Latent trait models and dichotomization of graded responses

This paper discusses thecompatibility of the polychotomous Rasch model with dichotomization of the response continuum. It is argued that in the case of graded responses, the response categories presented to the subject are essentially an arbitrary polychotomization of the response continuum, ranging for example from total rejection or disagreement to total acceptance or agreement of an item or statement. Because of this arbitrariness, the measurement outcome should be independent of the specific polychotomization applied, for example, presenting a specific multicategory response format should not affect the measurement outcome. When such is the case, the original polychotomous model is called compatible with dichotomization.A distinction is made between polychotomization or dichotomization before the fact, that is, in constructing the response format, and polycho- or dichotomization after the fact, for example in dichotomizing existing graded response data.It is shown that, at least in case of dichotomization after-the-fact, the polychotomous Rasch model is not compatible with dichotomization, unless a rather special condition of the model parameters is met. Insofar as it may be argued that dichotomization before the fact is not essentially different from dichotomization after the fact, the value of the unidimensional polychotomous Rasch model is consequently questionable. The impact of our conclusion on related models is also discussed.     

Self-selection biases in correlational studies based on questionnaires

It is commonly held that even where questionnaire response is poor, correlational studies are affected only by loss of degrees of freedom or precision. We show that this supposition is not true. If the decision to respond is correlated with a substantive variable of interest, then regression or analysis of variance methods based upon the questionnaire results may be adversely affected by self-selection bias. Moreover such bias may arise even where response is 100%. The problem in both cases arises where selection information is passed to the score indirectly via the disturbance or individual effects, rather than entirely via the observable explanatory variables. We suggest tests for the ensuing self-selection bias and possible ways of handling the ensuing problems of inference.The author would like to thank members of the Psychology Department at UWA for references on the illustrative example, namely the effects of sex-stereotyping on achievements in mathematics; thanks are also due to the anonymous reviewers whose comments resulted in material improvements to the paper.     

Personal identity and brain death: a critical response

The authors contend that there are logical inconsistencies in a theory put forth by Michael Green and Daniel Wikler ("Brain death and personal identity," Philosophy and Public Affairs 1980 Winter; 9(2): 105-133) to justify the brain death concept of death. Green and Wikler had asserted that individuals cease to exist and are dead when the criteria for continuity in their personal identity are not met. Having argued that the theory of personal identity is misguided, Agich and Jones suggest that further research into the ontological foundation of brain death concepts should begin, not by rejecting medical or moral considerations, but by carefully defining the main competing concepts of brain death as brain stem death, cerebral death, death of the brain as a whole, and whole brain death, and then by relating these concepts to the ontological conditions for being a live individual or person.     

Interpersonal dominance and coronary prone behavior

Type A “coronary-prone behavior” is a risk factor for coronary artery and heart disease. Questionnaire research indicates that interpersonal dominance is one of the strongest behavioral correlates of the Type A behavior pattern, although little effort has been made to demonstrate a link between the behavioral manifestations of interpersonal dominance and Pattern A responding. This study was conducted to establish such a link. All possible combinations of extreme As (N = 42) and Bs (N = 42) were matched in dyads that negotiated extreme bipolar opposite positions on a “teacher dismissal” issue. Analysis of process and outcome behaviors suggested that type A individuals are unilaterally more dominant than their Type B counterparts. Possible physiological mechanisms mediating dominance and cardiovascular disease are discussed.     

Temporal integration and vibrotactile backward masking

Subjects were presented with vibrotactile target patterns to their left index fingertips. The target patterns varied in the number of line segments that they contained and were presented in the presence or absence of a backward-masking stimulus. The stimulus onset asynchrony (SOA) between the target and masker was varied. In an identification task, subjects' errors indicated that the effect of the masker at brief SOAs was to increase the perceived number of line segments in the target. This effect diminished with increasing SOA, and at the longest SOAs subjects confused targets with patterns containing the same number of line segments but varying in how the line segments were related. In an estimation task, the effect of the masker was to increase the number of line segments estimated to be contained in the target pattern. The effect of the masker at brief SOAs is discussed in terms of an integration theory of vibrotactile backward masking. At longer SOAs, the results suggest that the masker may interfere with the extraction of relational information in the target pattern.     

Shape constancy and polar perspective

The distortion of polar perspective depends on the depth of the tridimensional shape and on the observation distance. In four experiments using 54 undergraduates as subjects, we found that a compensation process which takes depth and observation distance into account corrects for such distortions. Compensation was demonstrated in experiments in which deceptive information on depth and on observation distance was provided. The result was distortions of the perceived shapes that would be expected if compensation were based on the deceptive information.     

Intermittent versus continuous visual control: a reply to Elliott

Recently, Elliott (1986) has reported data that he claims are inconsistent with my hypothesis that a short-term motor memory system exists for guiding locomotion and other actions in space (Thomson, 1983). In fact, methodological flaws in Elliott's design make such conclusions unjustified and inappropriate. Moreover, insofar as comparisons can be made at all, the results are completely consistent with my own data.     

Range effects in successive discrimination

In two sets of experiments we examined pigeons' discrimination performance with a visual flicker-rate continuum, using a conventional successive discrimination procedure. In the first experiment, responses during the intermediate stimulus value were never reinforced, while responses during stimuli on either end of the continuum were reinforced periodically. In the second experiment, responses during stimuli from one end of the continuum were never reinforced, while responses during stimuli from the other end of the continuum were reinforced periodically. Results from both experiments show that discrimination between unchanged positive and negative stimulus values is a function of the range over which the total stimulus set varies. These range effects are comparable to effects found in absolute judgment tasks in human and animal psychophysics. In addition, the range effects reported here are not due to channel capacity, but may depend instead on variability in judgment criteria.     

Perceptual interactions in two-word displays: familiarity and similarity effects

Previous studies have demonstrated the existence of perceptual interactions in the processing of two-word displays such as SAND LANE. When postcued to report one of the two words, subjects often make migration errors, in that the report of the specified word includes a letter of the other word (e.g., LAND or SANE instead of SAND). We find that migrations depend on the abstract, structural similarity of the strings, but not on the physical similarity; on whether the strings are words; and on whether the possible migration responses are words. We also rule out an interpretation of migration errors that attributes them to a guessing strategy. Our findings are interpreted in terms of models in which both strings simultaneously access high-level structural knowledge, that is, knowledge about what sequences of letters fit together to form familiar wholes.