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<p class="MsoNormal" style="background:white">Vision science has lost another brilliant mind. My first introduction to Jack was through a lengthy letter he sent to Don MacLeod, Mary Hayhoe, and me around 1979, the beginning of which is printed below. I was
a graduate student at the time in Don’s lab at UCSD, using tiny S cone isolated flashes to psychophysically map the S cones near the foveal center, which supported the idea, controversial at the time, that they were sparse. Jack’s equation-laden letter, which
I confess was thoroughly opaque to me on first reading, would ultimately provide the theoretical framework for more than a decade of research in my fledgling laboratory at the University of Rochester. Jack became my muse and mentor, tutoring me about how
the sampling theorem could be used to relate acuity, aliasing, and photoreceptor topography. He was fond of conveying the principles of photoreceptor sampling by shining a helium neon laser through photographic transparencies of gratings and arrays of pinholes
sandwiched together, capitalizing on far-field diffraction to do Fourier transforms. Jack, wearing that wide grin he had when he was excited about an idea, was so pleased with himself, and appropriately so for the time, doing Fourier transforms at the speed
of light, without the need to struggle with the sluggish computers and poor image processing tools of that era. An example of a diffraction pattern of a photoreceptor pinhole array (without the grating) using Jack’s method appears below. He liked to call
this the desert island spectrum. The idea was that there was a single palm tree at the origin, the undiffracted DC component, surrounded by a dark annulus with no energy, which was the desert, outside of which lay a ring-shaped sea of power, which was concentrated
at spatial frequencies inversely proportional to the cone spacing. The desert in this spectrum was key in Jack’s thinking, because it provided a range of spatial frequencies the brain could reconstruct with minimal aliasing artifact. If the notion that
a desert island is lurking in this spectrum doesn’t immediately resonate, you will understand why early on I thought “Yellott’s ring” was a better name. Attaching his name to that spectrum seems especially appropriate now. Jack’s frequency domain representation
was incredibly useful in providing insight into the resolution limit imposed by the cone mosaic as well as the aliasing effects that would ensue if the sampling limit were exceeded. Jack and I decided to submit papers simultaneously to Science magazine, his
a theoretical paper on the implications of his desert island spectrum and mine on psychophysical evidence for aliasing of gratings seen only with S cones. Science summarily rejected both papers as usual, but Jack launched a vigorous appeal and convinced them
to publish in 1983 not only his paper but mine too! Soon after, I built a laser interferometer to avoid the eye’s aberrations and to test Jack’s theoretical predictions about aliasing by the complete foveal cone mosaic. I have fond memories of Jack, along
with his close friend Al Ahumada, visiting Rochester in the summer of 1984 I think it was, to visualize foveal aliasing for themselves. You can imagine my profound relief when Jack announced, after what seemed like an interminably long time peering into the
interferometer, that he could indeed see it. Jack was always a bountiful source of ideas and inspiration. His mentorship provided me with a valuable lesson in how successful partnerships in science often rest on complementary expertise. Certainly, experiments
on visual resolution and aliasing that I undertook throughout the 80s and into the early 90s would have been rudderless without the theoretical foundation Jack provided.<o:p></o:p></p>
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<p class="MsoNormal" style="background:white">If you read Beau Watson’s post on Jack, you will see that we share very much the same memories: Jack sitting in the sand in front of the Three Crowns Hotel when ARVO was held in Sarasota, Florida. Hawaiian shirt,
shorts, and sandals, ruggedly handsome, deeply tanned. From my midwestern perspective, Jack was the quintessential hip California surfer dude, a first impression that was strikingly incongruous with the impressive scholar behind the sunglasses. As soon as
the conversation began, Jack’s brilliance dazzled. He had a way of delivering information that was humble, enthusiastic, and always warm and generous. Maybe we got a crisp tutorial on Fourier optics, maybe he would recount a detailed history of the discovery
of DNA, or maybe he would opine on the origin of the green flash as we sat hoping for that rare event as the sun set into the Gulf. What I wouldn’t give for just one more opportunity to hang on the beach and learn remarkable new things from Jack Yellott.<o:p></o:p></p>
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<p class="MsoNormal" style="background:white">David Williams<o:p></o:p></p>
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