Effects of extradimensional discrimination training upon previously acquired stimulus control

In Experiment 1, three groups of pigeons were taught to discriminate vertical lines (positive) from horizontal (negative). One group was then given true-discrimination training between two colors, a second group was equally reinforced for responding to the colors (pseudodiscrimination), while the third group was not run. The pseudodiscrimination group then provided a flatter gradient on the dimension of line orientation than either of the others, which did not differ. A second experiment demonstrated that this flattening effect could be completely counteracted when pseudodiscrimination was followed by true discrimination before the generalization test. The results are discussed within the framework of current research on attentional factors governing generalization gradients; pseudodiscrimination affects tests of stimulus control rather than its acquisition. When it intervenes between acquisition and testing, it appears to produce a “lapse” rather than a “loss” of the memory of the first-trained stimuli.     

Within-modality and cross-modality attentional blinks in a simple discrimination task

Following up on studies of the "attentional blink," we studied interference between successive target stimuli in visual and auditory modalities. In each experiment, stimuli were two tones and four dots, simultaneously presented for 1,800 msec. Targets were brief intensity changes in either a tone or a dot. Subjects gave unspeeded responses. In four experiments, our results showed interference between targets in the same modality, but not across modalities. We conclude that, under our experimental conditions, restrictions in concurrent target identification are largely modality specific.     

Behaviors observed during S- in a simple discrimination learning task

Key pecking of pigeons was reinforced with food in the presence of a horizontal line and never reinforced in the presence of a vertical line. Highly stereotyped behaviors, as well as key pecking, were observed and recorded in the presence of both stimuli. Results showed that a high proportion of time spent in the presence of the horizontal line was occupied by key pecking, a high proportion of time in the presence of the vertical line was occupied by stereotyped nonkey-pecking behaviors, and intermediate proportions of time spent in the presence of intermediate stimuli were occupied by each class of behavior during generalization tests. Similar running rates (number of key pecks divided by observed key-pecking time) were obtained in the presence of all stimuli, indicating that changes in time rather than tempo accounted for the changes in overall rates of key pecking. An exception occurred in responding to the horizontal line as differential performance was developing. In addition to an increase in time spent key pecking, increased running rates occurred in seven of eight birds, suggesting that both time allocation and tempo play a role in behavioral contrast of overall rates of key pecking.     

Lesions of the rat postsubiculum impair performance on spatial tasks.

Previous studies have identified a population of neurons in the postsubiculum that discharge as a function of the rat's head direction in the horizontal plane (Taube, Muller, & Ranck, 1990a). To assess the contribution of these cells in spatial learning, Long-Evans rats were tested in a variety of spatial and nonspatial tasks following bilateral electrolytic or neurotoxic lesions of the postsubiculum. Compared to unlesioned control animals, lesioned animals were impaired on two spatial tasks, a radial eight-arm maze task and a Morris water task, although the performance scores of both lesion groups improved over the course of behavioral testing. In contrast, lesioned animals were unimpaired on two nonspatial tasks, a cued version of the water maze task and a conditioned taste-aversion paradigm. In addition, lesioned animals showed transient hyperactivity in an open-field activity test. These results support the concept that neurons in the postsubiculum are part of a neural network involved in the processing of spatial information.     

Short-term rhythms in the performance of a simple motor task

Following the discovery of short-term rhythmicities In physiological processes, a study was conducted to investigate existence of similar rhythms in motor behavior. Two groups of eight subjects each were tested every 10 or 20 min respectively in the performance of a linear positioning task with augmented auditory and proprioceptive feedback, for 10 consecutive hr. Each testing sample consisted of five trials with knowledge of results (KR), followed by five trials without knowledge of results (NKR). Between tests subjects drank constant amounts of fluids and urine flow was measured. Movement accuracy in the NKR condition varied rhythmically with periodicities centered at 100 min/ cycle. No comparable rhythms were found in the KR trials or in movement time. Urine flow also varied rhythmically with similar dominant periodicities, but these rhythms were unrelated to rhythms in error. The findings are interpreted to indicate rhythmic modulations in the efficiency of short-term storage and information processing from movement execution. Significance of these results to current views of motor control is discussed.     

