was strongly correlated with two measures of relative delay to reinforcement.

Time perception with and without a concurrent nontemporal task.

Prospective time estimates were obtained from human subjects for stimulus durations ranging from 2 to 23 sec. Presence and absence of a concurrent nontemporal task was manipulated within subjects in three experiments. In addition, location of the task within temporal reproduction trials and psychophysical method were varied between groups in Experiments 2 and 3, respectively. For long-duration stimuli, the results of all three experiments conformed to results in the literature, showing a decrease in perceived duration under concurrent task conditions, in accord with attentional resource allocation models of timing. The effects of task location and psychophysical method on time estimates were also compatible with this analysis. However, psychophysical functions obtained under task conditions were fit well by power functions, an outcome that would not be anticipated on the basis of attention theory. The slopes of the functions under no-task conditions were steeper than those under task conditions. The data support the perceptual hypothesis that different sources of sensory input mediate timing under task and no-task conditions.

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.

Sign and goal tracking during delay and trace autoshaping in pigeons

In two experiments, pigeons were exposed to an autoshaping procedure in which a keylight was followed by food under delay or trace conditions, while measures were taken of keypecking and time spent near the key. In Experiment 1, the birds in the trace group spent less time near the key than did the delay birds. Moreover, the trace birds exhibited a pattern of withdrawal from the key during the trial. In Experiment 2, visual observations of the birds’ location and latencies to eat both indicated that the trace birds’ withdrawal from the conditioned stimulus was accompanied by goal tracking. The difference in performance between the delay and trace conditions was taken as evidence that a trace stimulus may exert control over behavior as an occasion setter.

The effects of schedules of reinforcement on instruction-following in human subjects with verbal and nonverbal stimuli

The experiment reported here represents a partial replication of an experiment by Newman, Buffington, and Hemmes (in press) and analyzes responding in college students as a function of three different schedules of reinforcement (FR 1, FR 2, FR 3) and either verbal discriminative stimuli (instructions) or nonverbal discriminative stimuli (different colored cards). All consequences (tokens) were based on behavior consistent either with the verbal discriminative stimulus (SD) or with the nonverbal SD. The schedule of reinforcement varied across subjects, and accuracy of the verbal and nonverbal SDs varied across phases from. Results showed that the behavior of all continuous reinforcement (FR 1) subjects was sensitive to the accuracy of the verbal SDs, but the behavior of subjects in the nonverbal SD conditions showed more sensitivity than the behavior of subjects in verbal conditions under intermittent schedules (FR 2 and FR 3). These findings suggest that the behavior of subjects in experiments where instructions are sometimes pitted against actual contingencies of reinforcement is a function not only of the instruction, but also of the type of reinforcement schedule used.

The start-stop procedure: Estimation

In four experiments investigating human timing, subjects produced estimates of sample durations by bracketing their endpoints. On each trial, subjects reproduced a sample duration by pressing a button before the estimated sample duration elapsed (start time) and releasing it after the estimated duration elapsed (stop time). From these responses, middle time (start + stop/2) and spread time (stop — start) were calculated, representing the point of subjective equality and the difference limen, respectively. In all experiments, subjects produced middle times that varied directly with sample duration. In Experiment 2, middle times lengthened when feedback was withheld. Consistent with Weber timing, spread times, as well as the standard deviation of middle times, varied directly with middle time (Experiments 1, 3, and 4). On the basis of an internal clock model of timing (Gibbon & Church, 1990), the data permitted inferences regarding memory processes and response threshold. Correlations between start and stop times and between start and spread times agreed with earlier findings in animals suggesting that the variance of temporal estimates across trials is based in part upon the selection of a single temporal memory sample from a reference memory store and upon one or two threshold samples for initiating and terminating each estimate within a trial.

Pigeons' performance under differential reinforcement of low rate schedules depends upon the operant ☆ ☆☆

Abstract Pigeons were reinforced with grain for pecking a key or depressing a foot treadle according to differential reinforcement of low rate (DRL) schedules. Birds which depressed a treadle performed efficiently on DRL schedules as high as DRL 35-sec; while birds reinforced for keypecking showed low efficiency under DRL 14-sec. While treadle pressing and keypecking differ along a number of dimensions (including force requirement of the operant and differences in temporal distributions of responses), the present results are consistent with an interpretation based on differences in the degree to which these two responses are elicited by periodic presentations of food.