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PubMed1998

Visual-motor, visual-perceptual, and fine motor outcomes in very-low-birthweight children at 5 years.

The prevalence and severity of visual-motor deficits and the relation of visual-motor function to visual perception and fine motor skills was examined in a group of 83 neurologically and intellectually normal (IQ >84) very-low-birthweight (VLBW) children at age 5. Fifteen children (17%) had below average visual motor scores (<1SD below mean). While relatively few children (N=9) had below average scores in visual perception (11%), 58 (71%) had below average scores for fine motor skills. Nineteen (23%) were considered impaired (<1.5SD); of these, eight were severely impaired (<2SD). Fine motor scores were significantly lower in children who had been born <28 weeks' gestation, with hyaline membrane disease, or had required a longer period of ventilation. There was significant correlation between visual-motor and fine motor scores (r = 0.50, P < 0.001) and between visual-motor and visual perception scores (r = 0.42, P < 0.001). The implications of these findings and management of these 'normal' children need further research. Previous reports of visual-motor dysfunction in school-age VLBW children could be related to fine motor difficulties.

Apgar Score↗
PubMed2004

Where bottom-up meets top-down: neuronal interactions during perception and imagery.

Functional magnetic resonance imaging (fMRI) studies have identified category-selective regions in ventral occipito-temporal cortex that respond preferentially to faces and other objects. The extent to which these patterns of activation are modulated by bottom-up or top-down mechanisms is currently unknown. We combined fMRI and dynamic causal modelling to investigate neuronal interactions between occipito-temporal, parietal and frontal regions, during visual perception and visual imagery of faces, houses and chairs. Our results indicate that, during visual perception, category-selective patterns of activation in extrastriate cortex are mediated by content-sensitive forward connections from early visual areas. In contrast, during visual imagery, category-selective activation is mediated by content-sensitive backward connections from prefrontal cortex. Additionally, we report content-unrelated connectivity between parietal cortex and the category-selective regions, during both perception and imagery. Thus, our investigation revealed that neuronal interactions between occipito-temporal, parietal and frontal regions are task- and stimulus-dependent. Sensory representations of faces and objects are mediated by bottom-up mechanisms arising in early visual areas and top-down mechanisms arising in prefrontal cortex, during perception and imagery respectively. Additionally non-selective, top-down processes, originating in superior parietal areas, contribute to the generation of mental images, regardless of their content, and their maintenance in the 'mind's eye'.

Adult↗
PubMed2005

Early modulation of visual cortex by sound: an MEG study.

Sound can alter visual perception. This has been recently demonstrated by a strong illusion in which a single flash is perceived as multiple flashes when accompanied by multiple brief sounds. While psychophysical findings on this sound-induced flash illusion indicate that the modulations of visual percept by sound occur at a perceptual processing level, it remains unclear at what level of perceptual processing these interactions occur and what mechanisms mediate them. Here we investigated these questions using MEG. We found modulation of activity in occipital and parietal scalp locations, when comparing illusion trials with visual-alone and auditory-alone trials. This modulation occurred as early as 35-65 ms from the onset of the visual stimulus. Activity was also modulated in the occipital and parietal areas as well as anterior areas at a later ( approximately 150 ms post-stimulus) onset. No significant interactions were observed in occipital and parietal areas in trials in which illusion was not perceived. These results indicate that the auditory alteration of visual perception as reflected by the illusion is associated with modulation of activity in visual cortex. The early onset of these modulations suggests that a feed-forward or lateral circuitry is at least partially involved in these interactions.

Acoustic Stimulation↗
PubMed2006

Role of the calcarine cortex (V1) in perception of visual cues for saccades.

OBJECTIVE: To determine the initial level at which the pathways for cue perception, saccades and antisaccades diverge. METHODS: Two procedures: single pulse transcranial magnetic stimulation (sTMS) over posterior occiput and backward masking were used. A visual cue directed saccades to the left or right, either a pro-saccade (to the side of the cue but beyond it) or an antisaccade, i.e., contraversive saccade. No visual target was presented. RESULTS: Latencies of the two types of saccades did not differ. Focal sTMS applied unilaterally over V1 suppressed both perception of a cue flashed 80-90ms earlier contralaterally (but not ipsilaterally) and the appropriate saccade. Masking at a delay of 100ms abolished the appropriate saccade and cue perception. CONCLUSIONS: V1 is essential for the perception of a flashed cue and for executing appropriate pro- and contraversive saccades. Masking may occur beyond V1, where the pathways for perception and for saccades at least to the next visual processing level start separating. SIGNIFICANCE: VI is needed for rapid, accurate perceptual and motor responses to the crudest (left versus right) cues. It is unlikely that the "where" system can have a major direct input bypassing V1.

