Stimulus functions within a fixed-interval clock schedule: Reinforcement,punishment, and discriminative stimulus control

Pigeons received food for responding on a fixed-interval 32-sec schedule divided into three equal parts, each correlated with a distinctive, response-independent, visual stimulus. Response rate was very low during the first two thirds of the interval but high during the terminal third. When a response-dependent brief stimulus correlated with the terminal third was arranged for each response in the presence of the stimuli correlated with the first two thirds, response rate was enhanced, especially in the middle third. However, response rate was suppressed when each response in the presence of the stimulus correlated with the final third produced a brief stimulus correlated with the initial third. A similar suppressive effect occurred when each response produced a brief stimulus correlated with the middle third. Response suppression decreased over successive response-dependent brief-initial-stimulus manipulations. The results were interpreted in terms of reinforcement, punishment, and discriminative stimulus control by visual stimuli correlated with parts of a fixed-interval schedule.     

The effect of filled and empty intervals on clock and memory processes in pigeons

According to the mixed memory model (Penney, Gibbon, & Meck, Journal of Experimental Psychology: Human Perception and Performance, 26, 1770–1787, 2000), different clock rates for stimuli with different nontemporal properties must be stored within a single reference memory distribution in order to detect a difference between the clock rates of the different signals. In Experiment 1, pigeons were trained in a between-subjects design to discriminate empty intervals (bound by two 1-s visual markers) and filled intervals (a continuous visual signal). The intervals were signaled by different visual stimuli, and they required responses to different sets of comparison stimuli. Empty intervals were judged as being longer than filled intervals. The difference between the point of subjective equality (PSE) for the empty intervals and the PSE for the filled intervals increased proportionally as the magnitudes of the anchor duration pairs were increased from 2 and 8 s to 4 and 16 s. In Experiment 2, the pigeons were trained to discriminate intervals signaled by the absence of houselight illumination (Group Empty) or the presence of houselight illumination (Group Filled). The psychophysical timing functions for these intervals were identical to each other. The results of Experiment 1 indicate that memory mixing is not necessary for detecting a timing difference between empty and filled intervals in pigeons. The results of Experiment 2 suggest that the nature of the stimuli that signal the empty and filled intervals impacts how pigeons judge the durations of empty and filled intervals.     

Interval timing under a behavioral microscope: Dissociating motivational and timing processes in fixed-interval performance

The distribution of latencies and interresponse times (IRTs) of rats was compared between two fixed-interval (FI) schedules of food reinforcement (FI 30 s and FI 90 s), and between two levels of food deprivation. Computational modeling revealed that latencies and IRTs were well described by mixture probability distributions embodying two-state Markov chains. Analysis of these models revealed that only a subset of latencies is sensitive to the periodicity of reinforcement, and prefeeding only reduces the size of this subset. The distribution of IRTs suggests that behavior in FI schedules is organized in bouts that lengthen and ramp up in frequency with proximity to reinforcement. Prefeeding slowed down the lengthening of bouts and increased the time between bouts. When concatenated, latency and IRT models adequately reproduced sigmoidal FI response functions. These findings suggest that behavior in FI schedules fluctuates in and out of schedule control; an account of such fluctuation suggests that timing and motivation are dissociable components of FI performance. These mixture-distribution models also provide novel insights on the motivational, associative, and timing processes expressed in FI performance. These processes may be obscured, however, when performance in timing tasks is analyzed in terms of mean response rates.     

Signaled reinforcement effects on fixed-interval performance of the rat

In three experiments using fixed-interval schedules with a 500-msec delay of reinforcement, rats receiving a localized light signal during the delay leverpressed more slowly than rats trained without the signal. In Experiment 1 these groups showed no differences in temporal patterning of responding, but in the remaining two experiments the signaled rats showed better patterning than the unsignaled rats. In Experiments 2 and 3 rats receiving a diffuse tone signal during the delay instead of a light pressed more rather than less rapidly than the unsignaled group. Their patterning was better than that of the unsignaled rats in one of these experiments. Several explanations for both the attenuation and enhancing effects of signaling reward are discussed.     

