A low-cost method for digitizing videotaped continuous movements on the Macintosh

We describe an inexpensive means of digitizing videotaped positions of moving points, such as the positions of the joints of a person who is performing an action. Single-frame video images and a Macintosh computer monitor are optically superimposed, using a half-silvered mirror, and the positions of reference points in the video image are manually clicked in by the operator, so that the screen coordinates of the reference points on each frame can be stored in a text file for later analysis. The digitizing program records comments and identifying information along with the position data.     

Cooperative selection of movements: The optimal selection model

How one selects a movement when faced with alternative ways of doing a task is a central problem in human motor control. Moving the fingertip a short distance can be achieved with any of an infinite number of combinations of knuckle, wrist, elbow, shoulder, and hip movements. The question therefore arises: how is a unique combination chosen? In our model, choice is achieved by consideration of the similarity between the task requirements and the optimal biomechanical performance of each limb segment. Two variants of the model account for the movements that are selected when subjects freely oscillate the fingertip and when they tap against an obstacle. An important feature of both is that the impulse of collision with an obstacle (as in drumming with the hand or tapping with the finger) is assumed to be controlled in part by aiming for a point beyond the surface being struck. Thus, a force-related control variable may be represented and controlled spatially.     

On choosing between movement sequences: comments on Rose (1988)

One method of investigating human motor programming is to determine how the choice reaction time for a memorized response sequence depends on the composition of that sequence as well as the other sequence that may be required. Using this method, Rose (1988) found that the total number of responses in the two possible response sequences predicts the choice reaction time to initiate either one. On the basis of this result, Rose claimed that the hierarchical editor (HED) model of motor programming, developed by Rosenbaum, Inhoff, and Gordon (1984), may have to be reevaluated. In this commentary I argue that Rose's results are inconsistent with a precursor of the HED model, not with the HED model itself, that the HED model actually provides a better fit to Rose's data than her total-number-of-responses model, that in general, choice reaction time does not increase with the total number of possible responses, and that structural relations between alternative movement sequences are the main determinants of choice reaction time. Taken as a whole, the results suggest that possible responses are not held in completely readied form before being selected for execution. A further implication is that the storage capacity of the motor output buffer (the MOB) is extremely limited.     

Characteristics and treatment of batterers

This article summarizes the substantial research conducted in the last decade concerning the characteristics of batterers. While certain characteristics appear to be associated with these abusers, no specific profile has emerged. Treatment programs have focused on anger management, improving communication, improving self-esteem, changing beliefs, and stress management, but research has not determined the effectiveness of these programs. Various approaches for treating abusers are presented in this article, including psychoeducational groups for batterers and conjoint therapy for couples. The legal system's use of diversion programs for referral/sentencing of batterers is also discussed as an important method for reducing spouse abuse.     

Perception and extrapolation of velocity and acceleration.

A moving target disappeared behind a screen and subjects predicted when the target passed behind a marker on the screen. When the target moved with constant velocity, predictions were extremely accurate, regardless of the spatial and temporal exposure and concealment of the target and regardless of its rate of velocity. When the target accelerated, accuracy of prediction decreased with increasing acceleration and with increasing target concealment. Analyses of the results suggest that the perception of velocity and acceleration is direct and accurate and that extrapolation of velocity and acceleration incorporates concrete and abstract characteristics of the motion that was seen. It is proposed that the motion perception system is tuned to accelerated rather than to constant velocity movement.     

Comparing item characteristic curves

Test items are often evaluated and compared by contrasting the shapes of their item characteristics curves (ICC's) or surfaces. The current paper develops and applies three general (i.e., nonparametric) comparisons of the shapes of two item characteristic surfaces: (i) proportional latent odds, (ii) uniform relative difficulty, and (iii) item sensitivity. Two items may be compared in these ways while making no assumption about the shapes of item characteristic surfaces for other items, and no assumption about the dimensionality of the latent variable. Also studied is a method for comparing the relative shapes of two item characteristic curves in two examinee populations.The author is grateful to Paul Holland, Robert Mislevy, Tue Tjur, Rebecca Zwick, the editor and reviewers for valuable comments on the subject of this paper, to Mari A. Pearlman for advice on the pairing of items in the examples, and to Dorothy Thayer for assistance with computing.     

Stimulus-response compatibility in the programming of speech

Subjects chose between sequences of one syllable (e.g.,/gi/vs./bi/), two syllables (e.g.,/gibi/ vs./gubu/), and three syllables (e.g.,/gibidi/ vs. gubudu/), when/i/sequences were signaled by high-pitched tones and/u] sequences were signaled by low-pitched tones (high compatibility), or the reverse (low compatibility). Choice times were additively affected by sequence length and compatibility. A second experiment showed attenuated compatibility effects for sequences with different vowels in the first and second syllables. These results replicate previously reported results for choices between finger sequences, which suggests that the same programming methods are used in both output domains. Evidently, choices between response sequences can be achieved by selecting a distinguishing parameter and assigning it in a serial fashion to partially prepared motor subprograms.     

Rule use in character classification: Are serial and parallel processing discrete?

Contrary to predictions of a stochastic self-terminating search model, choice reaction times were lower for rulebound positive sets than for nonrulebound positive sets when memory set sizes were varied and stimulus probabilities were held constant. The result suggests that rule use and chunking, as opposed to probability alone, facilitate character classification. As a corollary, it is proposed that serial and parallel processing differ in degree rather than in kind. The extent to which the memory set has been chunked is the critical variable affecting Ss’ scanning practices.