Attention↗
PubMed2000

Social perception from visual cues: role of the STS region.

Social perception refers to initial stages in the processing of information that culminates in the accurate analysis of the dispositions and intentions of other individuals. Single-cell recordings in monkeys, and neurophysiological and neuroimaging studies in humans, reveal that cerebral cortex in and near the superior temporal sulcus (STS) region is an important component of this perceptual system. In monkeys and humans, the STS region is activated by movements of the eyes, mouth, hands and body, suggesting that it is involved in analysis of biological motion. However, it is also activated by static images of the face and body, suggesting that it is sensitive to implied motion and more generally to stimuli that signal the actions of another individual. Subsequent analysis of socially relevant stimuli is carried out in the amygdala and orbitofrontal cortex, which supports a three-structure model proposed by Brothers. The homology of human and monkey areas involved in social perception, and the functional interrelationships between the STS region and the ventral face area, are unresolved issues.

Journal Article↗
PubMed1993

Impaired visual motion perception in the contralateral hemifield following unilateral posterior cerebral lesions in humans.

Contrast thresholds for a number of tasks were measured in the contralateral and ipsilateral upper quadrants of the visual field (eccentricity = 10 degrees) before and after an occipito-parietal surgical resection, in one patient, carried out for intractable epilepsy. Postoperatively the contrast thresholds for discriminating the speed of movement of drifting sine-wave gratings were elevated by greater than a log unit in the contralateral field with little or no change in the detection thresholds for the same stimuli. Contrast thresholds for opposite direction-of-motion (DOM) discrimination of a contrast modulated (CMod) grating (a 'non-Fourier' motion stimulus) were also elevated by about a log unit in the contralateral hemifield but thresholds for DOM discrimination of a sine-wave (luminance modulated, LMod) grating were unaffected. Contrast thresholds for orientation discrimination of stationary gratings (a non-motion task) were unaffected. This general pattern of results was found in two other patients following lateral occipital surgical resections. Eight other patients with occipito-temporal (two cases), parietal (three cases) and medial occipital lobe lesions (three cases) showed no difference between the two hemifields on any of the tasks. Comparison of the location of the lesions leads to the conclusion that damage to the lateral occipital gyri is responsible for the pattern of visual deficit observed. Damage to an extra-striate visual area concerned with motion perception (the human homologue of primate V5-MT) may have occurred. There has been no previous description of impairment of motion perception localized to a hemifield in humans. The characteristics of the residual motion perception in these cases is described further in the accompanying article [Plant and Nakayama (1993), Brain, 116, 1337-1353].

Adult↗
PubMed1993

Inattention and the perception of visual features.

Subjects selectively attended to one of two interleaved, novel figures while ignoring the other figure. In subsequent tests administered to determine the extent to which the ignored figure was perceived, recognition of shape and the location of contour gaps was at the chance level. Moreover, recognition of the presence of contour gaps was significantly below the chance level. These results indicate that preattentive visual processing of unattended objects is too crude to encode global shape and local features such as contour gaps. It is suggested that preattentive processing creates visual representations of unattended objects that contain very limited information about features.

Adult↗
PubMed2000

[Basic principles of physics in optical imaging of the human eye].

Creation of a real picture of the observed object on the retina by optical system of the eye is the primary physical condition of the visual perception. Absorption of the light energy initiates the sequence of further physicochemical, biochemical and psychophysiological events partially taking place already in the retina but mostly in the higher cerebral and spinal centres. So the visual perception and its final evaluation is the result of a complicated complex of processes where the optical imaging itself plays the role of the starting factor. In the publication particularly the physical substance of the optical imaging on refraction surfaces between media with different refraction index has been accentuated. The laws of reflection and refraction and their origin are derived in the terms of the physical (Maxwell equations) and geometrical (Fermat principle, principle of the mutual independence of light beams) optics. In the adequate extent the development and structure of the eye and the whole visual complex, the bases of the quantification of the visual perception and contemporary opinions on mechanisms of the colour vision (trichromatic theory) have been described. The publication is completed by a mathematical appendix explaining some relations usually absent in the biomedical literature.

