Recognition of lateralized halftone and outline images of everyday objects in conditions of masking

Recognition of the shapes of halftone and outline images of everyday objects in conditions of lateralized tachystoscopic presentation and different levels of noise masking (with “raindrops”) by humans was studied. Mean group data for 15 subjects demonstrated significantly better recognition of outline images of everyday objects by the left hemisphere of the brain than the right at all levels of masking. Increases in masking produced gradual and significant degradation of recognition as compared with controls (recognition of unmasked figures). Recognition of outline images at all levels of masking was significantly better than recognition of halftone images of the same objects. In men, there were no significant differences between hemispheres either at different levels of masking or for different types of stimuli. The neurophysiological mechanisms and functional significance of these effects are discussed. Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavliva, Vol. 58, No. 1, pp. 56–62, January–February, 2008.     

Mechanisms of recognition of the outlines of “vanishing” optotypes

The aim of the present work was to study the interaction between the optical properties of images of “ disappearing” optotypes and their recognition thresholds. The “disappearing” optotypes were figures with complex outlines and had a unique property-they were close to the threshold of recognition and observation, which increases the accuracy of measurement of visual acuity and the subjects’ attention to them. The recognition distances of “disappearing” optotypes were measured. A relationship was found between the recognition distance of “disappearing” optotypes and different optical density profiles on the one hand and the spatial and spatial frequency characteristics of the stimuli on the other. The decisive factor determining the threshold of recognition of optotypes in spatial frequency terms is its spatial frequency spectrum; that in spatial terms is the width of the black/white pair or black-white triad in the complex outline. Regardless of the shape of the optotype, one of the most important limiting factors was the concordance of this test with the scattering function of the subject’s eye optics. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 91, No. 9, pp. 1080–1090, September, 2005.     

Studies of the Perception of Incomplete Outline Images of Different Sizes

The aim of the present work was to assess the range of angular sizes of fragmented images of objects at which perception of the images was scale-independent. Measurements were made of human subjects’ recognition thresholds for the shapes of the objects over a wide range of angular sizes (0.19–50°). The experiments used the Gollin test – a method for studying the recognition of fragmented outline images of objects with which the observer is familiar. The results obtained demonstrated that there is a wide range of angular sizes, from 1.0° to 50°, over which the perception thresholds of incomplete outline images do not change with changes in size, along with a narrow range of stimulus sizes, 0.19–1.0°, over which there is a significant size dependence. We suggest that the increase in thresholds and the failure to recognize images of small size occur as a result of an increased contribution of sampling noise at the level of the human retina.     

Human response to environmental noise: the role of perceived control

Negative impacts of noise exposure on health and performance may result in part from “learned helplessness,” the syndrome of deficits typically produced by exposure to uncontrollable events. People may perceive environmental noise to be uncontrollable, and several effects of noise exposure appear to parallel “learned helplessness” deficits. In the present socioacoustic survey (N = 1,015), perceived control over aircraft noise correlated negatively with some effects of noise (though not others). Furthermore, these effects were better predicted by perceived control than by noise level. These observational data support the claim that “learned helplessness” contributes to the effects of noise exposure.     

The Optical-Geometrical Characteristics and Thresholds of Perception of Fragmented Outline Figures

Measurements were made of the threshold of recognition of cumulatively forming line figures. The threshold value of the outline, expressed in pixels, depended on the length of the outline of the whole unfragmented figure. Relative threshold values were constant, and for the measures of figure fragments used in the present study, averaged 12.5%. A spatial frequency analysis of the test images was performed. Variation of the amplitude-frequency parameters of the spectra of the images of various figures with threshold fragmentation was minimal as compared with the variation of these parameters in figures with subthreshold or suprathreshold levels of fragmentation.     

Optical-geometrical characteristics of fragmented figures and integral perception thresholds in repeated tests

The causes of reductions in the integral perception threshold for fragmented figures in repeat trials using the Gollin test were investigated. The first study involved four trials with 5-day intervals using one set of figures. The amplitude-frequency characteristics of the test stimuli were interpreted using correlation analysis, as were the thresholds in each trial. The second study involved two trials with a three-day interval. On repeat testing, half of the figures were known (from the first test) to the subjects. In addition, half of the figures (both familiar and unfamiliar) were fragmented such that their amplitude-frequency characteristics had values similar to those in the first test. The results showed that the decrease in thresholds were mainly due to optimization of the functioning of the mechanisms operating with the statistical rather than the subject characteristics of the images.     

