Stress management: Approaches and interventions

The different approaches, possible interventions and subsequent evaluation problems related to stress management and counselling are discussed in relation to the other symposium papers.     

Effects of methylphenidate (Ritalin) on information processing in hyperactive children

The effect of methylphenidate on information-processing efficiency was studied in 12 hyperactive, nonretarded children. Performance on six efficiency tasks (Posner Letter Matching, Reaction Time, Memory Search, Category Verification, Item Identification, and Word-Span) and a general measure of on-task behavior were compared for children receiving methylphenidate or a placebo. The median drug dosage was .38 mg/kg, and it was ingested 1 1/2 hours prior to testing. Children blind to the drug-placebo condition were tested on 4 days. In general, methylphenidate-related improvements in attention to on-task behaviors were found. An overall analysis of processing speed suggested that methylphenidate improved efficiency. Methylphenidate significantly decreased reaction times to simple and complex stimulus arrays; differences due to the drug remained even when on-task attentive behaviors were statistically removed. Significantly fewer identification errors occurred on the Posner task in the methylphenidate condition. Results indicated that methylphenidate improved general attentional behaviors and positively influenced processes that define perceptual efficiency.The first author was supported by NIH Training Grant No. HD 07184. We appreciate the assistance of Dr. Robert Sweeney in carrying out this research and the useful comments of Ellen B. Ryan and Jeanne D. Day.     

Measuring the effect of multiple eye fixations on memory for visual attributes

Because of limited peripheral vision, many visual tasks depend on multiple eye fixations. Good performance in such tasks demonstrates that some memory must survive from one fixation to the next. One factor that must influence performance is the degree to which multiple eye fixations interfere with the critical memories. In the present study, the amount of interference was measured by comparing visual discriminations based on multiple fixations to visual discriminations based on a single fixation. The procedure resembled partial report, but used a discrimination measure. In the prototype study, two lines were presented, followed by a single line and a cue. The cue pointed toward one of the positions of the first two lines. Observers were required to judge if the single line in the second display was longer or shorter than the cued line of the first display. These judgments were used to estimate a length threshold. The critical manipulation was to instruct observers either to maintain fixation between the lines of the first display or to fixate each line in sequence. The results showed an advantage for multiple fixations despite the intervening eye movements. In fact, thresholds for the multiple-fixation condition were nearly as good as those in a control condition where the lines were foveally viewed without eye movements. Thus, eye movements had little or no interfering effect in this task. Additional studies generalized the procedure and the stimuli. In conclusion, information about a variety of size and shape attributes was remembered with essentially no interference across eye fixations.     

Common region: a new principle of perceptual grouping.

A new principle of grouping is proposed that is based on elements being located within a common region of space. Demonstrations analogous to Wertheimer's original displays show that this factor strongly influences perceived grouping and is capable of overcoming the effects of other powerful grouping factors such as proximity and similarity. Grouping by common region is further shown to depend on perceived depth relations, indicating that it is influenced by processes that occur after at least some depth perception has been achieved. Further demonstrations suggest that it is dominated by the smallest background area and that it can follow a hierarchical embedding scheme. It is argued that common region cannot be reduced to the effects of proximity, closure, or any other previously known factor and therefore constitutes a genuinely new principle of grouping.     

Color, consciousness, and the isomorphism constraint

The relations among consciousness, brain behavior, and scientific explanation are explored in the domain of color perception. Current scientific knowledge about color similarity, color composition, dimensional structure, unique colors, and color categories is used to assess Locke's "inverted spectrum argument" about the undetectability of color transformations. A symmetry analysis of color space shows that the literal interpretation of this argument--reversing the experience of a rainbow--would not work. Three other color to color transformations might work, however, depending on the relevance of certain color categories. The approach is then generalized to examine behavioral detection of arbitrary differences in color experiences, leading to the formulation of a principled distinction, called the "isomorphism constraint," between what can and cannot be determined about the nature of color experience by objective behavioral means. Finally, the prospects for achieving a biologically based explanation of color experience below the level of isomorphism are considered in light of the limitations of behavioral methods. Within-subject designs using biological interventions hold the greatest promise for scientific progress on consciousness, but objective knowledge of another person's experience appears impossible. The implications of these arguments for functionalism are discussed.     

Truth, Sense and Reference

Books reviewed in this essay:
Wolfgang Carl, Frege's Theory of Sense and Reference: Its Scope and its Origins
William P. Alston, A Realist Conception of Truth     

Identification of gender in domestic-cat faces with and without training: perceptual learning of a natural categorization task

Three experiments were conducted to determine whether human observers could identify the gender of 40 domestic cats (20 female, 20 male) depicted in individual color photographs. In experiment 1a, observers performed at chance for photographs depicting whole cats, cat heads (bodies occluded), and cat bodies (heads occluded). Experiment 1b showed that chance performance was also obtained when the photographs were full-face close-ups of the cats. Experiment 2a revealed that even with gender-identification training on 30 (15 female, 15 male) of the 40 face close-ups, observers were unable to generalize their training to reliably identify the gender of the 10 remaining test faces (5 female, 5 male). However, experiment 2b showed that gender-identification training with the 14 most accurately identified faces from experiment 1b (7 female, 7 male) was successful in raising gender identification of the 10 test faces above chance. Experiments 3a and 3b extended this facilitative effect of gender-identification training to a population of animal-care workers. The findings indicate that, with appropriate training, human observers can identify the gender of cat faces at an above-chance level. A perceptual category learning account emphasizing the on-line formation of differentiated male versus female prototypes during training is offered as an explanation of the findings.     

Memory for objects and parts

Performance on whole comparisons of two whole objects was compared to that for partial comparisons of a whole object and a part. In particular,same-different comparisons were measured for sequential displays of two-dimensional line figures. The comparisons were analogous to those in the word priority paradigm (Johnson, 1975). The whole comparisons were found to be more accurate and faster than the partial comparisons. This whole advantage was also found for accuracy using a two-alternative forced-choice procedure. This effect was found for brief displays of a single object and for longer duration displays of two objects. It was also found for three different sets of line figures. In contrast, the whole advantage was not found for unconnected figures. These findings were interpreted in the context of hierarchical representations of objects and parts.