Electromagnetic Phenomena↗
PubMed2003

Neural substrates of perceptual enhancement by cross-modal spatial attention.

Orienting attention involuntarily to the location of a sudden sound improves perception of subsequent visual stimuli that appear nearby. The neural substrates of this cross-modal attention effect were investigated by recording event-related potentials to the visual stimuli using a dense electrode array and localizing their brain sources through inverse dipole modeling. A spatially nonpredictive auditory precue modulated visual-evoked neural activity first in the superior temporal cortex at 120-140 msec and then in the ventral occipital cortex of the fusiform gyrus 15-25 msec later. This spatio-temporal sequence of brain activity suggests that enhanced visual perception produced by the cross-modal orienting of spatial attention results from neural feedback from the multimodal superior temporal cortex to the visual cortex of the ventral processing stream.

Acoustic Stimulation↗
PubMed1999

The perception of visual images encoded in musical form: a study in cross-modality information transfer.

This study demonstrates the ability of blind (previously sighted) and blindfolded (sighted) subjects in reconstructing and identifying a number of visual targets transformed into equivalent musical representations. Visual images are deconstructed through a process which selectively segregates different features of the image into separate packages. These are then encoded in sound and presented as a polyphonic musical melody which resembles a Baroque fugue with many voices, allowing subjects to analyse the component voices selectively in combination, or separately in sequence, in a manner which allows a subject to patch together and bind the different features of the object mentally into a mental percept of a single recognizable entity. The visual targets used in this study included a variety of geometrical figures, simple high-contrast line drawings of man-made objects, natural and urban scenes, etc., translated into sound and presented to the subject in polyphonic musical form.

Humans↗
PubMed2002

Stable perception of visually ambiguous patterns.

During the viewing of certain patterns, widely known as ambiguous or puzzle figures, perception lapses into a sequence of spontaneous alternations, switching every few seconds between two or more visual interpretations of the stimulus. Although their nature and origin remain topics of debate, these stochastic switches are generally thought to be the automatic and inevitable consequence of viewing a pattern without a unique solution. We report here that in humans such perceptual alternations can be slowed, and even brought to a standstill, if the visual stimulus is periodically removed from view. We also show, with a visual illusion, that this stabilizing effect hinges on perceptual disappearance rather than on actual removal of the stimulus. These findings indicate that uninterrupted subjective perception of an ambiguous pattern is required for the initiation of the brain-state changes underlying multistable vision.

Adolescent↗
PubMed2002

Context effects in visual length perception: role of ocular, retinal, and spatial location.

In three experiments, we examined the transfer of orientation-contingent context effects between the eyes and across portions of the retina with or without variation in external spatial location. Previous research had shown that vertical lines are judged long, relative to horizontal lines, when the stimulus set comprises relatively long horizontals and short verticals (Contextual Condition B), as compared with the reverse when the stimulus set comprises relatively short horizontals and long verticals (Contextual Condition A). Consequently, the contextual set of stimuli influences the magnitude of the horizontal-vertical illusion (HVI), decreasing its size under Contextual Condition A and increasing its size under Contextual Condition B. Experiment 1 showed that exposing one eye to different stimulus contexts modulated the size of the HVI at the exposed eye but had little or no effect at the other eye. Experiments 2 and 3 showed that the effect of the contextual sets generalized poorly across adjacent portions of the retina but transferred almost perfectly across different locations in external space when retinal location was constant. Thus, orientation-contingent context effects in visual length perception appear to be specific to the eye and to the region of the retina stimulated, suggesting that these effects reflect relatively early and local changes in sensitivity, rather than relatively late and general shifts in response criteria.

Adolescent↗
PubMed2006

Asymmetries for the visual expression and perception of speech.

