Mechanisms of inferential order judgments in humans (Homo sapiens) and rhesus monkeys (Macaca mulatta).

If A > B, and B > C, it follows logically that A > C. The process of reaching that conclusion is called transitive inference (TI). Several mechanisms have been offered to explain transitive performance. Scanning models claim that the list is scanned from the ends of the list inward until a match is found. Positional discrimination models claim that positional uncertainty accounts for accuracy and reaction time patterns. In Experiment 1, we trained rhesus monkeys (Macaca mulatta) and humans (Homo sapiens) on adjacent pairs (e.g., AB, BC, CD, DE, EF) and tested them with previously untrained nonadjacent pairs (e.g., BD). In Experiment 2, we trained a second list and tested with nonadjacent pairs selected between lists (e.g., B from List 1, D from List 2). We then introduced associative competition between adjacent items in Experiment 3 by training 2 items per position (e.g., B?C?, B?C?) before testing with untrained nonadjacent items. In all 3 experiments, humans and monkeys showed distance effects in which accuracy increased, and reaction time decreased, as the distance between items in each pair increased (e.g., BD vs. BE). In Experiment 4, we trained adjacent pairs with separate 9- and 5-item lists. We then tested with nonadjacent pairs selected between lists to determine whether list items were chosen according to their absolute position (e.g., D, 5-item list > E, 9-item list), or their relative position (e.g., D, 5-item list     

Serial learning by rhesus monkeys: II. Learning four-item lists by trial and error.

Three rhesus macaque monkeys were trained to produce novel 4-item lists (A → B → C → D) on which all items were displayed from the start of training. Subjects were previously trained to produce 4-item lists by adding one item at a time (A, A → B, A → B → C, and A → B → C → D; lists K. B. Swartz et al., 1991). Those lists could be mastered by responding to each new item last. To learn lists on which all items were displayed from the start of training, subjects had to recall the consequences of errors and correct responses to each item. Errors ended the trial; correct responses to A, B, or C allowed the trial to continue. A correct response to D produced food reward. Although the probability of executing a 4-item list correctly by chance was .04, each subject mastered 4 novel 4-item lists by trial and error. The ability of monkeys to use a trial-and-error strategy to learn novel lists provides a basis for studying the development of serial expertise in animals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Serial learning with a wild card by pigeons (Columba livia): Effect of list length.

Pigeons (Columba livia) learned 3-, 4- or 5-item lists prior to subset and wild card tests. On the latter, a novel item replaced 1 of the list items. Pigeons who learned 3-item lists responded accurately on all subset pairs (AB, BC, and AC) and on all types of 3-item wild card trials (WBC, AWC, & ABW). Pigeons who learned 4- and 5-item lists responded at chance levels of accuracy on all subsets that did not contain a start or an end item (BC, BD, & CD, respectively, on 4- and 5-item subset tests). On wild card trials, they exceeded chance levels of performance only when the wild card replaced the last item (ABCW & ABCDW trials). Monkeys (Cebus apella) trained to produce a 5-item list perform accurately on all subsets and wild cards. (M. R. D'Amato & M. Colombo; see PA Vols 75:19198 and 77:9086). These differences provide strong evidence that pigeons and monkeys form qualitatively different representations of lists containing four or more items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Concurrent conditional discrimination tests of transitive inference by macaque monkeys: List linking.

Processing of serial information was assessed by training six macaques on a five-item list of objects arranged into the four conditional pairs, A–B+, B–C+, C–D+, and D–E+. An analogous list (F through 1) was similarly trained. Subsequently, both lists were linked by training on E–F+, a pair that provided adjacent elements from each list. Then, all unique and trained object pairs from both lists were presented as a test. Results indicated that the objects were retained as a single, linearly organized list with choice accuracy directly related to interitem distance between paired objects. A second experiment explored the consequences of incidence of conflicting information on list organization. In both experiments, selections depended on representational processes and supported the view that monkeys and pigeons retain serial lists in qualitatively different ways. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning about associations: Evidence for a hierarchical account of occasion setting.

