Iterative least squares estimates of communality: Initial estimate need not affect stabilized value

A common criticism of iterative least squares estimates of communality is that method of initial estimation may influence stabilized values. As little systematic research on this topic has been performed, the criticism appears to be based on cumulated experience with empirical data sets. In the present paper, two studies are reported in which four types of initial estimate (unities, squared multiple correlations, highestr, and zeroes) and four levels of convergence criterion were employed using four widely available computer packages (BMDP, SAS, SPSS, and SOUPAC). The results suggest that initial estimates have no effect on stabilized communality estimates when a stringent criterion for convergence is used, whereas initial estimates appear to affect stabilized values employing rather gross convergence criteria. There were no differences among the four computer packages for matrices without Heywood cases.     

Memory trace stabilization leads to large-scale changes in the retrieval network: a functional MRI study on associative memory

Spaced learning with time to consolidate leads to more stabile memory traces. However, little is known about the neural correlates of trace stabilization, especially in humans. The present fMRI study contrasted retrieval activity of two well-learned sets of face-location associations, one learned in a massed style and tested on the day of learning (i.e., labile condition) and another learned in a spaced scheme over the course of one week (i.e., stabilized condition). Both sets of associations were retrieved equally well, but the retrieval of stabilized association was faster and accompanied by large-scale changes in the network supporting retrieval. Cued recall of stabilized as compared with labile associations was accompanied by increased activity in the precuneus, the ventromedial prefrontal cortex, the bilateral temporal pole, and left temporo–parietal junction. Conversely, memory representational areas such as the fusiform gyrus for faces and the posterior parietal cortex for locations did not change their activity with stabilization. The changes in activation in the precuneus, which also showed increased connectivity with the fusiform area, are likely to be related to the spatial nature of our task. The activation increase in the ventromedial prefrontal cortex, on the other hand, might reflect a general function in stabilized memory retrieval. This area might succeed the hippocampus in linking distributed neocortical representations.     

The relationship between sighting dominance and the fading of a stabilized retinal image

The fading of a stabilized retinal image in the sighting and the nonsighting dominant eye was studied using the Haidinger’s brush target. Reaction time to the complete disappearance of the stabilized image was significantly longer when the target was input to the sighting eye. The greater persistence of stabilized targets in the sighting eye suggests possible differences in the neural channels from the two eyes or processing differences in the two monocular channels that are related behaviorally to eye dominance.     

Visual short-term memory during smooth pursuit eye movements

Visual short-term memory (VSTM) was probed while observers performed smooth pursuit eye movements. Smooth pursuit keeps a moving object stabilized in the fovea. VSTM capacity for position was reduced during smooth pursuit compared with a condition with eye fixation. There was no difference between a condition in which the items were approximately stabilized on the retina because they moved with the pursuit target and a condition in which the items moved across the retina because they were stationary in space. The reduction of capacity for position was eliminated when miniature items were presented on the pursuit target. Similarly, VSTM capacity for color did not differ between smooth pursuit and fixation. The results suggest that visuospatial attention is tied to the target during smooth pursuit, which impairs VSTM for the position of peripheral objects. Sensory memory during smooth pursuit was only slightly impaired.     

Suppression of optokinesis by a stabilized target: Effects of instruction and stimulus frequency

Subjects viewed a foveally stabilized target presented against a background field of dots moving sinusoidally. Several different modes of viewing the target were used (subjects were instructed to gaze, look, or hold), and the frequency of sinusoidal field motion was varied from 1/32 to 2 Hz. In line with previous findings, the presence of a stabilized target resulted in substantial suppression of optokinesis. The characteristics of this suppression (gain and phase of slow residual eye movements) were dependent on both the mode of viewing the target and the frequency of field motion. When subjects used an imaginary target, little suppression occurred. These findings provide an overall profile of dynamic characteristics of mechanisms involved in the suppression of optokinesis. They support the view that this suppression is significantly determined by the presence of a target against a moving background (even without retinal slip), and by the mode of attending to the target.     

Suppression of optokinesis by a stabilized target: effects of instruction and stimulus frequency.

