Alexander N. Sokolov

Orientation specificity in biological motion perception

We addressed the issue of how display orientation affects the perception of biological motion. In Experiment 1, spontaneous recognition of a point-light walker improved abruptly with image-plane display rotation from inverted to upright orientation. Within a range of orientations from 180° to 90°, it was dramatically impeded. Using ROC analysis, we showed (Experiments 2 and 3) that despite prior familiarization with a point-light figure at all orientations, its detectability within a mask decreased with a change in orientation from upright to a range of 90°–180°. In Experiment 4, a priming effect in biological motion was observed only if a prime corresponded to a range of deviations from upright orientation within which the display was spontaneously recognizable. The findings indicate that display orientation nonmonotonically affects the perception of biological motion. Moreover, top-down influence on the perception of biological motion is limited by display orientation.

Recognition of point-light biological motion displays by young children.

We tested the ability of children 3–5 years of age to recognise biological motion displays. Children and adults were presented with moving point-light configurations depicting a walking person, four-legged animals (dogs), and a bird. Participants were able to reliably recognise displays with biological motion, but failed in the identification of a static (four consecutive frames taken from each sequence) version. The results indicate that, irrespective of the highly reduced and unusual structural information available in point-light displays, biological motion is sufficient for reliable recognition of human and non-human forms at an age as early as 3 years. Moreover, 5-year-olds exhibit the ceiling level of recognition. The findings are discussed in the context of the neuropsychological and brain mechanisms involved in biological motion perception.

Chocolate and the brain: neurobiological impact of cocoa flavanols on cognition and behavior.

Cocoa products and chocolate have recently been recognized as a rich source of flavonoids, mainly flavanols, potent antioxidant and anti-inflammatory agents with established benefits for cardiovascular health but largely unproven effects on neurocognition and behavior. In this review, we focus on neuromodulatory and neuroprotective actions of cocoa flavanols in humans. The absorbed flavonoids penetrate and accumulate in the brain regions involved in learning and memory, especially the hippocampus. The neurobiological actions of flavanols are believed to occur in two major ways: (i) via direct interactions with cellular cascades yielding expression of neuroprotective and neuromodulatory proteins that promote neurogenesis, neuronal function and brain connectivity, and (ii) via blood-flow improvement and angiogenesis in the brain and sensory systems. Protective effects of long-term flavanol consumption on neurocognition and behavior, including age- and disease-related cognitive decline, were shown in animal models of normal aging, dementia, and stroke. A few human observational and intervention studies appear to corroborate these findings. Evidence on more immediate action of cocoa flavanols remains limited and inconclusive, but warrants further research. As an outline for future research on cocoa flavanol impact on human cognition, mood, and behavior, we underscore combination of functional neuroimaging with cognitive and behavioral measures of performance.

Gamma-band MEG activity to coherent motion depends on task-driven attention

We examined gamma-band magnetoencephalographic (MEG) activity in humans manipulating attention to visual stimuli by auditory distractors. After exposure to both visual and auditory noise (a baseline), subjects attended to the first of two stimuli (either regular motion of bars or a tone sequence) presented asynchronously, and responded to its offset. A spectral power analysis revealed an increased, relative to baseline, 40 Hz MEG response to attended coherent motion. The enhancement occurred within the initial 50-250 ms from motion onset over modality-specific (occipital) cortices. The increase was not observed when attention was captured by auditory distractors. Our findings suggest that 40 Hz activity in the human visual cortex is related to integration of featural information that is supported by attention.

Reciprocal modulation of neuromagnetic induced gamma activity by attention in the human visual and auditory cortex.