Effects of stimulus change in prepunishment alley segments on self-punitive behavior

Three experiments investigated the effects of stimulus change during extinction on self-punitive behavior. In Experiment 1, changing alley brightness cues in all three segments of the alley prior to extinction eliminated self-punitive behavior. That is, subjects given shock in the third alley segment during extinction did not differ from nonshocked subjects in alley speed or in the number of trials to extinction. In Experiment 2, with shock also administered in the third alley segment, self-punitive behavior was eliminated when the stimulus change was made in segment 1 or in segments 1 and 2 but was obtained when the change occurred in segment 2 or in the lower startbox. In Experiment 3, shock was administered in the second alley segment. Self-punitive behavior was not obtained when the lower startbox cues were changed but was obtained with stimulus change in the upper startbox or in segment 1. The results are consistent with an expanded version of the Mowrer-Brown conditioned-fear hypothesis.     

Effects of response-independent stimuli on fixed-interval and fixed-ratio performance of rats: a model for stressful disruption of cyclical eating patterns

Binge eating is often associated with stress-induced disruption of typical eating patterns. Three experiments were performed with the aim of developing a potential model for this effect by investigating the effect of presenting response-independent stimuli on rats’ lever-pressing for food reinforcement during both fixed-interval (FI) and fixed-ratio (FR) schedules of reinforcement. In Experiment 1, a response-independent brief tone (500-ms, 105-dB, broadband, noisy signal, ranging up to 16 kHz, with spectral peaks at 3 and 500 Hz) disrupted the performance on an FI 60-s schedule. Responding with the response-independent tone was more vigorous than in the absence of the tone. This effect was replicated in Experiment 2 using a within-subject design, but no such effect was noted when a light was employed as a disrupter. In Experiment 3, a 500-ms tone, but not a light, had a similar effect on rats' performance on FR schedules. This tone-induced effect may represent a release from response-inhibition produced by an aversive event. The implications of these results for modeling binge eating are discussed.     

Effects of extended fixed-interval training on reversed scallops

Two groups of pigeons were used to determine if different amounts of fixed-interval training with an added clock resulted in different local response rates when the clock was reversed. One group of seven pigeons received 120 reinforcements on a fixed-interval 90-sec schedule, while the other group received 1200 reinforcements. Following training, the added clock was reversed in extinction. Reversed scallops were obtained for both of the groups. Only the group with extended training showed an increase in responding during the previously reinforced segment of the interval. This suggests the development of greater temporal control with extended training.     

Preference between fixed-interval and variable-interval schedules of reinforcement: Separate roles of temporal scaling and predictability

Pigeons’ preference between fixed-interval and variable-interval schedules was examined using a concurrent-chains procedure. Responses to two concurrently available keys in the initial links of the concurrent chains occasionally produced terminal links where further responses were reinforced under either a fixed- or variable-interval schedule. In previous studies, preferences for the variable schedule with such a procedure have been interpreted as reflecting atemporal scaling process that heavily weights the shorter intervals in the variable schedule. The present experiment examined whetherpredictability, i.e., the presence of external stimuli correlated with the reinforcement interval, might also influence preference in such situations. When the two intervals in a variable schedule were made predictable by being associated with different key colors, preference for that schedule increased. This increase was reliable but small in magnitude and transient when initial-link responses only occasionally produced terminal links; it was large in magnitude when only one response in the initial link was required to produce the appropriate terminal-link schedule. The results suggest that preference between fixed and variable schedules may be influenced both by temporal scaling and to a lesser extent by predictability of the reinforcement intervals.     

Arousal and short-term memory: Effects of caffeine and trial spacing on delayed-alternation performance

Two experiments tested the prediction of Kesner’s (1973) parallel memory-stores theory that arousal reduces retention in short-term memory. Using rats as subjects, the effect of caffeine on delayed-alternation performance in a spatial discrimination was investigated. Trial spacing was also manipulated, both alone and in combination with the drug variable. The results showed that, with massed trials, caffeine facilitated alternation at the short delay and inhibited it at the longer delays tested. Using spaced trials, caffeine decreased alternation at all delays. Spaced trials produced overall superior performance as compared with massed trials. This pattern of results is consistent with the view that caffeine reduces short-term retention but, paradoxically, can also increase performance under massed trials by decreasing proactive interference (i.e., retention) from earlier trials.     