Subjects viewed a foveally stabilized target presented against a background field of dots moving sinusoidally. Several different modes of viewing the target were used (subjects were instructed to gaze, look, or hold), and the frequency of sinusoidal field motion was varied from 1/32 to 2 Hz. In line with previous findings, the presence of a stabilized target resulted in substantial suppression of optokinesis. The characteristics of this suppression (gain and phase of slow residual eye movements) were dependent on both the mode of viewing the target and the frequency of field motion. When subjects used an imaginary target, little suppression occurred. These findings provide an overall profile of dynamic characteristics of mechanisms involved in the suppression of optokinesis. They support the view that this suppression is significantly determined by the presence of a target against a moving background (even without retinal slip), and by the mode of attending to the target.     

A longitudinal analysis of the attention networks in 6- to 11-year-old children

Attention is critical for everyday functioning. Posner and Petersen’s model of attention describes three neural networks involved in attention control—the alerting network for arousal, the orienting network for selecting sensory input and reorienting attention, and the executive network for the regulatory control of attention. No longitudinal research has examined relative change in these networks in children. A modified version of the attention network task (ANT) was used to examine changes in the three attention networks, three times over 12 months, in 114 6-, 8- and 10-year-olds. Findings showed that the alerting network continued to develop over this period, the orienting network had stabilized by 6 years, and the conflict network had largely stabilized by 7 years. The reorienting of attention was also assessed using invalid cues, which showed a similar developmental trajectory to the orienting attention network and had stabilized by 6 years. The results confirm that age 6 to 7 years is a critical period in the development of attention, in particular executive attention. The largest improvement over the evaluation period was between 6 and 7 years; however, subtle changes were found in attention beyond 8 years of age.     

Quality of life in transplant patients, compared to other stressful health situations in pulmonary patients

Transplantation may imply severe biopsychosocial impairments. In order to know the quality of life of patients one year after transplantation, 58 subjects were compared to three different groups of patients (stabilized and acute COPD patients, and lung cancer patients in a surgery unit). Patients filled in two questionnaires: EORTC QLQ-C30 (quality of life) and HAD (anxiety and depression). The quality of life dimensions with inter-group differences were physical, role, emotional and cognitive functioning, global health status, and a number of symptoms (fatigue, dyspnea, insomnia and appetite loss). There were differences in depression, and but not in anxiety. Transplant and surgical patients showed better quality of life and affective status than chronic pulmonary patients. Discriminant analysis showed that the transplant group was the best described group. We conclude that patients, one year after transplantation, show similar quality of life as asymptomatic hospitalised patients, somewhat better than chronic patients in a stabilized stage of the disease, and much better than severe chronic patients.     

Frames of reference in mobile augmented reality displays

In 3 experiments, the authors investigated spatial updating in augmented reality environments. Participants learned locations of virtual objects on the physical floor. They were turned to appropriate facing directions while blindfolded before making pointing judgments (e.g., "Imagine you are facing X. Point to Y"). Experiments manipulated the angular difference between the learning heading and the imagined heading and between the actual heading and the imagined heading. The effect of actual-imagined on pointing latency was observed for naive users but not for users with brief training or instructions concerning the fact that objects can move with body movements. The results indicated that naive users used an environment-stabilized reference frame to access information arrays, but with experience and instruction the nature of the representation changed from an environment stabilized to a body stabilized reference frame.     

Stabilized images: The search for pattern elements

In a series of four experiments, the fragmentation of stabilized lines and angles viewed in different orientations was studied. With high inter-O agreement, it was possible to demonstrate reliable differences among patterns, with resistance to fading being a function of both pattern and orientation. The results were discussed in terms of possible supraretinal stages of pattern analysis.     

Seven-minute rhythms in stable avoidance conditioning

Investigation of the “inextinguishable” locomotor avoidance reflex revealed periodic oscillating of reaction times, motor reaction times, and latent periods, when the conditional stimuli were applied every half minute. These rhythmic properties were verified by autocorrelation. Frequency distribution of all significant wavelengths occurring in rhythmic processes of stabilized conditioning showed seven-minute wavelengths for the most part and smaller numbers of wavelengths of 5 to 9 and 14 minutes. A significant number of wavelengths of 3.5 minutes was not seen. Locomotor avoidance conditioning permitted separate automatic registration of reaction times and motor reaction times. The two values showed synchronous periodic courses in stabilized conditioning, with the motor reaction times being longer. The periodicities found, thought to be due to controlling processes in the central nervous system, can be explained in either or both of two ways: the periodic courses represent a frequency range of a structured time mechanism in the sense of a “clock inherent in an organism”; the rhythms of conditional processes represent an adaptation mechanism in organism-environment interrelations. It can be assumed that the two mechnanisms work synergistically.     

