Effects of signaling retention interval length on delayed matching-to-sample in pigeons.

Pigeons were trained initially on a delayed matching task in which colors served as sample and comparison stimuli. During subsequent training, additional stimuli compounded with the sample signaled whether that trial involved a short (1 s) or a long (5 s) delay. In Experiment 1, miscuing reduced accuracy at the short delay markedly and tended to increase accuracy at the long delay slightly. Experiments 2 and 3 revealed a robust effect of cuing when the cues followed sample termination, thereby refuting the view that such cues evoke differential attention to the sample stimulus. Experiment 4 revealed that the cues did not influence rate of forgetting, and Experiment 5 revealed no effect of point of cue placement within the retention interval. It was concluded that cues correlated with retention interval length modulated matching accuracy independently of memory, perhaps by signaling different rates of reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sources of visual interference in delayed matching-to-sample with pigeons.

In 2 experiments, independent groups of pigeons were trained on an identity matching task involving line orientations as sample and comparison stimuli. An overhead houselight was illuminated continuously throughout each training session or was never illuminated during training sessions. During subsequent testing, the lighting conditions during the delay were the same as in training on some trials, but on other trials they were opposite those of training during either the entire delay (Exp 1) or during a portion of the delay (Exp 2). In Ss trained with the houselight off, turning the houselight on during the delay produced a large and enduring disruption in matching accuracy. In Ss trained with the houselight on, turning the houselight off during the delay produced only a moderate and temporary disruption in matching accuracy. In pigeons, as in monkeys, sustained retroactive interference effects obtain only when the level of illumination is increased during the delay interval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some observations of the effects of intertrial interval and delay on delayed matching to sample in pigeons.

Accuracy of delayed matching to sample was studied in 12 Silver King pigeons at different combinations of length of intertrial interval (ITI) and length of delay. When ITI and delay were varied between sessions in Exps I and II, accuracy increased monotonically with ITI and decreased monotonically with delay. Evidence was found for constancy of performance at equivalent ratios of ITI to delay, and percentage of correct choices was linearly related to the log of this ratio. In Exps III and IV, ITI was manipulated as a within-sessions variable. In contrast to the effect of this variable when manipulated between sessions, accuracy improved only from the shortest interval to the next shortest interval and remained constant at all longer intervals. In Exp IV, it was found that performance improved as a direct function of the mean ITI for sessions and that this relation was not affected by the degree of ITI variability within sessions. Findings resemble the effects of temporal variables on autoshaping, and the possibility that some common processes are involved in delayed matching and autoshaping is discussed. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retention interval and intertrial interval in a serial learning or delayed discrimination task.

In 4 experiments, 58 male albino rats were provided with the same 3-event decreasing series (18-1-0) of food pellets in a runway to investigate tracking—running fast to 18 pellets and running slow to 1 and 0 pellets. Results show that when more than 1 daily trial was given, tracking was acquired more slowly and was disrupted by a shift in retention interval from 15 sec to 5 min. Tracking was also disrupted by a shift from 1 to 2 trials each day. Results indicate that when given 1 18-1-0 trial each day, Ss partitioned events on a 1st-event/subsequent-event basis, that little forgetting occurred even at long retention intervals, that somewhat different memories signaled events when 1 or more than 1 18-1-0 trial occurred each day, and that retention interval deficits could arise owing to the same or similar memories' signaling different events. Results limit the generality of 3 hypotheses suggested by H. L. Roitblat (see record 1983-09709-001) and by S. J. Haggbloom and M. W. Ekdahl (1985): that as retention interval increases, rats find it increasingly difficult to remember and utilize serial position cues; that tracking in serial tasks is not influenced by number of trials each day; and that there are specific stimuli associated with each retention interval that when changed, necessarily disrupt performance. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Timing in pigeons: Effects of the similarity between intertrial interval and gap in a timing signal.

Previous research suggests that when a fixed interval is interrupted (known as the gap procedure), pigeons tend to reset memory and start timing from 0 after the gap. However, because the ambient conditions of the gap typically have been the same as during the intertrial interval (ITI), ambiguity may have resulted. In the present experiment, the authors found that when ambient conditions during the gap were similar to the ITI, pigeons tended to reset memory, but when ambient conditions during the gap were different from the ITL pigeons tended to stop timing, retain the duration of the stimulus in memory, and add to that time when the stimulus reappeared. Thus, when the gap was unambiguous, pigeons timed accurately. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The intermixed-blocked effect in human perceptual learning is not the consequence of trial spacing.

