Biomedical subjects

Jeffrey J Tsai

Publications and source records attributed to Jeffrey J Tsai.

4 recordsLinked to original sources

PubMed2005

Binocular depth perception from unpaired image points need not depend on scene organization.

Dichoptic stimuli containing unmatched features can produce depth perception despite the absence of binocular disparity, a phenomenon known as da Vinci stereopsis. Unmatched points can arise from depth discontinuities and partial occlusion in the real world. It has been hypothesized that spatial organization of unmatched image features as dictated by the ecological optics of occlusion might determine perceived depth in da Vinci stereopsis. We tested this hypothesis by creating dichoptic stimuli containing unmatched points in which local cues and overall organization could be dissociated. For these stimuli, observers' perception of depth did not depend on the organization of the scene, but only on the local cues. This finding shows the perceived depth of unpaired points need not depend on reconstructing the spatial organization of depth discontinuities in real-world scenes.

Depth Perception↗

PubMed2003

Reading a population code: a multi-scale neural model for representing binocular disparity.

Although binocular neurons in the primary visual cortex are sensitive to retinal disparity, their activity does not constitute an unambiguous disparity signal. A multi-spatial-scale neural model for disparity computation is developed to examine how population activity might be interpreted to overcome ambiguities at the single neuron level. The model incorporates a front end that encodes disparity by a family of complex cell-like energy units and a second stage that reads the population activity. Disparity is recovered by matching the population response to a set of canonical templates, derived from the mean response to white noise stimuli at a range of disparities. Model predictions are qualitatively consistent with a variety of psychophysical results in the literature, including the effects of spatial frequency on stereoacuity and bias in perceived depths, and the effect of standing disparity on increment thresholds. Model predictions are also consistent with data on qualitative appearance of complex stimuli, including depth averaging, transparency, and corrugation. The model also accounts for the non-linear interaction of disparities in compound grating stimuli. These results show that a template-match approach reduces ambiguities in individual and pooled neuronal responses, and allows for a broader range of percepts, consistent with psychophysics, than other models. Thus, the pattern of neural population activity across spatial scales is a better candidate for the neural correlate of depth perception than the activity of single neurons or the pooled activity of multiple neurons.

Depth Perception↗

PubMedDate not supplied

Differentiating recurrent or residual nasopharyngeal carcinomas from post-radiotherapy changes with 18-fluoro-2-deoxyglucose positron emission tomography and thallium-201 single photon emission computed tomography in patients with indeterminate computed tomography findings.

The aim of this study was to compare the accuracy of 18-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) and thallium-201 (Tl-201) single photon emission computed tomography (SPECT) in differentiating recurrent/residual nasopharyngeal carcinomas (NPC) from post-radiotherapy (RT) changes in patients with indeterminate computed tomography (CT) findings. Twenty NPC patients with indeterminate CT findings were included at least 4 months after RT. CT, FDG-PET, Tl-201 SPECT and biopsy were performed within 1 week. The final diagnoses were based on biopsy findings and clinical follow-up for at least 6 months. For differentiating recurrent/residual NPC from post-RT changes in patients with indeterminate CT findings, the sensitivity, specificity and accuracy of FDG-PET were 100.0%, 92.3% and 96.0%, respectively. The sensitivity, specificity and accuracy of Tl-201 SPECT were 91.7%, 92.3% and 92.0%, respectively. Based on this study's findings, we can conclude FDG-PET is more sensitive but equally specific as Tl-201 SPECT is differentiating recurrent/residual NPC from post-RT changes in patients with indeterminate CT findings.

Adolescent↗

PubMedDate not supplied

The clinical usefulness of dual phase 201Tl thyroid scan for false-negative fine-needle aspiration cytological diagnoses in non-functioning cold thyroid nodules.

We evaluated the clinical usefulness of dual phase 201Tl thyroid scan for 11 patients with false-negative fine-needle aspiration (FNA) cytological diagnoses to detect malignant non-functioning thyroid nodules. Benign FNA cytological diagnoses categorized by experienced pathologists were considered as false-negative diagnoses because the final diagnoses of surgical histopathology were malignant. Dual phase thyroid scan, including an early image and a delayed image, were acquired at 10 minutes and 3 hours, respectively, after 2 mCi (74 MBq) of 201Tl was injected intravenously. Dual phase 201Tl thyroid scan findings were visually interpreted as malignant or benign diagnoses. Dual phase 201Tl thyroid scan could accurately diagnose all of the 11 patients with false-negative FNA cytological diagnoses. We concluded that dual phase 201Tl thyroid scan was very useful in detecting malignant non-functioning thyroid nodules in 11 patients with false-negative FNA cytological diagnoses.

Adolescent↗