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.     

Reversal learning of object and positional discriminations by mink, ferrets and skunks

Mink, ferrets and skunks were tested on successive reversals of two-choice object or positional discriminations in a modified Wisconsin General Training Apparatus. All species showed considerable improvement in performance after considerable training and some subjects exhibited one-trial reversal learning. Mink and ferrets persistently made more errors when position cues were relevant than when object cues were relevant; the reverse was true of skunks.     

Effects of fornix transection upon associative memory in monkeys: Role of the hippocampus in learned action

Thirty-three monkeys took part in seven experiments designed to elucidate further the effect of fornix transection on learning and memory. In the first experiment the monkeys had to remember whether stimulus objects had previously been paired with reward or no reward, and they had to use this memory to guide choice between stimulus objects at retention tests according to an arbitrary rule which they had learned: to choose objects previously paired with no reward in preference to objects previously paired with reward. Fornix transection produced a severe and permanent impairment in this task. In the second experiment the monkeys also had to remember object-reward associations but the performance rule was more natural: to choose objects previously paired with reward. Here fornix transection had no effect. The third experiment required the monkeys to remember, given a stimulus object, which of two events of equal valence had previously been the outcome of displacing that object. The two events were either a peanut and a sultana or a black penny and a white penny of equal secondary reinforcing value. Performance was unimpaired by fornix transection. The fourth experiment also demonstrated, in a different paradigm, unimpaired recall of sensory events. The fifth experiment demonstrated an impairment following fornix transection in acquisition of simultaneous spatial-visual conditional discriminations; the sixth demonstrated normal learning by fornix-transected monkeys of a successive spatial-visual conditional discrimination and the seventh demonstrated unimpaired acquisition of a simultaneous auditory-visual conditional discrimination. These results, when considered in detail and together, are incompatible with existing hypotheses of hippocampal function. A new hypothesis is discussed.     

An apparatus for the automatic presentation of object discriminations to monkeys

Object discriminations have traditionally been presented to monkeys by hand in the Wisconsin General Test Apparatus. This method is time-consuming and prone to various kinds of experimenter error. It has proved possible to administer object discriminations automatically by using a modification of the Gloster Saro VM 51 vending machine. This machine, which has space for up to 371 objects, moves them on trays by two electric motors, and the control circuits of these are adapted for external operation by relays and modular programming equipment. A series of simple object discriminations or a concurrent (serial) discrimination task can then be given by remote control. The objects are so treated that by touching either of them the animal completes a circuit, enabling the response to be recorded and appropriately reinforced. Learning in the apparatus seems to be about as efficient as in the Wisconsin General Test Apparatus.     

Hypothesis analysis of sameness-difference learning-set by capuchin monkeys

Sameness-difference discriminations were presented to capuchin monkeys and hypothesis analysis was applied to the data. Learners and nonlearners evidenced differences in overall performance and in relative strengths of hypotheses. Learners initially displayed markedly more random than position responding whereas nonlearners evidenced more position than random responding and remained particularly prone to position habits. Stimulus preference and aversion, suppressed by learners by the end of training, reemerged at the onset of two-object discriminations containing previously preferred and aversive stimuli. Hypothesis analysis indicated that when preferred stimuli were positive the correct hypothesis was more evidenced, and stimulus preference or aversion as well as random hypotheses were less evidenced, than when aversive stimuli were positive.     

Deterioration of planning ability with age in Japanese monkeys (Macaca fuscata)

To investigate the ability of aged monkeys to plan and the effect of aging on this ability, performance in a food retrieval task was assessed in aged and younger Japanese monkeys (Macaca fuscata). In this task, the monkeys had to retrieve food items by selecting from a set of 9 holes, each of which contained 1 food item. Results showed that task performance declined significantly with age. All monkeys showed, to a greater or lesser extent, some consistent patterns in their sequence of selecting holes for retrieving the food item. An analysis of these selection patterns indicated that the younger monkeys showed more consistent sequences in selection than the aged monkeys. Furthermore, success in the task performance correlated strongly with higher consistency in the sequence of selecting holes. The authors simulated performance for this task by monkeys without any strategies or plans. The results suggest that the empirical data were far more systematic than the simulated data. Thus, the authors conclude that Japanese monkeys have the ability to plan and that this ability to plan deteriorates with age.     