A robust finding in humans and animals is that intermixed exposure to 2 similar stimuli (AX/BX) results in better discriminability of those stimuli on test than does exposure to 2 equally similar stimuli in 2 separate blocks (CX_DX)--the intermixed-blocked effect. This intermixed-blocked effect may be an example of the superiority of spaced over massed practice; in the intermixed, but not the blocked exposure regime, each presentation of a given stimulus (e.g., AX) is separated from the next by the presentation of its partner (BX). Two experiments with human participants replicated the intermixed-blocked effect and showed that the effect was not due to the spacing of exposure trials. A mechanism for the intermixed-blocked effect is proposed, which combines theories from associative learning and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of differential sample responding in the differential outcomes effect involving delayed matching by pigeons.

The role of differential sample responding in the differential outcomes effect was examined. In Exp 1, pigeons were trained on a one-to-many matching task with differential sample responding required. Differential outcomes were associated with samples and comparisons, with comparisons only, or with neither samples nor comparisons. Slopes of delay functions for trials with pecked versus nonpecked samples suggested use of a single-code-default strategy in the nondifferential-outcomes group but not in the differential-outcomes groups. In Exp 2, differential sample responding and differential outcomes were manipulated independently. Again, there were significant differences in the relative slopes of the delay functions. Results suggest that differential outcomes exert their effect independently of differential sample responding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contextual cueing in multiconjunction visual search is dependent on color- and configuration-based intertrial contingencies.

Three experiments examined memory-based guidance of visual search using a modified version of the contextual-cueing paradigm (Jiang & Chun, 2001). The target, if present, was a conjunction of color and orientation, with target (and distractor) features randomly varying across trials (multiconjunction search). Under these conditions, reaction times (RTs) were faster when all items in the display appeared at predictive (“old”) relative to nonpredictive (“new”) locations. However, this RT benefit was smaller compared to when only one set of items, namely that sharing the target's color (but not that in the alternative color) appeared in predictive arrangement. In all conditions, contextual cueing was reliable on both target-present and -absent trials and enhanced if a predictive display was preceded by a predictive (though differently arranged) display, rather than a nonpredictive display. These results suggest that (1) contextual cueing is confined to color subsets of items, that (2) retrieving contextual associations for one color subset of items can be impeded by associations formed within the alternative subset (“contextual interference”), and (3) that contextual cueing is modulated by intertrial priming. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Expression of renewal is dependent on the extinction-test interval rather than the acquisition-extinction interval.

A recent finding suggested that when extinction occurs shortly after acquisition, renewal of an extinguished fear response (fear-potentiated startle) to a light conditioned stimulus (CS) is diminished (Myers, Ressler, & Davis, 2006). The present study attempted to extend this finding using a white-noise CS and freezing as the behavioral measure of fear. In Experiments 1A and 1B, we observed renewal whether extinction occurred 10 min or 24 hr after acquisition. In contrast, renewal was not observed if test occurred 10 min after extinction (Experiment 2). Experiment 3 demonstrated that expression of extinction at the 10-min extinction-test interval was attenuated by a pretest subcutaneous injection of the γ-aminobutyric acid (GABA) inverse agonist FG7142. These findings suggest that renewal is influenced more by the extinction-test interval than the acquisition-extinction interval. Further, the failure to see renewal 10 min after extinction suggests that there is a separate context memory that undergoes a different consolidation function than the CS-no US memory formed during extinction. Finally, the expression of extinction appears to be GABA dependent regardless of the extinction-test interval or the test context. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Element and compound matching-to-sample performance in pigeons: The roles of information load and training history.