In 2 experiments rats were trained on a switching discrimination, with 4 occasion setters, A, B, C, and D and 2 target stimuli, x and y. When signaled either by A or by B, x was reinforced with food and y was not, whereas when signaled either by C or by D these reinforcement relations were reversed (i.e., A: → x+, A: y → ?, B: x → +, B: y → ?, C: x → ?, C: y → +, D: x → ?, D: y → +). In a subsequent Stage A was paired with shock, and then the degree to which food–reinforced (Experiment 1a) and nonreinforced (Experiment 1b) presentations of x and y were capable of eliciting fear was assessed. Those conditioned stimulus (CS)/unconditioned stimulus (US) relations that had been operative in the presence of the fear-eliciting occasion setter A (i.e., x → +, y → ?) elicited more fear than the alternative CS/US combinations (i.e., x → ?, y → +). The implications of these findings are discussed with reference to theories of occasion setting and of configural learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Value transfer in a simultaneous discrimination appears to result from within-event Pavlovian conditioning.

When pigeons acquire a simple simultaneous discrimination, some of the value acquired by the S+ transfers to the S–. The mechanism underlying this transfer of value was examined in three experiments. In Experiment 1, pigeons trained on two simultaneous discriminations (A?+?B– and C?+?D–) showed a preference for B over D. This preference was reduced, however, following the devaluation of A. In Experiment 2, when after the same original training, value was given to D, the pigeons' preference for C did not significantly increase. In Experiment 3, when both discriminations involved partial reinforcement (S±), A?+?C– training resulted in a preference for B over D, whereas B?+?D– training resulted in a preference for A over C. Thus, simultaneous discrimination training appears to result in bidirectional within-event conditioning involving the S+ and S–. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeons (Columba livia) associate time intervals with symbols in a touch screen task: Evidence for ordinality but not summation.

The present experiments examined whether pigeons can sum symbols that are associated with various temporal consequences in a touch screen apparatus. Pigeons were trained to discriminate between two visual symbols that were associated with 0, 1, 2, 3, 4, or 5 s either of delay to 4 s of hopper access (delay group) or duration of hopper access (reward group). In Experiment 1, the pigeons in both groups learned to select the symbol associated with the more favorable outcome, and they successfully transferred this discrimination to novel symbol pairs. However, when tested with 2 pairs of symbols associated with different summed durations, they responded on the basis of a simple response rule rather than the sum of the symbol pair. In Experiment 2, the reward group was presented with four symbols at once and was allowed to successively choose one symbol at a time. All pigeons chose the symbols in order from largest to smallest. This indicates that pigeons formed an ordered representation of symbols associated with different time intervals, even though they did not sum the symbols. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Using the peak procedure to measure timing and counting processes in pigeons.

In 4 experiments, it was shown that the peak procedure can be used to study timing and counting in pigeons. In Experiment 1, pigeons were trained to peck at a green key that briefly flashed red every second. After training under a fixed interval 20 s/fixed number 20 flashes schedule of reinforcement, time and number were dissociated on empty test trials by varying the flash rate. The peak-time curves for different flash rates suggested that pigeons were using a strategy of responding to the first dimension, time or number, that crossed a threshold for initiating and terminating response. Experiments 2 and 3 showed that pigeons could be trained to time or count on empty trials by reinforcing response to only time or number. It was found in Experiment 4 that the set to time or count transferred to a new fixed interval 30 s/fixed number 30 flashes schedule of reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned inhibition in the spatial domain.

Using a variation on the standard procedure of conditioned inhibition (Trials A+ and AX?), rats (Rattus norvegicus) in a circular pool were trained to find a hidden platform that was located in a specific spatial position in relation to 2 individual landmarks (Trials A → platform and B → platform; Experiments 1a and 1b) and to 2 configurations of landmarks (Trials ABC → platform and FGH → platform; Experiment 2a). The rats also underwent inhibitory trials (Experiment 1: Trials AZ → no platform; Experiment 2a: Trials CDE → no platform) interspersed with these excitatory trials. In both experiments, subsequent test trials without the platform showed both a summation effect and retardation of excitatory conditioning, and in Experiment 2a rats learned to avoid the CDE quadrant over the course of the experiment. Two further experiments established that these results could not be attributed to any difference in salience between the conditioned inhibitors and the control stimuli. All these results contribute to the growing body of evidence consistent with the idea that there is a general mechanism of learning that is associative in nature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning of absolute and relative distance and direction from discrete visual landmarks by pigeons (Columba livia).

