Note on changes in response latency following discrimination training in the monkey

Two monkeys were trained to press and hold down a telegraph key in the presence of a red light. Subsequent release of the key in response to a white cross superimposed on the red background was followed by reinforcement. Key release in response to a white circle on the red background was never reinforced. Latencies for the key release response to the reinforced stimulus (cross) were considerably shorter and less variable than those to the unreinforced stimulus (circle).     

Note on use of extreme criterion groups in item discrimination analysis

The purpose of this note is to reconsider the Kelley-Cureton definition of optimal extreme groups for estimating item-criterion correlations. Optimal tail per cents are derived, using the criterion of minimum sampling variance of the tetrachoric correlation coefficient, and the findings are related to earlier work of Mosteller. It is shown that upper and lower 27 per cent groups yield the most precise estimate of the tetrachoric coefficient only when the population correlation is close to zero. When the population value is .4, extreme 20 per cent groups provide estimates with the smallest sampling error variance. It is further shown, however, that 27 per cent extremes yield highly efficient estimates. Thus no change is recommended in traditional item analysis procedures.     

Effects of postresponse visual stimuli on visual discrimination learning in the rhesus monkey

To learn more about the mechanism (or mechanisms) involved with postresponse stimulus processing during discrimination learning, a series of studies was conducted with monkeys to determine why the combined relevant and irrelevant stimuli impair learning more than irrelevant stimuli appearing alone. It was found that: (a) the greater size and complexity of the combination of stimuli were not responsible for the greater deficit, while the presence of the relevant stimuli (S^D and S^Δ) within the stimulus combination apparently was; (b) the more similar the postresponse irrelevant stimuli were to the relevant stimuli the greater the deficit that resulted; and (c) monkeys that had earlier learned to discriminate the relevant and irrelevant features of a combination showed no learning impairment when this same stimulus combination was later presented after the response during a new learning problem. These results were interpreted as evidence that: (1) processes associated with learning a discrimination problem do not end with the execution of a choice response; (2) postresponse stimuli produce greater impairment in discrimination learning when they are distorted versions of the relevant stimuli; and (3) the impairment resulting from postresponse irrelevant stimuli occurs primarily when this misinformation is processed and misperceived as being relevant to learning the discrimination problem.     

Repeated acquisition and discrimination reversal in the squirrel monkey (Saimiri sciureus)

Repeated acquisition and discrimination reversal tasks are often used to examine behavioral relations of, respectively, learning and cognitive flexibility. Surprisingly, despite their frequent use in cognitive neuroscience and behavioral pharmacology, variables that control performance under these two tasks have not been widely studied. The present studies were conducted to directly investigate the controlling variables in nonhuman primates. Squirrel monkeys were trained with a touchscreen variant of the repeated acquisition task in which a novel pair of S⁺/S^? stimuli was presented daily. Subjects learned to discriminate the two stimuli (acquisition) and, subsequently, with the contingencies switched (reversal). Results indicate that rates of both acquisition and reversal learning increased across successive sessions, but that rate of reversal learning remained slower than acquisition learning, i.e., more trials were needed for mastery. Subsequent experiments showed this difference between the rate of learning novel discriminations and reversal was reliable for at least 5 days between acquisition and reversal and notwithstanding the interpolation of additional discriminations. Experimental analysis of the S⁺/S^? elements of the tasks revealed that the difference in the rate of learning could not be attributed to a relatively aversive quality of the S^? or to a relatively appetitive quality of the S⁺, but, rather, to contextual control by the S⁺/S^? stimulus complex. Thus, if either element (S⁺ or S^?) of the stimulus complex was replaced by a novel stimulus, the rate of acquisition approximated that expected with a novel stimulus pair. These results improve our understanding of fundamental features of discrimination acquisition and reversal.     

A note on further experiments on the effects of meprobamate on discrimination performance in the monkey

A previous experiment (Gross and Weiskrantz, 1961) has shown that performance on a successive auditory discrimination task is impaired by injections of meprobamate. The present two brief experiments indicate that the drug also impairs simultaneous visual discrimination performance, although not to the same degree as found earlier for auditory discrimination. The original finding, therefore, cannot be attributed simply to unique features of the auditory discrimination situation, such as the “go—no-go” response contingency. Since neither overtraining nor drug habituation appears to be of great importance, it is suggested that the lesser effect of the drug in these experiments reflects the greater stability of visual than auditory habits in the monkey.

Earlier work has shown that meprobamate and reserpine can cause a severe deterioration in auditory discrimination performance of monkeys (Gross and Weiskrantz, 1961). This result was taken as supporting a hypothesis, growing out of still earlier research, that tranquillizers decrease the utilization of sensory information (Weiskrantz and Wilson, 1956; Weiskrantz, 1957).

