Age related size invariance in perception of illusory and fragmented contours

We investigated invariant perception to sizes of images. Observers were schoolmates of 7-17 years and adults. Two types of stimuli were used: fragmented line drawing of common objects and discs with deleted sectors, which represented illusory Kanizsa contours when discs were in particular positions. In experiments with fragmented images, we found an improvement in image recognition with observers' age, increasing up to 13-14 years. The probability of recognition of fragmented line drawings increased significantly with decreasing stimulus size for children of 7-12 years, indicating that size invariance at recognition for fragmented line drawings was absent in these children. However, size invariance was found for observers of 13-17 years and for adults in this task. At Kanizsa illusion appearance, the ratio of the separation between discs and disc diameter was smaller when we used larger disc diameters. This ratio increased with increasing age of observers. Obtained results provide evidence for the absence of size invariance when perceiving the Kanizsa illusion in our experimental conditions.     

Age-related size invariance in perception of illusory and fragmented contours

We investigated invariant perception to sizes of images. Observers were secondary school students aged 7–17 years and adults. Two types of stimuli were used: fragmented line drawing of common objects and discs with deleted sectors which represented illusory Kanizsa contours, when discs were in particular positions. In experiments with fragmented images, we found an improvement in image recognition with observer’s age, increasing up to 13–14 years. The probability of recognition of fragmented line drawings increased significantly with decreasing stimulus size for children aged 7–12 years, indicating that size invariance at recognition for fragmented line drawings was absent in these children. However, size invariance was found for observers aged 7–12 years and for adults in this task. Upon the Kanizsa illusion appearance, the ratio of the separation between discs and disc diameter was smaller when we used larger disc diameters. This ratio increased with increasing age of observers. The obtained results provide evidence for the absence of size invariance when perceiving the Kanizsa illusion under our experimental conditions.     

Body fat, abdominal fat, and body fat distribution is related to left atrial diameter in young children

In adults, the size of the left atria (LA) has important prognostic information. In obese adults, adolescents and children enlargement of LA have been observed. This has not been investigated on a population-based level in young children. We therefore assessed if total body fat mass (TBF), abdominal fat, and body fat distribution were related to LA diameter. Cross-sectional study of 244 children (boys = 137 and girls n = 107) aged 8-11 years, recruited from an urban population-based cohort. Dual-energy X-ray absorptiometry (DXA) measured total lean body mass, TBF, and abdominal fat mass (AFM). Body fat was also calculated as a percentage of body mass (BF%). Body fat distribution (AFM/TBF) was calculated. Echocardiography was performed with two-dimensional guided M-mode. LA diameter was measured and left ventricular mass (LVM) was calculated. Systolic blood pressure and diastolic blood pressure were measured and maturity assessed according to Tanner. There were significant (P < 0.05) univariate correlations for all children between TBF (r = 0.40), BF% (r = 0.32), AFM (r = 0.41), and AFM/TBF (r = 0.41) vs. LA diameter. Multiple regression analyses with the inclusion of possible confounders such as lean body mass, blood pressure, gender, age, and Tanner stage revealed that TBF, AFM, and AFM/TBF were all independently related to LA diameter. Differences in the different body fat measurements explained 6-9% of the variance in LA size. These results demonstrated that both total body fat, AFM, and body fat distribution are already at a young age negatively and independently associated to LA diameter.     

Stereoscopic subsystems for position in depth and for motion in depth.

