Developmental changes in hierarchical visual stimulus recognition in children aged 5-10 years

Reaction time (RT) and performance accuracy in hierarchical visual stimulus recognition at local and global levels were studied in 95 healthy 5-6, 6-7, 7-8 and 9-10-year-old children and 10 adults. Task performance of all examined subjects, both children and adults, was faster and more accurate during global feature recognition (global advantage effect), with increased RT to incongruent stimuli in local condition (global interference effect). Significant inter-individual differences were found in the youngest group (5-6-year-olds): 7 children from the total number of 37 subjects failed to show the global advantage and global interference effects. Significant progressive shifts in performance accuracy during hierarchical stimulus recognition at both local and global levels were observed in the period between 6-7 and 7-8 years and then between 9-10 years and adulthood. The time course of age-dependent changes in recognition time was different for the global and local features of the hierarchical stimuli: the RT significantly decreased in every successive age group for local feature recognition beginning from 6-7-year-old children, whereas there was no significant difference between 7-8 and 9-10-year-old children in the RT of the recognition of the global feature. In the two younger groups (5-6 and 6-7 years), the stimulus type affected performance in a specific manner: RT increased to both incongruent and neutral stimuli irrespective of the level of the target feature. It was assumed that nonlinear developmental trends in hierarchical stimulus recognition parameters depend on both maturation of visual information processing and development of executive functions, especially those related to selection of relevant signals.     

Event-related potentials to faces: the effects of priming and recognition

Short-term visual memory, as in both implicit priming and explicit recognition tasks, can be demonstrated by decreased reaction times, the ability to preferentially select previously presented objects from lists and the ability to more readily complete previously exposed words from fragmented letters. The visual processing of faces occurs separately from the visual processing of non-face stimuli, within discrete areas of bilateral posterior inferotemporal cortices. While visual recognition and memory of faces are independent of those for non-faces, their processing appears to be similar. We have demonstrated an electrophysiologic correlate of short-term visual memory in a face-matching paradigm. We have observed a series of evoked potential components consisting predominantly of a C140, C180 and C240 with a posterior, bitemporal distribution. The priming effect is reflected by a diminution of C240 amplitude in the response to repeated pictures of faces compared to novel pictures of faces. These data reflect a previously unreported set of neurophysiological observations on short-term visual memory for faces.     

Event-related potentials at different stages of the operation of visual working memory

Trace fixation and comparison with incoming information was studied using event-related potentials (ERPs) recorded from various cortical areas during passive viewing and matching of two consecutive pictures. Visual stimuli differing in the spatial location of elements (4 × 4 square patterns with random positions of 4 black and 12 white squares) and phonological stimuli (differently written letters) were used. Trace fixation was studied by comparing the ERPs generated in response to the first (reference) stimulus in the pair with those generated during passive viewing. Sensory analysis of the reference stimuli was observed in the time interval 128–196 ms. For the patterns presented, it was reflected by an increased amplitude of the N1 component in the caudal areas as compared with passive viewing. The phonological stimuli produced a higher amplitude of a positive wave in the frontotemporal area in the same time interval. Processing of subsequent information to be stored in memory was observed in the interval 232–452 ms. Processing of patterns was reflected by a decreased positivity, most pronounced in the left temporo-parieto-occipital area. Comparison of a trace with incoming information was studied by comparing the ERPs generated in response to the first (reference) and second (test) stimuli. The number of cortical areas involved in the sensory analysis of the test stimuli was larger than the number involved in the analysis of the reference stimuli. Comparison of the new information with the trace was reflected by an increased amplitude of the late positive wave (components P3, Pc, and Pc-Nc) in the frontocentral and caudal cortical areas. The topographic changes in the late positive components depended on the type of stimulus.     

The influence of recognition of a visual stimulus on evoked potentials of the projection and non-projection areas of the cerebral cortex]

Evoked potentials (EP) were recorded in the projection and non-projection areas of the cerebral cortex in juveniles in response to exposures of structured visual stimuli with subthreshold and supraliminal durations. The data obtained have shown that recognition of the presented stimulus is attended with intensification of the EP late complex. This effect is most pronouned in the central and frontal parts of the cortex. The Nv component with a 240 to 300 msec latency has a more regular connection with recognition as compared with other components.     

Manifestations of the genotypic causality of human evoked potentials during perception of various visual stimuli

Intrapair resemblance of the wave form and amplitude-temporal parameters of evoked potentials (EPs) to flashes, chess field, house image, the word "house" and a series of other stimuli was evaluated in 20 pairs of monozygotic and 20 pairs of homosexual dizygotic adult twins. In the occipital area the maximum of genetic dependence was characteristic of EPs to flashes, the minimum--of EPs--to the word "house". In vertex EPs parameters genotypic effects were manifest irrespectively of the stimulus type. Genotypic dependence differed for the amplitudes and latencies of separate EP components.     

