Determinants of serial discrimination learning by squirrel monkeys

Squirrel monkeys were presented multiple serial discriminations 1, 2, 4, and 8 problems long. They were then presented problems designed to separate the effects of within-list associative interference from the effects of within-problem intertrial interval as list length was increased. The Ss committed consistently fewer errors after Trial 1 reward than after Trial 1 nonreward and showed strong stimulus perseveration. An increase in within-problem intertrial interval from 30 sec to 4 min had no effect whereas the associative interference resulting from increased problem length caused a small but significant performance decrement. Old and new problems had about equal effects on serial discrimination. The findings indicated that squirrel monkeys are relatively insensitive to within-problem associative interference.     

A primacy effect in monkeys when list position is relevant

In Experiment 1 (1a and 1b), Rhesus monkeys (Macaca mulatta) learned lists of two-choice visual discriminations in which list position was relevant to discrimination performance. For example, Stimulus A was the rewarded stimulus if it was presented at List Position 1, but was not rewarded if it was presented at any other position in the list; similarly, Stimulus B was rewarded only at List Position 2, and so on. In learning these lists, all animals showed a marked primacy effect. In Experiment 2 (2a and 2b), Rhesus monkeys and Cynomolgus monkeys (M. fascicularis) learned lists of visual discriminations in which each visual stimulus occupied a fixed position in a list, but list position was not relevant to discrimination performance. For example, Stimulus E was always rewarded, and was always presented at List Position 1. To increase the salience of list beginning as a distinctive event, successive presentations of the list were separated by 24-hr intervals. In Experiment 2 there was no primacy effect, however. These results show for the first time that a primacy effect can be obtained in visual discrimination learning by monkeys. Furthermore, they suggest that it is obtained only when list position is relevant to the discrimination learning task.     

Conservation training in four-year-old children

In Experiment 1 two training procedures were used to teach four-year-olds to conserve. Verbal rule instruction consisted of providing verbal rules and demonstrations of the operations referred to by the rules. Feedback consisted of providing verbal feedback contingent upon the children's responses. One week after training on conservation of number and length the children were given a posttest which included tests of conservation of number, length, and mass. Children who were given verbal rule instruction conserved significantly more on the number and length posttest problems than children who were not. However, this learning did not transfer to the mass problems, possibly because mass is not naturally acquired until some time after conservation of number and length. The feedback training procedure had no effect on conservation performance. In Experiment 2, the verbal rule instruction procedure was used to train four-year-olds on conservation of length and mass. One week after training the children were tested on both conservation of number, which is typically acquired before length and mass, and conservation of weight, which is typically acquired after length and mass, as well as on conservation of length and mass. Children who were given training conserved more on all four types of problems than children in the control group.     

Repetition effects in directed forgetting: evidence for retrieval inhibition

Four experiments were conducted in support of a role for memory retrieval inhibition in directed forgetting. In each experiment, subjects were presented a list of words, some of which they were instructed to remember and some of which they were instructed to forget. After a recall test for all the words, the list was repeated. This time, however, all the words were presented with instructions that they be remembered. The improvement in recall from Trial 1 to Trial 2 was greater for the “forget” (F) words than for the “remember” (R) words. This difference was not due to a memorization-difficulty, item-selection effect (Experiment 2), a differential priority for rehearsal or output position given to the F items on Trial 2 (Experiment 3), or the greater number of F items left to be learned after Trial 1 (Experiment 4). Thus, the differential improvement from List 1 to List 2 for the F items was interpreted as a release of retrieval inhibition owing to the change in cue from forget to remember.     

Some characteristics of concurrent discrimination and retention by monkeys

Before and after learning-set training, 12 rhesus monkeys were tested on the acquisition and retention of tasks consisting of eight concurrent object discrimination problems. Training on the concurrent discrimination was administered unitil a fairly stringent acquisition criterion was met. Under these procedures, retention, unlike acquisition, was little influenced by initial object preferences. Excellent retention was observed both before and after learning-set training. In a second experiment, these same monkeys were tested on a series of concurrent tasks which provided different numbers of objects as the sets of correct and incorrect discriminanda. Task solutions depended largely upon acquiring and retaining a list of correct objects despite designation of the large or small sets as the correct one. The animals seemed not to use “exclusion” strategies even when this might have provided an efficient task solution. It was considered that the monkeys' performances were based on stimulus sampling characteristics like those seen in other discrimination testing situations.     