We describe psychophysical evidence that the human visual system contains information-processing channels for motion in depth in addition to those for position in depth. These motion-in-depth channels include some that are selectively sensitive to the relative velocities of the left and right retinal images. We propose that the visual pathway contains stereoscopic (cyclopean) motion filters that respond to only a narrow range of the directions of motion in depth. Turning to the single-neuron level we report that, in addition to neurons turned to position to depth, cat visual cortex contains neurons that emphasize information about the direction of motion at the expense of positional information. We describe psychophysical evidence for the existence of channels that are sensitive to change size, and are separate from the channels both for motion and for flicker. These changing-size channels respond independently of whether the stimulus is a bright square on a dark ground or a dark square on a bright ground. At the physiological level we report single neurons in cat visual cortex that respond selectively to increasing or to decreasing size independently of the sign of stimulus contrast. Adaptation to a changing-size stimulus produces two separable after-effects: an illusion of changing size, and an illusion of motion in depth. These after-effects have different decay time constants. We propose a psychophysical model in which changing-size filters feed a motion-in-depth stage, and suppose that the motion-in-depth after-effect is due to activity at the motion-in-depth stage, while the changing-size after-effect is due to to activity at the changing-size and more peripheral stages. The motion-in-depth after-effect can be cancelled either by a changing-size test stimulus or by relative motion of the left and right retinal images. Opposition of these two cues can also cancel the impression of motion in depth produced by the adapting stimulus. These findings link the stereoscopic (cyclopean) motion filters and the changing-size filters: both feed the same motion-in-depth stage.     

Mismatch negativity in the brain evoked potentials induced by short duration acoustic stimuli in adolescents in the norm and those with attention deficit

The effect of stimulus duration on the mismatch negativity of the auditory event-related potentials was studied in healthy children and those with attention-deficit symptoms. The minimum stimulus duration with which a MMN was elicited by frequency deviant was 50 ms in healthy children. The MMN was absent with shorter stimuli (11 ms and 30 ms). These parametres are close to those in adults. As to children with attention-deficit symptoms the MMN was insignificant with all tested stimulus durations (11 ms, 30 ms, 50 ms).     

Motor control of voluntary arm movements

The motor control of pointing and reaching-to-grasp movements was investigated using two different approaches (kinematic and modelling) in order to establish whether the type of control varies according to modifications of arm kinematics. Kinematic analysis of arm movements was performed on subjects' hand trajectories directed to large and small stimuli located at two different distances. The subjects were required either to grasp and to point to each stimulus. The kinematics of the subsequent movement, during which subject's hand came back to the starting position, were also studied. For both movements, kinematic analysis was performed on hand linear trajectories as well as on joint angular trajectories of shoulder and elbow. The second approach consisted in the parametric identification of the black box (ARMAX) model of the controller driving the arm movement. Such controller is hypothesized to work for the correct execution of the motor act. The order of the controller ARMAX model was analyzed with respect to the different experimental conditions (distal task, stimulus size and distance). Results from kinematic analysis showed that target distance and size influenced kinematic parameters both of angular and linear displacements. Nevertheless, the structure of the motor program was found to remain constant with distane and distal task, while it varied with precision requirements due to stimulus size. The estimated model order of the controller confirmed the invariance of the control law with regard to movement amplitude, whereas it was sensitive to target size.     

Subjective Size Perception Depends on Central Visual Cortical Magnification in Human V1

In the Ebbinghaus illusion, the context surrounding an object modulates its subjectively perceived size. Previous work implicates human primary visual cortex (V1) as the neural substrate mediating this contextual effect. Here we studied in healthy adult humans how two different types of context (large or small inducers) in this illusion affected size perception by comparing each to a reference stimulus without any context. We found that individual differences in the magnitudes of the illusion produced by either type of context were correlated with V1 area defined through retinotopic mapping using functional MRI. However, participants'' objective ability to discriminate the size of objects presented in isolation was unrelated to illusion strength and did not correlate with V1 area. Control analyses showed no correlations between behavioral measures and the overall V1 area estimated probabilistically on the basis of neuroanatomy alone. Therefore, subjective size perception correlated with variability in central cortical magnification rather than the anatomical extent of primary visual cortex. We propose that such changes in subjective perception of size are mediated by mechanisms that scale with the extent to which an individual''s V1 selectively represents the central visual field.     

