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.     

Recovery of Locomotion in Monkeys With Spinal Cord Lesions

This study reanalyzes kinematically (via film) the pre- and postoperative locomotor behavior of 4 of the 10 monkeys with partial spinal cord lesions (T8) briefly described by Eidelberg, Walden, and Nguyen (1981). The behavior of the remaining 6 monkeys is qualitatively described. The analysis reveals that 5 of the animals initially exhibited unilateral hind limb stepping. Hind and forelimb cycle durations often differed postoperatively; the hind limbs commonly showed increased values, whereas forelimb cycle durations were reduced: ipsilateral interlimb phase values were usually inconsistent. A review of prior studies of primate spinal cord lesions indicates that sparing of the ventrolateral quadrant may not be essential for locomotor recovery (cf. Eidelberg, Walden, & Nguyen, 1981). Furthermore, this review as well as the kinematic analysis indicates that primates with very significant spinal lesions can stilI exhibit locomotor movements. Thus, although the primate's spinal cord seems less able than other mammals' to readily organize locomotor movements (Eidelberg, Walden, & Nguyen, 1981), the total absence of stepping in primates with completely transected cords is unexpected and warrants further research.     

Stimulus recognition and the mere exposure effect.

A meta-analysis of research on Zajonc's (1968) mere exposure effect indicated that stimuli perceived without awareness produce substantially larger exposure effects than do stimuli that are consciously perceived (Bornstein, 1989a). However, this finding has not been tested directly in the laboratory. Two experiments were conducted comparing the magnitude of the exposure effect produced by 5-ms (i.e., subliminal) stimuli and stimuli presented for longer durations (i.e., 500 ms). In both experiments, 5-ms stimuli produced significantly larger mere exposure effects than did 500-ms stimuli. These results were obtained for polygon (Experiment 1), Welsh figure (Experiment 2), and photograph stimuli (Experiments 1 and 2). Implications of these findings for theoretical models of the mere exposure effect are discussed.     

Self-report, peer-report, and teacher-report measures of childhood depression: an analysis by item.

We explored the low correlation among different types of childhood depression measures at the item level. The items from the Children's Depression Inventory (CDI), Peer Nomination Inventory of Depression (PNID), and the Child Behavior Checklist-Teacher Report Form (CBCL-T) were combined, and both first- and second-order factor analyses were conducted. Results indicate that self-report, peer-report, and teacher-report assessments of depression measure generally uncorrelated constructs. Second-order analysis suggests that depression as a global construct is being measured to some degree by items from all three instruments. Canonical analysis was employed to identify items that best predicted CDI, PNID, and CBL-T summary scores simultaneously. Also, the relationship between specific items with similar content was investigated. Results from these analyses generally supported a conclusion that the three types of measures yield scores that are primarily independent and that the use of summary scores is not masking stronger relationships within measures. These findings have implications for clinical practice and construct elaboration.     

Effects of Pointing Rate and Availability of Visual Feedback on Visual and Proprioceptive Components of Prism Adaptation

While looking through laterally displacing prisms, subjects pointed 60 times straight ahead of their nose at a rate of one complete movement every 2 or 3 s, with visual feedback available early in the pointing movement or delayed until the end of the movement. Sagittal pointing was paced such that movement speed covaried with pointing rate. Aftereffect measures (obtained after every 10 pointing trials) showed that when the limb became visible early in a pointing movement, proprioceptive adaptation was greater than visual, but when visual feedback was delayed until the end of the movement, the reverse was true. This effect occurred only with the 3-s pointing rate, however. With the 2-s pointing rate, adaptation was predominately proprioceptive in nature, regardless of feedback availability. Independent of the availability of visual feedback, visual adaptation developed more quickly with 3-s pointing, whereas proprioceptive adaptation developed more rapidly with 2-s pointing. These results are discussed in terms of a model of perceptual-motor organization in which the direction of coordinative (guidance) linkage between eye-head (visual) and hand-head (proprioceptive) systems (and consequently the locus of discordance registration and adaptive recalibration) is determined jointly by pointing rate and feedback availability. An additional effect of pointing rate is to determine the rate of discordant inputs. Maximal adaptive recalibration occurs when the input (pointing) rate matches the time constant of the adaptive encoder in the guided system.     

Factors and Taxa, Traits and Types, Differences of Degree and Differences in Kind

ABSTRACT A taxon is a nonarbitrary class whose existence is conjectured as an empirical question, not a mere semantic convenience. Numerous taxa are known to exist in nature and society (chemical elements, biological species, organic diseases, geological strata, kinds of stars, elementary particles, races, cultures, Mendelizing mental deficiencies, major psychoses, vocations, ideologies, religions). What personality types, if any, occur in the nonpathological population remains to be researched by sophisticated methods, and cannot be settled by fiat or "dimensional" preference. The intuitive concept of taxonicity is to be explicated by a combination of formal-numerical and causal criteria. Taxometric methods should include consistency tests that provide Popperian risk of strong discorroboration. In social science, latent class methods are probably more useful than cluster algorithms.     

Reliability and validity of the Coolidge Axis II Inventory: a new inventory for the assessment of personality disorders.

This group of studies describes the development of a 200 item, self-report, 4-point true-false inventory (Coolidge Axis II Inventory [CATI]) to assess personality disorders according to the criteria established in the Diagnostic and Statistical Manual of Mental Disorders (3rd ed., rev. [DSM-III-R]; American Psychiatric Association, 1987). The 13 personality disorder scales of the CATI had a mean test-retest reliability of .90 and a median internal consistency (Cronbach's alpha) of .76. There was a 50% concordance rate with clinician's diagnosis for 24 personality disordered patients. The median concurrent validity (raw score sums) between the CATI and the Millon Clinical Multiaxial Inventory-II for the 13 personality disorder scales was .58. Preliminary studies also support the reliability and validity of Depression, Anxiety, and Brain Dysfunction scales.     

The effect of hypnotically elicited testimony on jurors' judgments of guilt and innocence.

Survey data from several countries indicate that many people believe that hypnosis may increase the accuracy of an eyewitness's memory; most experimental research, however, suggests that this belief is inaccurate. This study examined whether the belief could influence judgments of guilt and innocence in a simulated criminal trial. The results indicated that British undergraduates were more likely to find a male defendant guilty when told that the testimony against him had been elicited under hypnosis. Results concerning a nonhypnotic memory facilitation technique were found to be inconclusive, and the salience of hypnotically elicited testimony was ruled out as a contributory element.