John S Pezaris

John S Pezaris
Harvard Medical School | HMS

About

34
Publications
5,368
Reads
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2,107
Citations
Citations since 2017
7 Research Items
605 Citations
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2017201820192020202120222023020406080100
2017201820192020202120222023020406080100

Publications

Publications (34)
Article
Full-text available
Simulated artificial vision is used in visual prosthesis design to answer questions about device usability. We previously reported a striking increase in equivalent visual acuity with daily use of a simulation of artificial vision in an active task, reading sentences, that required high levels of subject engagement, but passive activities are more...
Article
Full-text available
The visual pathway is retinotopically organized and sensitive to gaze position, leading us to hypothesize that subjects using visual prostheses incorporating eye position would perform better on perceptual tasks than with devices that are merely head-steered. We had sighted subjects read sentences from the MNREAD corpus through a simulation of arti...
Article
Full-text available
Visual prostheses serve to restore visual function following acquired blindness. Acquired blindness (as opposed to congenital blindness) has many causes, including diseases such as retinitis pigmentosa, glaucoma, and macular degeneration, or trauma such as caused by automobile accident or blast damage from explosions. Many of the blindness-causing...
Article
Full-text available
Despite appearing automatic and effortless, perceiving the visual world is a highly complex process that depends on intact visual and oculomotor function. Understanding the mechanisms underlying spatial updating (i.e., gaze contingency) represents an important, yet unresolved issue in the fields of visual perception and cognitive neuroscience. Many...
Article
Full-text available
Simulations of artificial vision are used to provide the researcher an opportunity to explore different aspects of visual prosthesis device design by observing subject performance on various tasks viewed through the simulation. Such studies typically use normal, sighted subjects to measure performance at a given point in time. Relatively few studie...
Chapter
The lateral geniculate nucleus of the thalamus (LGN) is a well-studied structure in the early visual pathway that links the retina to the primary visual cortex. As a deep structure, it has been long overlooked by the visual prosthesis field due to surgical inaccessibility. The unrelated field of deep brain stimulation has developed safe and effecti...
Article
Full-text available
Visual perceptual grouping, the process of forming global percepts from discrete elements, is experience-dependent. Here we show that the learning time course in an animal model of artificial vision is predicted primarily from the density of visual elements. Three naïve adult non-human primates were tasked with recognizing the letters of the Roman...
Article
Full-text available
The psychophysics of reading with artificial sight has received increasing attention as visual prostheses are becoming a real possibility to restore useful function to the blind through the coarse, pseudo-pixelized vision they generate. Studies to date have focused on simulating retinal and cortical prostheses; here we extend that work to report on...
Article
Full-text available
Simulation in normally sighted individuals is a crucial tool to evaluate the performance of potential visual prosthesis designs prior to human implantation of a device. Here, we investigated the effects of electrode count on visual acuity, learning rate and response time in 16 normally sighted subjects using a simulated thalamic visual prosthesis,...
Patent
A visual prosthesis and methods of allowing a subject to view visual information from an artificial source are provided. The visual prosthesis has one or more electrodes operative to deliver electrical signals to a lateral geniculate nucleus of a mammal, a power supply operative to provide power to the electrodes, a visual information translator op...
Article
Full-text available
Mapping neuronal responses in the lateral geniculate nucleus (LGN) is key to understanding how visual information is processed in the brain. This paper focuses on our current knowledge of the dynamics the receptive field (RF) as broken down into the classical receptive field (CRF) and the extra-classical receptive field (ECRF) in primate LGN. CRFs...
Article
Existing efforts to develop a visual prosthesis have concentrated on stimulation of the retina or the primary visual cortex. We are pursuing a third approach which targets the dorsal lateral geniculate nucleus of the thalamus (LGN). We hypothesized that highly localized electrical stimulation of the LGN would generate focal percepts corresponding t...
Article
Full-text available
Common causes of blindness are diseases that affect the ocular structures, such as glaucoma, retinitis pigmentosa, and macular degeneration, rendering the eyes no longer sensitive to light. The visual pathway, however, as a predominantly central structure, is largely spared in these cases. It is thus widely thought that a device-based prosthetic ap...
Article
Full-text available
In this paper, placement parameters for microstimulation electrodes in a visual prosthesis are evaluated based on retinotopic models of macaque and human lateral geniculate nucleus. Phosphene patterns were simulated for idealized microwire electrodes as well as for currently available clinical electrodes. For idealized microwire electrodes, spacing...
Article
Full-text available
Electrical stimulation of the visual system might serve as the foundation for a prosthetic device for the blind. We examined whether microstimulation of the dorsal lateral geniculate nucleus of the thalamus can generate localized visual percepts in alert monkeys. To assess electrically generated percepts, an eye-movement task was used with targets...
Article
Full-text available
Electrical stimulation of the thalamus has been widely used to test for the existence of monosynaptic input to cortical neurons, typically with stimulation currents that evoke cortical spikes with high probability. We stimulated the lateral geniculate nucleus (LGN) of the thalamus and recorded monosynaptically evoked spikes from layer 4 neurons in...
