Biomedical subjects

B H Tsou

Publications and source records attributed to B H Tsou.

9 recordsLinked to original sources

PubMed2001

Sensorimotor adaptation to violations of temporal contiguity.

Most events are processed by a number of neural pathways. These pathways often differ considerably in processing speed. Thus, coherent perception requires some form of synchronization mechanism. Moreover, this mechanism must be flexible, because neural processing speed changes over the life of an organism. Here we provide behavioral evidence that humans can adapt to a new intersensory temporal relationship (which was artificially produced by delaying visual feedback). The conflict between these results and previous work that failed to find such improvements can be explained by considering the present results as a form of sensorimotor adaptation.

Adult↗

PubMed2001

Perception of forbidden colors in retinally stabilized equiluminant images: an indication of softwired cortical color opponency?

In color theory and perceptual practice, two color naming combinations are forbidden-reddish greens and bluish yellows-however, when multicolored images are stabilized on the retina, their borders fade and filling-in mechanisms can create forbidden colors. The sole report of such events found that only some observers saw forbidden colors, while others saw illusory multicolored patterns. We found that when colors were equiluminant, subjects saw reddish greens, bluish yellows, or a multistable spatial color exchange (an entirely novel perceptual phenomena); when the colors were nonequiluminant, subjects saw spurious pattern formation. To make sense of color opponency violations, we created a soft-wired model of cortical color opponency (based on winner-take-all competition) whose opponency can be disabled.

Color Perception↗

PubMed2001

Perception of spatiotemporal random fractals: an extension of colorimetric methods to the study of dynamic texture.

Recent work establishes that static and dynamic natural images have fractal-like l/falpha spatiotemporal spectra. Artifical textures, with randomized phase spectra, and 1/falpha amplitude spectra are also used in studies of texture and noise perception. Influenced by colorimetric principles and motivated by the ubiquity of 1/falpha spatial and temporal image spectra, we treat the spatial and temporal frequency exponents as the dimensions characterizing a dynamic texture space, and we characterize two key attributes of this space, the spatiotemporal appearance map and the spatiotemporal discrimination function (a map of MacAdam-like just-noticeable-difference contours).

Colorimetry↗

PubMed1994

Grating and flicker sensitivity in the near and far periphery: naso-temporal asymmetries and binocular summation.

A variety of recent physiological and psychophysical experiments provide evidence for a large asymmetry between nasal and temporal processing outside of the central 40 degrees of visual field. Binocular processing has also been found to be reduced outside of this region even though the individual left and right eye fields continue to overlap for a full 120 degrees. In an effort to help quantify these findings, monocular and binocular grating and flicker contrast sensitivities were measured in the fovea and in the near and far periphery. The results show a large asymmetry between nasal and temporal retinal grating sensitivity in the far periphery especially at high spatial frequencies. A smaller asymmetry was found for flicker but no differential effect of flicker frequency was found. The summation results are consistent with previous findings in showing greatly reduced binocular processing outside of the central 40 degrees; this is especially true for the grating stimuli. These results are discussed with respect to possible physiological mechanisms.

Adult↗

PubMed1988

Spectral sensitivity for flicker and acuity criteria.

Different channels in the visual system mediate the detection of flicker and the detection of high spatial frequencies. The magnocellular channel is optimized for flicker detection, whereas the parvocellular channel is optimized for color vision and spatial resolution. The spectral sensitivity of the magnocellular (flicker) channel is obtained by combining cone inputs in the ratio R/G = 5/3; the spectral sensitivity of the parvocellular channel is obtained with the ratio R/G = 2/3. However, when the parvocellular channel is used for resolution, the sensitivity changes from R/G = 2/3 to R/G = 5/3. By hypothesis, this occurs because only parvocellular centers resolve high spatial frequencies and because parvocellular centers are distributed in the same ratio as cones feeding magnocellular cells.

Color Perception↗

PubMed1985

Flicker photometry and achromatic-channel structure.

It is widely assumed that the near-perfect additivity of heterochromatic flicker photometry implies the existence of an achromatic channel in the visual system, which accurately sums R- and G-cone signals. For flicker photometry to be additive, the channel that detects the flicker stimulus need not add cone signals.

Color Perception↗

PubMed1985

Retinal involvement in Morquio's syndrome (MPS IV).

Prior to this report, pigmentary degeneration of the retina had been described in four of the six types of mucopolysaccharidosis (MPS). However, it had not been described in Morquio's syndrome. To the authors' knowledge, the case presented represents the first patient with Morquio's syndrome demonstrating ophthalmoscopic and electrophysiologic abnormalities. The patient demonstrated arteriolar narrowing, as well as an increased photopic b-wave implicit time, decreased scotopic b-wave amplitude, and a slightly abnormal electro-oculogram (EOG). At 43 years of age, this patient represents the oldest individual with Morquio's syndrome tested electrophysiologically. It is proposed that the retinal involvement in the disease is mild but progressive and therefore perhaps is not seen in younger patients but becomes apparent in older persons with Morquio's syndrome.

Adult↗

PubMed1982

Strabismus surgery and its effect upon infant development in congenital esotropia.

Parents of children with congenital esotropia have reported improvements in their child's fine motor development and visual functions after surgery. Eighteen patients with congenital esotropia were tested pre- and post-operatively with The Bayley Scales of Infant Development to determine if these observations were valid. A three-point increase in the Bayley raw score of strabismus patients was noted after operation that is significant at the 0.01 level, as compared to the performance of age-matched controls. An improvement in fine motor skills was observed in 35% of the children, and visually directed reaching and grasping increased in 41%. Item #87 on the Bayley, which requires the child to recognize depressions without monocular clues, appears to be related specifically to depth perception. On this item, the study population showed the greatest improvement.

Child Development↗

PubMed1981

Visual acuities in infants with congenital cataracts operated on prior to 6 months of age.

Seven infants with complete bilateral cataracts were operated on and fitted with extended-wear silicone contact lenses. The infants were matched to 16 normal control subjects. A modified preferential looking technique was used to assess visual acuity; the Bayley Scale of infant Development was administered to measure psychological development. Of the seven infants with cataracts, those operated on prior to 8 weeks of age seemed to have normally developing vision. All others showed a substantial visual lag when compared with the control group. Bayley scores for infants operated on early (before 8 weeks) fell within the range of normal variability. The infants operated on later demonstrated a statistically significant lag in development. Also, a pendular nystagmus was noted in those infants with cataracts who were operated on later.

Age Factors↗