Perception of pictorial human faces by baboons: Effects of stimulus orientation on discrimination performance

The effect of stimulus rotation was assessed in four Guinea baboons (Papio papio), using pictures of familiar human faces presented in a computerized go/no-go task. In Experiment 1, 2 baboons were initially trained to discriminate upright faces, and 2 others were trained to discriminate upside-down faces. For the two groups, postlearning discrimination was impaired when the training faces were rotated 180°. In Experiment 2, upright and upside-down priming faces appeared prior to the display of target faces. For the two groups, response times were faster when the prime and the target faces had the same orientations than when they were depicted under different orientations. Finally, Experiments 3 and 4 identified variations in facial contours as the most salient discriminative cue controlling performance in 2 baboons. Altogether, our results provide no evidence that the baboons processed the pictures as representations of faces. It is suggested that the effect of rotation derived from the encoding of the pictorial faces as meaningless mono-oriented shapes, rather than as natural human faces.     

Overall and local contrast in multiple schedules: Effects of stimulus similarity and discrimination performance

An experiment with pigeons related overall and local behavioral contrast to similarity between stimuli signaling multiple-schedule components. Similarity was defined both physically and by discrimination performance. Initial and final baseline conditions used two equal random-interval schedules. During two intervening test periods, the schedule accompanying one component was changed to extinction. In the first test, components alternated strictly; in the second test, random component sequences were used. Signaling wavelength stimuli were separated by 1.5, 2, or 14 nm. Overall positive contrast occurred reliably, but its amount depended neither on wavelength difference nor on discrimination performance. Local positive contrast was less frequently observed when signaling stimuli were physically dissimilar; however, the effect was most closely related to actual discrimination performance. The relationship between discrimination and local contrast was nonmonotonic, indicating maximum local contrast at intermediate discriminations.     

Independent effects of stimulus and cycle duration in conditioning: The role of timing processes

Rats received delay conditioning procedures with a white-noise conditioned stimulus (CS), a food unconditioned stimulus (US), and head entries into the food cup as the conditioned response. The stimulus duration (S) and the interval between food deliveries (C) were varied between groups:S=15, 30, 60, and 120 sec;C=90, 180, and 360 sec. The stimulus/cycle duration ratio was negatively related to the asymptotic level of conditioning but had no effect on the rate of acquisition. Conditioning and timing of responses emerged together in training. Timing occurred during the CS-US interval (ISI) and the US-US interval (ITI), as evidenced by increasing response rate gradients that were steeper for shorter intervals. The effects of the stimulus/cycle ratio on conditioning were attributed to independent timing of theS andC durations. Serial-, parallel-, and single-process accounts of conditioning and timing are compared.     

Effects of memory reactivation treatments on postdiscrimination generalization performance in pigeons

In Experiment 1, it was shown that generalization testing following successive discrimination training between two closely spaced wavelengths results in a sharp gradient with a peak of responding shifted from S+ so as to be further removed from S?. Testing after a 24-h delay resulted in a flatter gradient with greater peak (and area) shift. A 5-min pretest exposure to S+, reinforced or unreinforced, or to S? (unreinforced) reinstated immediate test performance; free reinforcement with no discriminative stimulus present had no such effect. Experiment 2 replicated the flattening of generalization gradients and enhanced peak shift in delayed testing. Free feeding in a pretest treatment with a distinctive food uniquely associated with the wavelength discrimination problem failed to reinstate immediate test performance. Experiment 3 tested the hypothesis that free feeding failed as a reactivation treatment because it did not engender keypecking. Subjects were trained to peck a vertical line stimulus before being given wavelength discrimination training. Again, the enhanced peak shift and greater flattening with delayed wavelength generalization testing was found. A pretest exposure to the vertical line stimulus elicited pecking but had no effect on subsequent wavelength generalization. Thus, only a reactivation treatment that included one of the discrimination training stimuli was effective in producing delayed test performance comparable to that obtained in an immediate test.     

