Spatial integration in human smooth pursuit

When viewing a moving object, details may appear blurred if the object's motion is not compensated for by the eyes. Smooth pursuit is a voluntary eye movement that is used to stabilize a moving object. Most studies of smooth pursuit have used small, foveal targets as stimuli (e.g. Lisberger SG and Westbrook LE. J Neurosci 1985;5:1662-1673.). However, in the laboratory, smooth pursuit is poorer when a small object is tracked across a background, presumably due to a conflict between the primitive optokinetic reflex and smooth pursuit. Functionally, this could occur if the motion signal arising from the target and its surroundings were averaged, resulting in a smaller net motion signal. We asked if the smooth pursuit system could spatially summate coherent motion, i.e. if its response would improve when motion in the peripheral retina was in the same direction as motion in the fovea. Observers tracked random-dot cinematograms (RDC) which were devoid of consistent position cues to isolate the motion response. Either the height or the density of the display was systematically varied. Eye speed at the end of the open-loop period was greater for cinematograms than for a single spot. In addition, eye acceleration increased and latency decreased as the size of the aperture increased. Changes in the density produced similar but smaller effects on both acceleration and latency. The improved pursuit for larger motion stimuli suggests that neuronal mechanisms subserving smooth pursuit spatially average motion information to obtain a stronger motion signal.     

Spatial grouping determines temporal integration.

To make sense out of a continuously changing visual world, people need to integrate features across space and time. Despite more than a century of research, the mechanisms of features integration are still a matter of debate. To examine how temporal and spatial integration interact, the authors measured the amount of temporal fusion (a measure of temporal integration) for different spatial layouts. They found that spatial grouping by proximity and similarity can completely block temporal integration. Computer simulations with a simple neural network capture these findings very well, suggesting that the proposed spatial grouping operations may occur already at an early stage of visual information processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial integration of band-pass filtered patterns in noise

Contrast energy thresholds were measured for noisy band-pass filtered Sloan letters, K, H, O, and a plus symbol (+) at various centre frequencies and bandwidths. For all patterns the efficiency and energy sensitivity of detection increased with filter bandwidth but decreased with increasing filter centre frequency. Hence, neither parameter alone can explain the changes in efficiency and energy sensitivity. Irrespective of centre frequency and bandwidth, efficiency and energy sensitivity were found to decrease as a single power function of image complexity (Z) defined as the product of the square of the median spatial frequency (fm) of the image energy spectrum and image area (A95) comprising 95% of total contrast energy of the stimulus. The product Z = fm2A95 describes image complexity in the sense that when f2m or A95 increase the number of details increase, too. The decrease of the efficiency of detection with increasing image complexity suggests that the proportion of the integrated image area decreases as the complexity of an image increases.     

Spatial and temporal aspects of infant color vision

The present paper constitutes a review of the literature on young infants' chromatic discrimination capabilities. A series of early studies showed that infants as young as two months postnatal can make at least some chromatic discriminations between stationary, homogeneous fields of different wavelength compositions. Current studies of spatial and temporal contrast sensitivity functions (CSFs) for red/green isoluminant stimuli suggest that spatial chromatic CSFs show developmental changes in sensitivity and spatial scale, but not curve shape; while temporal chromatic CSFs (tCSFs) show developmental changes in sensitivity and curve shape, but not temporal scale. Infants can also code the direction of motion of moving isoluminant red/green gratings, for both continuous and quadrature motion. The possible mechanisms that underlie infants' chromatic discriminations are discussed.     

Spatial and temporal integration of signals in foveal line orientation

The discrimination of the orientation of a line improves with line length, reaching an optimum when a foveal line is approximately 0.5 degrees long. We studied the effect of eliminating sections of the line, of displacing them out of alignment, and of delaying them. Orientation discrimination thresholds are only a little elevated when a 25-arcmin line is replaced by three equally spaced collinear 5-arcmin segments. Two collinear 5-arcmin segments show better thresholds than a single one when they are separated by as much as 20 arcmin. But thresholds are impaired by bringing line segments out of collinearity by as little as 1 arcmin. Asynchrony of up to 50 ms can be tolerated, but when the middle segment of a three-line pattern is delayed by approximately 100 ms there is active inhibition, thresholds being now higher than when the middle segment is absent. It is concluded that for signals to address the orientation discrimination mechanism optimally, they have to be contained inside a narrow spatial corridor and be presented within a time window of approximatley 50 ms, but that some spatial summation can take place over a length of > or = 0.5 degrees in the fovea. Because short lines made of black and white collinear segments do not have good orientation thresholds, whereas longer and interrupted lines do, it is concluded that what is involved is potentiating interaction between collinearly arranged neurons with identical orientation selectivity rather than summation of signals within the receptive fields of single neurons.     

Spatial and temporal congruity and auditory–visual integration in infants.

