This chapter provides an overview of the basic methods used in studying vision and the brain. The creation of these methods has played a central role in uncovering how various brain areas work, including those that are engaged in analyzing vision and in generating eye movements. Several Nobel Prizes and other major prizes have been awarded to individuals as a result of having created these methods and having generated major new discoveries with them. The chapter describes seven methods: A: Psychophysics, B: Neuroanatomy, C: Neurophysiology, D: Biochemical Analysis, E: Optogenetics, F: Two-Photon Imaging, and G: Brain Inactivation. Sections H and I provide an overview and a summary.

The input to the striate cortex (area V1) from the lateral geniculate nucleus is transformed to create orientation, direction, velocity, and spatial frequency selective neurons. Many area V1 cells receive a convergent input from the two eyes that contributes to stereoscopic depth perception. Feedback circuits from higher cortical areas modulate the responses of area V1 cells for higher level visual analysis. This chapter has six subsections. Section A discusses the general anatomy of the striate cortex. Section B deals with the functional properties of single cells in area V1. Section C examines the cytoarchitecture of the area. Section D examines the neural mechanisms that give rise to orientation and direction selectivities in area V1. Section E discusses feedback circuits to area V1. Section F provides a summary of the chapter.

This chapter examines the manner in which higher level organisms accomplish eye movements. The chapter has twelve sections. Section A outlines the basic facts about eye movements. Sections B and C describe the role the brainstem and the superior colliculi play in the control of eye movements. In sections D and E the cortical control of eye movements is described. In section F the effects of brain lesions are examined. In section G the role of excitatory and inhibitory circuits plays in eye-movement generation is described. In section H the neural control of smooth pursuit eye movements is outlined. Section I describes the neural mechanisms involved in keeping the two eyes in register. Section J describes the mechanisms involved in eye-movement stabilization. Section K discusses eye movements that arise during sleep. Section L provides an overview of the circuits involved in eye movement control. Section M provides a summary.

This chapter describes the basic layout of the visual system and examines some of the changes that have occurred in the visual system in the course of evolution. The chapter has three subdivisions. In section A, the manner in which images impinge on the retina of the two eyes in species with sideways and forward looking eyes is described. Section B delineates the manner in which the retinal ganglion cells connect to various areas of the brain that include the superior colliculus, the nucleus of the optic tract, the terminal nuclei, the lateral geniculate nucleus, and the visual cortex. Section C provides a summary of the chapter.

This study examined how effectively visual and auditory cues can be integrated in the brain for the generation of motor responses. The latencies with which saccadic eye movements are produced in humans and monkeys form, under certain conditions, a bimodal distribution, the first mode of which has been termed express saccades. In humans, a much higher percentage of express saccades is generated when both visual and auditory cues are provided compared with the single presentation of these cues [H. C. Hughes et al. (1994) J. Exp. Psychol. Hum. Percept. Perform., 20, 131153]. In this study, we addressed two questions: first, do monkeys also integrate visual and auditory cues for express saccade generation as do humans and second, does such integration take place in humans when, instead of eye movements, the task is to press levers with fingers? Our results show that (i) in monkeys, as in humans, the combined visual and auditory cues generate a much higher percentage of express saccades than do singly presented cues and (ii) the latencies with which levers are pressed by humans are shorter when both visual and auditory cues are provided compared with the presentation of single cues, but the distribution in all cases is unimodal; response latencies in the express range seen in the execution of saccadic eye movements are not obtained with lever pressing.