Experimental setting affects the performance of guppies in a numerical discrimination task

A recent study found that guppies (Poecilia reticulata) can be trained to discriminate 4 versus 5 objects, a numerical discrimination typically achieved only by some mammals and birds. In that study, guppies were required to discriminate between two patches of small objects on the bottom of the tank that they could remove to find a food reward. It is not clear whether this species possesses exceptional numerical accuracy compared with the other ectothermic vertebrates or whether its remarkable performance was due to a specific predisposition to discriminate between differences in the quality of patches while foraging. To disentangle these possibilities, we trained guppies to the same numerical discriminations with a more conventional two-choice discrimination task. Stimuli were sets of dots presented on a computer screen, and the subjects received a food reward upon approaching the set with the larger numerosity. Though the cognitive problem was identical in the two experiments, the change in the experimental setting led to a much poorer performance as most fish failed even the 2 versus 3 discrimination. In four additional experiments, we varied the duration of the decision time, the type of stimuli, the length of training, and whether correction was allowed in order to identify the factors responsible for the difference. None of these parameters succeeded in increasing the performance to the level of the previous study, although the group trained with three-dimensional stimuli learned the easiest numerical task. We suggest that the different results with the two experimental settings might be due to constraints on learning and that guppies might be prepared to accurately estimate patch quality during foraging but not to learn an abstract stimulus–reward association.     

Fatigue during prolonged performance on a simple compensatory tracking task

Two basic activities are involved in radar operating, watchkeeping and target tracking. Deterioration of watchkeeping performance has been explained by a hypothesis which relates absence of sensory variation and failure to attend to one part of the display continuously (Broadbent, 1951). This paper describes a preliminary experiment to examine deterioration on a simple compensatory tracking task.

Twenty-one subjects were each tested for an uninterrupted period of two hours. They were required to keep a target correctly aligned by cranking a handwheel at a constant speed, and it was expected that failures to attend to the display would result in target deviations. Analysis of the results showed that both number of errors and mean duration of errors increased significantly in consecutive half-hour periods, and that there were large individual differences in performance.     

Differential involvement of M1-type and M4-type muscarinic cholinergic receptors in the dorsomedial striatum in task switching

Previous experiments have demonstrated that the rat dorsomedial striatum is one brain area that plays a crucial role in learning when conditions require a shift in strategies. Further evidence indicates that muscarinic cholinergic receptors in this brain area support adaptations in behavioral responses. Unknown is whether specific muscarinic receptor subtypes in the dorsomedial striatum contribute to a flexible shift in response patterns. The present experiments investigated whether blockade of M1-type and/or M4-type cholinergic receptors in the dorsomedial striatum underlie place reversal learning. Experiment 1 investigated the effects of the M1-type muscarinic cholinergic antagonist, muscarinic-toxin 7 (MT-7) infused into the dorsomedial striatum in place acquisition and reversal learning. Experiment 2 investigated the effects of the M4-type muscarinic cholinergic antagonist, muscarinic-toxin 3 (MT-3) injected into the dorsomedial striatum in place acquisition and reversal learning. All testing occurred in a modified cross-maze across two consecutive sessions. Bilateral injections of MT-7 into the dorsomedial striatum at 1 or 2 microg, but not 0.05 microg impaired place reversal learning. Analysis of the errors revealed that MT-7 at 1 and 2 microg significantly increased regressive errors, but not perseverative errors. An injection of MT-7 2 microg into the dorsomedial striatum prior to place acquisition did not affect learning. Experiment 2 revealed that dorsomedial striatal injections of MT-3 (0.05, 1 or 2 microg) did not affect place acquisition or reversal learning. The findings suggest that activation of M1-type muscarinic cholinergic receptors in the dorsomedial striatum, but not M4-type muscarinic cholinergic receptors facilitate the flexible shifting of response patterns by maintaining or learning a new choice pattern once selected.     

The performance of a simple motor task with kinaesthetic sense loss

Two related studies were carried out, to test the suitability of the nerve compression block as a technique in the investigation of kinaesthesis in motor skills.

In both studies a key tapping task was used. Each experimental group was composed of six volunteer subjects. It was found that kinaesthetic sensation was eliminated after pressure had been applied for 20-25 min., but muscle power was not seriously affected at this stage of the block. The results also showed a pronounced performance decrement in the absence of kinaesthetic feedback, and that this decrement was not due to emotional or other disturbances caused by the experimental procedure. The loss of tactile sensation was also observed.     