Pigeons were trained to match color and line orientation element or compound samples in a symbolic matching-to-sample task. In subsequent test sessions with element and compound samples, there was an initial superiority of element matching for the element-trained group and of compound matching for the compound-trained group. This difference persisted over the course of 100 test sessions for the element-trained group, whereas element- and compound-matching accuracy converged for the compound-trained group. In a second experiment, in which sample duration was manipulated, element-matching accuracy was superior to compound-matching accuracy for both groups. Thus, element-matching accuracy was superior to compound-matching accuracy under conditions that rule out generalization decrement and training history as explanations. The data are interpreted as supporting the view that the dimensions of visual compound stimuli compete for a limited cognitive resource. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral contrast in pigeons depends upon the operant.

Reinforced 3 male Carneaux pigeons for depressing a foot treadle according to multiple VI/VI schedules. After rates of responding stabilized, the schedule in 1 component was changed to extinction. This manipulation resulted in either no change or a decrease in rate of responding in the unchanged component. The Ss were then reinforced for key pecking under the same procedure. When key pecking was the operant, the experimental manipulation resulted in behavioral contrast. Results are discussed in terms of Pavlovian * Instrumental interactions. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Marking in pigeons: The role of memory in delayed reinforcement.

A previous study by the 1st author and colleagues (see record 1980-27237-001) showed that if reinforcement is delayed, rats find it difficult to learn the correct path through a maze, but learning improves dramatically if a brief tone or light is presented after every choice response. The marking hypothesis suggests that the unexpected stimulus directs attention to the preceding response, thereby marking it in memory. To explore the generality of this phenomenon, in the present 4 experiments 102 pigeons were reinforced after a delay for pecking half of a split key. A change in key color following a choice response produced significantly greater learning than did no marker or one following a response during the intertrial interval (Exp I), though an immediate marker was only slightly more effective than one delayed 3 sec (Exp II). In Exps III and IV, the marker followed either a correct or an incorrect response on food trials, and whichever response was marked increased substantially. Marking thus appears to be a robust and powerful phenomenon, capable of substantially modifying behavior in a variety of species and settings. Reasons why markers may sometimes interfere with learning rather than enhance it are suggested. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of hippocampal lesions and intertrial interval on single-alternation performance in the rat.

Trained 7 unoperated male Long-Evans hooded rats and 14 Ss with bilateral hippocampal or cortical lesions made by aspiration on a go, no-go task in which bar presses were reinforced on alternate trials. Performance was evaluated with both latency ratios (latency to 1st response on go trials/latency to 1st response on no-go trials) and response ratios (total responses on no-go trials/total responses on go trials). Ss were trained to criterion at successively increasing durations of ITI (10, 20, 40, and 80 sec.). While Ss with hippocampal lesions acquired the task more rapidly than controls with the initial 10-sec ITI, they were severely impaired when tested with the longer ITIs. (23 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of prenatal fructose infusions upon metabolic condition of the newborn

Changes of total blood sugars, glucose, fructose, lactate, pyruvate, acid-base balance and free fatty acids were followed in 15 healthy newborns whose mothers received fructose infusions during labour. The results were compared with 20 control newborns and with 10 newborns after prenatal glucose infusions. The levels of total blood sugars during 24 h after infusions remained higher after fructose than in 2 other groups. The values of lactate and pyruvate increased, but the lactate/pyruvate ratio remained unchanged. The free fatty acids were lower than in the control group. Results show that fructose is not a suitable source of energy for the human fetus even under normal conditions.     

Testing models of delayed sequence discrimination in pigeons: The advance key procedure.

In 2-event delayed sequence discrimination (DSD) training, one arrangement (temporal order) of 2 sample stimuli is the positive sequence and the remaining are the negative sequences for keypecking during a subsequent test stimulus. Three models of the DSD task were tested in 2 experiments with 8 White Carneaux pigeons. In Exp I Ss were allowed to terminate a trial by pecking the "advance key" during the sample stimuli or to let the test stimulus progress to the next trial. In the absence of a peck to the advance key, the trial continued to the completion of the test stimulus. In Exp II, Ss were forced to choose actively between advancing to the next trial and continuing through the current trial. Choice between the advance and continue keys was required with the occurrence of each of the successive sample stimuli and the test stimulus. Although the addition of forced choice resulted in more uniform effects, Ss were able to identify negative sample sequences with the occurrence of the 1st negative sample event in both experiments. Results support the prospective memory model but not the retrospective and hybrid models of temporal sequence recognition in the 2-event DSD task. (French abstract) (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of intertrial food presentations on anticipatory goal-tracking in the rat