In an open-field search task, pigeons (Columba livia) were trained to search for a goal located at the midpoint of the hypothetical line connecting two discrete visual landmarks positioned 60 cm apart. In Experiment 1, global orienting cues were absent. After reaching training criteria, pigeons were tested with novel interlandmark distances. Search location and error on test trials suggested pigeons learned relative distance. In Experiment 2, a global orienting cue was present. After reaching training criteria, pigeons were again tested with novel interlandmark distances. Results suggested pigeons learned relative and absolute distances. In Experiment 3, pigeons searched at the midpoint of rotated arrays in both the presence and absence of an orienting cue indicating learning of relative direction. In Experiment 4, pigeons searched in the appropriate goal direction when presented with a single landmark in the presence of the orienting cue but not in its absence indicating learning of absolute direction. Results implicate a stable frame of reference as critical to spatial coding strategies and suggest pigeons are able to code location based on absolute and relative distance and direction from discrete visual landmarks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of similarity in human associative learning.

In 2 experiments, humans received sequences of patterns that were similar (AX→BX, AY→BY, AZ→BZ) or dissimilar (CX→DY, CY→DZ, CZ→DX). The patterns were portrayed as bugs that could be eliminated with 2 insecticide sprays (red or blue). Either spray eliminated bugs with Features A and C, and participants learned by trial and error to use one spray (e.g., red) to eliminate bugs with Feature B and the other spray (e.g., blue) to eliminate those with Feature D. In Experiment 1, participants' spray choice for bugs with Feature A came to match that used to eliminate bugs with Feature B, but there was no such associative transfer between Features C and D. That is, similarity promoted associative transfer of responding between paired patterns when the features used to manipulate similarity (i.e., X, Y, and Z) were irrelevant. In Experiment 2, in which X, Y, and Z were relevant to the solution of configural discrimination, similarity hindered such associative transfer. These results complement those found in pigeons (R. A. Rescorla & D. J. Gillan, 1980) and indicate that similarity should not be accorded independent status as a principle of associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lateralization of Spatial Learning in the Avian Hippocampal Formation.

The authors investigated lateralization of spatial learning within the avian hippocampal formation (HF). In Experiment 1, homing pigeons (Columba livia) with unilateral lesions of the right or left HF were trained to locate a goal in a square room containing local landmarks and global room cues. All groups learned the task. During probe trials, when landmarks were rotated or removed, intact pigeons and left HF-lesioned pigeons relied exclusively on global room cues to locate the food goal. Pigeons with right HF lesions were the only group to demonstrably use the landmarks. The results suggest that the right HF is preferentially involved in the representation of global environmental space, whereas only the left HF may be sensitive to local landmarks for navigation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feature-positive discrimination learning.

In Experiments 1, 2, and 3, pigeons were trained with an ABC+ BCo discrimination, in which three stimuli, A, B, and C, were presented together and paired with food, and the compound BC was followed by nothing; they were also trained with a DEF+ Eo Fo discrimination in which stimuli E and F were presented separately and followed by nothing, whereas the compound DEF was paired with food. On completion of discrimination training, test trials with the feature A consistently revealed a higher rate of responding than with D. In Experiment 4, reinforced presentations of D were intermixed with the DEF+ Eo Fo discrimination. Test trials revealed that E enhanced responding when it was paired with F, but it had the opposite effect when paired with D. The results are seen as being more consistent with a configural than an elemental model of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Summation of symbols by pigeons (Columba livia): The importance of number and mass of reward items.

In each of 3 experiments, different sets of 4 pigeons (Columba livia) were trained to discriminate between 2 visual symbols that covered wells containing food items that varied in number, mass, or both. In Experiment 1, the symbols were associated with 0, 1, 3, 5, 7, or 9 pieces of grain reward. The pigeons learned to choose the symbol corresponding to the larger reward, and on summation tests, they chose the pair of symbols that summed to the larger total reward. When number of food pellets was varied but mass of reward was held constant in Experiment 2, preference for the larger number symbols failed to appear. When number was held constant and mass was varied in Experiment 3, the pigeons showed a clear preference for the larger mass symbols on single-symbol and summation tests. These findings show that pigeons summate the value of symbols and are more likely to represent symbols by mass of food reward than by number of food items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Negative patterning is easier than a biconditional discrimination.

Two groups of rats were trained for 50 days on different discriminations in a magazine approach paradigm. One group was trained with a negative patterning schedule and a positive patterning schedule concurrently: they received intermixed trials of A+, B+, AB-, C-, D-, CD+ (A, B, C, and D are four distinct stimuli; the plus sign denotes reinforcement with food, and the minus sign denotes nonreinforcement). The second group of rats was trained with the same four stimuli arranged as compounds and reinforced according to the biconditional schedule AB+, CD+, AC-, and BD-. The first group learned the positive patterning schedule much more quickly than the negative patterning schedule, but they learned the negative patterning schedule more effectively than the second group learned the biconditional schedule. The authors discuss the implications of these findings for models of stimulus representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer between contextual conditional discriminations: An examination of how stimulus conjunctions are represented.

