Midline and off-midline tongue and right- and left-hand vibrotactile thresholds of stutterers and normal-speaking individuals

Vibrotactile thresholds for 7 male stutterers and 7 normal-speaking men (age range for both groups = 19 to 32 yr.) were obtained from the right, midline, and left sides of the lingual dorsum, and the thenar eminences of both hands. The stutterers showed slightly higher (less sensitive) mean thresholds than the normal speakers for all three lingual test sites. This was not the case for the thresholds obtained from both hands. The preliminary data suggest that oral peripheral sensory integrity might be somewhat different for stutterers than for normal-speaking individuals.     

Reliability coefficients as a function of individual differences induced by a learning process assuming identical organisms

In this article we show that a particular mathematical learning model, the Bower-Trabasso (1964) concept identification model taken together with an assumption of independence of replicate measurements, implies the existence of substantial and statistically significant performance differences across individuals. The individual differences in turn imply a sizeable reliability coefficient. These results contradict naive intuition, for this model (like many other mathematical models of learning) assumes that all individuals begin the experiment with identical parameter values for the process under study. Thus at least one such model has the characteristic of implying the generation of individual performance differences among originally identical organisms.Examination of data from an experiment by Cotton shows that the Hoyt reliability coefficient under classical test theory, a lower bound for the (composite) reliability of total scores for a series of trials, increases with the number of trials analyzed and exceeds the corresponding theoretical values implied by the Bower-Trabasso model. An experiment by Levine was also analyzed because its use of blank trials between feedback trials permitted direct calculation of composite reliability (or more properly stated composite consistency). For this experiment, the theoretical development just discussed (Case I) was used together with Restle's hypothesis selection model specialized to include a local consistency assumption, the so-called P₂ model of Gregg and Simon (Case II). Moderate conformity of empirical and theoretical reliabilities was found, with discrepancies between observed and predicted values usually being smaller with Case II. However, the Hoyt reliability coefficient is not a lower bound for composite reliability in Case II, because composite reliability is underestimated when identical stimuli are not used for comparable trials.Despite the Bower-Trabasso assumption of no initial differences, it seems reasonable to attribute the difference between predicted and obtained reliabilities to preexisting individual differences. Implications of the tentative conclusion that individual differences in concept identification performance are attributable to a combination of preexisting differences and differences induced in a current task are discussed briefly.     

Relationships between two systems of factor analysis

Considering only population values, it is shown that the complete set of factors of a correlation matrix with units in the diagonal cells may be transformed into the factors derived by factoring these correlations with communalities in the diagonal cells. When the correlations are regarded as observed values, the common factors derived as a transformation of the complete set of factors of the correlation matrix with units in the diagonal cells satisfy Lawley's requirement for a maximum likelihood solution and are a first approximation to Rao's canonical factors.     

The desirability of control

The psychological construct of desirability of control was related to several theoretical statements (e.g., Kelley, 1971; White, 1959) and areas of current research (e.g., Glass & Singer, 1972; Deci, 1975) in psychology. A scale designed to measure individual differences in the general level of motivation to control the events in one's life was presented. The Desirability of Control Scale was found to have substantial internal consistency (.80) and test-retest reliability (.75), as well as discriminant validity from measures of locus of control (Rotter, 1966) and social desirability (Crowne & Marlowe, 1960). The results of an illusion of control study (cf. Langer, 1975) provided construct validation: only subjects high in the desire for control displayed a belief in personal control over chance outcomes. Construct validation was also provided from studies on learned helplessness and hypnosis. The practical, as well as theoretical, value of the instrument was discussed.This research was facilitated by National Science Foundation grant BNS78-08834 to Harris Cooper.