A discrimination based on punishment

Twelve white rats learned to press a bar or lever when this act was intermittently followed by pellets of food. Once a stable rate of pressing had been established, the animals were subjected to electric shock as a punishment for each response during alternate five minute periods within the experimental session. A difference in rates during the safe and punished phases was manifested both by the experimental group (8 rats), who were provided with a light as a signal when it was safe to respond, and also, contrary to expectation, by the control group (4 rats), who continued in darkness throughout the session. The differential responding by the control group was greatly reduced, however, when the duration of each phase was reduced from five minutes to one.

The investigation was then continued to determine the role of some of the other factors in the situation. Increasing the severity of the shock increased the difference between the light and the dark rates. Withholding the pellets of food reduced the overall rates but did not affect the light-dark discrimination. Withholding the shock, on the other hand, permitted an increase in rate and caused the animals to lose their discrimination; when food had previously been withheld, however, so that the rate of response was relatively low, this deterioration in the discrimination was not as rapid as before. Restoration of the discrimination training under a lower hunger drive confirmed the finding that the formation of the discrimination was quite rapid and showed that the level of drive did not affect the proportionality between the rates in the light and in the darkness. These findings were interpreted by comparing the current procedure with those previously used in studies of avoidance reactions and conflict.     

The influence of positive and negative reinforcement on selective attention in the rat

In Experiments 1 and 2 rats were trained under two multiple schedules of reinforcement. In one, bar pressing during a tone-light compound stimulus was reinforced under a variable-interval food reinforcement schedule. In the other multiple schedule, bar pressing avoided grid shock on a free-operant schedule. In both multiple schedules, a discrimination was maintained by an extinction schedule that was operative during the absence of the tone-light compound. In Experiments 1 and 2 the intensity of the tone-light compound was manipulated over three levels. Subsequent extinction tests revealed that light was attended to, almost exclusively of the tone, when food reinforcement had maintained bar pressing. On the other hand, the tone gained considerable attentional control under the shock avoidance schedule. This stimulus-reinforcer interaction was maintained for all three levels of the compound intensity. In Experiment 3 it was investigated whether this interaction was associative by presenting shock during the absence of the tone-light compound when food reinforcement maintained responding, and food during the absence of the compound when shock avoidance maintained responding. Since both food and shock were presented during a single session for both schedules, nonassociative effects of the reinforcing stimuli were equivalent across the schedules. Nevertheless, the stimulus-reinforcer interaction was maintained, indicating that the interaction was an associative effect.     

The effects of electroconvulsive shock on the action of a reinforcing stimulus

Three experiments sought to evaluate the effect of electroconvulsive shock on the action of a reinforcing stimulus. In all experiments behavior was maintained on a 2 min variable interval schedule for food reinforcement. Foot shock at the termination of a buzzer stimulus served as the reinforcing stimulus for conditioned suppression during the ensuing buzzer interval. Omission of foot shock at the termination of the buzzer stimulus was followed by normal responding (no conditioned suppression) during the next buzzer interval. In Exp I electroconvulsive shock followed foot shock at varying time intervals. In the first subsidiary experiment electroconvulsive shock followed an unreinforced buzzer stimulus at varying time intervals. In the second subsidiary experiment electroconvulsive shock followed foot shock at varying time intervals and an additional buzzer stimulus was sounded between the termination of foot shock and the onset of electroconvulsive shock. These three experiments demonstrated that electroconvulsive shock invariably abolished the effects of the reinforcing stimulus if it followed conditioning by no more than 10.0 sec and never had an effect if it followed conditioning by 12.5 sec or more; electroconvulsive shock was not acting as a reinforcing stimulus in this situation.     

Chaining and secondary reinforcement based on escape from shock

Three white rats were trained to press a bar while being shocked. This produced a white noise. After 30 sec they were allowed to terminate both the shock and the noise by nosing a pigeon key. Comparison of the rates of pressing before and after the onset of the noise indicated that the noise itself was the immediate reinforcing agent for pressing. Furthermore, control tests showed that pressing was maintained only if it produced the noise: either omission of the noise or elimination of the dependency of the noise on the occurrence of the response led to a gradual abolition of pressing. When automatic termination of the shock was substituted for the key nosing requirement, however, only the key nosing extinguished. This indicated that the effectiveness of the noise as a reinforcer did not depend on its status as a discriminative stimulus for some other form of operant behavior.     