Executive brain functions after exposure to nocturnal traffic noise: effects of task difficulty and sleep quality

The after-effects of nocturnal traffic noise on cognitive performance and inhibitory brain activity were investigated. Twenty participants (18–30 years) performed an easy and a difficult visual Go/Nogo task with simultaneous EEG recording after a quiet night and then during three nights when aircraft noise was presented with equivalent noise levels of 39, 44, and 50 dBA, respectively, between 11 p.m. to 7 a.m. Based on subjective sleep quality rating, participants were separated into “good” versus “bad” sleepers. The performance and inhibition-related components (N2, P3) of event-related potentials were analysed. The N2 and P3 amplitudes were smaller and latencies were prolonged in the difficult than in the easy task. This effect was more pronounced for Nogo than for Go trials. The Nogo-P3 amplitude was smaller in Noise than in “Quiet” conditions in the difficult task only. In the difficult task, the Nogo-P3 latency was prolonged in bad sleepers than in good sleepers. The Nogo-P3 amplitude was reduced in Noise as compared to “Quiet” conditions in bad sleepers only. Sleep quality in bad sleepers worsened steadily with increasing noise levels. No effects of noise or subjective sleep quality on performance were found. Inhibitory processes appear to be selectively impaired after nocturnal noise exposure. The task difficulty and perceived sleep quality are important factors modulating noise effects. The results suggest that nocturnal traffic noise increase physiological costs for inhibitory functioning on the day even if no overt performance decrement is observed.     

Nonlinear analysis of biological systems using short M-sequences and sparse-stimulation techniques

The m-sequence pseudorandom signal has been shown to be a more effective probing signal than traditional Gaussian white noise for studying nonlinear biological systems using cross-correlation techniques. The effectiveness is evidenced by the high signal-to-noise (S/N) ratio and speed of data acquisition. However, the “anomalies” that occur in the estimations of the cross-correlations represent an obstacle that prevents m-sequences from being more widely used for studying nonlinear systems. The sparse-stimulation method for measuring system kernels can help alleviate estimation errors caused by anomalies. In this paper, a “padded sparse-stimulation” method is evaluated, a modification of the “inserted sparse-stimulation” technique introduced by Sutter, along with a short m-sequence as a probing signal. Computer simulations show that both the “padded” and “inserted” methods can effectively eliminate the anomalies in the calculation of the second-order kernel, even when short m-sequences were used (length of 1023 for a binary m-sequence, and 728 for a ternary m-sequence). Preliminary experimental data from neuromagnetic studies of the human visual system are also presented, demonstrating that the system kernels can be measured with high signal-to-noise (S/N) ratios using short m-sequences.     

The role of lines and corners of geometric figures in recognition performance

A relative role of lines and corners of images of outline geometric figures in recognition performance was studied psychophysically. Probability of correct response to the shape of the whole figure (control) and figures with lines or corners masked to a different extent was compared. Increase in the extent of masking resulted in a drop of recognition performance that was significantly lower for figures without corners, than for figures without part of their lines. The whole 3D figures were recognized better than 2D ones, whereas the opposite relations were observed under conditions of masking. Significant gender difference in a recognition performance was found: men recognize entire and partly masked figures better than women. Possible mechanisms of relatively better recognition of figures with corners than with lines are discussed in connection with finding of high sensitivity of many neurons in the primary visual cortex to line crossing and branching.     

Association between locus of control in childhood and psychotic symptoms in early adolescence: Results from a large birth cohort

Introduction. Episodic memory is significantly impaired in people with schizophrenia. The precise cause of this impairment has yet to be determined, as the formation of episodic memories is dependent on other processes, some of which also show impairment in schizophrenia. One such process is closure, that is, the filling-in of missing information. Failure to close adequately incomplete stimuli may cause people with schizophrenia to store inadequate or piecemeal representations in memory.

Methods. Forty people with schizophrenia and 21 healthy comparison subjects participated in the study. The experiment was divided into six blocks, each of which involved both an encoding and a recognition phase. During the encoding phase, 20 figures were presented sequentially and participants had to determine whether each was symmetric or asymmetric. These figures were either complete or fragmented at three different levels. In subsequent recognition phase, 40 abstract figures (20 new and 20 old) were presented. All figures were complete in this phase.