The impact of metamemory and domain-specific knowledge on memory performance

This paper consists of two major parts. First, research exploring possible interactions between metamemory and domain-specific knowledge in influencing children’s text recall and comprehension is briefly summarized. Overall, the findings indicate that metacognitive knowledge does make a difference even in cases where domain-specific knowledge is rich. Second, a recent experiment conducted in our lab and investigating the generalizability of this conclusion for sort-recall tasks is described in more detail. Third — and fourth-grade soccer experts and novices were first given a comprehensive metamemory questionnaire and then administered a sort-recall tasks using two different picture lists: whereas one list included items from various semantical categories (e.g., animals, clothes), the other list was composed of soccer pictures that could be classified in several categories such as players, kicks, or equipment. The results showed that although domain-specific knowledge had a strong impact on recall of the soccer list, general metacognitive knowledge made an independent contribution, particularly for the group of soccer experts. More specifically, good metamemory positively affected the recall of experts but had no impact on novices’ memory performance.     

Conditioned and unconditioned stress-induced analgesia: Stimulus preexposure and stimulus change

Aversive events such as electric shock lead to analgesia. There have been differing views with regard to whether the aversive event itself can lead to analgesia as a direct unconditioned reaction, or whether the analgesia is instead a reaction to fear conditioned to cues present during shock or to other associative processes initiated by the aversive event. Maier (1989, 1990) has argued that aversive events such as shock lead to both types of analgesia, with the type observed depending on test conditions. Unconditioned analgesia was argued to be present soon after shock, with conditioned analgesia replacing the unconditioned form if the subject is allowed to remain in the shock environment. Consistent with this argument, the experiments reported here show that (1) preexposure to the environment in which shock later occurs has no effect on the analgesia soon after shock, but eliminates the later analgesia; (2) the initial postshock analgesia is unaffected by removing the subject from the shock environment to a different environment, but the later reaction is prevented by such a change; (3) returning the subject to the shock environment after confinement in a nonshock environment rearouses an analgesic reaction; and (4) this rearousal does not occur if the subject has first been confined to the shock environment without shock.     

Effects of violent and non-violent computer game content on memory performance in adolescents

The present study focuses on the short-term effects of electronic entertainment media on memory and learning processes. It compares the effects of violent versus non-violent computer game content in a condition of playing and in another condition of watching the same game. The participants consisted of 83 female and 94 male adolescents with a mean age of 17.6 years. The dependent variables are memory for previously learnt verbal and visual material, memory for media-related content and physiological measures of stress (heart rate, cortisol, salivary alpha-amylase). Besides the group comparisons, potential mediation effects and gender differences were examined. The results show that violent content leads to a poorer memory performance for verbal material and to an increased heart rate. The heart rate, however, does not mediate the effect on memory performance. Genders differ regarding their abilities to memorise verbal and visual material, with females showing a better performance (independent of the experimental condition), and for memorising media-contents, where the males outperform females (also independent of experimental condition). The study supports the assumption that violent and arousing media content has a negative short-term effect on simultaneous information processing and learning and that there are gender-specific media effects.     

The relative roles of IQ and cognitive processes in reading disability

The purpose of the present study was to explore the relative roles of IQ and cognitive processes in reading performance. A sample of 443 Spanish children (264 male, 179 female) ranging in age from 7 to 13 years were classified into four groups according to IQ scores (<80, 80–90, 90–110, >110) and reading disabled (RD) and normally achieving readers (NR) were compared. The findings indicate that IQ scores were not related to the differences between children with RD and NR. We found that reading‐related cognitive deficits do differentiate between RD and NR children. Therefore, IQ scores do not make a significant contribution to our understanding of reading disability.     

Overshadowing and associability change: Examining the contribution of differential stimulus exposure

In two appetitive conditioning experiments with rats, we investigated the mechanisms responsible for demonstrations of the superior associability of overshadowed conditioned stimuli (CSs) relative to control CSs. In Experiment 1, we investigated whether previous demonstrations were a consequence of differences in the relationship between the CSs and the unconditioned stimulus (US) or of differences in the conditions of exposure to the CSs. Rats received trials with X, Y, and an AB compound, but no delivery of the US (X–, Y–, AB–). A subsequent AY–, AX+, BY + test discrimination revealed that the AY/BY component of the discrimination was solved more readily than the AY/AX component—suggesting the contribution of an exposure effect. In Experiment 2, we better equated the conditions of exposure between A and Y by using AB+, XY+, X– training in Stage 1. In Stage 2, instrumental responses were rewarded during an AY compound. A final test revealed that Y took better control of instrumental responding than did A. The results of these experiments are discussed in terms of classical and contemporary theories of learning and attention.