The influence of the spatial and temporal relation of auditory and visual stimuli on 6-mo-old infants' perception of these stimuli as attributes of a common object was explored in 4 studies. In Exp I, after familiarization with an object that moved in synchrony with a periodic sound coming from it, the 89 Ss associated the object and sound; they looked more at the familiar than a novel object in the presence of the familiar sound, but not in the presence of a novel sound. Exp II with 22 Ss showed evidence for association following experience in which an object and sound were spatially congruent but exhibited a form of temporal incongruity (continuous movement and periodic sound). In contrast, no evidence of auditory–visual association was shown after familiarization in which the object and sound were temporally congruent but spatially incongruent (Exp III; 21 Ss) or in which object and sound were spatially congruent but exhibited a different form of temporal incongruity (periodic movement and continuous sound; Exp IV with 23 Ss). (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thymus hyperplasia, differential diagnosis in the wheezing infant

Desmopressin (DDAVP), a synthetic analogue of vasopressin, has been shown to improve the bleeding time in patients with cirrhosis. The duration of this effect and the hemodynamic changes associated with DDAVP have not been studied so far. To evaluate these issues, 14 cirrhotics with portal hypertension were studied in basal conditions and after DDAVP (0.3 uk/kg). In 8 patients, hemostatic tests were done at basal conditions and 1, 3, 6 and 24 hs after drug administration. In the remaining 6 patients, mean arterial pressure, cardiac output, portal and femoral blood flows were evaluated. Hemodynamic parameters were measured by Doppler ultrasound. DDVP caused a marked decrease in bleeding time at 1, 3, 6 and 24 hs (14 +/- 9 vs 8 +/- 3, 7 +/- 4, 6 +/- 4 and 8 +/- 4 min, respectively); the decrease was maximal and statistically significant at 6 hs (55 +/- 15%, p < 0.02) after DDAVP infusion. Bleeding time reduction was observed in every patient studied. In the hemodynamic study, DDAVP caused a mild but significant decrease in mean arterial pressure (12 +/- 8%, p < 0.05); no significant changes were observed in the rest of hemodynamic parameters studied. These findings show that DDAVP can be used to shorten the bleeding time for a period of at least 24 hs in patients with cirrhosis, without deleterious hemodynamic effects. This beneficial effect may be of potential relevance in the medical management of patients with chronic liver diseases.     

Spatial memory and path integration studied by self-driven passive linear displacement. I. Basic properties

According to path integration, the brain is able to compute the distance of a traveled path. In this research we applied our previously reported method for studying memory of linear distance, a crucial mechanism in path integration; our method is based on the overt reconstruction of a passive transport. Passive transport is a special case of navigation in which no active control is performed. Blindfolded subjects were first asked to travel 2 m forward, in darkness, by driving with a joystick the robot on which they were seated. The results show that all subjects but two undershot this distance, i.e., overestimated their own displacement. Then, subjects were submitted to a passive linear forward displacement along 2, 4, 6, 8, or 10 m, and had to reproduce the same distance, still blindfolded. The results show that the distance of the stimulus was accurately reproduced, as well as stimulus duration, peak velocity, and velocity profile. In this first condition, the imposed velocity profile was triangular and therefore stimulus distance and duration were correlated. In a second condition, it was shown that distance was correctly reproduced also when the information about stimulus duration was kept constant. Here, different velocity profiles were used as stimuli, and most subjects also reproduced the velocity profile. Statistical analyses indicated that distance was not reproduced as a consequence of duration, peak velocity, or velocity profile reproduction, but was uniquely correlated to stimulus distance. The previous hypothesis of a double integration of the otolith signal to provide a distance estimate can explain our results. There was a large discrepancy between the accuracy with which the subjects matched the velocity profiles and that of distance reproduction. It follows that, whereas the dynamics of passive motion are stored and available to further use, distance is independently estimated. It is concluded that vestibular and somatosensory signals excited by passive transport can be used to build a dynamic as well as a static representation of the traveled path. We found a close quantitative similarity between the present findings on distance reproduction and those obtained from active locomotion experiments in which the same paradigm was used. This resemblance suggests that the two types of navigation tasks draw on common physiological processes and extends the relevance of our results to naturally occurring path integration.     