Hemispheric asymmetry of visual evoked potentials during human recognition of facial emotional expressions

Visual evoked potentials (VEP) in standard 16 EEG derivations were recorded in 26 young men and 20 women during recognition of facial emotional expressions and geometric figures. The stimuli were presented on a computer screen in the center of the visual field or randomly in the right or left vision hemifields. Peak VEP latency and mean amplitude in 50-ms epochs were measured; spatiotemporal VEP dynamics was analyzed in a series of topographic maps. The right hemisphere was shown to be more important in processing emotional faces. The character of the asymmetry was dynamic: at earlier stages of emotion processing the electrical activity was higher in the right inferior temporal region compared to the left symmetrical site. Later on the activity was higher in the right frontal and central areas. The dynamic mapping of "face-selective" component N180 of VEPs revealed the onset of activation over the right frontal areas that was followed by the fast activation of symmetrical left zones. Notably, this dynamics didn't correlate with the hemifield of stimuli exposition. The degree of asymmetry was lower during presentation of figures, especially in the inferior temporal and frontal regions. The prominent asymmetry of information processes in the inferior temporal and frontal areas was suggested to be specific for recognition of facial expression.     

Event-related potentials to conjunctions of spatial frequency and orientation as a function of stimulus parameters and response requirements

ERPs were recorded from subjects who were required to push a button in response to a given conjunction of spatial frequency and orientation (target), and to ignore conjunctions sharing with the target only frequency (frequency-relevant), only orientation (orientation-relevant), or neither (irrelevant). Differences between ERPs to irrelevant and frequency-relevant stimuli were identified as frontal selection positivity (Fz, 150–200 msec post-stimulus), selection negativity (Oz, just after 200 msec), and vertex N2b (200–250 msec). For relevant orientations, the selection negativity and the N2b were also found, but the frontal selection positivity was elicited only when the spatial frequency was relevant as well. Neither of these 3 waves was sensitive to spatial frequency or orientation per se. Other waves (N80, N180) did show such sensitivity, but this was independent of stimulus relevance. Hence, direct evidence for the neural-specificity theory, stating that task-related selective ERP responses reflect differential enhancement of activity in stimulus-specific pathways, was not obtained. It is further concluded that ERPs associated with selection of frequency and orientation are highly comparable to those associated with other visual dimensions (e.g., color), and that selection of multiple visual dimensions may be hierarchical at one level of processing and independent at another.     

Event-related potentials in the dorsal hippocampus of rats during an auditory discrimination paradigm

The relation of the hippocampal neuronal activity to the rat event-related potential (ERP) generation was examined during an auditory discrimination oddball paradigm. ERPs were recorded using a linearly-arranged series of electrodes chronically implanted at the skull, in the frontoparietal cortex, in the CA1 and CA3 regions of the dorsal hippocampus and in the thalamus. The target tone elicited N40, P100, N200, and P450 at the skull electrode. The non-target tone, on the other hand, prominently evoked only the P100 component. At the intracranial electrodes, the ERP amplitude at the latency of the skull P450 was significantly greater in the CA3 region than that at other recording sites, although a phase reversal was not observed. The results indicate that the P450 of the rat may correspond to the human P3, and that the neuronal activity in the hippocampus is involved in its generation.     

Frequency-contrast sensitivity of visual stimulus perception in patients with schizophrenia treated with atypical and typical antipsychotics

The effects of typical and atypical antipsychotics on the perception of visual stimuli that preferentially activate magnocellular or parvocellular visual channels have been studied. The threshold contrast sensitivity in healthy individuals and patients with schizophrenia has been recorded. The Gabor-like sinusoidal brightness gratings and spatial frequencies of 0.4, 3.6, and 17.9 cycles/degree were presented to the tested objects. The patients were divided into two groups, one receiving the therapy with atypical antipsychotics, and the other, with typical ones. The contrast sensitivity for low and medium spatial frequencies (i.e., for the stimuli corresponding to magnocellular channels) decreased compared to the norm. Note that the decrease in the contrast sensitivity for the low spatial frequencies in the patients treated with atypical antipsychotics is significantly more pronounced compared to the cohort that received typical antipsychotics.     

Effect of genotype on evoked potentials of the left and right hemispheres during perception of visual stimuli

Intrapair similarity of evoked potentials (EPs) to light flash, checkerboard, house picture, the word "house" and a number of other stimuli was estimated in 20 pairs of monozygotic and 20 pairs of dizygotic adult twins of the same gender. In the right temporal area the level of the genotypic control of amplitude-temporal parameters of EPs on the whole is higher than in the left one; the more prominent this difference is in responses to spatial-structural stimuli. In the left temporal area, the genotypic control is manifested in latencies of components of EPs to linguistic stimuli.