Biomedical subjects

Chuan Hou

Publications and source records attributed to Chuan Hou.

11 recordsLinked to original sources

PubMed2006

Neural correlates of shape-from-shading.

Visual evoked potentials were recorded during presentation of a single stimulus that generated bi-stable perceptual alternation between two different three-dimensional percepts. One interpretation (asymmetric) changed depth structure from flat to corrugated in depth and the other (symmetric) had the appearance of a flat surface translating laterally behind a set of apertures. Responses during perception of the asymmetric three-dimensional structure contained larger negative components than did responses during perception of the symmetric three-dimensional structure. Control experiments suggest that the interpretation of depth structure is selected after junction information caused by the interplay between shading and object shape is extracted.

Adult↗

PubMed2006

Sweep visual evoked potential grating acuity thresholds paradoxically improve in low-luminance conditions in children with cortical visual impairment.

PURPOSE: Children with cortical or cerebral visual impairment (CVI) often experience photophobia. In a study conducted to test whether this clinical phenomenon affects visual function, the sweep visual evoked potential (VEP) was used to evaluate cortical responses to grating stimuli in two luminance conditions: low and normal. METHODS: Twenty children (age range, 7 months to 4 years 10 months) with CVI and 17 age-matched control subjects were examined. Testing conditions consisted of a swept grating stimulus shown against a normal background luminance (109 cd/m2) and against a low-luminance background (20 cd/m2). Thresholds in these two luminance conditions were compared. Response amplitudes across the spatial frequency domain were also compared. RESULTS: Children with CVI paradoxically have improved grating acuity thresholds when the stimulus is shown using a low-luminance background (P=0.006). Response amplitudes are also increased in low luminance. In control children, luminance had no significant effect on response amplitudes or thresholds. CONCLUSIONS: Increased luminance causes a worsening of acuity thresholds in children with CVI. Response amplitudes are also diminished in normal luminance. This finding has implications for optimal viewing and learning conditions for children with CVI.

Blindness, Cortical↗

PubMed2006

[Study on crossed and uncrossed disparity evoked potential of dynamic random dot stereogram].

OBJECTIVE: To analyze the disparity evoked potentials (DEP) of fine disparities, coarse disparities, crossed disparities and uncrossed disparities and provide parameters of impersonal examining stereopsis. METHODS: A software package for generating dynamic random dot stereogram (DRDS) was developed as a visual stimulus to elicit DEP in 30 normal subjects. The DEP of every subject was recorded in different crossed and uncrossed disparity stimuli (4', 8', 15', 23', 30', 45', 53', 60', 72', 87', 102', 124', 150' of arc). RESULTS: (1) the constant negative-positive complex wave was observed in different disparity stimuli. (2) The N wave's latency of -45' was the longest, the N wave's latency of -150' was the shortest among crossed disparities. The N wave's latency of 4', 23' was the longest, the N wave's latency of 124' was the shortest among uncrossed disparities. (3) The amplitude peak of P wave occurred at -23', -60', -150' among crossed disparities. The amplitude peak of P wave occurred at 15', 45', 72' among uncrossed disparities. (4) All characteristic crossed disparities were smaller than the uncrossed disparities. The change orderliness of small crossed disparities was different from that of small uncrossed disparities. CONCLUSIONS: The N wave's latency and the P wave's amplitude can be used as parameters to impersonally examine stereopsis. These results suggest that stereopsis can be divided into fine crossed stereopsis, fine uncrossed stereopsis, coarse crossed stereopsis, and coarse uncrossed stereopsis.

Adolescent↗

PubMed2005

Experience-expectant development of contour integration mechanisms in human visual cortex.

Extended contours are a common feature of natural images. Most previous studies have considered contour integration as a two-dimensional process of linking like-oriented elements along their common orientation axis. Yet contours exist in a three-dimensional world, and one might therefore ask about the relationship between contour integration and binocular vision. Using an event-related potential assay of contour integration, we demonstrate that patients with strabismic amblyopia show a relative insensitivity to Gabor-defined contours in their dominant eyes, all of which had normal acuity. These deficits were not seen in the dominant eyes of patients with anisometropic amblyopia without strabismus, but were present in the amblyopic eyes of patients with either strabismus or anisometropia. Deficits were also found in both eyes of strabismus patients who had normal visual acuity in each eye, but who had strongly reduced or absent stereopsis. These results suggest that the maturation of contour detection mechanisms depends at least in part on the presence of normal binocular interaction during a developmental critical period.

Amblyopia↗

PubMed2005

Delayed visual attention caused by high myopic refractive error.

Delayed visual maturation (DVM) is usually a retrospective diagnosis given to infants who are born with no or poor visually-directed behavior, despite normal acuity on objective testing, but who recover months later. This condition can be organized into several types based on associated neurodevelopmental or ocular findings, but the etiology of DVM is probably complex and involves multiple possible origins. Here we report two infants who presented with delayed visual maturation (attention). They were visually unresponsive at birth but were later found to have high myopic errors. Patient 1 had -4 D right eye, -5 D left eye. Patient 2 had -9 D o.u. Upon spectacle correction at 5 and 4 months, respectively, both infants immediately displayed visually-directed behavior, suggesting that a high refractive error was the cause of inattention in these patients. These findings could add to knowledge surrounding DVM and the diagnosis of apparently blind infants. Findings presented here also indicate the importance of prompt refractive error measurement in such cases.

Attention↗

PubMed2005

Development of sensitivity to texture and contour information in the human infant.