Mental Representation of Arm Motion Dynamics in Children and Adolescents

Motor imagery, i.e., a mental state during which an individual internally represents an action without any overt motor output, is a potential tool to investigate action representation during development. Here, we took advantage of the inertial anisotropy phenomenon to investigate whether children can generate accurate motor predictions for movements with varying dynamics. Children (9 and 11 years), adolescents (14 years) and young adults (21 years) carried-out actual and mental arm movements in two different directions in the horizontal plane: rightwards (low inertia) and leftwards (high inertia). We recorded and compared actual and mental movement times. We found that actual movement times were greater for leftward than rightward arm movements in all groups. For mental movements, differences between leftward versus rightward movements were observed in the adults and adolescents, but not among the children. Furthermore, significant differences between actual and mental times were found at 9 and 11 years of age in the leftward direction. The ratio R/L (rightward direction/leftward direction), which indicates temporal differences between low inertia and high inertia movements, was inferior to 1 at all ages, except for the mental movements at 9 years of age, indicating than actual and mental movements were shorter for the rightward than leftward direction. Interestingly, while the ratio R/L of actual movements was constant across ages, it gradually decreased with age for mental movements. The ratio A/M (actual movement/mental movement), which indicates temporal differences between actual and mental movements, was near to 1 in the adults'' groups, denoting accurate mental timing. In children and adolescents, an underestimation of mental movement times appeared for the leftward movements only. However, this overestimation gradually decreased with age. Our results showed a refinement in the motor imagery ability during development. Action representation reached maturation at adolescence, during which mental actions were tightly related to their actual production.     

Center-of-mass alterations and visual illusion of extent

In the present communication, we have developed a computational model related to the conception of positional coding via centers-of-masses (centroids) of the objects’ luminance distributions. The model predictions have been tested by the results of our psychophysical study of geometrical illusion of extent evoked by a modified Brentano figure consisting of three separate spots clusters. In experiments, the centroids of the clusters were manipulated by varying the positions of additional non-target spots flanking the stimulus terminators. A good correspondence between the model predictions and the illusion magnitude changes provided convincing evidences in favor of “centroid” explanation of origin of the illusion investigated.     

Going round in circles: shape effects in the Ebbinghaus illusion

The Ebbinghaus illusion has traditionally been considered as either a sensory or a cognitive illusion, or some combination of these two. Cognitive contrast explanations take support from the way the illusion varies with the degree of shape similarity between the test and inducing elements; we show, however, that contour interaction explanations may account for this result too. We therefore tested these alternative theories by measuring the illusion with different test shapes as well as different inducer shapes, in all combinations. We found that for angular or hexagonal test shapes there is no similarity effect, and for some shape combinations there is no significant illusion, in contradiction to both of the traditional hypotheses. Instead, we suggest that an integrated model of visual processing is needed to account for the illusion.     

Multicenter study on the immunogenicity and safety of two recombinant vaccines against hepatitis B

The immunogenicity and safety of a new recombinant hepatitis B vaccine from the Instituto Butantan (Butang) were evaluated in a multicenter, double-blind, prospective equivalence study in three centers in Brazil. Engerix B was the standard vaccine. A total of 3937 subjects were recruited and 2754 (70%) met all protocol criteria at the end of the study. All the subjects were considered healthy and denied having received hepatitis B vaccine before the study. Study subjects who adhered to the protocol were newborn infants (566), children 1 to 10 years old (484), adolescents from 11 to 19 years (740), adults from 20 to 30 years (568), and adults from 31 to 40 years (396). Vaccine was administered in three doses on the schedule 0, 1, and 6 months (newborn infants, adolescents, and adults) or 0, 1, and 7 months (children). Vaccine dose was intramuscular 10 microg (infants, children, and adolescents) or 20 microg (adults). Percent seroprotection (assumed when anti-HBs titers were > 10 mIU/ml) and geometric mean titer (mIU/ml) were: newborn infants, 93.7% and 351.1 (Butang) and 97.5% and 1530.6 (Engerix B); children, 100% and 3600.0 (Butang) and 97.7% and 2753.1 (Engerix B); adolescents, 95.1% and 746.3 (Butang) and 96% and 1284.3 (Engerix B); adults 20-30 years old, 91.8% and 453.5 (Butang) and 95.5% and 1369.0 (Engerix B); and adults 31-40 years old, 79.8% and 122.7 (Butang) and 92.4% and 686.2 (Engerix B). There were no severe adverse events following either vaccine. The study concluded that Butang was equivalent to Engerix B in children, and less immunogenic but acceptable for use in newborn infants, adolescents, and young adults.     