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.     

Processing a display even after you make a response to it. How perceptual errors can be corrected

We know that when people make responses which they did not intend they can discover this by monitoring kinaesthetic and visual feedback. It is less clear whether they can also correct perceptual errors which occur when they mistake one signal for another. It was argued that, if they can sometimes do this, extra errors which occur when discriminations become more difficult may be detected and corrected. Experiment I compared the ability of young fit subjects to detect errors made during easy and during difficult discriminations between tone signals. There was no evidence that any additional errors made to difficult discriminations were detected. Fast errors were detected, slower errors were not. The results were consistent with the idea that subjects can detect fast motor errors by monitoring feedback, but that they cannot detect perceptual mistakes.

In Experiment II subjects made easy and difficult line length discriminations. Displays lasted for 100 ms, 200 ms or 500 ms and were followed by random masks. In this case, fast errors were again corrected more frequently than slow errors but eight aspects of the data suggest that subjects could, and did, correct perceptual as well as motor mistakes and that they managed to do this by continuing to process a display after the moment at which they may have initiated an impulsive response to it. The data are interpreted in terms of a “Committee Decision” model for extended perceptual processing previously applied to other, similar data by Rabbitt and Rodgers (1977) and Rabbitt, Cumming and Vyas (1978).     

Similarity between concurrent visual discriminations: Dimensions and objects

Accuracy is of ten reduced when two visual discriminations must be made concurrently (“divided attention”). According to a hypothesis originally proposed by Treisman (1969) and Aliport (1971), this result should depend on the similarity of required discriminations. When discriminations concern different visual dimensions, they should be made in somewhat separate visual subsystems, reducing interference between them. This prediction was tested in two experiments, involving discriminations of shape, size, orientation, and spatial frequency. In differentconditions of divided attention, concurrent discriminations concerned either the same or different dimensions, and either one or two objects. The results showed that performance depends only on the number of relevant objects, not on the number or similarity of required discriminations. They suggest that selective attention to an object is a coordinated state in which the outputs of multiple visual subsystems are made concurrently available for control of behavior.     

Olfactory discrimination learning in mice lacking the fragile X mental retardation protein

An automated training system was used to compare the behavior of knockout (KO) mice lacking the fragile X mental retardation protein with that of wild-type (WT) mice (C57Bl/6 strain) in the acquisition and retention of olfactory discriminations. KO and WT mice did not differ in the acquisition of a four-stage nose poke shaping procedure. In two separate experiments, mutant mice required substantially more training to acquire a series of novel olfactory discrimination problems than did control mice. The KO mice required significantly more sessions to reach criterion performance, made significantly more errors during training, and more often failed to acquire discriminations. Both KO and WT mice showed similar error patterns when learning novel discriminations and both groups showed evidence of more rapid learning of later discriminations in the problem series. Both groups showed significant long-term memory two or four weeks after training but WT and KO mice did not differ in this regard. A group of well-trained mice were given training on novel odors in sessions limited to 20–80 trials. Memory of these problems at two day delays did not differ between WT and KO mice. Tests using ethyl acetate demonstrated that WT and KO mice had similar odor detection thresholds.     

Effect of small cue-response separation on pattern discrimination in macaques (Macaca fuscata and M. mulatta)

In order to elucidate the nature of the effect of small cue-response separations on pattern discriminations by monkeys, three studies were performed. When training on a pattern discrimination with a cue-response separation was discontinued during performance at the chance level, there was no saving on the rate of learning a second task (with identical cues but a different cue-response separation) relative to the performance of naive control animals. By contrast, when training was discontinued at a performance level a little better than chance, there was significant saving on learning a second task. After learning the second task, a third task with new pattern cues was learned, with marked saving on the duration of performance at the chance level. The results indicate that during the initial stage of performance at the chance level, monkeys do not attend to cues if there is even a small separation between the cue and the response site.     