Producing either positive or negative tendencies to a stimulus associated with shock

A technique is described in which rats are pretrained with reinforcement to bar press. Each bar press was associated with a tone. This tone was later paired with one of two aspects of an electric shock, either at the onset or at the end of the shock, in a situation in which the shock is inescapable. These animals were retested in the operant situation under conditions of extinction, but with tone present as a conditioned reinforcer. The finding was that animals for which the tone was associated with shock onset extinguished quickly, whereas animals for which the tone was paired with shock termination extinguished more slowly.     

Studies in olfactory acuity. I: Measurement of olfactory thresholds in the rat

The capacity of the rat to respond to olfactory cues has been studied in three experimental situations: (i) an elevated Y-maze, (ii) a rectangular choice apparatus in which extraneous environmental cues were present, and (iii) a circular choice apparatus from which such cues were either excluded or randomized.

No rat showed any sign of learning on the Y-maze even after extensive training and the application of electric shock as deterrent for error.

Some rats succeeded in performing an olfactory discrimination in the rectangular choice apparatus but learning was retarded, and in some cases inhibited, by the counter-influence of non-olfactory factors.

All rats readily learned an identical discrimination when shielded from such cues in the circular choice apparatus which provides a satisfactory medium both for training and for the study of olfactory acuity.

Differences in the behaviour of rats on these three types of apparatus suggest first, that the formation of learned habits based on olfaction depends on the close contiguity of stimulus and reward, and second that the sense of smell possesses weak orientating properties by comparison with those exerted by other modalities. The findings thus help to explain differences in the ease or di+culty uith which olfactory discriminations have been established by earlier workers.     

The timing of bar-pressing behaviour

The time spent by a rat in a bar-pressing situation is made up of active time spent n pressing, eating time, and extra time spent in other activities. With a well trained rat, active time and extra time are small, and eating time mainly determines the rate of reward delivery. Active time is affected by a change of weight on the bar, the time between reward deliveries is affected by the amount of reward, and the extra time is affected by extinction conditions.

There is not a one-to-one correspondence between periods of activity at the knob and rewards.

The term “response” and some variables based on it are given empirical referents, which show that much research and theorizing on bar-pressing behaviour has been concerned with only a small selection of the rat's bar-pressing activities. Some reasons for this restriction are the use of the simple weighted bar, the lack of a rationale for bar-pressing research, and the practice of not watching the rat during an experiment.     

Relationship of motivation and method of testing to distribution of practice phenomena in rotary pursuit

Women college students (N = 120) practised 60 r.p.m. rotary pursuit for 12 minutes, rested for approximately 25 minutes and then practised for 12 minutes more. During the initial period, thirty-six 20-second trials were given, 20 subjects each practising with intertrial rests of o seconds, 20 seconds, 50 seconds, 2 minutes and 5 minutes. In the 12-minute post-rest or testing period, 10 subjects in each of these groups practised continuously, and 10 were given 20-second trials separated by 5-minute rests.

Greater distribution was found to lead to better performance in the initial period, except that the 5-minute inter-trial-rest group did not perform as well as the 2-minute group.

The warm-up decrement was dependent on the degree of distribution of practice in the initial period, being greater with greater massing of trials. As measured by the backward-extrapolation method, less was shown when testing practice was continuous than when it was distributed.

The temporary work decrement was far greater in magnitude than the permanent work decrement. If permanent work decrement was present at all, it was small in magnitude; approximately one-half was due to the conditions under which it was tested for, rather than to the degree of distribution in the initial stages of practice.     

Strength duration curves for elegtrical stimulation of the human eye

Baumgardt's surprising report of a minimum at about 30 milliseconds in the strength-duration curve for electrical stimulation of the human eye is confirmed. Arguments are presented against his explanation of the phenomenon.

An alternative hypothesis is developed: that the complex strength-duration curve is due to the interaction of on and off processes, which are separately excited by the make and break of the current: that these processes summate when separated by 30 milliseconds but are mutually inhibitory at 70 milliseconds: that these processes are the same as those known to be aroused by light. Two new experiments are designed to test this hypothesis, and the predicted result has been obtained from each.

Experiments are devised which show that the site of stimulation is the retina.

The accuracy of the method is discussed. Over the range 10 to 100 milliseconds distortion is found to be small. For shorter pulses distortion is to be expected in all cases, and it is suggested that the chronaxie is an expression merely of the condenser effect of the tissues. The use of this term should be discontinued in connection with stimulation through the skin.

Some parallels between these results and brightness comparison experiments with light are pointed out. The nature and location of the interaction is discussed.     

Contextual conditional discriminations

Three experiments used a discriminated operant procedure to study conditional discrimination learning in rats. The first experiment showed that rats were capable of learning a biconditional discrimination in which two contexts served as conditional cues signalling the reinforcement contingencies associated with two discriminative stimuli. The discrimination was learned equally well when one discriminative stimulus signalled food, the other its absence, and when one stimulus signalled food, the other extinction plus mild footshock.