Discrimination of Image Orientation in the Presence of Distractors

We studied the influence of additional images (distractors) on the recognition of test objects, which included low-contrast Landolt circles with sizes of 1.1, 1.5, and 2.2 angular degrees and were presented eccentrically at 13.2 degrees from fixation. The distractors were either Landolt Cs or full circles with the same spatial characteristics. The distance between the test objects and the distractors varied from 2.2 to 24.2 angular degrees. The subjects were required to report the orientation of the tests (simple task) or to report the orientation of the tests and the shape of the distractor (dual task). The first group of subjects performed both simple and dual tasks, while the second group only performed the simple task. A significant deterioration of performance was recorded at all tested separations in both tasks; it was more pronounced in the dual task. The percent of correct responses was lower when Landolt circles were distractors as compared with full circles. The subjects tended to report the orientation of the distractors instead of tests in the cases of small and large separations. The recognition of distractors was also performed at a lower level in the cases of small and large distances. The data show that attention contributes to the task performance in two ways: the features of tests and distractors are integrated, or the tests are substituted by distractors.     

Brightness contrast effects in monkey lateral geniculate nucleus.

Brightness contrast effects shown by single cells in the macaque's lateral geniculate nucleus were studied with black and white lines of various widths, consisting of either: (1) "simultaneous contrast" stimuli in which the line was produced by luminance changes in the flanking areas or (2) "successive contrast" stimuli in which the line itself changed in luminance. Line widths that gave optimal responses and response magnitudes themselves were similar for the two types of stimulus, except for the widest lines used (2 degrees). Thus, simultaneous brightness contrast is a primary determinant of the response of primate LGN cells but only within 2 degrees of the center of the receptive field. Neural processing up to this level cannot therefore explain the long distance effects of simultaneous brightness contrast in human perception.     

Spatial perception and vestibulomotor responses in man

A study was made on normal human subjects, using a stabilograph to investigate changes in posture produced in response to transcutaneous galvanic stimulation of the right labyrinth. Results were obtained for different head positions and under the illusion of head and trunk rotation produced by stimulating (vibrating) the gulteus maximus muscle. In the absence of illusion of movement, the direction of the vestibulomotor response was determined by the position of the head in relation to the feed: with the normal head position, the body swayed on a frontal plane, and on a sagittal plane when the heat turned through 90°. Vestibulomotor responses were sagittally oriented, as with real head turning, when illusory head and trunk turning through 90° was produced by vibration. When the illusion of head rotation (in relation to the feet) was not produced by this stimulus, the direction of the postural response was not produced by this stimulus, the direction of the postural response was determined by the real orientation of the head. It is concluded that the spatial perception system plays a major part in controlling spatially oriented vestibulomotor responses.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 779–787, November–December, 1986.     

Perceptual distance and the moon illusion

The elevated moon usually appears smaller than the horizon moon of equal angular size. This is the moon illusion. Distance cues may enable the perceptual system to place the horizon moon at an effectively greater distance than the elevated moon, thus making it appear as larger. This explanation is related to the size-distance invariance hypothesis. However, the larger horizon moon is usually judged as closer than the smaller zenith moon. A bias to expect an apparently large object to be closer than a smaller object may account for this conflict. We designed experiments to determine if unbiased sensitivity to illusory differences in the size and distance of the moon (as measured by d') is consistent with SDIH. A moon above a 'terrain' was compared in both distance and size to an infinitely distant moon in empty space (the reduction moon). At a short distance the terrain moon was adjudged as both closer and smaller than the reduction moon. But these differences could not be detected at somewhat greater distances. At still greater distances the terrain moon was perceived as both more distant and larger than the reduction moon. The distances at which these transitions occurred were essentially the same for both distance and size discrimination tasks, thus supporting SDIH.     