Texture discrimination and bounding contour extraction are essential parts of the object segmentation and shape discrimination process. As such, successful texture and contour processing are key components underlying the development of the perception of both objects and surfaces. By recording visual-evoked potentials, we investigate whether young infants can detect orientation-defined textures and contours. We measured responses to an organized texture comprised of many Gabor patches of the same orientation, alternated with images containing the same number of patches, but all of random orientation. These responses were compared with a control condition consisting of the alternation between two independently random configurations. Significant difference potentials were found as early as 2-5 months, as were significant odd harmonics in the test conditions. Responses were also measured to Gabor patches organized either as circles (all patches tangent to an imaginary circular path) alternated with pinwheels (all patches having a fixed orientation offset from the path). Infants between 6 and 13 months also showed sensitivity to the global organization of the elements along contours. Differential responses to our texture and contour stimuli and their controls could only have been generated by mechanisms that are capable of comparing the relative orientation of 2 or more patches, as no local information at a single patch distinguished the random and organized textures or the circle and pinwheel configurations.

Adult↗

PubMed2004

Normal vernier acuity in infants with delayed visual maturation.

PURPOSE: Measures of vernier acuity may correlate accurately with measures of Snellen acuity. We used the sweep visual evoked potential to determine whether vernier acuity is normal in children with delayed visual maturation (DVM). DESIGN: Case series of two infants. METHODS: Thresholds for grating and vernier acuity were measured electrophysiologically in two infants with DVM using the sweep visual evoked potential. Acuity thresholds were calculated for each of these visual functions. RESULTS: Two infants with DVM had normal thresholds for grating and vernier acuity, even though their visual behavior as determined clinically was abnormal. CONCLUSIONS: Some children with DVM have normal acuity thresholds, even though the behaviors associated with vision are delayed or absent.

Developmental Disabilities↗

PubMed2003

Development of the spatial organization and dynamics of lateral interactions in the human visual system.

Psychophysical thresholds and neuronal responses for isolated stimuli are strongly modified by nearby stimuli in the visual field. We studied the orientation and position specificity of these contextual interactions using a dual-frequency visual-evoked potential technique in developing human infants and adults. One set of small, oriented stimulus elements (targets) was tagged with a temporal frequency f1 of 4.52 Hz. The addition of an abutting second set of similar patches (flankers) tagged at f2 = 2.58 Hz had three effects: (1) The flankers reduced the second and fourth harmonic responses to the targets. This reduction was independent of flanker orientation or position and age. (2) The response to the combination of targets and flankers also contained nonlinear interaction terms (1f1 +/- 1f2) that were tuned for flanker orientation and position in adults, but only for flanker orientation in infants 8-31 weeks of age. (3) Nonlinear interaction terms recorded at 2f1 +/- 2f2 were large and untuned for flanker orientation and position in adults but were nearly absent in the youngest infants. The three forms of nonlinear interaction, thus, have differences in sensitivity to flanker orientation and position and differential growth trends, indicating that they are generated by different mechanisms. These three forms of interaction could serve different functional roles. The first process provides a nonselective gain control that is fully functional in early infancy. The second process, which develops slowly, is selective for the specific form of the stimuli. The third process, which is also immature, pools across orientation.

Adolescent↗

PubMed2003

Transient, idiopathic nystagmus in infants.

The aim of this study was to characterize children with transient nystagmus. Eleven children (six males, five females) developed nystagmus in infancy and then experienced regression of the problem, usually within a few months. Mean age at onset was 2.7 months, and mean age at regression was 8.5 months. No etiology could be ascertained in any of the patients, although four children had other eye or vision abnormalities (regressed retinopathy of prematurity, n=1; asymmetric fundus colobomata, n=1; delayed visual maturation, n=2). Results of this study suggest that mechanisms which allow ocular motor stability undergo a period of postnatal maturation, during which nystagmus can occur, but also during which nystagmus may disappear. Not every case of transient nystagmus should be categorized as spasmus nutans. There is a subset of infants and young children who develop transient nystagmus with no other findings and in whom the nystagmus disappears.

Age of Onset↗

PubMed2003

[Stereopsis of the patients after cataract extraction and intraocular lens implantation].

OBJECTIVE: To understand the stereopsis of the patients after cataract extractation and intraocular lens implantation and the related factors. METHODS: In this study were examined the stereopsis of 30 patients who had undergone cataract extraction and intraocular lens implantation and whose post-operative vision acuity measurements were 0.5 or higher. RESULTS: These patients' steroacuity, anisometropia, aniseikonia and scotoma were: 407.67" +/- 390.19", 1.53D +/- 1.96D, 3.93% +/- 3.51%, 3.17" +/- 1.98" respectively. There was no significant correlation between steroacuity anisometropia and aniseikonia. There was siganificant positive correlation between steroacuity and scotoma. CONCLUSIONS: Intraocular lens implantation may ameliorate anisometropia and aniseikonia of the patients after cataract extraction and reduce the damage to stereopsis.

Adult↗

PubMed2002

[An epidemiological study on senile cataract in urban and rural areas of Chengdu].

OBJECTIVE: To find out the status and distribution characteristics of senile cataract, which is one of the common disease affecting the quality of life of the elderly people. METHODS: One thousand and sixteen people aged 60 or more in the urban and rural areas of Chengdu were included by cluster random sampling and investigated by questionnaire method and medical examination. RESULTS: It was found that the prevalence of senile cataract was 52.3% in urban area and 51.3% in rural area. The prevalence was higher in women than in men, and it increased with age. The prevalence of senile cataract by past diagnosis was lower than that by present medical examination; this difference was found obvious in the rural area. CONCLUSION: The prevention and treatment of senile cataract should be strengthened.

Aged↗