Interests

I am interested in vision, and the development and organization of the primary visual cortex. This includes studying how the genes and environment interact in early post-natal development, how cellular mechanisms contribute to perceptual processing, and how disorders such as amblyopia and glaucoma may affect visual function. I use computer models to simulate developmental mechanisms, cats as experimental models for visual processing, and humans as subjects for psychophysical research. Present and past research projects include the following:

• Application of neural net models to the formation of computational maps of ocular dominance and orientation columns in the visual cortex
• Analysis of columnar organization in the cat visual cortex using optical recording of stimulus evoked neural activity
• Multi-electrode recording methods for the comparison of receptive field properties in simultaneously recorded clusters of neurons
• Quantitative analysis and modeling of spatial summation in simple and complex cell receptive fields in cat visual cortex
• Physiological and psychophysical studies of the mechanisms of vernier hyperacuity
• The development of clinically diagnostic psychophysical tests of visual function in glaucoma
• Early detection of glaucoma using mathematical modelling of optic nerve head shape and neural network methods for classifying images as normal or glaucomatous.

Gallery

Multiple unit responses to natural scene movies in primary visual cortex

We use natural scene movies (those shown here courtesy of the Peter Konig lab) that were captured by attaching a video camera to a cat's head and allowing it to roam freely in the woods. We present these movies while recording multiple units simultaneously from cat primary visual cortex. In the movie files below, spikes from different neurons are each assigned a different audible pitch. Neurons are also separated in stereo space. A pulse of a given pitch represents a spike from a specific neuron at that time. In this way, you can listen to the entire population of neurons responding to the movie stimulus in real time.

The first movie is a repeated stimulus, which gives a sense of the reliability of the responses.

The second movie is a continuous movie without repeats.

These movies are encoded using the DivX format. You'll need to have the DivX codec (for Windows/Mac) installed on your system. The best solution in Windows is to install the free K-Lite codec pack. Linux users can get the DivX codec here, or can simply install Mplayer.

3-D neuron localization from multiunit recordings in cat visual cortex

We designed several 16 and 54-channel silicon electrodes, formerly made by the University of Michigan's Center for Neural Communication Technology, now made by NeuroNexus. These "polytrodes" comprise a 2D planar array of closely-spaced (46-70 µm) electrode sites, arranged into two or three columns (colinear and staggered). The intersite distance is optimized for precise 3D spatial clustering of multiple single units, yet the arrays are sufficiently long to span an entire cortical column.

We have pursued methods to refine and validate our 3D spatial clustering algorithm, including confocal imaging in brain slice preparations.

Combined optical imaging with multiunit silicon electrode recordings

Guided by surface vascular superimposed over orientation maps imaged in areas 17/18 of cat striate cortex, we make simultaneous recordings from 100 or more units in all cortical laminae.

In the animation shown here the cross hairs mark the location of silicon electrode recordings made in various features of the orientation map; in singularities (pinwheels), discontinuities (fractures), and linear zones.

Simulation of a cortical polymap for 8 binary sub-features

Simulation of a cortical polymap for 8 binary sub-features. Each coloured domain represents a particular permutation of features. Adjacent domains differ by only one sub-feature. Individual sub-features form a pattern of irregular stripes and blobs.

For further details see: Swindale NV (2000) How many maps are there in visual cortex? Cerebral Cortex 7:633-43.

Computer simulation of the formation of ocular dominance and orientation maps in primary visual cortex

For further details see: Swindale, NV (1996) The development of topography in the visual cortex: a review of models. Network 7:161.