Figural After-Effects or the Contrast Illusion

The contrast illusion was studied systematically for a long time by D. N. Uznadze. Experimental findings characteristic of this illusion were published by him first in the Russian (8) and then in the German (18) languages. To produce this illusion, two circles of different size were tachistoscopically presented to the subject 10 or 15 times. After each presentation the subject was required to state which of the circles was the larger: the right or the left. This was the experiment to establish a set [ustanovka] in the course of which the subject developed the readiness, or set, to perceive unequal objects, as is established in critical (control) tests. In the critical test, the subjects, to whom circles of equal size are shown, continue to perceive them as unequal, because they act against a pre-developed set. The effect based on an established set lasts for several displays and, what is of particular interest to us in the given instance, the circle which seems larger is not the one on the side where the larger circle had been presented in the experiments to produce persistent images, but that on the opposite side (where the smaller circle had been seen). This was the manner in which the contrast illusion was discovered, subsequently named the "Uznadze effect" by J. Piaget, who in turn proposed a technique for measuring the strength of this illusion. (17)     

Visually induced plasticity of auditory spatial perception in macaques

When experiencing spatially disparate visual and auditory stimuli, a common percept is that the sound originates from the location of the visual stimulus, an illusion known as the ventriloquism effect. This illusion can persist for tens of minutes, a phenomenon termed the ventriloquism aftereffect. The underlying neuronal mechanisms of this rapidly induced plasticity remain unclear; indeed, it remains untested whether similar multimodal interactions occur in other species. We therefore tested whether macaque monkeys experience the ventriloquism aftereffect similar to the way humans do. The ability of two monkeys to determine which side of the midline a sound was presented from was tested before and after a period of 20-60 min in which the monkeys experienced either spatially identical or spatially disparate auditory and visual stimuli. In agreement with human studies, the monkeys did experience a shift in their auditory spatial perception in the direction of the spatially disparate visual stimulus, and the aftereffect did not transfer across sounds that differed in frequency by two octaves. These results show that macaque monkeys experience the ventriloquism aftereffect similar to the way humans do in all tested respects, indicating that these multimodal interactions are a basic phenomenon of the central nervous system.     

Contextual fear conditioning differs for infant, adolescent, and adult rats

Contextual fear conditioning was tested in infant, adolescent, and adult rats in terms of Pavlovian-conditioned suppression. When a discrete auditory-conditioned stimulus (CS) was paired with footshock (unconditioned stimulus, US) within the largely olfactory context, infants and adolescents conditioned to the context with substantial effectiveness, but adult rats did not. When unpaired presentations of the CS and US occurred within the context, contextual fear conditioning was strong for adults, weak for infants, but about as strong for adolescents as when pairings of CS and US occurred in the context. Nonreinforced presentations of either the CS or context markedly reduced contextual fear conditioning in infants, but, in adolescents, CS extinction had no effect on contextual fear conditioning, although context extinction significantly reduced it. Neither CS extinction nor context extinction affected responding to the CS–context compound in infants, suggesting striking discrimination between the compound and its components. Female adolescents showed the same lack of effect of component extinction on response to the compound as infants, but CS extinction reduced responding to the compound in adolescent males, a sex difference seen also in adults. Theoretical implications are discussed for the development of perceptual-cognitive processing and hippocampus role.     

Visual priming and perception of small pictures in a scene with multiscale objects

Biederman et al. [1, 2] have shown that the priming effect does not depend on the difference between the angular sizes of the test stimulus and the primer. However, these two and other similar studies investigated only a small range of the angular sizes of stimuli. Vakhrameeva et al. [3] have shown that there exist two perceptionally different size ranges: perception of the objects with an angular size varying between 1–1.5 and 50 degrees was found to be invariant, but for the objects whose angular size is less than 1–1.5 degrees, their perception is no longer invariant. In this study, the presence of the priming effect has been investigated in the match-to-sample task with such a difference in the angular sizes of the primer and test stimuli that the sizes of the primer (about 4 degrees) and the test stimulus (about 0.5 degrees) belonged to two different size ranges. The sample stimulus was presented with and without noise superposition. It has been shown that the priming effect is suppressed when the size difference between the primer and the test stimulus is large. A congruent primer can have a positive impact on the recognition of the test objects, but this occurs under the viewing conditions complicated by noise superposition.