For attentional control of behavior, the brain permanently resolves a competition between the impressions supplied by different senses. Here, using a dual-modality temporal order detection task, we studied attentional modulation of oscillatory neuromagnetic activity in the human cerebral cortex. On each trial, after simultaneous exposure to visual and auditory noise, subjects were presented with an asynchronous pair of a visual and an auditory stimulus. Either of the two stimuli could occur first equally often, their order was not cued. Subjects had to determine the leading stimulus in a pair and attentively monitor it to respond upon its offset. With the attended visual or auditory stimuli, spectral power analysis revealed marked enhancements of induced gamma activity within 250 ms post-stimulus onset over the modality-specific cortices (occipital at 64 Hz, right temporal at 53 Hz). When unattended, however, the stimuli led to a significantly decreased (beneath baseline) gamma response in these cortical regions. The gamma decreases occurred at lower frequencies ( approximately 30 Hz) than did the gamma increases. An increase in the gamma power and frequency for the attended modality and their decrease for the unattended modality suggest that attentional regulation of multisensory processing involves reciprocal changes in synchronization of respective cortical networks. We assume that the gamma decrease reflects an active suppression of the task-irrelevant sensory input. This suppression occurs at lower frequencies, suggesting an involvement of larger scale cell assemblies.

Biological motion shown backwards: the apparent-facing effect.

We examined how showing a film backwards (reverse transformation) affects the visual perception of biological motion. Adults and 6-year-old children saw first a point-light quadruped moving normally as if on a treadmill, and then saw the same display in reverse transformation. For other groups the order of presentation was the opposite. Irrespective of the presentation mode (normal or reverse) and of the facing of the point-light figure (rightward or leftward), a pronounced apparent-facing effect was observed: the perceptual identification of a display was mainly determined by the apparent direction of locomotion. The findings suggest that in interpreting impoverished point-light biological-motion stimuli the visual system may neglect distortions caused by showing a film backwards. This property appears to be robust across perceptual development. Possible explanations of the apparent-facing effect are discussed.

Perceived dynamics of static images enables emotional attribution.

Perception of intentions and dispositions of others is an essential ingredient of adaptive daily-life social behaviour. Dynamics of moving images leads to veridical perception of social attributes. Anecdotal observations in art, science, and popular culture indicate that dynamic imbalance can be revealed in static images. Here, we ask whether perceived dynamics of abstract figures is related to emotional attribution. Participants first estimated instability of geometric shapes rotated in 15° steps in the image plane, and then rated the intensity of basic emotions that can be ascribed to the figures. We found no substantial link between the deviation of the figures from the vertical orientation and perceived instability. Irrespective of shape, a strong positive correlation was found between negative emotions and perceived instability. By contrast, positive emotions were inversely linked with deviation of the figure from vertical orientation. The work demonstrates for the first time that dynamics conveyed by static images enables specific emotional attributions, and agrees well with the assumption that neural networks for production of movements and understanding the dispositions of others are intimately linked. The findings are also of importance for exploring the ability to reveal social properties through dynamics in normal and abnormal development, for example in patients with early brain injury or autistic spectrum disorders.

Periventricular leukomalacia specifically affects cortical MEG response to biological motion

Periventricular leukomalacia (PVL) underlies most of the neurological morbidity including visual‐perceptual deficits in survivors of premature birth. However, it is unknown whether and, if so, how PVL affects functional cortical activity.

Oscillatory MEG response to human locomotion is modulated by periventricular lesions.

Veridical processing of biological movement is of immense value for adaptive behavior and social communication. Here we ask whether and, if so, how oscillatory cortical magnetoencephalographic (MEG) response to biological motion is modulated by early damage to periventricular regions that might affect the pathways interconnecting subcortical structures with cortex and cortico-cortical connectivity. The visual sensitivity to biological motion was lower in adolescents with periventricular leukomalacia (PVL). In controls, the evoked oscillatory MEG response (26.5 Hz) to biological motion peaked at a latency of 170 ms over the right temporo-parietal cortex. This increase was absent in PVL patients. By contrast, peaks in the oscillatory response to biological motion of lower frequency (23.5 Hz) were found in PVL patients later, at a latency of 290 ms over the left temporal region. The findings provide the first evidence for modulation of oscillatory cortical activity by periventricular lesions. The data suggest that PVL affects the brain connectivity with the right temporo-parietal cortex leading to disintegration of the neural network engaged in biological motion processing.

Eye movements in German‐speaking children with and without dyslexia when reading aloud

Acta Ophthalmol. 2010: 88: 681–691