Effects of Fimbria-Fornix, Hippocampus, and Amygdala Lesions on Discrimination Between Proximal Locations.

The conditioned cue preference (CCP) task was used to study the information required to discriminate between spatial locations defined by adjacent arms of an 8-arm radial maze. Normal rats learned the discrimination after 3 unreinforced preexposure (PE) sessions and 4 food paired-unpaired training trials. Fimbria-fornix lesions made before, but not after, PE, and hippocampus lesions made at either time, blocked the discrimination, suggesting that the 2 structures processed different information. Lateral amygdala lesions made before PE facilitated the discrimination. This amygdala-mediated interference with the discrimination was the result of a conditioned approach response that did not discriminate between the 2 arm locations. A hippocampus/fimbria-fornix system and an amygdala system process different information about the same learning situation simultaneously and in parallel. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial memory in dogs (Canis familiaris) on a radial maze.

Working spatial memory in dogs (Canis familiaris) was tested in Experiments 1 and 2 on an 8-arm radial maze. When dogs chose freely among all 8 arms containing food in Experiment 1, they learned to enter all 8 arms with progressively fewer arm visits over trials. In Experiment 2, 2 groups of dogs were forced to visit 4 randomly chosen arms on the maze and then tested for memory of these arm visits using a win-shift rule for 1 group and a win-stay rule for the other group. Dogs performed better with the win-shift rule than with the win-stay rule. In Experiment 3, reference memory was investigated by using a 4-arm maze on which 0, 1, 3, and 6 pieces of food were consistently placed on different arms. Dogs learned to visit the arms with the larger amounts before the arms with the smaller amounts. Dogs’ memory capacity in these studies was found to be surprisingly low. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Food searching strategies of rats: Variables affecting the relative strength of stay and shift strategies.

Examined the extent to which the food searching strategies of rats are influenced by training, information about food in an initially visited site, and type of memory required for correct choices. Exp I used a discrete-trial, delayed conditional-discrimination procedure on a T-maze with 32 male Sprague-Dawley rats. Ss entered 1 arm of the maze and were given a choice between that arm (stay strategy) or the other arm (shift strategy). During the initial visit, S either consumed all the food (depletion condition) or only some of it (nondepletion condition). Ss given the shift-depletion task learned most rapidly; those given the stay-depletion task learned most slowly. Depletion increased the rate at which the shift discrimination was learned but decreased the rate at which the stay discrimination was learned. Exp II used a similar procedure with the Maier 3-table maze and 16 male albino rats; the same pattern of results was found. Exp III, conducted with 15 male Sprague-Dawley rats, required each S to learn both a win-stay and a lose-shift contingency and to use associative memory. Early in training, Ss used only a shift strategy but eventually learned the discrimination. Results indicate that the shift-stay balance is influenced by the rat's species-specific predisposition, reinforcement contingencies, amount of food in the initially visited place, and the extent to which recognition memory by itself is sufficient to solve the discrimination. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfaction and the "data" memory system in rats.

Conducted studies to characterize the memory system involved in successive olfactory discrimination learning in rats. Two odors emanated from different arms of a radical maze; 1 of the arms contained a water reward. After training on 4 to 5 pairs of odors Ss learned to discriminate the members of a new pair in 5–20 trials. Experiments in which either member of the pair was compared with a novel cue indicated that the Ss learn both positive and negative odors, rather than ignoring the negative cue. The memories for the odors were apparently persistent, and no evidence for retroactive interference from subsequent training was obtained. Animals trained on 3 component odors with 2 in common did not recognize the elements that were unshared when these were presented by themselves. Even when 1 of the 2 shared components was combined with the differentiating component into a cue the new cue was treated as a novel odor. Inclusion of a previously learned simple odor in a complex odor did affect the learning of that odor. Findings, combined with those of previous studies in which lesions were used, suggest that learning that a series of odor discriminations involves a version of the "data" memory system described by cognitive psychologists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Can a pigeon simultaneously process temporal and numerical information?

On the basis of an experimental procedure first used with rats by W. H. Meck and R. M. Church (see record 1984-08708-001), pigeons were trained to discriminate between sequences of light flashes that varied in both total duration and number of flashes. Subsequent tests for number and time control showed that birds simultaneously processed temporal and numerical information and that degree of control by each dimension was affected by numerical discrimination training. Pigeons also learned to respond accurately to ambiguous flash sequences in which time and number indicated different responses. The use of postsequence cues to disambiguate these sequences indicated the selective retrieval of time and number information from working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coping with discrimination: How disadvantaged group members perceive the discrimination that confronts them.