A role for olfaction in object recognition by normal and hippocampal-damaged rats

To examine how olfactory and visual factors affect object discriminations in rats with and without hippocampus damage, the authors trained Long-Evans rats on simple object discriminations. They then examined how these discriminations were affected by rotations of the objects, by coating the objects in a transparent acrylic coating, or by both rotating and coating the objects in acrylic. The rats displayed no impairments when the objects were only sprayed in acrylic, and they displayed minor impairments when the objects were rotated. However, when the objects were both rotated and acrylic coated, the rats displayed severe impairments. This suggests that the rats are solving the rotated-only phase based on surface features of the objects (probably odor) and not based on the visual information. Such species' biases for obtaining object information are important factors to consider when designing and interpreting visual memory experiments across species. There was no difference in performance between the rats with hippocampus damage and the sham rats, and this is consistent with the literature on similar tasks.     

Qualitative block design analysis in posttraumatic stress disorder

Qualitative and quantitative Block Design performance was examined in Vietnam combat veterans with PTSD diagnoses (n = 23) and Vietnam combat veterans without PTSD or other mental disorders diagnoses (n = 19). Results indicated that PTSD-diagnosed veterans committed more single block rotations than the comparison sample, and that their errors occurred more frequently in right hemispace than errors made by the comparison sample. The two groups did not differ in the number of configural errors made, errors committed in left hemispace, or in quantitative performance measures. Findings are suggestive of relative left hemisphere hypoactivation and are congruent with prior research documenting cerebral asymmetries in emotional disorders.     

Detection of a deficit in visual discrimination of pattern following lesions of anterior cortex: role of type of motivation.

6 albino rats were trained under appetitive motivation to perform diametrically opposed visual discriminations of pattern via opposite eyes. Small lesions were subsequently placed unilaterally in anterior neocortex. Following a period of post-surgical recovery, subjects were re-trained on the diammetrically opposed discriminations in alternating 10-trial blocks. Every subject made more post-surgical errors on the discrimination mediated by the eye contralateral to the lesion. Since albino rats have virtually complete decussation of the visual system, this indicates selective impairment in mediation of performance of pattern discrimination in the part of the lesioned hemispheres. Thus, findings previously obtained in studies involving aversive motivation are general to appetitively motivated tasks.     

Single and concurrent discrimination learning by monkeys after lesions of inferotemporal cortex

Three monkeys with bilateral lesions of inferotemporal cortex and three unoperated controls (all previously sophisticated at visual discriminations) learned 60 discriminations between pairs of multi-featured computer-generated patterns. They then learned 5 problem sets, each composed of 5 pairs of the same kind learned concurrently, and finally 20 more single discriminations.

Previous reports that inferotemporal lesions selectively impair concurrent learning were disconfirmed; given practice at learning pairs concurrently, the inferotemporals learned these at a similar rate to single pairs. Analysis of intra-problem learning supported the suggestion that the lesion affects visual identification (the ability to distinguish objects within a large population) rather than visual association or memory.     

Everyday scale errors

Young children occasionally make scale errors – they attempt to fit their bodies into extremely small objects or attempt to fit a larger object into another, tiny, object. For example, a child might try to sit in a dollhouse-sized chair or try to stuff a large doll into it. Scale error research was originally motivated by parents' and researchers' informal accounts of these behaviors. However, scale errors have only been documented using laboratory procedures designed to promote their occurrence. To formally document the occurrence of scale errors in everyday settings, we posted a survey on the internet. Across two studies, participants reported many examples of everyday scale errors that are similar to those observed in our labs and were committed by children of the same age. These findings establish that scale errors occur in the course of children's daily lives, lending further support to the account that these behaviors stem from general aspects of visual processing.     