Results. Memory performance of both groups was affected similarly by fragmentation, with an additional increase in performance afforded by a slight fragmentation for participants with schizophrenia.

Conclusion. Slight fragmentation may have induced a perceptual difficulty that was mild enough to increase visual processing without compromising it. Closure was thus not involved in the episodic memory deficit of people with schizophrenia.     

Auditory dominance over vision in the perception of interval duration

The “ventriloquist effect” refers to the fact that vision usually dominates hearing in spatial localization, and this has been shown to be consistent with optimal integration of visual and auditory signals (Alais and Burr in Curr Biol 14(3):257–262, 2004). For temporal localization, however, auditory stimuli often “capture” visual stimuli, in what has become known as “temporal ventriloquism”. We examined this quantitatively using a bisection task, confirming that sound does tend to dominate the perceived timing of audio-visual stimuli. The dominance was predicted qualitatively by considering the better temporal localization of audition, but the quantitative fit was less than perfect, with more weight being given to audition than predicted from thresholds. As predicted by optimal cue combination, the temporal localization of audio-visual stimuli was better than for either sense alone.     

Immobility and Hyperthermia in the Tail Suspension Test: Association with the Porsolt Test and the Reflex Startle Reaction in 11 Inbred Mouse Strains and the Effects of Genetic Knockout of MAO A

Immobility and hyperthermia induced by unavoidable stress imposed by the tail suspension test (TST) and the acoustic startle reaction were assessed in mice of 11 inbred strains and in Tg8 mice, which have genetic knockout of MAO A. Sharp genotypic differences in immobility were seen, while there was no correlation with the hyperthermic response to the TST. A correlation was found between the extent of immobility in the TST and the startle reaction. Studies of 11 strains of mice revealed a positive correlation between the duration of immobility in the TST and the Porsolt “despair test.” Genetic knockout of MAO A, one of the key enzymes in catecholamine and serotonin metabolism in the brain, weakened the startle reaction and TST-induced hyperthermia but had no significant effect on the immobility of Tg8 mice, which provides evidence of differences in the neurochemical regulation of these reactions. These data provide grounds for using the TST as a “dry” Porsolt test and identify TST-induced hyperthermia as a model for reactions to unavoidable stress.     

Studies of the Behavior of “Impulsive” and “Self-Controlled” Animals in an “Emotional Resonance” Test

Rats divided on the basis of a test in which they were presented with the “right” to choose a more valuable but delayed or a less valuable but immediate reinforcement into “impulsive” and “self-controlled” groups were studied using the “emotional resonance” method. These experiments showed that none of the rats of the “self-controlled” group, selecting the more valuable but delayed reinforcement, avoided defensive arousal signals from another individual of the same species, preferring to spend a large proportion of time in the dark “house.” Most (80%) of the animals of the “impulsive” group spent more than half the experimental period in the light sector, thus saving the partner from electrical stimulation. It is suggested that there are several common mechanisms underlying these two types of behavior.     

Influence of “animal hypnosis” on the motor polarizational dominant in rabbits

The influence of the state of “animal hypnosis” in rabbits on the course and preservation of the motor polarizational dominant created by the action of a direct current anode on the region of the sensorimotor cortex was investigated. The mechanogram of both forelimbs was recorded. It was demonstrated that the state of “animal hypnosis” induced against the background of the optimum of the dominant inhibits the motor reaction of the “dominant” limb to sensory test stimuli. This inhibition is maintained for a long time, up to two to four days. The motor polarizational dominant does not extinguish under the influence of “animal hypnosis,” but is inhibited; after the extinction of the traces of the “hypnosis,” the motor dominant reaction recovers under the influence of sensory test stimuli alone, without the repeated use of the direct current. Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow. Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 45, No. 1, pp. 132–139, January–February, 1995.     

Resistance of fetal membranes to concentrated force applications and reconciliation of puncture and burst testing

To further the characterization of the chorioamniotic membrane’s physical properties, we assessed its ability to withstand a concentrated force. Probes of various diameters were used to puncture 275 specimens from 11 membranes. Values for “strength”/thickness, “stiffness”/thickness, and “toughness”/thickness all showed positive linear correlations (p<0.001) with the increase ofd/D, the ratio of probe diameter to specimen diameter. “Ductility” was independent of diameter, though a logarithmic regression did fit the data marginally (p<0.05). The separate fracture of the amnion and chorion, which is reflected in ductility measurements, results in an increase in the distance the membrane can be deflectedin vitro. In vivo, this behavior would translate to a reduction of pressure exerted on the remaining membrane, while the integrity of the protective sac is maintained. The data pool of mechanical characteristics was enlarged by reconciling data that were gathered by either of two testing methods: puncturing or bursting; the latter method involves the application of force over the entire surface of the test specimen.     