Information content and reward processing in the human striatum during performance of a declarative memory task

Negative feedback can signal poor performance, but it also provides information that can help learners reach the goal of task mastery. The primary aim of this study was to test the hypothesis that the amount of information provided by negative feedback during a paired-associate learning task influences feedback-related processing in the caudate nucleus. To do this, we manipulated the number of response options: With two options, positive and negative feedback provide equal amounts of information, whereas with four options, positive feedback provides more information than does negative feedback. We found that positive and negative feedback activated the caudate similarly when there were two response options. With four options, the caudate’s response to negative feedback was reduced. A secondary goal was to investigate the link between brain-based measures of feedback-related processing and behavioral indices of learning. Analysis of the posttest measures showed that trials with positive feedback were associated with higher posttest confidence ratings. Additionally, when positive feedback was delivered, caudate activity was greater for trials with high than with low posttest confidence. This experiment demonstrated the context sensitivity of feedback processing and provided evidence that feedback processing in the striatum can contribute to the strengthening of the representations available within declarative memory.     

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

In each of four experiments, rats were provided with the same three-event decreasing series (18-1-0) of 0.045-g food pellets in a runway. Tracking, running fast to 18 pellets and running slow to 1 and 0 pellets, was investigated as a function of the temporal interval elapsing between the events of the series (the retention interval), shifts in retention interval, and number of trials each day (or the intertrial interval), a trial being defined as presentation of each of the three events of the series. Neither retention interval, which varied from 15 s to 30 min in various investigations, nor shifts in retention interval affected tracking when only one trial was given each day. But when more than one daily trial was given, tracking was acquired more slowly and was disrupted by a shift in retention interval from 15 s to 5 min. Tracking was also disrupted by a shift from one to two trials each day. These results indicate that when given one 18-1-0 trial each day, the rat partitions events on a first-event/subsequent-event basis; that little forgetting occurs even at long retention intervals; that somewhat different memories signal events when one or more than one 18-1-0 trial occurs each day; and that retention interval deficits can arise owing to the same or similar memories' signaling different events. The results described limit the generality of three hypotheses suggested in two recent investigations: that as retention interval increases, rats find it increasingly difficult to remember and utilize serial position cues; that tracking in serial tasks is not influenced by number of trials each day; and that there are specific stimuli associated with each retention interval which, when changed, necessarily disrupt performance.     

How checking breeds doubt: Reduced performance in a simple workingmemory task

A paradox of memory research is that repeated checking results in a decrease in memory certainty, memory vividness and confidence [van den Hout, M. A., & Kindt, M. (2003a). Phenomenological validity of an OCD-memory model and the remember/know distinction. Behaviour Research and Therapy, 41, 369-378; van den Hout, M. A., & Kindt, M. (2003b). Repeated checking causes memory distrust. Behaviour Research and Therapy, 41, 301-316]. Although these findings have been mainly attributed to changes in episodic long-term memory, it has been suggested [Shimamura, A. P. (2000). Toward a cognitive neuroscience of metacognition. Consciousness and Cognition, 9, 313-323] that representations in working memory could already suffer from detrimental checking. In two experiments we set out to test this hypothesis by employing a delayed-match-to-sample working memory task. Letters had to be remembered in their correct locations, a task that was designed to engage the episodic short-term buffer of working memory [Baddeley, A. D. (2000). The episodic buffer: a new component in working memory? Trends in Cognitive Sciences, 4, 417-423]. Of most importance, we introduced an intermediate distractor question that was prone to induce frustrating and unnecessary checking on trials where no correct answer was possible. Reaction times and confidence ratings on the actual memory test of these trials confirmed the success of this manipulation. Most importantly, high checkers [cf. VOCI; Thordarson, D. S., Radomsky, A. S., Rachman, S., Shafran, R, Sawchuk, C. N., & Hakstian, A. R. (2004). The Vancouver obsessional compulsive inventory (VOCI). Behaviour Research and Therapy, 42(11), 1289-1314] were less accurate than low checkers when frustrating checking was induced, especially if the experimental context actually emphasized the irrelevance of the misleading question. The clinical relevance of this result was substantiated by means of an extreme groups comparison across the two studies. The findings are discussed in the context of detrimental checking and lack of distractor inhibition as a way of weakening fragile bindings within the episodic short-term buffer of Baddeley's (2000) model. Clinical implications, limitations and future research are considered.     