A series of tests was devised to assess stereoscopic depth processing, motion parallax depth processing, binocular integration and hand-eye coordination in normal, stereoblind, and stereo deficient subjects. Using a random- dot stereoscopic display viewed through a stereoscope we established that of the 262 subjects tested, 177 were categorized as having normal stereoscopic depth perception, 28 as being stereo deficient and 57 as being stereoblind. These three groups of subjects processed motion parallax information for depth equally well, but the stereoblind and stereo deficient subjects had significantly longer reaction times. On the hand-eye coordination tests the stereoblind subjects performed significantly less well than did normal and stereo deficient subjects, whose performance on these tests was similar. Our binocular integration tests revealed significantly less integration in stereoblind subjects than in normal and stereo deficient subjects. The tests we have devised will be useful for the accurate assessment of various forms of treatment for amblyopia and strabismus for the reinstatement of depth perception, hand-eye coordination and binocular integration.

Creating a prosthetic device for the blind is a central future task. Our research examines the feasibility of producing a prosthetic device based on electrical stimulation of primary visual cortex (area V1), an area that remains intact for many years after loss of vision attributable to damage to the eyes. As an initial step in this effort, we believe that the research should be carried out in animals, as it has been in the creation of the highly successful cochlear implant. We chose the rhesus monkey, whose visual system is similar to that of man. We trained monkeys on two tasks to assess the size, contrast, and color of the percepts created when single sites in area V1 are stimulated through microelectrodes. Here, we report that electrical stimulation within the central 5° of the visual field representation creates a small spot that is between 9 and 26 min of arc in diameter and has a contrast ranging between 2.6% and 10%. The dot generated by the stimulation in the majority of cases was darker than the background viewed by the animal and was composed of a variety of low-contrast colors. These findings can be used as inputs to models of electrical stimulation in area V1. On the basis of these findings, we derive what kinds of images would be expected when implanted arrays of electrodes are stimulated through a camera attached to the head whose images are converted into electrical stimulation using appropriate algorithms.

A visual stimulus display was created that enabled us to examine how effectively the three depth cues of disparity, motion parallax and shading can be integrated in humans and monkeys. The display was designed to allow us to present these three depth cues separately and in various combinations. Depth was processed most effectively and most rapidly when all three cues were presented together indicating that these separate cues are integrated at yet unknown sites in the brain. Testing in humans and monkeys yielded similar results suggesting that monkeys are a good animal model for the study of the underlying neural mechanisms of depth perception.

on electrical stimulation of area V1 are concerned, three central facts remain: (1) Schmidt et al, to our knowledge, have not published anything on implanting electrodes into human visual cortex after 1996, following the death of subject MAB (Schmidt et al 1996; Wagenaar 2004; Ings 2007; Wikipedia as of November 18, 2009). (2) Shortcomings pertaining to the longevity of electrodes implanted into the brain have not been solved, as evidenced by the paper of Bradley et al (2005). (3) The algorithms needed to convert visual images to electrical brain stimulation for veridical percepts have not been worked out. Because of these problems, our paper (Schiller and Tehovnik 2008) advocates carrying out research on animals before invasive procedures are used in humans. The remarkable success of the cochlear implant is in large part attributable to the 10 years of research carried out on cats by Clark (2003). We believe that behaving rhesus monkeys are an excellent model for developing a visual prosthetic device based on electrical stimulation of area V1 for the following reasons (Schiller and Tehovnik 2008): (1) The visual system of monkeys is highly similar to that of humans. (2) The central representation of the visual field in area V1 in these animals is largely lissencephalic and lies right below the skull, allowing relatively easy and accurate access. (3) Monkeys can detect electrical stimulation of this area at extremely low current levels (1 ^ 2 mA). (4) Monkeys can be trained to respond specifically to electrical stimulation that enables investigators to determine what kind of visual images the activation creates.