This study explored asymmetries for movement, expression and perception of visual speech. Sixteen dextral models were videoed as they articulated: 'bat,' 'cat,' 'fat,' and 'sat.' Measurements revealed that the right side of the mouth was opened wider and for a longer period than the left. The asymmetry was accentuated at the beginning and ends of the vocalization and was attenuated for words where the lips did not articulate the first consonant. To measure asymmetries in expressivity, 20 dextral observers watched silent videos and reported what was said. The model's mouth was covered so that the left, right or both sides were visible. Fewer errors were made when the right mouth was visible compared to the left--suggesting that the right side is more visually expressive of speech. Investigation of asymmetries in perception using mirror-reversed clips revealed that participants did not preferentially attend to one side of the speaker's face. A correlational analysis revealed an association between movement and expressivity whereby a more motile right mouth led to stronger visual expressivity of the right mouth. The asymmetries are most likely driven by left hemisphere specialization for language, which causes a rightward motoric bias.

Adolescent↗
PubMed2006

Spreading photoparoxysmal EEG response is associated with an abnormal cortical excitability pattern.

Photosensitivity or photoparoxysmal response (PPR) is a highly heritable electroencephalographic trait characterized by an abnormal cortical response to intermittent photic stimulation (IPS). In PPR-positive individuals, IPS induces spikes, spike-waves or intermittent slow waves. The PPR may be restricted to posterior visual areas (i.e. local PPR with occipital spikes only) or spread to anterior non-visual cortical regions (i.e. PPR with propagation). The mechanisms underlying the PPR and causing its spread remain to be clarified. In unmedicated PPR-positive individuals and PPR-negative control participants without any history of previous seizures, we used focal transcranial magnetic stimulation (TMS) to investigate the excitability of the visual or primary motor cortex (M1). In the first experiment [18 healthy control subjects (i.e. without PPR in electroencephalography: 6 females, mean age 26.5 +/- 7.34 years) and 17 healthy participants with PPR (7 females, mean age 25.18 +/- 12.2 years) were studied], occipital TMS was used to elicit phosphenes or to suppress the visual perception of letter trigrams. PPR-positive individuals with propagation had lower phosphene thresholds and steeper stimulus-response curves than individuals without PPR or with occipital spikes only. Occipital TMS also induced a stronger suppression of visual perception in PPR-positive subjects with propagation relative to subjects without PPR or with occipital spikes. In the second experiment, we applied TMS over the right M1 without concurrent IPS and measured the motor threshold, the stimulus response curve, and the duration of the cortical silent period (CSP) in PPR positive individuals with propagation and in PPR-negative control participants [15 right-handed healthy subjects without PPR (3 males, mean age 17.7 +/- 3.6 years) and 14 right-handed healthy individuals showing a PPR with propagation (3 males, mean age 17.4 +/- 3.9 years)]. PPR-positive individuals showed no changes in these excitability measures relative to the PPR-negative control participants. We also measured the modifiability of the CSP by continuous IPS at a frequency of 18 or 50 Hz. While IPS reduced the duration of the CSP in PPR-negative control subjects, IPS had no effect on the duration of the CSP in PPR-positive individuals. Our results provide first time evidence that the propagation of the PPR is associated with increased excitability of the occipital but not the motor cortex. The stronger inhibitory effect of TMS on visual perception and the failure of IPS to shorten the CSP in PPR-positive participants may possibly reflect adaptive changes that prevent the provocation of seizures during the PPR.

Adolescent↗
PubMed1995

The functional architecture of human visual motion perception.

UNLABELLED: A powerful paradigm (the pedestal-plus-test display) is combined with several subsidiary paradigms (interocular presentation, stimulus superpositions with varying phases, and attentional manipulations) to determine the functional architecture of visual motion perception: i.e. the nature of the various mechanisms of motion perception and their relations to each other. Three systems are isolated: a first-order system that uses a primitive motion energy computation to extract motion from moving luminance modulations; a second-order system that uses motion energy to extract motion from moving texture-contrast modulations; and a third-order system that tracks features. Pedestal displays exclude feature-tracking and thereby yield pure measures of the first- and second-order systems which are found to be exclusively monocular. Interocular displays exclude the first- and second-order systems and thereby to yield pure measures of feature-tracking. RESULTS: both first- and second-order systems are fast (with temporal frequency cutoff at 12 Hz) and sensitive. Feature tracking operates interocularly almost as well as monocularly. It is slower (cutoff frequency is 3 Hz) and it requires much more stimulus contrast than the first- and second-order systems. Feature tracking is both bottom-up (it computes motion from luminance modulation, texture-contrast modulation, depth modulation, motion modulation, flicker modulation, and from other types of stimuli) and top-down--e.g. attentional instructions can determine the direction of perceived motion.

Attention↗