Two experiments examined how disadvantaged group members perceive the discrimination that confronts them. Women reacted to negative feedback after receiving information about the probability that they had been discriminated against. In both experiments, attribution to discrimination was a function of situational ambiguity. When discrimination was certain, participants attributed their failure to discrimination. When discrimination was ambiguous, however, participants minimized discrimination and attributed their failure to themselves. The second experiment investigated the role of perceived control in the minimization of personal discrimination. Results indicated that disadvantaged group members were reluctant to blame their performance on discrimination because they were placing control for their outcomes in the hands of others rather than their own. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of a spatial discrimination by rats as a function of age.

144 female albino Sprague-Dawley rats, equally divided among 3 levels of food deprivation, were given 10 trials/day on a spatial discrimination until 1 errorless day occurred. 1/2 of the Ss were 33 days old (juveniles) when training began; the other Ss were between 100 and 120 days old (adults). Results show that juveniles learned more slowly than adults, and Ss given a smaller daily food ration learned in fewer trials. The age-related difference in learning rate was interpreted to be a consequence of relatively ineffective inhibitory processes among the juveniles in view of the associated differences in sequence of choices and other behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal lesions impair retention of discriminative responding based on energy state cues.

The present research investigated the hypothesis that the hippocampus is involved with the control of appetitive behavior by interoceptive “hunger” and “satiety” signals. Rats were trained to solve a food deprivation intensity discrimination problem in which stimuli produced by 0-hr and 24-hr food deprivation served as discriminative cues for the delivery of sucrose pellets. For Group 0+, sucrose pellets were delivered at the conclusion of each 4-min session that took place under 0-hr food deprivation, whereas no pellets were delivered during sessions that took place when the rats had been food deprived for 24 hr. Group 24+ received the reverse discriminative contingency (i.e., they received sucrose pellets under 24-hr but not under 0-hr food deprivation). When asymptotic discrimination performance was achieved (indexed by greater incidence of food magazine approach behavior on reinforced compared with nonreinforced sessions), half of the rats in each group received hippocampal lesions, and the remaining rats in each group were designated as sham- or nonlesioned controls. Following recovery from surgery, food deprivation discrimination performance was compared for lesioned and control rats in both Groups 0+ and 24+. Discriminative responding was impaired for rats with hippocampal lesions relative to their controls. This impairment was based largely on elevated responding to nonreinforced food deprivation cues. In addition, hippocampal damage was associated with increased body weight under conditions of ad libitum feeding. The results suggest that the inhibition of appetitive behavior by energy state signals may depend, in part, on the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Foraging on the radial maze: The role of travel time, food accessibility, and the predictability of food location.

Reports on an experiment in which rats foraged in a 4-arm radial maze containing 4 feeders in each arm, with different percentages of baited feeders in each arm (0%, 25%, 50%, or 75%). The effects of three variables were examined: (1) Arm entrances were open or blocked to increase travel time between arms; (2) Feeders were uncovered or covered to decrease accessibility to food; (3) Food locations were randomly changed between sessions or remained fixed. Rats learned to discriminate between the 0% arm and arms containing food when food locations were fixed but not when food locations were random. Rats also learned the locations of baited feeders within arms with fixed food locations, but selectively visited baited feeders only if the feeders were covered. Comparisons of obtained data with computer simulations indicated that rats foraged near optimality. Patterns of foraging were best accounted for by a molecular maximizing model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bait-shyness acquisition is impaired by VMH lesions that produce obesity.

Lesioned Carworth CFE female rats in the area of the ventromedial nucleus of the hypothalamus (VMH) before or after avoidance learning. Prelesioned Ss learned to avoid familiar saccharin-sweetened water associated with apomorphine less rapidly, and during extinction lost the avoidance more rapidly than controls. Ss lesioned after avoidance learning continued to avoid, and during extinction lost the avoidance at the same rate as controls. When given ad-lib food and water, lesioned Ss became obese. 1 tentative interpretation is that VMH-lesioned rats overrespond to environmental stimuli, including their food. This interferes with gustatory-visceral associations needed for satiety and bait-shyness acquisition. Another possibility is that overresponding to environmental stimuli and impaired gustatory-visceral associations are both direct consequences of VMH lesions. (32 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential outcome effects in Pavlovian biconditional and ambiguous occasion setting tasks.

Three experiments with rats explored the differential outcome effect (DOE) using a Pavloian magazine approach conditioning preparation. Experiment 1 compared groups trained on a biconditional discrimination (AX+, AY?, BX?, BY+) with differential or nondifferential outcomes, and Experiment 2 examined this using an ambiguous occasion setting task (e.g., AX+, X?, Y+, AY?). In both experiments, subjects trained with differential outcomes learned the tasks better than subjects trained with nondifferential outcomes. Furthermore, subjects given differential outcome training learned the positive occasion setting component of the ambiguous task more efficiently than the negative occasion setting component, although both were enhanced by differential outcome training. Experiment 3 demonstrated that the ambiguous occasion setting task was reversed more readily when the target–outcome relations (as opposed to the modulator–outcome relations) were maintained during the reversal phase. These data suggest that an acquired distinctiveness effect may be responsible for the DOE in Pavlovian learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhanced frustrative nonreward effect following 6-hydroxydopamine lesions of the lateral septum in the rat.