In 2 experiments, when rats were placed in 1 pair of contexts, A and B, 2 relationships were in force (X→food and Y→no food), and when they were placed in another pair of contexts, C and D, the complementary relationships were operative (Y→food and X→no food). In Experiment 1, rats then received a 2nd discrimination that was either contextually congruent (in A and B, Y→food and X→no food; in C and D, X→food and Y→no food) or contextually incongruent (in A and D, Y→food and X→no food; in C and B, X→food and Y→no food) with the 1st discrimination. In Experiment 2, the 1st discrimination, involving X and Y, was interleaved with a 2nd discrimination, involving V and W, that was again either congruent (in A and B, V→food and W→no food) or incongruent (in A and D, V→food and W→no food) with the 1st discrimination. The congruent discriminations were acquired more readily than were the incongruent discriminations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Serial position effects in recognition memory for odors.

Five experiments examined recognition memory for sequentially presented odors. Participants were presented with a sequence of odors and then had to identify an odor from the list in a test probe containing 2 odors. All experiments demonstrated enhanced recognition of odors presented at the start and end of a series, compared with those presented in the middle of the series when a 3-s retention interval between list termination and test was used. In Experiments 2 and 3, when a 30-s or 60-s retention interval was used, participants performed at slightly lower levels, although the serial position function was similar to that obtained with the 3-s retention interval. These results were noted with a 5-item (Experiments 1 and 4), 7-item (Experiment 2), 6-item (Experiment 3), and 4-item (Experiment 5) list of odors. As the number of test trials increased, recognition performance decreased, indicating a strong role for olfactory fatigue or interference in these procedures. A verbal suppression task, used in Experiments 4 and 5, had little influence on serial-position-based performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Abstract-concept learning carryover effects from the initial training set in pigeons (Columba livia).

Three groups of pigeons were trained in a same/different task with 32, 64, or 1,024 color-picture stimuli. They were tested with novel transfer pictures. The training-testing cycle was repeated with training-set doublings. The 32-item group learned the same/different task as rapidly as a previous 8-item group and transferred better than the 8-item group at the 32-item training set. The 64- and 1,024-item groups learned the task only somewhat slower than other groups, but their transfer was better and equivalent to baseline performances. These results show that pigeons trained with small sets (e.g., 8 items) have carryover effects that hamper transfer when the training set is expanded. Without carryover effects (i.e., initial transfer from the 32- and 64-item groups), pigeons show the same degree of transfer as rhesus and capuchin monkeys at these same set sizes. This finding has implications for the general ability of abstract-concept learning across species with different neural architectures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of structure: I. Implications for connectionist theories of discrimination learning.

In each of 4 experiments animals were given a structural discrimination task that involved visual patterns composed of identical features, but the spatial relations among the features were different for reinforced and nonreinforced trials. In Experiment 1 the stimuli were pairs of colored circles, and pigeons were required to discriminate between patterns that were the mirror image of each other. A related task was given to rats in Experiment 2. Subjects solved these discriminations. For Experiment 3, some pigeons were given a discrimination similar to that used in Experiment 1, which they solved, whereas others received a comparable task but with 3 colored circles present on every trial, which they failed to solve. The findings from Experiment 3 were replicated in Experiment 4 using different patterns. The results are difficult to explain by certain connectionist theories of discrimination learning, unless they are modified to take account of the way in which compound stimuli are structured. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some factors that determine the influence of a stimulus that is irrelevant to a discrimination.

In 5 autoshaping experiments pigeons received 3 stimuli, A, B, and C, for a discrimination in which food was presented after the simultaneous compounds AC and BC, but not after the simultaneous compound ABC. The ease with which this discrimination was mastered was facilitated by presenting C continuously throughout each session (Experiment 1), by presenting C by itself for nonreinforced trials (Experiment 2), and by pairing C by itself consistently with food (Experiment 3). Presenting C by itself and pairing it with food according to a partial reinforcement schedule had no significant influence on the acquisition of the discrimination (Experiments 4 and 5). The results are consistent with a configural theory of associative learning that suggests that experience with a stimulus alters its salience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)