In Experiment 2 it was shown that prior training on such a conditional discrimination enhanced the subsequent context specificity of simple conditioning relative to control groups of animals for whom the prior training had not been conditional. Experiment 3 showed that a reversal of the significance of one pair of discriminative stimuli produced no spontaneous reversal in performance to a second, target, pair.

The pattern of results is best accounted for by an analysis of contextual conditional discrimination learning in terms of stimulus configurations and offers no support for the notion that rats may learn a general conditional rule or set.     

A conditioned reinforcer maintained by temporal association with the termination of shock

Two experiments were conducted to determine whether a stimulus can be established as a positive conditioned reinforcer by associating it with the termination of shock, but without training the animal to make any response in its presence. In the first, six rats were conditioned to press a bar to terminate shock on a variable ratio schedule; white noise was then substituted as the immediate consequence, with the shock terminating 30 sec after the last press in its presence. It was found that the rate of pressing in the absence of noise depended on the contingency between the pressing and the noise. The second experiment sought to determine whether the difference in rates before and after the onset of the noise was due to the reinforcement of prior responding by the onset of the noise or to the suppression of subsequent responding by differential reinforcement of competing behavior. Six more rats were trained in the same manner, but with shock terminating 30 sec after the onset of the noise, regardless of what the animal did in its presence. Again the rate was higher before the onset of the noise, indicating that pressing was indeed maintained by the noise as a conditioned reinforcer.     

Physiological drives investigated by means of injections into the cerebral ventricles of the rat

A technique is described for permanently implanting a cannula in the lateral ventricle of the rat, and the effects on certain physiological drives of various substances injected by this route were investigated.

Food intake was significantly reduced by intraventricular glucose, while intra-ventricular fructose, insulin, glucagon and a lipid-mobilizing agent were without effect. Drinking was elicited by hypertonic saline and suppressed by hypotonic solutions. The intake of salt was not effected by intraventricular low-sodium solutions. Intraventricular procaine, but not alcohol, induced an akinetic state. Intraventricular glucose failed to relieve hypoglycaemic coma.

The significance of some of these findings is discussed in relation to the hypothalamic regulation of hunger.     

Food-avoidance in hungry pigeons, and other perplexities

Twenty-three pigeons were subjected to a series of procedures in which the key-peck's effects ranged from immediate, differential food reinforcement, through delayed reinforcement, the production of stimulus changes with and without probable secondary reinforcement, the prevention of food presentation ("food-avoidance"), to extinction. Neither primary nor secondary food reinforcement appeared to be essential for the maintenance or acquisition of key pecking. The food-avoidance contingency failed to suppress responding in any subject. Only complete extinction, when pecking produced neither food nor stimulus changes, eliminated all pecking for most subjects. A combination of stimulus-change reinforcement and food reinforcement appeared to account for the results, but only if it could be assumed that the presence of food in a procedure enhanced the reinforcing power of stimulus change, whether or not the food was also dependent upon responding. Such an interaction between reinforcers may be involved in the phenomenon of autoshaping.     

Reaction times for simple shape discriminations requiring one or both visual cortices

Reaction times for a simple two-choice shape discrimination requiring either one or both visual cortices were measured.

In a total reaction time of around 400 millisec. the difference found was 3.0 ± 2.6 millisec. If subjects were weighted according to number of observations, and -- 1.34 ± 1.68 millisec. if thery were weighted according to reciprocals of variances of differences of means; that is, it was not significant.     

Programme for experiments on thinking

In remembering, items are used in the form in which they are alleged to have been perceived at some time in the past. In thinking, however, evidence is given and the essential character of the process is to move beyond this evidence, but in line with it, to something for which so far, no exact or complete perceptual basis is claimed.

From an experimental point of view the best approach is to consider thinking as a high level skill, and to design experiments in the light of what has been discovered during recent years about the learning, practice and achievements of skill on a psycho-motor level.

When this is done, it turns out that the thinking process can usefully be considered as one in which gaps are filled up in accord with specific evidence provided. The fundamental gap-filling processes are either of interpolation or of extrapolation.

In the present paper the methodology proposed is developed and illustrated in a preliminary manner.     

Dichoptic induction of Mccollough-type effects

If left-oblique and right-oblique black/white gratings are presented alternately to one eye, and unpatterned red and green fields are presented alternately to the other, orientation-sensitive chromatic after-effects are induced. With the colour-stimulated eye the hue usually seen on a test grating is complementary to that originally paired with its orientation, with the pattern-stimulated eye the hue is the same as that originally paired.