Tested the effect of local injections of 6-hydroxydopamine (6-OHDA [3 μg/1 μl]) into the lateral septum in a paradigm that leads to an energizing behavior, through a possible frustrative effect, induced by partial or total omission of reward in hungry adult male Sprague-Dawley rats. Biochemical assays in the septum showed that 6-OHDA reduced endogenous dopamine and, to a lesser extent, noradrenaline concentrations and left intact noncatecholaminergic neurons such as serotoninergic terminals. In a double straight alley, Ss were exposed to an acquisition phase, a partially reinforced phase, and an extinction phase. Ss with lesions ran faster for food than controls in the partial reinforcement or extinction situation. The 2 groups also behaved similarly after the 1st 6 trials of the extinction phase. When Ss were tested in a leverpress conditioning task, lesioned and control Ss learned this task equally well, both with respect to the number of leverpresses and the time to obtain a fixed number of food pellets. In the 1st 5 min following the omission of reward, the number of leverpresses increased more for the lesioned Ss than for controls, a difference that disappeared in the later stages of the test. Results indicate that the loss of septal dopaminergic innervation produces behavioral effects similar to those obtained after total destruction of the same areas by electrocoagulation. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of left frontal lesions on the selection of context-appropriate meanings.

The present study examined the role of the left frontal cortex in strategic aspects of semantic processing. Participants were tested in a semantic priming task involving the meaning access of ambiguous and unambiguous words. Patients with left or bilateral frontal lesions failed to develop semantic facilitation of context-appropriate homograph meanings relative to age-matched controls. When the ambiguous words, however, were replaced by unambiguous words, patients with left frontal lesions improved to normal levels of semantic priming. This pattern of results seems difficult to explain in terms of a problem to access semantic information per se or to use contextual cues. The findings are, however, consistent with a deficit in selecting context-appropriate meanings in the presence of competing meanings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response–reinforcer versus stimulus–reinforcer pretraining influences S+ versus S– discriminative control.

In 2 experiments, 60 male Long-Evans rats trained on a visual discrimination task (leverpresses reinforced) received stimulus–reinforcer (noise–food) trials, no training, or response–reinforcer (reinforcement of keypressing) training. Ss then learned an auditory discrimination (keypresses reinforced), in which the positive stimulus (S+) was a noise (N) and the negative stimulus (S–) was a tone (T). Noise–food training resulted in the greatest enhancement of leverpressing on N trials and the least suppression on T trials during a summation test. Prior training of keypress responses produced the opposite pattern of results. Findings are interpreted as reflecting the operation of the combination laws that R. A. Rescorla and A. R. Wagner (1972) proposed to account for intracompound dynamics in classical conditioning. (36 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Intertrial interval as a contextual stimulus: Further analysis of a novel asymmetry in temporal discrimination learning.

Four experiments investigated discrimination learning when the duration of the intertrial interval (ITI) signaled whether or not the next conditional stimulus (CS) would be paired with food pellets. Rats received presentations of a 10-s CS separated half the time by long ITIs and half the time by short ITIs. When the long ITI signaled that the CS would be reinforced and the short interval signaled that it would not be (Long+/Short?), rats learned the discrimination readily. However, when the short ITI signaled that the CS would be reinforced and the long interval signaled that it would not (Short+/Long?), discrimination learning was much slower. Experiment 1 compared Long+/Short? and Short+/Long? discrimination learning with 16-min/4-min or 4-min/1-min ITI combinations. Experiment 2 found no evidence that Short+/Long? learning is inferior because the temporal cue corresponding to the short interval is ambiguous. Experiment 3 found no evidence that Short+/Long? learning is poor because the end of a long ITI signals a substantial reduction in delay to the next reinforcer. Long+/Short? learning may be faster than Short+/Long?because elapsing time involves exposure to a sequence of hypothetical stimulus elements (e.g., A then B), and feature-positive discriminations (AB+/A?) are learned quicker than feature-negative discriminations (A+/AB?). Consistent with this view, Experiment 4 found a robust feature-positive effect when sequentially presented CSs played the role of elements A and B. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Involvement of the retrosplenial cortex in processing multiple conditioned stimuli.