The effects of restraint and noncontingent preshock on subsequent escape learning in the rat

Three experiments investigated the effects of restraint and of inescapable fixed duration preshocks on subsequent shuttlebox escape-from-shock learning. Fixed-intensity preshock, random-intensity preshock, and no-preshock conditions were included in each experiment. In Experiment 1, restraining the rat in a harness prior to escape training retarded escape acquisition. There was no effect of preshock. In Experiment 2, both restraint and high fixed-intensity (1.0 mA) preshock retarded escape acquisition, when escape training occurred either immediately or 24 hr after preshock. In Experiment 3, movement was punished by positively correlating preshock intensity with the rat's movement; this treatment retarded escape conditioning. No effects were found for low fixed-intensity or random-intensity preshock nor for a condition in which movement was rewarded during preshock. The retarding effects of restraint and certain types of preshock were explained in terms of interfering instrumental responses.     

Facilitative effects of forgetting from short-term memory on growth of long-term memory in retardates

Competing explanations of the beneficial effect of spacing in retardate discrimination learning were tested. Three-trial multidimensional (“junk”) problems were presented concurrently to educable retardates with MAs over 8 years. The spacing interval spearating Trials 1 and 2 was filled with either zero, four, or eight interpolations, the interpolations being either trials on similar junk problems or repetitions of a single, well-learned dot-pattern discrimination. The principal findings were that: (1) while short-term retention of junk problems (as measured by Trial 2 performance) suffered greater interference from similar junk interpolations than from dot-pattern interpolations, long-term learning (as measured by a delayed Trial 3) was superior following the highly interfering junk problems; and (2) spacing facilitated learning only following highly interfering interpolations. These results are inconsistent with consolidation and rehearsal theories but support the prediction of the Sperber. Greenfield, and House (Journal of Experimental Psychology, 1973, 99) spacing model that forgetting from short-term memory facilitates retardate learning.     

Reward schedule effects in extinction: Intertrial interval, memory, and memory retrieval

Rats were trained in a runway such that partial reward occurred on Trial 1 of the day and consistent reward on subsequent massed trials (Group PRT1), or consistent reward occurred on Trial 1 of the day and partial reward on subsequent massed trials (Group PRTM). Under spaced (24-hr) extinction, Group PRT1 was more resistant to extinction than Group PRTM and under massed (1-min) extinction, Group PRTM was more resistant to extinction than Group PRT1. These findings suggest that (a) distinctive stimuli are associated with Trial 1 of the day and with subsequent massed trials, (b) these distinctive stimuli function as retrieval cues for memories, memory retrieval being independent of intertrial interval, and (c) behavior in extinction is controlled by a stimulus compound consisting of the memory of nonreward plus stimuli which accompany the memory of nonreward on rewarded acquisition trials.     

Resistance to continuous delay of reinforcement or extinction following partial delay or partial reinforcement in acquisition: A direct comparison

Rats received either partial reward (PR) or partial delay (PD) in acquisition with one, two, or three delay or nonreward trials followed by an immediately rewarded trial or one delay or nonreward trial followed by an immediately rewarded trial. These four groups were then split in half and given either continuous delay or continuous nonreward (extinction) in a “response persistence” phase. In addition, two continuously reinforced groups, one experiencing continuous delay, and the other experiencing extinction were included. The results showed that response persistence was greater when PD groups were given continuous delay rather than extinction, but the opposite was true for PR groups. The “length” (1, 2, or 3 versus 1 nonreward or delay trial) also transferred to the response persistence phase with the length 1, 2, and 3 conditions being more persistent than the 1 length conditions. The results were discussed with respect to theoretical notions of response persistence.     

The effects of cue reliability on infants' manual search.

Nine-month-old babies were presented a manual search problem in which toys were hidden in one of two containers, and then the containers were transposed. Over a series of training trials either two, one, or no cues were perfectly correlated with the location of the toy. The infants' first searches became more accurate over training trials in conditions with consistent container and/or position cues. In the final training trial block search performance was best with two cues, intermediate with one cue, and least accurate in the no-cue condition. In a subsequent reversal procedure, in which the toy was placed in the previously unused hiding place, the number of correct first searches also differed according to the nature of cues available across hidings. The implications for learning the concept of object permanence are discussed.     

Serial list combination by monkeys (Macaca mulatta): test cues and linking

This investigation assessed prospective bases of non-human primate cognitive operations that support serial list memory. Four macaques learned 3-, 5-item ordered lists of objects (as two-choice problems) and then either did or did not (in a within-subject design) receive training on pairs that linked the three original lists into a 15-item serial order. Next, subjects experienced selective exposure trials on object pairs that either maintained or contrasted to the serial position relationships seen during original learning. Subsequent comprehensive tests assessed the interactive effects of linking and exposure conditions on choosing in accord with a combined 15-item serial order. Linking readily induced monkeys to merge lists into a 15-item order, but restricting early exposure to pairs with the same positional relationships as original training slowed, but did not prevent, list combination. Exposure to positional relationships congruent with the combined (15-item) list and different from those of original 5-item training aided both expression of the linking effect and acquisition after no link training. Thus, list linking facilitated serial reorganization by inducing release from error derived from memory for prior learned positional relationships. The task was recommended as a prospective evaluator of continuity of cognitive processes among species.     