In this study, we examined procedures that alter saccadic latencies and target selection to visual stimuli and electrical stimulation of area V1 in the monkey. It has been shown that saccadic eye movement latencies to singly presented visual targets form a bimodal distribution when the fixation spot is turned off a number of milliseconds prior to the appearance of the target (the gap period); the first mode has been termed express saccades and the second regular saccades. When the termination of the fixation spot is coincident with the appearance of the target (0 ms gap), express saccades are rarely generated. We show here that a bimodal distribution of saccadic latencies can also be obtained when an array of visual stimuli is presented prior to the appearance of the visual target, provided the elements of the array overlap spatially with the visual target. The overall latency of the saccadic eye movements elicited by electrical stimulation of area V1 is significantly shortened both when a gap is introduced between the termination of the fixation spot and the stimulation and when an array is presented. However, under these conditions, the distribution of saccadic latencies is unimodal. When two visual targets are presented after the fixation spot, introducing a gap has no effect on which target is chosen. By contrast, when electrical stimulation is paired with a visual target, introducing a gap greatly increases the frequency with which the electrical stimulation site is chosen.

There are more than forty million blind individuals in the world whose plight would be greatly ameliorated by creating a visual prosthesis. We begin by outlining the basic operational characteristics of the visual system, as this knowledge is essential for producing a prosthetic device based on electrical stimulation through arrays of implanted electrodes. We then list a series of tenets that we believe need to be followed in this effort. Central among these is our belief that the initial research in this area, which is in its infancy, should first be carried out on animals. We suggest that implantation of area V1 holds high promise as the area is of a large volume and can therefore accommodate extensive electrode arrays. We then proceed to consider coding operations that can effectively convert visual images viewed by a camera to stimulate electrode arrays to yield visual impressions that can provide shape, motion, and depth information. We advocate experimental work that mimics electrical stimulation effects non-invasively in sighted human subjects with a camera from which visual images are converted into displays on a monitor akin to those created by electrical stimulation.

A stimulus display was devised that enabled us to examine how effectively monkeys and humans can process shading and disparity cues for depth perception. The display allowed us to present these cues separately, in concert and in conflict with each other. An oddities discrimination task was used. Humans as well as monkeys were able to utilize both shading and disparity cues but shading cues were more effectively processed by humans. Humans and monkeys performed better and faster when the two cues were presented conjointly rather than singly. Performance was significantly degraded when the two cues were presented in conflict with each other suggesting that these cues are processed interactively at higher levels in the visual system. The fact that monkeys can effectively utilize depth information derived from shading and disparity indicates that they are a good animal model for the study of the neural mechanisms that underlie the processing of these two depth cues.

Five sets of displays are presented on the journal website to be viewed in conjunction with the text. We concentrate on the factors that give rise to the integration and disruption of the direction of apparent motion in two-dimensional and three-dimensional space. In the first set of displays we examine what factors contribute to the integration and disruption of apparent motion in the Ramachandran/Anstis clustered bistable quartets. In the second set we examine what factors give rise to the perception of the direction of motion in rotating two-dimensional wheels and dots. In the third and fourth sets we examine how the depth cues of shading and disparity contribute to the perception of apparent motion of opaque displays, and to the perception of rotating unoccluded displays, respectively. In the fifth set we examine how the depth cue of motion parallax influences the perception of apparent motion. Throughout, we make inferences about the roles which various parallel pathways and cortical areas play in the perceptions produced by the displays shown.

The latencies of saccades to suddenly appearing eccentric targets can have a bimodal distribution, with an early, express peak, and a late, regular peak (Fischer and Boch 1983, Brain Res 260: 21–26). Express saccades usually are a product of learning. The purpose of this study was to determine whether this learning is specific to the relative position of the target in space, the orbital position of the eye, or the vector of the saccade to be produced. Further, it was asked whether and how the frequency with which express saccades are generated is influenced by the immediately preceding saccadic vector and the familiarity of the targets. To this end, rhesus monkeys were trained to make saccadic eye movements to single targets and to two sequential targets that appeared at various positions relative to the head, relative to the initial fixation spot and relative to each other. The results show that the frequency with which express saccades are generated is determined by the saccadic vector that has to be generated and not by the relative position of a target in space, the orbital position of the eye, the immediately preceding saccadic vector, or the familiarity of the targets.