REVERSIBILITY OF PERSPECTIVE IN NORMAL AND STABILIZED VIEWING

Two hypotheses regarding the role of eye movements in reversibility of perspective were tested by having the subjects observe a reversible-perspective figure during normal and stabilized viewing. No difference in reversal rate was found between the two conditions. It is concluded that reversibility of perspective remains unaffected by the presence or absence of eye movements.     

What will they say?—Public Announcement Games

The last two decades have seen a rising interest in (a) the notion of a scientific phenomenon as distinct from theories and data, and (b) the intricacies of experimentally producing and stabilizing phenomena. This paper develops an analysis of the stabilization of phenomena that integrates two aspects that have largely been treated separately in the literature: one concerns the skills required for empirical work; the other concerns the strategies by which claims about phenomena are validated. I argue that in order to make sense of the process of stabilization, we need to distinguish between two types of phenomena: phenomena as patterns in the data (“surface regularities”) and phenomena as underlying (or “hidden”) regularities. I show that the epistemic relationships that data bear to each of these types of phenomena are different: Data patterns are instantiated by individual data, whereas underlying regularities are indicated by individual data, insofar as they instantiate a data pattern. Drawing on an example from memory research, I argue that neither of these two kinds of phenomenon can be stabilized in isolation. I conclude that what is stabilized when phenomena are stabilized is the fit between surface regularities and hidden regularities.     

Microgenetic patterns of adaptation on the Stroop task by patients with bronchial asthma and duodenal peptic ulcer

Microgenetic patterns of adaptation on the Stroop task were assessed by means of the Serial Color-Word Test given 21 patients with bronchial asthma and 20 with duodenal peptic ulcer, who were compared with 41 normal controls matched for sex, age, and education. Two measures were calculated on each of the five trials of the test, one of linear change and one of nonlinear change in reading times. As predicted, patients presented more frequently patterns characterized by high nonlinear change and less frequently stabilized patterns (low linear and nonlinear change of reading speed). Linear and nonlinear change were then calculated on the five linear change scores and the five nonlinear change scores; again patients presented more frequently patterns characterized by high nonlinear change on both the linear change scores and nonlinear change scores and less frequently stabilized patterns. These findings indicate strong similarities between the adaptation patterns of patients with ulcer and asthma and the microgenetic patterns previously known to characterize neurotic and psychotic patients. Furthermore, scores on the Serial Color-Word Test also differentiated between ulcer and asthma groups.     

Stabilized images: Functional relationships among populations of orientation-specific mechanisms in the human visual system

Two experiments are presented in which fading rates of stabilized line stimuli were measured following prolonged adaptation to nonstabilized grating patterns in various orientations. Results indicated that some orientation-specific effects are sensitive to small variations of orientation around an optimal orientation, as well as to stimuli rotated 90 deg from the optimal orientation. These data were interpreted in terms of interactions among populations of orientation-specific mechanisms in the human visual system.     

Effects of variable-interval value and amount of training on stimulus generalization.

In Experiment 1 pigeons pecked a key that was illuminated with a 501-nm light and obtained food by doing so according to a variable-interval (VI) schedule of reinforcement, the mean value of which differed across groups: either 30 s, 120 s, or 240 s. The pigeons in all three groups were trained for 10 50-min sessions. Generalization testing was conducted in extinction with different wavelengths of light. Absolute and relative generalization gradients were similar in shape for the three groups. Experiment 2 was a systematic replication of Experiment 1 using line orientation as the stimulus dimension and a mean VI value of either 30 s or 240 s. Again, gradients of generalization were similar for the two groups. In Experiment 3 pigeons pecked a key that was illuminated with a 501-nm light and obtained food reinforcers according to either a VI 30-s or a 240-s schedule. Training continued until response rates stabilized (> 30 sessions). For subjects trained with the 30-s schedule, generalization gradients were virtually identical regardless of whether training was for 10 sessions (Experiment 1) or until response rates stabilized. For subjects trained with the VI 240-s schedule, absolute generalization gradients for subjects trained to stability were displaced upward relative to gradients for subjects trained for only 10 sessions (Experiment 1), and relative generalization gradients were slightly flatter. These results indicate that the shape of a generalization gradient does not necessarily depend on the rate of reinforcement during 10-session single-stimulus training but that the effects of prolonged training on stimulus generalization may be schedule dependent.     

