Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Pattern Recognition and Machine Learning

Many current neurophysiological, psychophysical, and psychological approaches to vision rest on the idea that when we see, the brain produces an internal representation of the world. The activation of this internal representation is assumed to give rise to the experience of seeing. The problem with this kind of approach is that it leaves unexplained how the existence of such a detailed internal representation might produce visual consciousness. An alternative proposal is made here. We propose that seeing is a way of acting. It is a particular way of exploring the environment. Activity in internal representations does not generate the experience of seeing. The outside world serves as its own, external, representation. The experience of seeing occurs when the organism masters what we call the governing laws of sensorimotor contingency. The advantage of this approach is that it provides a natural and principled way of accounting for visual consciousness, and for the differences in the perceived quality of sensory experience in the different sensory modalities. Several lines of empirical evidence are brought forward in support of the theory, in particular: evidence from experiments in sensorimotor adaptation, visual \"filling in,\" visual stability despite eye movements, change blindness, sensory substitution, and color perception.

A sensorimotor account of vision and visual consciousness-Authors' Response-Acting out our sensory experience

State-of-the-art retinal optical coherence tomography

We have combined Fourier-domain optical coherence tomography (FD-OCT) with a closed-loop adaptive optics (AO) system using a Hartmann-Shack wavefront sensor and a bimorph deformable mirror. The adaptive optics system measures and corrects the wavefront aberration of the human eye for improved lateral resolution (~4 μm) of retinal images, while maintaining the high axial resolution (~6 μm) of stand alone OCT. The AO-OCT instrument enables the three-dimensional (3D) visualization of different retinal structures in vivo with high 3D resolution (4×4×6 μm). Using this system, we have demonstrated the ability to image microscopic blood vessels and the cone photoreceptor mosaic.

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Adaptive-optics optical coherence tomography for high-resolution and high-speed 3D retinal in vivo imaging

We demonstrate ultrahigh speed spectral / Fourier domain optical coherence tomography (OCT) using an ultrahigh speed CMOS line scan camera at rates of 70,000 - 312,500 axial scans per second. Several design configurations are characterized to illustrate trade-offs between acquisition speed, resolution, imaging range, sensitivity and sensitivity roll-off performance. Ultrahigh resolution OCT with 2.5 - 3.0 micron axial image resolution is demonstrated at approximately 100,000 axial scans per second. A high resolution spectrometer design improves sensitivity roll-off and imaging range performance, trading off imaging speed to 70,000 axial scans per second. Ultrahigh speed imaging at >300,000 axial scans per second with standard image resolution is also demonstrated. Ophthalmic OCT imaging of the normal human retina is investigated. The high acquisition speeds enable dense raster scanning to acquire densely sampled volumetric three dimensional OCT (3D-OCT) data sets of the macula and optic disc with minimal motion artifacts. Imaging with approximately 8 - 9 micron axial resolution at 250,000 axial scans per second, a 512 x 512 x 400 voxel volumetric 3D-OCT data set can be acquired in only approximately 1.3 seconds. Orthogonal registration scans are used to register OCT raster scans and remove residual axial eye motion, resulting in 3D-OCT data sets which preserve retinal topography. Rapid repetitive imaging over small volumes can visualize small retinal features without motion induced distortions and enables volume registration to remove eye motion. Cone photoreceptors in some regions of the retina can be visualized without adaptive optics or active eye tracking. Rapid repetitive imaging of 3D volumes also provides dynamic volumetric information (4D-OCT) which is shown to enhance visualization of retinal capillaries and should enable functional imaging. Improvements in the speed and performance of 3D-OCT volumetric imaging promise to enable earlier diagnosis and improved monitoring of disease progression and response to therapy in ophthalmology, as well as have a wide range of research and clinical applications in other areas.

Ultrahigh speed spectral / Fourier domain OCT ophthalmic imaging at 70,000 to 312,500 axial scans per second

Expression of the Axonal Guidance Receptors EPHA5 and EPHA6 Changes Across Retinal Development

Wavefront sensorless adaptive optics imaging was performed in human eyes using a stochastic parallel gradient descent algorithm in an adaptive optics scanning laser ophthalmoscope. Image quality was similar for wavefront sensorless and wavefront sensor-based control.

Wavefront Sensorless Adaptive Optics Imaging in the Living Eye

We present a direct slope reconstruction algorithm to control dual-deformable mirror adaptive optics systems. A global response matrix was derived from the response matrices of each deformable mirror. Simulation results validated this control method.

Direct Slope Reconstruction Algorithm for Woofer-Tweeter Adaptive Optics Systems

Longitudinal repeatability of imaging perfused retinal capillaries in normal human and non-human primate eyes using adaptive optics

The adaptive optics scanning laser ophthalmoscope (AOSLO) combines an ophthalmic adaptive optics system [1] with a confocal scanning laser ophthalmoscope [2]. Adaptive optics (AO) are used to overcome blur in retinal images that is caused by aberrations in the cornea and lens of the eye. By using adaptive optics, microscopic retinal features are visualized [3]. 30 frame-per-second imaging has revealed the flow of individual leukocytes in the smallest retinal capillaries. The increased optical sectioning ability allows for true optical sectioning of retinal layers. The AOSLO uses a 37-channel deformable mirror (Xinetics, Andover MA), combined with a Shack Hartmann wavefront sensor (400 µm lenslets, 24 mm focal length). 512 × 480 pixel images of a 1.5 × 1.4 degree field are captured at 30 frames per second. The imaging wavelength is 660 nm but other wavelength imaging is possible. The AOSLO measures and compensates for the wave aberrations at about 1 Hz simultaneously with image acquisition. Here we describe the latest advances in retinal imaging with the AOSLO instrument.

Hope M Queener

Papers

Expression of the Axonal Guidance Receptors EPHA5 and EPHA6 Changes Across Retinal Development

Wavefront Sensorless Adaptive Optics Imaging in the Living Eye

Direct Slope Reconstruction Algorithm for Woofer-Tweeter Adaptive Optics Systems

Longitudinal repeatability of imaging perfused retinal capillaries in normal human and non-human primate eyes using adaptive optics

Properties and performance of the adaptive optics scanning laser ophthalmoscope