Secretion, purification, and characterisation of barley alpha-amylase produced by heterologous gene expression in Aspergillus niger

The role of the actin cytoskeleton and/or GTPases of the Rho/Rac-family in glucose transport regulation was investigated in 3T3-L1 cells with clostridial toxins which depolymerize actin by inactivation of Rho/Rac (Clostridium difficile toxin B and Clostiridium sordellii lethal toxin (LT)) or by direct ADP-ribosylation (Clostridium botulinum C2 toxin). Toxin B and C2 reduced insulin-stimulated, but not basal, 2-deoxyglucose (2-DOG) uptake rates in 3T3-L1 fibroblasts. In parallel, the toxins produced morphological alterations of the cells reflecting disruption of the actin cytoskeleton. Both toxins reduced the maximum response to insulin but failed to alter the half-maximally stimulating concentrations of insulin. In 3T3-L1 adipocytes, the lethal toxin reduced the effect of insulin on 2-DOG uptake, whereas toxin B and C2 failed to affect glucose transport or cell morphology. When cells were exposed to the toxins after treatment with insulin, both toxin B and the lethal toxin, in contrast to the phosphatidylinositol (PI) 3-kinase inhibitor wortmannin, failed to reduce the 2-DOG uptake rates. Thus, both translocation to the plasma membrane and internalization of glucose transporters were inhibited by the toxins, whereas the PI 3-kinase inhibitor selectively affects translocation. The data suggest that the effects of the clostridial toxins on trafficking of glucose transporters are mediated by the depolymerization of the actin cytoskeleton and are an indirect consequence of Rho or Rac inactivation. It is suggested that pathways signalling through Rac or Rho may play a modulatory role in glucose transport regulation through their effects on the actin network.     

Infants at social risk: Relations among infant maltreatment, maternal behavior, and infant attachment behavior.

Fifty-six 12-mo-old infants, including 10 maltreated infants, 18 nonmaltreated high-risk infants, and 28 matched low-income controls, were videotaped in naturalistic settings at home with their mothers for 40 min and were observed 2 weeks later in the Ainsworth Strange Situation. Maltreating mothers were rated higher than nonmaltreating mothers on covertly hostile and interfering behaviors toward their infants at home. Maltreated infants were more avoidant of their mothers in the Strange Situation than nonmaltreated infants. Correlations between maternal behaviors at home and infant behaviors in the Strange Situation revealed that mothers whose infants displayed resistant behavior on reunion were rated at home as less verbally communicative and mothers whose infants displayed avoidant behavior on reunion were rated at home as more covertly hostile. Infants showing mixed avoidance and resistance were more likely to have extremely uncommunicative mothers than were infants who showed avoidance alone. Use of the behavioral rating scales for avoidance and resistance produced clearer findings than use of the final attachment classifications. Reasons for the discrepancies between analyses of classifications and analyses of behavior ratings were identified. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cytomegalovirus infection in the pregnant mother, fetus, and newborn infant

Two types of eukaryotic nuclear introns are known: the common U2-dependent class with /GU and AG/ terminal intron dinucleotides, and the rare U12-dependent class with /AU and AC/ termini. Here we show that the U12-dependent splicing system can splice introns with /GU and AG/ termini and that such introns occur naturally. Further, U2-dependent introns with /AU and AC/termini also occur naturally and are evolutionarily conserved. Thus, the sequence of the terminal dinucleotides does not determine which spliceosomal system removes an intron. Rather, the four classes of introns described here can be sorted into two mechanistic classes (U2- or U12-dependent) by inspection of the complete set of conserved splice site sequences.     

Aging, selective attention, and feature integration.

This study used feature-integration theory as a means of determining the point in processing at which selective attention deficits originate. The theory posits an initial stage of processing in which features are registered in parallel and then a serial process in which features are conjoined to form complex stimuli. Performance of young and older adults on feature versus conjunction search is compared. Analyses of reaction times and error rates suggest that elderly adults, in addition to young adults, can capitalize on the early parallel processing stage of visual information processing, and that age decrements in visual search arise as a result of the later, serial stage of processing. Analyses of a third, unconfounded, conjunction search condition reveal qualitatively similar modes of conjunction search in young and older adults. The contribution of age-related data limitations is found to be secondary to the contribution of age decrements in selective attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relation between social support, infant risk status and mother–infant interaction.

The purpose of this study was to describe the nature of the social support network of mothers from inner-city, poor families with high-risk infants and to examine the relation between mother's social support network and maternal behavior. When their infants were 3 months of age, mothers were interviewed concerning sources of support (e.g., fathers, relatives, and friends) and type of support received (i.e., goods, services, advice, and financial support). Observations of the mother–infant interaction in a free-play setting were also obtained. Results revealed that goods was the type of support most frequently mentioned, and relatives were mentioned as giving support more often than friends. Mothers of premature infants reported fewer people giving goods than mothers of term infants. The results of this study also indicated that source and type of support to mother were important factors for understanding maternal behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Newborn dopamine-beta-hydroxylase, minor physical anomalies, and infant temperament

The authors examined newborn anomaly scores for 193 normal infants in relation to obstetrical history, newborn dopamine-beta-hydroxylase (DBH), and 5-month (N=185) and 1-year (N=123) infant behavior, determined by a questionnaire completed by their mothers. There was no significant relationship between anomaly score and obstetrical history or 5-month infant temperament; low significant correlations were found between newborn DBH and 1) infant irritability and unsociable response and 2) 1-year anomaly scores and reported activity levels. The authors discuss the possible importance of these findings.