An analysis of performance by pre-school children on the KRISP and on a length discrimination task

The speed and accuracy of judgements made by pre-school children on the Kansas Reflection-Impulsivity Scale for Pre-schoolers (KRISP - Wright 1971, 1973) and on a two-choice length discrimination task were investigated. If subjects were relatively accurate on the KRISP then correct responses tended to be faster than errors while if subjects were relatively inaccurate errors were the faster. It is inferred that accurate subjects respond asymptotically in terms of a speed-accuracy tradeoff while inaccurate subjects set a less demanding criterion. Accurate subjects showed a tendency to increase inspection time as a function of item difficulty. This relation did not hold for inaccurate subjects.However, groups classified by means of the KRISP did not differ in either the speed of correct responses or accuracy of line length discriminations. For all groups judgement times were significantly related to stimulus differences and to stimulus ratios. There was no evidence that so-called impulsive children engage in less efficient and less detailed processing than other children.It is argued, contrary to the view of Kagan and his co-workers (e.g. Kakan 1966), that speed and accuracy of responding may not reflect a stable trait dimension. Rather children appear to be able to change their strategies according to the particular demands, implicit or explicit, of the task.     

Inhibition of return in a discrimination task

Inhibition of return (IOR) refers to a bias against returning visual attention to a location that has been recently attended. Although IOR has been demonstrated in a wide range of detection tasks, it has not been reliably shown in discrimination tasks. The results of the present experiment, in which eye movement responses and a cue-target procedure were used, indicate that IOR can exist in a discrimination task. Moreover, the results indicate that the amount of IOR in the discrimination task was approximately equal to that found in the detection task. The results suggest that IOR will be obtained in a discrimination task if the prior allocation of attention does not yield any useful information concerning the forthcoming discrimination judgment.     

Hippocampal formation lesions impair performance in an odor-odor association task independently of spatial context

The rodent hippocampal system is known to play an important role in memory. Evidence that this role is not limited to spatial memory has come from studies using a variety of non-spatial memory tasks. One example is the social transmission of food preference paradigm, a task in which rats learn an odor-odor association with no explicit spatial memory component. However, because training and testing in this task typically take place in the same environment, it is possible that memory for the spatial context in which odors are experienced during training is critical to subsequent retention performance. If this is the case, it might be expected that lesions of the hippocampal system would impair memory performance by disrupting the establishment of a representation of the training environment. We addressed this issue by training rats in one spatial context and then testing them either in the same or a different spatial context. Normal control rats performed equally well when tested in an environment that was the same or different from that used during training, and the retention impairment exhibited by rats with hippocampus plus subiculum lesions was equivalent in the two test environments. These results support the view that the hippocampal system is necessary for the flexible expression of nonspatial memories even when the spatial context in which the memory is acquired is not critical to retrieval.     

Acetylcholine actions in the dorsomedial striatum support the flexible shifting of response patterns

There is accumulating evidence that the dorsomedial striatum plays a significant role in the learning of a new response pattern and the inhibiting of old response patterns when conditions demand a shift in strategies. This paper proposes that activity of cholinergic neurons in the dorsomedial striatum is critical for enabling behavioral flexibility when there is a change in task contingencies. Recent experimental findings are provided supporting this idea. Measuring acetylcholine efflux from the dorsomedial striatum during the acquisition and reversal learning of a spatial discrimination shows that acetylcholine efflux selectively increases during reversal learning as a rat begins to learn a newly reinforced spatial location, but returns to near basal levels when a rat reliably executes the new choice pattern. Experimental findings are also described indicating that the blockade of muscarinic cholinergic receptors in the dorsomedial striatum does not impair acquisition of an egocentric response discrimination, but impairs reversal learning of an egocentric response discrimination. Based on these results, increased cholinergic activity at muscarinic receptors is part of a neurochemical process in the dorsomedial striatum that allows inhibition of a previously relevant response pattern while learning a new response pattern. In situations that demand behavioral flexibility, muscarinic cholinergic activity in the dorsomedial striatum may directly influence corticostriatal plasticity to produce changes in response patterns.