Abdominal exercise intensities on firm and compliant surfaces

Muscle activities at 15 sites were compared within a group of healthy young adults to evaluate their relative intensities during six abdominal exercises: partial and full sit-ups on a firm surface (floor) and on an exercise ball that was either stabilized or unstabilized. The most strenuous abdominal exercise overall (i.e., whole body workout) was the full sit-up on a firm surface which included significant muscle activities in the lower extremities. Exercise intensity was also high in the full and partial sit-ups when performed on a ball. The partial sit-up on the floor was the least strenuous of the six exercises. The greatest effect on the abdominal muscles was observed in the partial sit-up on a ball (stabilized and unstabilized). Results suggest that, although abdominal exercises on a ball may be gentler on the hip and lower back, overall exercise intensity is not necessarily lower than that on the floor. Moreover, partial sit-ups, both on the floor and on a ball, also required greater neck muscle activities than full sit-ups. In deciding what type of sit-up to do, exercise surface and different muscular activities between the partial and full sit-ups should be considered.     

Extended practice of reciprocal wrist and arm movements of varying difficulties

An experiment was designed to determine the degree to which reciprocal aiming movements of the wrist and arm with various accuracy requirements (Fitts' tasks) are enhanced by extended practice. The vast majority of research on motor learning shows performance improvement over practice. However, literature examining the effect of practice on Fitts' task performance is limited and inconclusive. Participants were asked to flex/extend their limb/lever in the horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between two targets as quickly and accurately as possible. The targets and current position of the limb were projected on the screen in front of the participant. Target width was manipulated with amplitude constant (16°) in order to create indexes of difficulty (ID) of 1.5, 3, 4.5, and 6. Contrary to the earlier reports, after 20 days of practice, we found minimal changes in movement time or the movement time-ID relationships for the arm and wrist over practice. However, the variability in the movement endpoints decreased over practice and wrist movements at ID=6 were characterized by shorter movement times and longer dwell times relative to arm movements with dwell time for the wrist increasing over practice. These data are consistent with the notion that Fitts' tasks provide a stable measure of perceptual-motor capabilities.     

Slippage of contact lenses and other artefacts in relation to fading and regeneration of supposedly stable retinal images

After-image experiments reveal that scleral-fitting contact lenses slip through several minutes of arc. Experiments in which they have been used to procure “stabilized” retinal images must therefore be reinterpreted. Light-weight, suck-on, limbal-seating cups are much better, but complete stabilization cannot be relied upon. Other possible artefacts in stabilized image work are described and are thought to be responsible for certain features of previous accounts of the appearance of stabilized images. Discounting features caused by artefacts, the image appears to blur, losing detail, and fade, losing contrast, within the first few seconds. Contrast and detail are not regained, but the milky, textureless image that remains fluctuates in appearance for a minute or so. Finally the fluctuations die out and a very blurred, cloudy version of the original scene persists.     

Differential effects of massage and heelstick procedures on transcutaneous oxygen tension in preterm neonates

The present study investigated the differential effects of heelsticks and tactile-kinesthetic massage on transcutaneous oxygen tension (TcPO₂) in preterm infants. The sample was comprised of 37 stabilized preterm neonates from the Neonatal Intensive Care Unit. During the heelstick procedure, TcPO₂ significantly declined an average of 14 mmHg. When compared to the tactile-kinesthetic massage, TcPO₂ levels during the heelstick (M = 39.8) were significantly lower than during the stimulation (M = 72.8). Mean TcPO₂ levels remained clinically safe during the four massage sessions evaluated. The TcPO₂ levels during kinesthetic stimulation were somewhat more varied, and movement and pressurization of the TcPO₂ electrode were investigated as possible artifactual explanations for this phenomenon. Overall, the findings indicate that social forms of touch such as tactile-kinesthetic massage do not appear to have a medically compromising effect on TcPO₂ in the preterm neonate. These findings are evaluated in relation to the “minimal touch” policy, and implications for future handling of the stabilized preterm neonate are discussed.