Four experiments examined the sensitivity of anticipatory goal-tracking in the rat to stimulus-food contingency. Contingency was manipulated by varying the probability of food delivery in the absence of a food-tray-light or clicker conditional stimulus (CS), while holding constant the probability of food coincident with the CS. CS control of anticipatory food tray investigation was examined after a period of context extinction in all experiments. Acquisition of stimulus control was undermined by the scheduling of intertrial food deliveries (Experiment 1). The rate of intertrial food deliveries influenced subsequent acquisition of CS control when all intertrial food deliveries were omitted (Experiment 2). When intertrial food deliveries were added to the training regimen subsequent to acquisition of CS control, that control was impaired (Experiments 3 and 4).     

Age-related differences in the impact of spacing, lag, and retention interval.

An experiment is reported that examines age-related differences in the lag effect and its relation to retention interval. A total of 30 young and 30 older adults received both once-presented pairs and twice-presented pairs that were tested in a continuous cued-recall paradigm either after a short retention interval (2 pairs intervening between the last presentation of a pair and its test) or a long retention interval (20 pairs intervening between the last presentation of a pair and its test). In addition, the twice-presented pairs were separated by either 0, 1, 4, 8, or 20 intervening pairs. The results replicated the interaction between retention interval and lag that has been reported by Glenberg (1976, Journal of Verbal Learning and Verbal Behavior, 15, 1–26). Furthermore, although the older adults performed considerably lower than the younger adults in overall recall performance, their data were remarkably similar to the younger adults in the patterning of means. A mathematical modeling procedure was used to fit the data to Estes' stimulus fluctuation model. The results of this modeling procedure suggest that, compared with younger adults, older adults (a) encode less contextual information at a given point in time and (b) have a slower rate of contextual fluctuation across time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flooding (response prevention) in rats: The effects of immediate vs. delayed flooding and of changed illumination conditions during flooding.

Conducted 2 experiments with a total of 204 female hooded rats to determine new methods for increasing the effectiveness of flooding (response prevention) in producing the cessation of avoidance responding in extinction. Results show that flooding was more effective when there was a cooling-off or delay period between acquisition and the administration of flooding. The increased efficacy of flooding was correlated with changes in the spontaneous behavior of Ss during flooding. The method of altering illumination conditions (visual stimulation) during flooding also made flooding more effective. Implications for theories of flooding are discussed. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Presence/absence-sample matching by pigeons: Divergent retention functions may result from the similarity of behavior during the absence sample and the retention interval.

Divergent choose-absence retention functions typically found in pigeons following presence/absence-sample matching have been attributed to the development of a single-code/default coding strategy. However, such effects may result from adventitious differential responding to the samples. In Experiment 1, retention functions were divergent only when differential sample responding could serve as the basis for comparison choice. In Experiment 2, when pecking did not occur during the retention interval, a choose-absence bias was found, but when pecking occurred during the retention interval, a choose-presence bias resulted. In Experiment 3, positive transfer was found when a stimulus associated with the absence of pecking replaced the absence sample but not when a stimulus associated with pecking replaced the presence sample. Thus, presence/absence-sample matching may not encourage the development of a single-code/default coding strategy in pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The proliferation of normal human fibroblasts is dependent upon negative regulation of p53 function by mdm2

Loss of function of the tumour suppressor gene p53 is a key event in most human cancers. Although usually occurring through mutation, in some tumour types this appears to be achieved via an indirect mechanism involving inappropriate expression of a functional inhibitor, mdm2, which binds to the transactivation domain of p53. This interaction offers an ideal potential target for novel cancer therapies. However, therapeutic specificity may depend on the extent to which this p53-inhibitory action of mdm2 is also required by normal cells. Transgenic data have already established that mdm2 is needed to prevent embryonic lethality, but the situation in adult cells is still unclear. Here we show that micro-injection of normal human fibroblasts with an antibody directed against the p53-binding domain of mdm2 induces expression of p53-responsive genes, and furthermore results in p53-dependent growth arrest. We conclude that normal cell proliferation can be dependent on negative regulation of p53 by mdm2, a finding which raises an important note of caution for mdm2-directed cancer therapies.