Lesions of retrosplenial cortex (RSP) disrupt spatial and contextual learning, suggesting that RSP may have a fundamental role in processing overlapping, or simultaneously presented stimuli. If so, then RSP lesions might also be expected to disrupt learning that requires the concurrent processing of phasic conditioned stimuli. In Experiment 1, rats were trained in a compound feature negative discrimination task in which a tone was presented and immediately followed by food on some trials, while on other trials a visual stimulus was simultaneously presented along with the tone and not reinforced. Normal rats learned to discriminate between the trials but RSP-lesioned rats exhibited low levels of conditioning on both types of trials. Experiment 2 demonstrated that this effect was not simply due to a general inability to form associations, since RSP-lesioned rats exhibited normal responding when the visual stimulus was presented alone and paired with food. These findings support the view that RSP has an important role in learning that involves the processing of simultaneously presented stimuli and have implications for understanding the functional relationship between the hippocampus and RSP. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Children's responses to ambiguous messages and their understanding of ambiguity.

Conducted 4 experiments to investigate whether a total of 212 young children (aged 4 yrs 6 mo to 7 yrs 3 mo) could respond differently to ambiguous and unambiguous messages if they were prevented from pointing at the potential referents. The exact nature of the bias that was operating was examined in the final 2 experiments, which investigated whether the differential responding to ambiguous and unambiguous messages was based on an understanding of ambiguity or on an awareness of certainty and uncertainty about the interpretation of ambiguous and unambiguous messages. It was found that Ss were more likely to respond differently to ambiguous and unambiguous messages if they were prevented from pointing at the potential referents. It was also found that the improvement in differential responding was not accompanied by an improvement in verbal judgments of message quality, and the differential responses were closely related to judgments of certainty and uncertainty about the interpretation of the message. Ss who did not know that verbal messages could be ambiguous could nevertheless respond differently to ambiguous and unambiguous messages by attending to their own certainty or uncertainty about the interpretation of those messages. They were more likely to do that when they were prevented from pointing at the potential references. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heuristic processing can bias systematic processing: Effects of source credibility, argument ambiguity, and task importance on attitude judgment.

High- and low-task-importance Ss (367 undergraduates) read a strong or weak unambiguous message or an ambiguous message that was attributed to a high- or low-credibility source. Under low task importance, heuristic processing of the credibility cue was the sole determinant of Ss' attitudes, regardless of argument ambiguity or strength. When task importance was high and message content was unambiguous, systematic processing alone determined attitudes when this content contradicted the validity of the credibility heuristic; when message content did not contradict this heuristic, systematic, and heuristic processing determined attitudes independently. Finally, when task importance was high and message content was ambiguous, heuristic and systematic processing again both influenced attitudes. Yet, source credibility affected persuasion partly through its impact on the valence of systematic processing, confirming that heuristic processing can bias systematic processing when evidence is ambiguous. Implications for persuasion and other social judgment phenomena are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste-potentiated odor aversion learning: Role of the amygdaloid basolateral complex and central nucleus.

Examined the relative contributions of the amygdaloid basolateral complex (ABL) and central nucleus (CN) to taste-potentiated odor aversion (TPOA) learning, an associative learning task that is dependent on information processing in 2 sensory modalities. In Exp 1, rats with neurotoxic lesions of these systems were trained on the TPOA task by presenting a compound taste–odor conditioned stimulus (CS), which was followed by LiCl administration. Results showed that ABL damage caused an impairment in potentiated odor aversion learning but no deficit in the conditioned taste aversion. In contrast, rats with CN damage learned both tasks. Exp 2 examined the effects of ABL damage on TPOA and odor discrimination learning. The odor discrimination procedure used a place preference task to demonstrate normal processing of olfactory information. Results indicated that although ABL-lesioned animals were impaired on TPOA, there was no deficit in odor discrimination learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of nicotinic acetylcholine receptor stimulation on negative occasion setting.

We have previously shown that nicotine enhances learning in a negative occasion setting task in which rats are trained to distinguish between two different trial types. During reinforced trials, a target stimulus (a tone) is presented and immediately followed by food reward. On nonreinforced trials, a feature stimulus (a light) is presented prior to the tone and indicates the absence of reward following presentation of the tone. The goal of the present study was to identify the behavioral mechanism through which nicotine affects this form of learning, and to determine which subtype(s) of nicotinic acetylcholine receptors mediate the effects of nicotine. Consistent with our prior findings, nicotine administration enhanced the ability of rats to discriminate between the two trial types. Nicotine enhanced the magnitude of the discrimination by decreasing responding to the tone on nonreinforced trials. Nicotine-treated rats also learned the discrimination in fewer sessions than control rats. A significant new finding was that nicotine also increased the orienting response to the light, suggesting that nicotine may enhance learning the serial feature negative discrimination by increasing attention to the visual feature. In addition, we found that RJR-2403, a selective α4β2 nicotinic receptor agonist, also enhanced discrimination. However, RJR-2403 did not affect responding on nonreinforced trials, nor did RJR-2403 affect orienting to the light. Together these data indicate that nicotine may enhance discrimination by enhancing tone-reward associability through α4β2 nicotinic receptors and by enhancing attention to the light through non-α4β2 receptor subtypes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)