The experiments reported here show that: (a) the time course of decay of these chromatic after-effects (for each eye) fits approximately the same power law as that found for the normal McCollough effect; (b) analogous chromatic after-effects, opposite in the two eyes, can be dichoptically induced using pairs of stimuli other than gratings, such as dot patterns differing in magnification.

These results suggest that strongly coloured light in one eye can induce a weakly complementary bias in the colour-signalling system of the other eye, at a level peripheral to the site of the McCollough-type adaptation.     

Subjective assessments of firmness: The use of a rating scale

An experiment was carried out to investigate the extent to which an absolute standard for firmness could be held independently of variations occurring within the samples being judged.

Although the method gave good results as a whole, it was found that, when correlating the ratings to the objective measurements, the absolute standards were not held independently of the average firmness of the groups being judged. In practice, if a certain sample was judged, within a “soft” series of samples, it would be rated as being firmer than when it was judged among “firm” samples. Certain differences in the effects of these changes were related to the nature of the subjects' previous experience.

When the results were considered on a relative comparison basis, it was found that a much lower threshold was achieved than had previously been obtained with judgments for springs using paired comparison methods. There were certain trends in the levels of discrimination with time. These trends are discussed.

The strength of grip of the subjects bore some relation to their initial rating values, but apparently was not related to their level of discrimination. Subjects who were able to exert a more constant pressure throughout the test did not seem to be any better at discriminating than were others.

Ratings made for a single sample two months after the main experiment were very similar to those previously given for the same sample.     

Asymmetry of perception of size between the right and left hands in normal subjects

A method of measuring the perception of size in the hands was applied to 4 0 righthanded and 40 left-handed normal subjects.

It was found that objects of equal size held simultaneously in each hand tend t o be judged to be unequal, and that, in the majority of subjects, the object held in the doniinant hand is perceived to be the smaller.

These results are discussed in the light of previous work, and some reference is made to the examination of pathological cases.     

The imaginaiy questionnaire

The experiment was designed to throw some light on the statistical problems in the analysis of questionnaire data. Previous work (unpublished) suggested that a simple choice response was partially determined by previous responses; and also that the nature of the determination was changed with changing length of series. A “null” experiment was devised in the form of a questionnaire without any questions, and the distribution of responses was studied with respect to the problems formulated.

The observations are discussed in three sections.

In the statistical discussion an alternative meaning to overall association or dissociation is advanced. This: relates association or dissociation to human behaviour in the serial response situation, rather than to qualities of the questionnaire. It is further suggested that association between specific, questions should be tested against the association in the whole questionnaire, and an appropriate treatment is indicated.

The observations depart from statistical randomness in certain ways. Answers made up almost entirely of one form of response are given less often than would be expected. Long sequences of the same type of response are relatively infrequent, and sequences of alternation of response are also rare. As the material is “null” it implies that the human concept of randomness differs from the statistical concept.

An attempt is made to define the human concept of randomness. It appears that a series of responses which has a pattern, or for which the subject can postulate a simple “cause” will not be accepted as random by the human subject. This raises problems of a perceptual and cognitive nature. It also has a bearing on the design of questionnaires. or experiments involving serial responses.     

Selective noise disturbance of the information input in short-term memory

The present experiment was designed in order to investigate the effects of noise produced intermittently during the input stage of serially displayed visual materials (6-digit lists). These materials were to be memorized and subsequently reproduced on a specially designed keyboard. The four experimental conditions were the following: (1) quiet (Q);

(2) noise uninterrupted during the presentation of each list (CN);

(3) noise emitted simultaneously with each list element (500 ms) (ND);

(4) noise emitted in the interval (140 ms) between each element (NA).

Record was taken of the errors and omissions, of key response initiating times and of hand movement times. As an additional variable, subjects were required to estimate the annoyance induced by each of the four conditions. All noise conditions yielded more errors and omissions than the Q-condition, with the highest rates occurring in the two conditions where noise was superimposed on the digits. Close analysis of the errors showed that the primacy end of the lists was the most affected by noise, whereas keying speed for correct reproductions remained relatively unaffected.

On the other hand, when the speed variable was split into a decision and a motor component, it turned out that the more a condition was judged as annoying, the more the time for response decision was delayed, while the reverse occurred for keying movement times. The latter effect could possibly be ascribed to arousal induced by the three noise conditions. It is argued that noise is liable to affect differently the various components of a task performance, either directly by interference with the intake of pertinent information, or indirectly through induced annoyance or through noise modulated arousal.

They particularly would like to thank Dr M. Coltheart for his great help in the preparation of the definitive version of the paper.