Effects of relative reinforcer frequency on complex color detection

Pigeons were trained under a discrete-trials detection procedure in which one of a set of color stimuli was presented on the center key and a single response turned off the stimulus and illuminated two side keys. Single responses to one or the other side key produced occasional reinforcers depending on the value of the color stimulus. In Experiment 1, one color-stimulus set comprised 559, 564, 569, and 574 nm, and right-key pecks were occasionally reinforced following presentations of members of this set. The other stimulus set comprised 579, 584, 589, and 594 nm, and left-key pecks were occasionally reinforced following presentations of members of this set. Across seven experimental conditions, the left/(left + right) relative reinforcer frequency was varied from .1 to .9. In Experiment 2, one stimulus set contained only one member, 574 nm, and right-key responses were occasionally reinforced following its presentation. Over 12 experimental conditions, two manipulations were carried out. First, the number of stimuli comprising the other stimulus set was increased from one (579 nm) to two (579 and 584 nm) to three (579, 584, and 589 nm) and to four (579, 584, 589, and 594 nm), and left-key responses were reinforced occasionally following center-key presentations of members of this set. Second, for each stimulus combination, the left/(left + right) relative reinforcer frequency was varied from .1 to .5 to .9 across three experimental conditions. The principal finding of Experiments 1 and 2 was that reinforcers and stimuli interacted in their effects on behavior. In Experiment 3, pairs of adjacent stimuli (5 nm apart) in the range 559 to 594 nm were presented in each experimental condition, and the left/(left + right) relative reinforcer frequency was held constant at .5. The data from all three experiments were analyzed according to a detection model describing performance in multiple-stimulus two-response procedures. This model provided independent measures of stimulus discriminability, contingency discriminability, and bias. The analysis showed that (a) consistent with the color-naming function, pigeons were better able to discriminate between higher nanometer values than lower nanometer values; (b) their ability to discriminate between the stimuli was independent of the number of wavelengths comprising each stimulus set; (c) they allocated delivered reinforcers very accurately to the previously emitted response; and (d) no consistent biases emerged.     

Algorithmic shaping and misbehavior in the acquisition of token deposit by rats

In two experiments, rats were trained to deposit ball bearings down a hole in the floor, using an algorithmic version of shaping. The experimenter coded responses expected to be precursors of the target response, ball bearing deposit; a computer program reinforced these responses, or not, according to an algorithm that mimicked the processes thought to occur in conventional shaping. In the first experiment, 8 of 10 rats were successfully shaped; in the second, 5 of 5 were successfully shaped, and the median number of sessions required was the same as for a control group trained using conventional shaping. In both experiments, “misbehavior,” that is, excessive handling and chewing of the ball bearings, was observed, and when the algorithmic shaping procedure was used, misbehavior could be shown to occur in spite of reduced reinforcement for the responses involved.     

Visually guided catching and tracking skills in pigeons: A preliminary analysis

Research on reaching, tracking, and catching in the pigeon has been hampered by limitations of technology. A new system was developed in which the target was a small rectangle presented on a video display terminal and the pecking response was detected with touch technology. The target moved up and down vertically with sinusoidal velocity. A coincidence between the location of the pigeon's beak and the cursor produced reinforcement. The pigeon pecked ahead and behind the target, but most pecks occurred behind the target so the dominant tracking strategy was lagging. The pigeon was adept at “catching” the target at many locations throughout the trajectory. Transfer of motor learning was tested on probe trials during which the trajectory changed from vertical to horizontal. On transfer trials the pigeons' dominant pattern of pecking immediately shifted from vertical to horizontal. The motor skill displayed by the pigeons was flexible and adaptive, suggesting that the pigeons had learned to track the cursor.     

Functional classes and equivalence relations

Three adult subjects were taught a set of two-choice simultaneous discriminations, with three positive and three negative stimuli; all possible combinations of positive and negative stimuli yielded nine different pairs. The discriminations were repeatedly reversed and rereversed, the former positive stimuli becoming negative and the former negative stimuli becoming positive. With all subjects, a reversal of the contingencies for one pair of stimuli became sufficient to change their responses to all of the other pairs. The reversals had produced functional stimulus classes. Then, all subjects showed conditional discriminations emerging between members of a functional class; given a sample from one class and comparisons from both classes, they selected the comparison that was in the same class as the sample. Next, 2 of the subjects showed that the within-class conditional relations possessed the symmetric and transitive properties of equivalence relations; after having been taught to relate new stimuli to existing class members, the subjects then matched other class members to the new stimuli. Subsequent tests of two-choice discriminations showed that the conditional discriminations had transferred functional class membership to the new stimuli. The 3rd subject, who did not show equivalence relations among functional class members, was also found to have lost the within-class conditional relations after the equivalence tests.     