The auditory task, as is almost always the case with monkeys as subjects, involved a “go—no-go” type of response contingency—i.e. the animal had to respond to the positive stimulus and had not to respond to the negative stimulus in order to achieve reward. It might be objected, therefore, that the deterioration in performance was associated not with discrimination as such but with the animals' willingness to perform at all. In fact, it was found that the animals tended to make most of their errors under the drugs by responding when they should not rather than not responding when they should.

The purpose of the present experiments, therefore, was to test the animals with a visual discrimination task in which both the positive and negative stimuli were presented simultaneously. An effect of the drug could not, in this situation, be characterized simply as altering the responsiveness of the animal. A further purpose in using visual stimuli was to test the generality of the earlier finding in a sense modality other than audition.     

Serial adaptation to conflicting prismatic rearrangement effects in monkey and man.

Seven adult male squirrel monkeys adapted successfully to prisms displacing in equal and opposite directions. After protracted training under certain conditions, they succeeded in conserving adaptation to both prisms without benefit of readaptation trials. Results obtained with thirty-six undergraduates under similar conditions of test (although for a much shorter period) are also reported.     

Visual discrimination with a single manipulandum following temporal ablations in the monkey

The aim of this investigation was to determine what effect variation in the conditions of cue presentation and response availability has on the visual discrimination performance of monkeys with bilateral inferior temporal ablations. Six animals were trained on one of two versions of a test of successive brightness discrimination. Common to both versions of this test was the availability of a single lever, manipulation of which in the presence of the positive cue constituted the correct response. Performance on this test was compared with performance on a pattern discrimination, for which the customary simultaneous two-choice procedure was used. It was found that the temporal removals were followed by definite impairment on the pattern discrimination (as expected), but no consistent change in efficiency at brightness discrimination could be attributed to the lesions. Alternative interpretations, making reference to the amount of pre-operative training on the brightness discrimination or the lack of differentiation between the correct and alternative responses in this test, are discussed.     

Trying to bridge some neuropsychological gaps between monkey and man.

It is puzzling that some anatomical systems in the brains of monkeys and men appear to function quite differently although there is no established basis for this either in their fine-grained anatomical organizations or in the inherent behavioural capacities of the two species. It is suggested that in some instances the discrepancies may arise because inappropriate tests have been used with the animals, and examples are given of positive evidence for cross-modal perception and a possible experimental basis for hemispheric specialization in the monkey. In other instances, they may derive from inadequate or inappropriate methods of testing human subjects, and attention is focused on two major examples: memory disorders associated with medial temporal lobe lesions and blindness associated with occipital lesions in man. In both examples it has been generally concluded that the human deficits are far more severe and even qualitatively different from those studied in the monkey. Evidence suggests that the discrepancies may be resolved if human subjects are tested not by means of 'commentary' questions (e.g 'do you see this? or 'do you recognize this?') but by methods that depend upon forced-choice or identification procedures that are more closely related to those used with animal subjects. It is argued that the study of dissociations between a capacity and its acknowledgement by a human subject may suggest a type of brain organization that is consistent both with the engineering approach that Craik would have fostered and also with one that places older and newer brain structures in the single evolutionary framework.     

Conditional discrimination with conceptual simultaneous and successive cues in the squirrel monkey (Saimiri sciureus)

At the end of several stages of training, 4 squirrel monkeys met an 87% criterion for choosing correctly between exemplars of the concept "sameness" and the concept "difference," the simultaneous cues, as a function of having been cued by an exemplar either of the concept "triangularity" (cued sameness) or "heptagonality" (cued difference), the successive cues, which were presented in random order. In addition, the best monkey met criterion when the exemplars of sameness and difference were presented 16 s after the withdrawal of the exemplar of triangularity or heptagonality, and the other monkeys performed successfully with shorter delays. The results are discussed in terms of (a) "working memory," (b) the significance for the evolution of behavior of investigating the conceptual capacities of animals, and (c) implications for language in nonhuman animals.     

The role of attention in the preparation of visually guided eye movements in monkey and man

Summary Neurophysiological data from single cells in the monkey's visual association cortex as well as saccadic reaction time measurements in monkey and man are reported. When a monkey directs his attention to a peripheral light stimulus the visual activation of cortical cells responsive to that stimulus is increased. If visual attention is directed to a particular part of the visual field the saccadic reaction time is long (around 200 ms in monkey and above 200 ms in man). In contrast, if attention is disengaged from any location to which it might have been engaged before, monkeys and men can execute express saccades, that is, saccades after extremely short and stable reaction times (around 75 ms in monkey and 100 ms in man). The results are interpreted in the context of a hypothesis according to which the initiation of voluntary, visually guided saccades includes three premotor mechanisms: the computation of the target location, the decision to make a saccade, and the disengagement of attention.     

The luminous experience and the scientific method

An encounter with the Light during a state of altered consciousness is a direct experience of God. The question of scientific proof is discussed.Mr. Nichelson, an author and consultant, studied philosophy at Kalamazoo College and theology at Harvard Divinity School.