Article
Full-text available
Many cortical structures have elevated firing rates during working memory, but it is not known how the activity is maintained. To investigate whether reverberating activity is important, we studied the temporal structure of local field potential (LFP) activity and spiking from area LIP in two awake macaques during a memory-saccade task. Using spect...
Article
Full-text available
Many cortical structures have elevated firing rates during working memory, but it is not known how the activity is maintained. To investigate whether reverberating activity is important, we studied the temporal structure of local field potential (LFP) activity and spiking from area LIP in two awake macaques during a memory-saccade task. Using spect...
Article
The dynamics of cell-to-cell interactions as measured by the coherence between spike trains can help elucidate local circuitry and phases of operation for networks of neurons. We compute the coherence between pairs of spike trains collected from macaque area LIP during a memory saccade task. Significant coherence is found for frequencies below 50Hz...
Article
Action potentials from small groups of physically adjacent neurons were recorded from the parietal cortex of two rhesus macaques performing a memory saccade task. Recordings were made using tetrodes and sorted into spike trains from individual cells. Auto- and crosscovariograms of spike times for individual cells and simultaneously recorded pairs o...
Article
Objective evaluation of spike sorting algorithms such as those used to decompose tetrode recordings into distinct spike trains requires a priori knowledge of the correct classification for a given recording. Intracellular recording can unambiguously assign spikes to a single neuron, and thus provide correct classification if signals from that neuro...
Conference Paper
Multiple single unit extracellular recordings were made using tetrodes in macaque posterior parietal cortex while the animal was performing a visual memory saccade task. Recordings were made over a 2×2 mm area at both superficial and deep locations in one hemisphere. Signals were analyzed using an Expectation-Maximization algorithm for spike separa...
Article
In recent years considerable attention among extracellular electrophysiologists has focused on the problem of simultaneously recording the activity of multiple neurons in behaving animals. Such recordings, it is hoped, will provide much-needed insight into the dynamics of neural ensemble computation and coding. Of particular interest are recordings...
Conference Paper
We have adapted the Recce-O’Keefe tetrode for use in monkey cortex. Eleven penetrations have been made over macaque area MT to evaluate the mechanical and electrical properties of our design. Experiments have been made with 15 and 25 μm insulated nichrome wire running through oil-filled 33 gauge stainless steel guide tubes. Electrically, the tetrod...
Conference Paper
Full-text available
We discuss a solution to the problem of separating waveforms produced by multiple cells in an extracellular neural recording. We take an explicitly probabilistic approach, using latent-variable models of varying sophistication to describe the distribution of waveforms produced by a single cell. The models range from a single Gaussian distribution o...
Article
Full-text available
. This paper presents the derivation and performance results of several new three-dimensional topologies. Various transformations can be applied to the conventional six-neighbor mesh in order to construct these topologies, which vary both in number of neighbors (degree) and logical connectivity. Analysis shows that after normalization for constant...
Conference Paper
Full-text available
This paper presents the derivation and performance results of several new three-dimensional topologies. Various transformations can be applied to the conventional six-neighbor mesh in order to construct these topologies, which vary both in number of neighbors (degree) and logical connectivity. Analysis shows that after normalization for constant pi...
Conference Paper
Full-text available
Many standardized hardware communication interfaces offer runtime flexibility and configurability at the cost of efficiency. An alternate approach is the use of a highly-efficient, minimal communication element, with as much communication decision-making as possible done at compile time. NuMesh is a packaging and interconnect technology supporting...
Article
1 Abstract In this paper, we develop a variety of graph em-beddings to the diamond lattice. Most of these em-beddings are obtained by composing two graph em-beddings — an embedding of the guest graph to the cartesian mesh, and then an embedding of the cartesian mesh to the diamond lattice. Therefore, each one of the embeddings serves equally well a...

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Projects

Projects (3)
Project
Investigating the development of visual function in simulations of artificial vision.
Project
We aim to elucidate the non-classical receptive field features of lateral geniculate nucleus neurons in awake, behaving non-human primates. To achieve this goal, we have developed ultra-thin multi-electrode arrays and ultra-high resolution naturalistic one-over-frequency full-color wide-field spatiotemporal noise stimuli. These tools, together with advanced eye movement tracking and computational analyses, have enabled us to discover previously-unreported response properties.
Project
We are developing a device to treat blindness caused by impaired retinogeniculate transmission. The device comprises hundreds of microelectrodes implanted in the lateral geniculate nucleus of the thalamus. Each electrode site is used to deliver electrical stimulation to a small region of neuronal tissue, resulting in a small, retinocentric, artificial percept called a phosphene. The phosphenes are used in aggregate to allow the user to perceive and explore the world. Our system accounts for motor commands that are used to drive eye movements in normal individuals, permitting an enhanced exploratory experience.