The influence of stimulus shape on orientation acuity

Orientation acuity was estimated for vertical and oblique bar stimuli. Discrimination thresholds were affected by changes in the length and width of the targets, falling as bar length was increased and, conversely, rising as the bars were made wider. These changes are complimentary, in that overall discrimination performance can be predicted by a single measure of the orientation “entropy” of the target, namely the height-to-width ratio. The data provide support for a model of orientation coding where discrimination performance is not simply a reflection of the signal-to-noise ratio in single cells in the striate cortex. Received: 10 July 1997 / Accepted: 5 November 1997     

Blood volume and body haematocrit of rats native to a simulated altitude of 3500 m

Circulating blood volume (BV) as the sum of circulating red cell volume (RCV) and plasma volume (PV) was estimated in rats native to a simulated altitude of 3500 m (“natives”), in rats born at sea level and later in life transferred to the simulated high altitude (“newcomers”), and in control sea-level rats. RCV per kg body weight (b.w.) was significantly larger in both “newcomers” and “natives” than in controls. PV per kg b.w. was in the “newcomers” insignificantly and in the “natives” significantly smaller than in the controls. BV per kg b.w. in both high altitude groups tended to be larger than in controls but the difference was not significant. Arterial haematocrit (Ahct) in the “newcomers” was significantly higher than in the controls, and in the “natives” significantly higher than in both other groups. Body haematocrit (the ratio of RCV and BV in per cent) was smaller than Ahct in all groups; this was more pronounced in the “newcomers” than in the controls and even more so in the “natives”. Apparently the haematocrit in the minute vessels of the organs of animals exposed to chronic hypoxic hypoxia increases much less than might be expected from changes of the Ahct. An attempt was made to evaluate the possible error of the more commonly used method of estimating BV, when only RCV, or only PV, is measured, and BV and its complementary fraction are calculated from arterial or venous haematocrit. When, in our results, BV was calculated from RCV and Ahct, the absolute values and also the differences between groups were somewhat underestimated. When BV was calculated from PV and Ahct, the BV itself, and particularly the differences between groups, were overestimated quite considerably. It is suggested that the only safe way to estimate BV is to measure RCV and PV separately.     

EEG Frequency-Amplitude Characteristics of the Successful Recognition of Emotional Speech

EEG frequency-amplitude characteristics were studied in two groups of subjects, with high and low “emotional hearing” measures. Comparison of power over the whole EEG range between the two groups of subjects led to the conclusion that the EEG activation level was significantly higher in subjects with low “emotional hearing” measures than in those with high levels. This group also showed a higher level of activation in the posterior temporal areas of the cortex of the right hemisphere on recognition of emotions in speech. Thus, high initial levels of cortical activation and greater EEG reactivity on hearing emotional phrases are factors hindering the recognition of emotional expression in speech.     

Differentiation between human and animal isolates of Cryptosporidium parvum using molecular and biological markers

Isolates of Cryptosporidium parvum obtained from infected humans, calves and lambs were typed using arbitrary primed polymerase chain reaction (AP-PCR) and isoenzyme electrophoresis. All animal isolates tested (n = 17) showed similar profiles in AP-PCR and isoenzyme typing. In AP-PCR assays, 9 out of 15 human isolates showed a distinct “human” profile while the remaining 6 isolates showed the “animal” profile. In isoenzyme typing, 5 human isolates which had shown “human” profiles in AP-PCR demonstrated a unique isoenzyme banding pattern, while 2 isolates which had shown “animal” profiles in AP-PCR gave the “animal” banding pattern. In a murine model of infection, all four animal isolates tested were highly infective but only one of four human isolates identified as “human” type in the AP-PCR and isoenzyme typing systems was infective. The good correlation between the data from the different typing systems supports the hypothesis that there are genetically distinct human and animal populations of C. parvum. Received: 27 May 1997 / Accepted: 15 September 1997