Schedules of reward shift in the double runway

Eighty food deprived rats received 62 trials in a double runway. On Trials 1-30, reward in the first goal box (GB1) was either always two food pellets or always zero pellets. All subjects received two pellets in the second goal box (GB2). On Trials 31-62 subjects in each preshift group (GB1 reward or GB1 nonreward) were shifted to the opposite GB1 reward level on 0, 25, 50, 75 or 100% of occasions. GB2 reward remained unaltered in all cases. For subjects experiencing reward decrease, second runway (A2) run and goal speeds after nonreward were generally enhanced, both within-group and in comparison with never rewarded controls. No such effect was evident on A2 start speed, nor was there any evidence to suggest that A2 performance after decreased reward was a function of the schedule of decrease. Increased GB1 reward resulted in general within-group impairment of A2 start and run speeds, with no effect on A2 goal performance. However, comparisons of speeds after increased reward with those of always rewarded controls revealed no difference on A2 start or run but indicated impairment of A2 goal performance. With the 50% schedule of reward increase, A2 run speeds after nonreward (the training level) exceeded those of never rewarded controls. Results are discussed with reference to McHose's contrast account of double runway phenomena and Amsel's frustration theory.     

The effect of the length of to-be-remembered lists and intervening lists on free recall: a reexamination using overt rehearsal

In 3 experiments, the authors investigated the effects of to-be-remembered (TBR) and intervening list length on free recall to determine whether selective rehearsal could explain the previous finding that recall was affected only by TBR list length. In Experiments 1 (covert rehearsal) and 2 (overt rehearsal), participants saw 5- and 20-word lists and had to recall the list prior to that last presented list. In Experiment 3, either 1 or 2 lists were presented, and recall of TBR list was postcued. Recall proportion decreased with increased TBR list length. Moreover, the authors found extended recency effects when recall was replotted by when words were last rehearsed (Experiments 2 and 3) and an effect of intervening list length when rehearsal was reduced (Experiment 3).     

Positive contrast following gradual and abrupt increases in reward magnitude using delay of reinforcement

In Experiment 1, rats were given a 1-pellet reward for 48 preshift trials. During a subsequent 20-trial postshift phase, one group was shifted to a 12-pellet reward on Trial 1, a second was shifted on Trial 11, and a third was given 1 more pellet each trial and then 12 pellets for the last 10 trials. The speeds of all three groups increased to a level above that of a control group given a 12-pellet food reward throughout training (positive contrast). In experiment 2, rats were shifted from 1 to 12 pellets either gradually or abruptly following either abbreviated training (9 trials) or extended training (20 trials). One group of control subjects received 12 pellets throughout training. The results revealed a positive contrast effect for gradually shifted subjects following extended training but not following abbreviated training. The abrupt shift procedure produced positive contrast following abbreviated training but only a marginal effect following extended training. These results indicate that, contingent upon the amount of preshift training, either gradual or abrupt reward increases may produce positive contrast.     

Remembrance of places lasts: Proactive inhibition and patterns of choice in rat spatial memory

A series of experiments was carried out to evaluate the notion that rats given a sequence of massed daily trials on the radial maze reset working memory at the end of each trial by deleting its contents. Although curves presented by D. S. Olton [Scientific American, 1977, 236, 82–98; In S. H. Hulse, H. Fowler, & W. K. Honig (Eds.), Cognitive processes in animal behavior, Hillsdale, N.J.: Erlbaum, 1978] show that rats return to errorless performance at the beginning of each trial after the first, the fact that accuracy falls less rapidly over choices on Trial 1 than on subsequent trials suggests a proactive inhibition (PI) effect. In Experiment 1, Olton's findings were replicated, and a PI effect was observed on Days 1–2 of testing. On Days 3–5, overall accuracy improved significantly and was associated with the development of a strong tendency for rats to enter adjacent alleys, which became particularly marked on the final trials of a day's testing. In order to prevent rats from achieving accurate performance by using an adjacent alleys pattern, a procedure was used in Experiment 2 which involved initial forced random choices followed by a retention test consisting of free choices. Repeated daily trials with this procedure yielded a significant PI effect, which was more marked at a 60-sec delay than at a 0-sec delay. Experiments 3 and 4 showed this PI effect to be robust and resistant to manipulations designed to produce release from PI. Both the PI effect and a strong tendency found in Experiment 1 for animals to avoid on the initial choices of Trial n those alleys most recently entered on Trial n?1 argue that rats do not reset working memory between trials.     

