Binocular stereoscopy in visual areas V-2, V-3, and V-3A of the macaque monkey.

Over 40 years ago, Hubel and Wiesel gave a preliminary report of the first account of cells in monkey cerebral cortex selective for binocular disparity. The cells were located outside of V-1 within a region referred to then as "area 18." A full-length manuscript never followed, because the demarcation of the visual areas within this region had not been fully worked out.

David Hubel and Torsten Wiesel.

While attending medical school at McGill, David Hubel developed an interest in the nervous system during the summers he spent at the Montreal Neurological Institute. After heading to the United States in 1954 for a Neurology year at Johns Hopkins, he was drafted by the army and was assigned to the Neuropsychiatry Division at the Walter Reed Hospital, where he began his career in research and did his first recordings from the visual cortex of sleeping and awake cats. In 1958, he moved to the lab of Stephen Kuffler at Johns Hopkins, where he began a long and fruitful collaboration with Torsten Wiesel.

On the failure of completion of lines passing through the blind regions related to the optic disc, and to scotomas of migraine auras.

We compared the appearance of a line passing through the optic-disc blind spot with that of lines passing just medial or just lateral to the blind spot. Though there is no well-defined gap in the line, we see a consistent difference, which is hard to describe. On the other hand, during a migraine aura experienced by one of us, lines passing through scintillating scotomas showed clear sharply defined gaps.

The way biomedical research is organized has dramatically changed over the past half-century: are the changes for the better?

Biomedical research in today's universities is usually carried out by groups consisting of a leader and 5-20 or so trainees. This is in sharp contrast with past generations, when research was usually done by individuals or small partnerships of two or three who thought up their own ideas and carried them out themselves. Group leaders today spend their time in an office, on a wide variety of administrative tasks, and have little or no time left for work at the bench.

Microsaccades: a neurophysiological analysis.

Microsaccades are the largest and fastest of the fixational eye movements, which are involuntary eye movements produced during attempted visual fixation. In recent years, the interaction between microsaccades, perception and cognition has become one of the most rapidly growing areas of study in visual neuroscience. The neurophysiological consequences of microsaccades have been the focus of less attention, however, as have the oculomotor mechanisms that generate and control microsaccades.

Scotopic foveal afterimages.

If, after being in the dark for many minutes, one views an extended surface under dim (scotopic) illumination, one fails to see any hint of the dark spot at the center of gaze that might be expected from the absence of rods in the fovea. Here we report that, if the surface is suddenly completely darkened, one sees for a few seconds a relatively bright spot, about 2 deg in size, at the point of fixation. If the surface is now restored to its original brightness, a dark spot of similar size appears where one fixates, that again lasts for several seconds.

Receptive field properties of neurons in the primary visual cortex under photopic and scotopic lighting conditions.

Knowledge of the physiology of the primate visual cortex (area V-1) comes mostly from studies done in photopic conditions, in which retinal cones are active and rods play little or no part. Conflicting results have come from research into the effects of dark adaptation on receptive field organization of cells in the retina and the lateral geniculate nucleus. These studies claim either that the effect of the surround disappears with dark adaptation or that it does not.

The function of bursts of spikes during visual fixation in the awake primate lateral geniculate nucleus and primary visual cortex.

When images are stabilized on the retina, visual perception fades. During voluntary visual fixation, however, constantly occurring small eye movements, including microsaccades, prevent this fading. We previously showed that microsaccades generated bursty firing in the primary visual cortex (area V-1) in the presence of stationary stimuli.

Color contrast in macaque V1.

We explored the neural basis for spatial color contrast (red looks redder surrounded by green) and temporal color contrast (red looks redder if preceded by green) in primary visual cortex (V1) of the alert macaque. Using pairs of stimuli, we found a subset of neurons that gave stronger responses to sequences of red and green spots and stronger responses to adjacent red and green spots. These cells combined their cone inputs linearly: for a red-ON-center cell, the sum of the OFF response to green and the ON response to red predicted the peak response to red preceded by green.

Microsaccadic eye movements and firing of single cells in the striate cortex of macaque monkeys.

When viewing a stationary object, we unconsciously make small, involuntary eye movements or 'microsaccades'. If displacements of the retinal image are prevented, the image quickly fades from perception. To understand how microsaccades sustain perception, we studied their relationship to the firing of cells in primary visual cortex (V1).

Stereopsis and binocularity in the squirrel monkey.

The squirrel monkey lacks anatomically demonstrable ocular dominance columns, and physiologically it has an ocular dominance distribution in V1 that is very different from that of macaques, with far fewer cells that strongly favor one eye over the other. We tested an alert squirrel monkey for physiological responses to stereoscopic stimuli by measuring evoked potentials in response to cytclopean patterns generated in dynamic random-dot stereograms. The monkey showed evoked responses both to changes in disparity and to shifts between correlation and uncorrelation between the two eyes.

Stereopsis and positional acuity under dark adaptation.

Though experience tells us we can perceive depth in dim light, it is not so obvious that one of the chief mechanisms for depth perception, stereopsis, is possible under scotopic conditions. The only studies on human stereopsis in the dark adapted state seem to be those of Nagel [(1902) Zeitschrift für Psychologie, 27, 264-266] and Mueller and Lloyd [(1948) Proceedings of the National Academy of Science, U.S.