Visual fixation and postural sway in children

Adults are able to use a visual target to reduce quiet-standing postural sway (Lee & Lishman, 1975). The present study was designed to determine whether children, under varying postural conditions, are also able to use a visual target to reduce postural sway. A second purpose was to determine the ability of children to visually fixate under different postural conditions. An inability to visually fixate may limit the usefulness of a visual target. The results indicate that, like adults, children are able to reduce sway in the presence of a visual target. Young children are less able than older children and adults to visually fixate. In addition, children show more spontaneous visual saccades in the no-target condition than in the target condition and more saccades in the Romberg stance than in a feet-together stance. The fact that saccades decrease with increasing age, even in the seated, head-stabilized condition, precludes the possibility that increased instability of the young children is the only cause of increased number of saccades.     

The child's perceptions of familial relationships: convergence between two assessment techniques

Children's (N = 28) perceptions of familial relationships were investigated with the Family Environment Scale (FES) and the Network of Relationships Inventory (NRI). The FES assesses overall impressions of the family, and the NRI measures perceptions of individual relationships. Because current family systems theory indicates that positive individual relationships within a dyad (e.g., child-mother) should be related to an overall favorable impression of the family system, we hypothesized that these two instruments should demonstrate convergence on selected dimensions. Results indicated that positive or negative relationships with an individual family member were related to how the child perceived the overall family system, supporting our hypothesis.     

On task and theory specificity

One of the significant limitations of the motor control and skill acquisition domain is that the theories, models, and hypotheses are, in most cases, task specific. Many lines of theorizing fail to hold up under even small changes in task constraints, although clearly the field does have some robust phenomena. It is proposed that a broader consideration of the role of task constraints, which is grounded in the methodology of nonlinear dynamics, may help to formulate a more general action theory of coordination and control.     

Autobiographical memory in a case of multiple personality disorder

Previous research on multiple personality disorder (MPD) has been concerned with between-personalities amnesia, and little attention has been paid to within-personality memory function. This study examined the autobiographical memory of a multiple personality patient, I.C., with cueing procedures that have proven useful in previous studies of normal and abnormal memory. Results indicated that I.C. was able to retrieve autobiographical episodes from the recent past, although her performance differed in several respects from that of matched controls. The study also revealed a striking deficit in I.C.'s autobiographical memory for childhood: She was unable to recall a single episode from prior to the age of 10 in response to various retrieval cues, whereas control subjects had no difficulty recalling numerous childhood episodes. This phenomenon of extended childhood amnesia has not been reported previously in studies of MPD.     

Hypnosis, suggestion, and placebo in the reduction of experimental pain

Two experiments compared placebo and hypnotic analgesia in high and low hypnotizable subjects. Experiment 1 demonstrated that hypnotic and placebo analgesia were equally ineffective in low hypnotizables, but that hypnotic analgesia was much more effective than placebo analgesia in high hypnotizables. Experiment 2 replicated these results, but also included low and high hypnotizables who were given a nonhypnotic suggestion for analgesia. Both the low and high hypnotizables in this group reported greater suggested than placebo analgesia and as much suggested analgesia as high hypnotizable hypnotic subjects. Both experiments found substantial discrepancies between the amount of pain reduction subjects expected from the various treatments and the amount of pain reduction they actually reported following exposure to those treatments. In Experiment 2, subjects in all treatments who reduced reported pain engaged in more cognitive coping and less catastrophizing than those who did not reduce pain. Theoretical implications are discussed.     

Probability of relapse after recovery from an episode of depression

Examined relapse rates in those individuals who have experienced an episode of unipolar depression as a function of the number of previous episodes, gender, age at onset of the episode (less than 40 vs. greater than 40), time since a previous episode, and depression level at time of interview. From of 6,742 participants, 2,046 were interviewed; of these, 1,130 had at least one, 513 reported a second and 173 reported a third episode. The probability for relapse was positively related to number of previous episodes, being female, depression level at time of interview, but not to age at onset (less than 40 vs. greater than 40). Women were also more likely to have more severe episodes. Participants with elevated depression symptoms reported a greater number of previous episodes. Following the first episode, there was a decline in hazard rate for men but not women; following the second episode, there was no change in vulnerability for men; for women, the results were ambiguous.