Acquisition and forgetting in monkeys' memory of informational object-reward associations

The first experiment showed the monkeys could recall whether an object had been rewarded with peanuts or with sultanas, two equally preferred foods. The second investigated the effect of rewarded trials with an object on monkeys' ability to recall a nonrewarded trial with the same object. The third demonstrated that monkeys could use the memory of reward to predict nonreward and the memory of nonreward to predict reward, in a Win-Shift Lose-Stay paradigm. The fourth found differences between Win-Shift Lose-Stay and Win-Stay Lose-Shift in the rate at which associations between objects and reward events were forgotten. These results are discussed in relation to D. L. Medin's (In A. M. Schrier, Ed., Behavioral primatology, Hillsdale, N.J.: Erlbaum, 1977, Vol. I, pp. 33–69) distinction between informational and hedonic effects of reward in monkeys. It is argued that the association between an object and a reward event is represented in memory by many independent traces, different traces recording the object's association with different attributes of the reward event.     

Effects of rodent prefrontal lesions on object-based, visual scene memory

It has been suggested that certain prefrontal areas contribute to a neural circuit that mediates visual object memory. Using a successive go/no-go visual scene discrimination task, object-based long-term memory was assessed in two rodent prefrontal regions. Rewarded trials consisted of a standard scene of four toy objects placed over baited food wells. The objects and their locations composing the standard scene remained constant for the duration of the study. Trials in which one of the standard scene objects was replaced with a novel object were not rewarded. Following the establishment of a significant difference between latency to approach the rewarded standard scene compared to latency to approach non-rewarded scenes, quinolinic acid or control vehicle was infused into either the prelimbic and infralimbic cortices or the anterior cingulate cortex. Following a 1 week recovery period, subjects were retested. Animals with prelimbic/infralimbic cortex lesions displayed a profound and sustained deficit, whereas, animals with anterior cingulate cortex lesions showed a slight initial impairment but eventually recovered. Both lesion groups acquired a simple single object discrimination task as quickly as controls indicating that the deficits on the original scene discrimination task were not due to motivational, response inhibition, or perceptual problems.     

Cue learning by rufous hummingbirds (Selasphorus rufus)

The authors investigated the use by wild-living rufous hummingbirds (Selasphorus rufus) of flower color pattern and flower position for remembering rewarded flowers. Birds were presented with arrays of artificial flowers, a proportion of which was rewarded. Once the locations were learned by the birds, the array was moved 2 m, and flower color pattern and/or rewarded positions were manipulated. The birds' ability to learn which were the rewarded flowers in this 2nd array was much more strongly affected by whether the rewarded flowers occupied the same positions as in the 1st array than by their color patterns.     

The effect of monetary reward and punishment on the repetition of responses under open and closed task conditions

Subjects were given one study and two test trials on a list of paired associates. Critical responses on the first test were those which were rewarded or punished by gain or withdrawal of money. Between subjects variables were (a) whether the critical responses on test 1 were right or wrong, and (b) whether subjects were informed of the second test before or after test 1. On test 2, subjects were asked to repeat their test 1 responses to the appropriate stimuli. When subjects were unaware that they would receive a second test, rewarding a response on test 1 increased its probability of repetition on test 2; punishment had no significant effect. When subjects were aware that they would be tested again, the reward/ punishment treatment had no effect. An explanation based on the Law of Effect is rejected in favour of a cognitive explanation, utilizing the total time hypothesis.     

Ambiguous-cue learning in preschool children: A test of the dimensional characteristics of task stimuli

Sixteen preschool children were administered a two-choice discrimination problem consisting of three stimulus compounds: the consistently rewarded stimulus, the consistently nonrewarded stimulus, and the ambiguous stimulus which was nonrewarded when paired with the positive, but rewarded when paired with the negative. When both pair of stimuli, positive-ambiguous and negative-ambiguous, were presented together the subject was required either to choose or to avoid the ambiguous stimulus depending upon the stimulus with which it was paired. In Experiment 1, when each of three stimuli (positive, negative, ambiguous) varied along one nonspatial cue dimension (color), performance was better on negative-ambiguous trials than positive-ambiguous trials. In Experiment 2, when the positive and negative stimuli varied along three nonspatial cue dimensions (colors and form) and the ambiguous stimulus varied along one of these dimensions (color), superior positive-ambiguous over negative-ambiguous performance was obtained. These findings complement those reported for other subjects and confirm Berch's (D. B. Berch, Learning and Motivation, 1974, 5, 135–148) predictions regarding use of differential numbers of cue dimensions.