Discrimination and generalization by rats of temporal stimuli lasting for minutes

In three experiments, rats learned to respond differentially to reinforced and nonreinforced trials when the length of the intertrial interval (ITI) predicted the trial outcome (reinforcement or nonreinforcement). Rats in control groups, for whom the length of the ITI did not predict the outcome, did not show differential performance on nonreinforced and reinforced trials. Generalization gradients obtained following discrimination training were comparable to those obtained following discrimination training with other types of discriminative stimuli. That is, groups which had shown differential performance in discrimination training yielded generalization gradients with fastest speeds at the previously reinforced ITIs, slowest speeds at the previously nonreinforced ITIs, and intermediate speeds at ITIs of intermediate length. Control groups yielded flat gradients across all ITIs tested. These effects were shown for relative time discrimination (short time = reinforcement, long time = nonreinforcement, or the reverse) and also for an absolute time discrimination (long and short time = reinforcement, middle time = nonreinforcement or the reverse). This method was effective for time duration measured in minutes rather than seconds, as is more commonly the case.     

Evidence against visual integration across saccadic eye movements

One of the classic problems in perception concerns how we perceive a stable, continuous visual world even though we view it via a temporally discontinuous series of eye movements. Previous investigators have suggested that our perception of a stable visual environment is due to anintegrative visual buffer, a special memory store capable of fusing the visual contents of successive fixations according to their environmental coordinates. In this paper, three experiments are reported that attempted to demonstrate the existence of an integrative visual buffer. The experimental procedure required subjects to mentally fuse two halves of a dot matrix presented in the same spatial region of a display, but separated by an eye movement so that each half was viewed only during one fixation. Thus, subjects had to integrate packets of visual information that had the same environmental coordinates, but different retinal coordinates. No evidence was found in any experiment for the fusion of visual information from successive fixations in memory, leaving the status of the integrative visual buffer in serious doubt.     

Attending to different levels of structure in a visual image

Two experiments are reported in which observers had to utilize information from one of two structural levels of visual stimulus patterns (large letters composed of smaller ones). They could utilize information more rapidly form one level only at the cost of slower utilization from the other. This trade off defines an empirical attention operating characteristic (AOC) which is consistent with a simple mathematical model of the perceptual process: when viewing a stimulus, the observer selects one of two alternative “attentional” strategies, where each strategy is optimal for utilizing information from one structural level, but less than optimal for the other.     

A Social Learning Approach to Increasing Blood Donations1

A field experiment conducted in high schools throughout the country was aimed at increasing the number of high school students who donate blood. Special interventions that emphasized psychological or educational approaches to heightening motivation to donate, as well as a combined intervention, were compared with the usual approach taken at blood drives. Psychological interventions in which social learning principles (modeling, perceptions of social norms) played important roles either alone or in combination with an educational (informational) approach were more successful in stimulating blood donations than either an educational approach alone or the approaches traditionally followed by the participating local blood centers. The results demonstrated that use of social learning principles in designing interventions to strengthen socially relevant altruistic behavior could be valuable both practically and theoretically.     

Activity of wrist muscles elicited during imposed or voluntary movements about the elbow joint

To examine the coordination of muscles during multijoint movement, we compared the response of wrist muscles to perturbations about the elbow joint with their activation during a volitional elbow movement. The purpose was to test the following two predictions: (a) Responses can occur in muscles not stretched by the perturbation, as has been reported for other multijoint systems; and (b) the motor pattern in response to a perturbation mimics an opposing volitional motor pattern across the two joints. We recorded the electromyographic (EMG) activity of elbow and wrist muscles as well as the flexion/extension motions at the elbow and wrist joints during individual trials that either involved a response to a torque perturbation that extended the elbow or required volitional elbow flexion. The results of this study confirmed that responses were elicited in the nonstretched wrist muscles when the elbow joint was perturbed. The same motor sequence of elbow and wrist flexors was present for both the volitional and perturbation task (with the forearm supinated), regardless of whether the wrist joint was immobilized or freely moving. The findings suggest that the nervous system relies on the purposeful coupling of elbow and wrist flexors to counter the inertial effects during the unrestricted voluntary movement, even though the coupling does not appear to be purposeful during the perturbation or with the wrist immobilized. The coupling of elbow and wrist flexors, however, was not rigidly fixed, as evidenced by muscle onsets that adapted over repeated perturbation trials and a reversal of the wrist muscle activated (wrist extensor) when the forearm was pronated. Hence, the coupling of muscle activities can be modified quantitatively when not beneficial and can be altered qualitatively with different initial configurations of the arm.     

Teaching cotherapy: Instructional and supervisory processes

A course on cotherapy for mental health practitioners is described. The authors strongly recommend that clinicians from all disciplines be taught and trained to do cotherapy, since it is a highly effective therapeutic modality in treating individuals, families and groups.     

Manifest needs of prospective counselors: a comparative study

Mean performances of 81 prospective counselors on each of the Edwards Personal Preference Schedule (EPPS; Edwards, 1959) needs were analyzed and statistically compared with performances of elementary school counselors, other school counselors, urban college students, professional women, Roman Catholic sisters, and the 1959 EPPS norm samples. Performances of the men and women in the prospective counselor group were similar. Men had a significantly higher need for achievement and dominance, but the significance did not reach .01. Two EPPS needs, intraception and nurturance, consistently differentiated the prospective counselor group. Comparisons across samples indicated that prospective counselors were most similar to the two counseling samples and, for the female subgroup of prospective counselors, to the sample of professional women. Largest across-sample differences were found between the female prospective counselors and the Roman Catholic sisters, between the female prospective counselors and norm samples of female college students and female adults, and between the male prospective counselors and the male adult norm sample.     

Duration of visible persistence in relation to stimulus complexity.

Visible persistence refers to the phenomenal impression that a stimulus is still present after its offset. A dispute exists whether visible persistence is due to temporal sluggishness in the visual pathway (neural hypothesis) or whether it is a byproduct of information-extraction processes under cognitive control (process hypothesis). This was investigated by manipulating stimulus complexity in five temporal integration experiments and one recognition memory experiment. According to the process hypothesis, complex stimuli should persist longer than simple stimuli because they require more information extraction. This prediction was not confirmed; in all six experiments, complexity was found to have no reliable effect on the duration of visible persistence. By contrast, and in accordance with earlier findings, complexity was shown to have a significant effect on a short-lived, nonvisible form of memory known as schematic persistenc. This pattern of results supports two major conclusions: First, that the effects of complexity reported in earlier research were probably on schematic--rather than visible--persistence; and second, that visible persistence must be regarded as a residual neural trace of an extinguished stimulus, rather than as a byproduct of information-extraction processes.     

Intelligence and race: further comments on J. P. Rushton's work.

A review of some implications of J.P. Rushton's 1988 and 1990 work on racial differences in brain mass (size or weight) suggests that his comments do not constitute a viable scientific theory.