Evidence for an error deadzone in compensatory tracking

Humans and monkeys show intermittent arm movements while tracking moving targets. This intermittency has been explained by postulating either a psychological refractory period after each movement and/or an error deadzone, an area surrounding the target within which movements are not initiated. We present a technique to detect and quantify the size of this deadzone, using a compensatory tracking paradigm that distinguishes it from a psychological refractory period. An artificial deadzone of variable size was added around a visual target displayed on a computer screen. While the subject was within this area, he received visual feedback that showed him to be directly on target. The presence of this artificial deadzone could affect tracking performance only if it exceeded the size of his intrinsic deadzone. Therefore, the size of artificial deadzone at which performance began to be affected revealed the size of the intrinsic deadzone. Measured at the subjects' eye, the deadzone was found to vary between 0.06 and 0.38 degrees, depending on the tracking task and viewing conditions; on the screen, this range was 1.3 mm to 3.3 mm. It increased with increasing speed of the target, with increasing viewing distance, and when the amplitude of the movement required was reduced. However, the deadzone size was not significantly correlated with the subjects' level of performance. We conclude that an intrinsic deadzone exists during compensatory tracking, and we suggest that its size is set by a cognitive process not simply related to the difficulty of the tracking task.     

Backward walking: a simple reversal of forward walking?

The purpose of this study was to determine whether backward walking represented a simple temporal reversal of forward walking and, hence, could be controlled by a reversed cycling of the same group of neurons. Electromyographic (EMG), joint angle, joint moment, and joint muscle power patterns were compared for forward and backward walking, in 6 subjects. The joint angle patterns with the time-base of the backward walking reversed were similar, with the exception of the ankle. The moment patterns were similar except for the knee, whereas the joint muscle powers were almost reversed-polarity images of each other. This suggests that somewhat similar muscle activation patterns could be used to produce both modes of locomotion, but the temporal cycling of muscle contraction would be reversed: Concentric muscle activity in forward walking would become eccentric activity in backward walking, and visa versa. The EMG results generally supported these findings.     

Measuring gender differences: The expressive dimension and critique of androgyny scales

This paper calls for a new approach to the measurement of gender similarities and differences in personality. Critiques of current measures that are based on the measurement of stereotypical masculinity and femininity are reviewed, and an alternative measure is presented. It avoids many of the problems in the other scales by measuring expressiveness and instrumentality in such a way that they are not confounded with variables such as independence or autonomy. Results with this measure in five different samples are presented. These confirm our theoretical definitions of expressiveness and instrumentality, and suggest that only the expressive or relational dimension consistently differentiates samples of women and men.We thank Mary Rothbart for her insightful and constructive comments on an earlier draft; Leisha Sanders, Marcia DeCaro, Vickie Van Nortwick, and Lyn Cogswell for their clerical assistance; the Center for the Study of Women in Society for financial support; and Liza Kuecker and Patricia Gwartney-Gibbs for providing data used in the analysis. An earlier version of this paper was presented at the 1984 annual meeting of the Pacific Sociological Association.     

STIMULUS (INSTRUCTIONAL) FADING DURING EXTINCTION OF SELF-INJURIOUS ESCAPE BEHAVIOR

Three individuals with developmental disabilities were exposed to a series of assessment conditions to identify the source of reinforcement for their self-injurious behavior. In each case, self-injury occurred most often in instructional (demand) situations containing a brief time-out from the task contingent on self-injury, indicating that the behavior was an escape response (i.e., maintained by negative reinforcement). Treatment was implemented in a multiple baseline across subjects design and consisted of extinction (prevention of escape) plus instructional fading (initial elimination of instructions followed by their gradual reintroduction). Results showed that the combined treatment produced immediate and large reductions in self-injury that were maintained as the frequency of instructions was increased across sessions to match the original baseline rate of presentation. Results of a component analysis conducted with 1 subject suggested that stimulus fading accelerated the behavior-reducing effects of extinction.     

Extensionality, underdetermination and indeterminacy

I am grateful to Burton Dreben, Warren Goldfarb, Don Gustafson, Jim Higginbotham, Jerrold Katz, Joe Levine, Ted Morris, Nick Pappas, Hilary Putnam, Georges Rey and Bob Richardson for helpful discussions and comments on the issues discussed in this paper. Also I thank an anonymous reviewer for Erkenntnis for helpful comments.     

Comparison of the factors influencing interviewer hiring decisions for applicants with and those without disabilities

Two studies present an examination of the factors that influence hiring decisions for applicants with, and those without, disabilities in the employment interview. In Study 1, an integrative conceptual model of interviewer hiring decisions was proposed and tested in a field sample of applicants with disabilities. Interviewers provided ratings for 70 unstructured interviews with disabled applicants. Study 2 examined the fit of the model in an independent field sample of interviews with fully-able applicants (n=165). Results supported the model among both groups of applicants. Implications and recommendations for future research are discussed.This paper has been improved greatly through the suggestions of John Binning, Michael Campion, Robert L. Dipboye, Miles Patterson, and Mark Tubbs, and Lisa Brady and Jennifer Malatesta. Study 1 was partially funded by a grant from the U.S. Office of Special Education and Rehabilitative Services to the Wright State University Office of Disability Services (Theodore L. Hayes, co-Principal Investigator).     

Judging a book by its cover: Interpretative effects of content on problem-solving transfer

We examine how cover stories of isomorphic problems affect transfer. Existing models posit that people retain content in problem representations and that similarities and differences between the “undeleted” cover stories might interfere with recognition of structural similarities.We propose that cover stories can affect transfer in another way—by inducing semantic knowledge that modifies problem structures. Two experiments examined how people represent and solve permutation problems dealing with random assignment of elements from one set to elements from another set. Although the problems were structurally isomorphic, cover stories involving different pairs of element sets led subjects to abstract different “interpreted structures.” Problems involving objects and people (e.g., prizes and students) led subjects to abstract an asymmetric structure (“get”) and problems involving similar sets of people (e.g., doctors and doctors) led subjects to abstract a symmetric structure (“pair”). Transfer was mediated by similarities and differences between the interpreted structures of the learned and the novel problems.