Development of the appearance-reality distinction

Young children can express conceptual difficulties with the appearance-reality distinction in two different ways: (1) by incorrectly reporting appearance when asked to report reality (“phenomenism”); (2) by incorrectly reporting reality when asked to report appearance (“intellectual realism”). Although both phenomenism errors and intellectual realism errors have been observed in previous studies of young children's cognition, the two have not been seen as conceptually related and only the former errors have been taken as a symptom of difficulties with the appearance-reality distinction. Three experiments investigated 3- to 5-year-old children's ability to distinguish between and correctly identify real versus apparent object properties (color, size, and shape), object identities, object presence-absence, and action identities. Even the 3-year-olds appeared to have some ability to make correct appearance-reality discriminations and this ability increased with age. Errors were frequent, however, and almost all children who erred made both kinds. Phenomenism errors predominated on tasks where the appearance versus reality of the three object properties were in question; intellectual realism errors predominated on the other three types of tasks. Possible reasons for this curious error pattern were advanced. It was also suggested that young children's problems with the appearance-reality distinction may be partly due to a specific metacognitive limitation, namely, a difficulty in analyzing the nature and source of their own mental representations.     

Differences in performance of young and old monkeys on a visuospatial memory task

Two groups of stumptailed macaques (Macaca arctoides) were compared in terms of performance on a visuospatial working memory task involving repeated presentations of an array of 15 doors, each of which concealed one food reward at the start of a session. Rewards obtained by the subject were not replaced. Errors were defined as responses to doors previously pushed open during the session. Both groups generally obtained all rewards and showed improved performance across sessions, but old monkeys consistently made more errors than young ones, especially in the latter half of a given session. Further, old monkeys were less diverse in the errors they made, indicating different response strategies by the two groups.     

Contrasting effects of lateral striate and superior colliculus lesions on visual discrimination performance in rhesus monkeys.

Rhesus monkeys with lesions of lateral striate cortex, monkeys with superior colliculus lesions, and unoperated monkeys were tested for retention of a preoperatively acquired pattern discrimination. The three groups of monkeys were then tested in two-choice, color, color discrimination tests, one involving varying degrees of stimulus-response (S-R) separation and the other, administered several months later, involving various directions of S-R separations. The monkeys were also tested in a series of two-choice pattern discriminations, following each of which they were tested for relearning when the patterns were masked with bars or circles. The monkeys with lateral striate lesions were moderately retarded in retention of the pattern discrimination, whereas those with superior colliculus lesions were not. The monkeys with colliculus lesions, but not those with lateral striate lesions, were impaired in both S-R separation tests, which demonstrates that their deficit was not transient or solely due to a difficulty in shifting the gaze in one direction. The lateral striate monkeys, unlike those with colliculus lesions, were dificient in relearning discriminations between masked patterns. These findings suggest that superior colliculus and striate cortex may be involved in two different aspects of attention: respectively, shifting attention (and orientation) from one spatial locus to another and maintaining attention on fixated stimuli. Alternative interpretations of the effects of the lesions, based on their retinotopic loci, are discussed.     

Sensory-perceptual qualities of images

Four experiments demonstrated that such sensory-perceptual features of objects as weight, color, and numerosity affect imaginal performance involving images of those objects. For example, imaginary transport times of objects increased with both the hypothetical weight of the imagined object and the distance traversed. The transport functions were steeper when a map of the terrain was imagined than when it was perceived, suggesting that imaginal performance of heft did not parallel more perceptually guided performance. Corresponding to the view that images activate noncanonical information from long-term memory, mental transport times were longer for maps of familiar terrains than for those of presumably unelaborated unfamiliar terrains. Further, the effects of imaginary color discriminations depended on the familiarity of the object being imagined. Images of customarily colored familiar objects were generated faster when projected onto a surface of the same color than when projected onto a surface of another color, whereas images constructed from unfamiliar targets were recognized more accurately when the target's color differed substantially from that of the ground than when it differed by a smaller amount. The results were predicted by a model that assumed that images may incorporate ancillary characteristics in addition to canonical information.