Andrew John Parker

Andrew John Parker
Otto-von-Guericke-Universität Magdeburg | OvGU · Institute of Biology (IBIO)

MA, PhD, ScD
Also contactable at andrew.parker@dpag.ox.ac.uk

About

201
Publications
22,177
Reads
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7,245
Citations
Introduction
Our work covers a wide range of topics in vision, with a particular emphasis on linking neuronal activity to perceptual judgments. We study the physiology of binocular depth and its relationship with other sources of information about three-dimensional shape. We use both magnetic resonance imaging in humans and electrophysiological recordings in experimental animals
Additional affiliations
July 1996 - present
University of Oxford
Position
  • Professor
March 1985 - July 1996
University of Oxford
Position
  • University Lecturer in Physiology
Education
October 1976 - July 1980
University of Cambridge
Field of study
  • Psychology
October 1973 - June 1976
University of Cambridge
Field of study
  • Natural Sciences

Publications

Publications (201)
Article
Full-text available
Loss of shape recognition in visual-form agnosia occurs without equivalent losses in the use of vision to guide actions, providing support for the hypothesis of two visual systems (for "perception" and "action"). The human individual DF received a toxic exposure to carbon monoxide some years ago, which resulted in a persisting visual-form agnosia t...
Article
As we move through the world, our eyes acquire a sequence of images. The information from this sequence is sufficient to determine the structure of a three-dimensional scene, up to a scale factor determined by the distance that the eyes have moved. Previous evidence shows that the human visual system accounts for the distance the observer has walke...
Article
Full-text available
Our ability to coordinate the use of our left and right eyes and to make use of subtle differences between the images received by each eye allows us to perceive stereoscopic depth, which is important for the visual perception of three-dimensional space. Binocular neurons in the visual cortex combine signals from the left and right eyes. Probing the...
Article
The identification of brain regions that are associated with the conscious perception of visual stimuli is a major goal in neuroscience. Here we present a test of whether the signals on neurons in cortical area V1 correspond directly to our conscious perception of binocular stereoscopic depth. Depth perception requires that image features on one re...
Article
Stereoscopic vision enables the perception of depth. To study the brain mechanisms behind stereoscopic vision using noninvasive brain imaging (magnetic resonance brain imaging; MRI), scientists need to reproduce the independent views of the left and right eyes in the brain scanner using "dichoptic" displays. However, high-quality dichoptic displays...
Chapter
In the article under review in this chapter, a discussion between an art historian and neuroscientists led to a collaborative project to study the influence of authenticity on the reception of artwork. Brain-scanning with functional magnetic resonance imaging led to the identification of a number of distinct areas of the cortex that might be implic...
Article
Full-text available
The visual perception of 3D depth is underpinned by the brain’s ability to combine signals from the left and right eyes to produce a neural representation of binocular disparity for perception and behaviour. Electrophysiological studies of binocular disparity over the past 2 decades have investigated the computational role of neurons in area V1 for...
Article
Full-text available
Noninvasive diffusion-weighted magnetic resonance imaging (dMRI) can be used to map the neural connectivity between distinct areas in the intact brain, but the standard resolution achieved fundamentally limits the sensitivity of such maps. We investigated the sensitivity and specificity of high-resolution postmortem dMRI and probabilistic tractogra...
Article
Full-text available
Binocular vision is created by fusing the separate inputs arriving from the left and right eyes. ‘Eye dominance’ provides a measure of the perceptual dominance of one eye over the other. Theoretical models suggest that eye dominance is related to reciprocal inhibition between monocular units in the primary visual cortex, the first location where th...
Article
Variability in cortical neural activity potentially limits sensory discriminations. Theoretical work shows that information required to discriminate two similar stimuli is limited by the correlation structure of cortical variability. We investigated these information-limiting correlations by recording simultaneously from visual cortical areas V1 an...
Preprint
The visual perception of 3D depth is underpinned by the brain's ability to combine signals from the left and right eyes to produce a neural representation of binocular disparity for perception and behavior. Electrophysiological studies of binocular disparity over the past two decades have investigated the computational role of neurons in area V1 fo...
Preprint
Full-text available
The visual perception of 3D depth is underpinned by the brain's ability to combine signals from the left and right eyes to produce a neural representation of binocular disparity for perception and behavior. Electrophysiological studies of binocular disparity over the past two decades have investigated the computational role of neurons in area V1 fo...
Preprint
Full-text available
Our binocular world is seamlessly assembled from two retinal images that remain segregated until the cerebral cortex. Despite the coherence of this input, there is often an imbalance between the strength of these connections in the brain. ‘Eye dominance’ provides a measure of the perceptual dominance of one eye over the other. Theoretical models su...
Article
Despite advances in deep neural networks for object recognition, the function of the mid-level stages of visual processing in the mammalian cortex evades a simple description. This review focuses on the status of cortical area V4 to present evidence for a diversity of roles for mid-level visual areas. Some properties of V4 neurons resemble the stat...
Article
Full-text available
When children grow up, the first word or first step in walking is always a significant event [...]
Preprint
Full-text available
Human psychophysical studies demonstrate that visual detection thresholds are sometimes close to the limits imposed by the physics of the stimulus. Another potential limit is the variable spiking of cortical neurons, which theoretically reduces information about the stimulus. The correlation structure of noise in the cortical population is critical...
Article
Full-text available
Perceptual decisions are thought to depend on the activation of task-relevant neurons, whose activity is often correlated in time. Here, we examined how the temporal structure of shared variability in neuronal firing relates to perceptual choices. We recorded stimulus-selective neurons from visual area V5/MT while two monkeys (Macaca mulatta) made...
Article
We investigated the relationship between neurochemical and hemodynamic responses as a function of image contrast in the human primary visual cortex (V1). Simultaneously acquired BOLD-fMRI and single voxel proton MR spectroscopy signals were measured in V1 of 24 healthy human participants of either sex at 7 tesla field strength, in response to prese...
Article
Full-text available
Studies of changes in cerebral neocortical thickness often rely on small control samples for comparison with specific populations with abnormal visual systems. We present a normative dataset for FreeSurfer-derived cortical thickness across 25 human visual areas derived from 960 participants in the Human Connectome Project. Cortical thickness varies...
Preprint
Full-text available
Studies of changes in cerebral neocortical thickness often rely on small control samples for comparison with specific populations with abnormal visual systems. We present a normative dataset for FreeSurfer-derived cortical thickness across 25 human visual areas derived from 960 participants in the Human Connectome Project. Cortical thickness varies...
Article
Full-text available
Lesions of primary visual cortex (V1) lead to loss of conscious visual perception with significant impact on human patients. Understanding the neural consequences of such damage may aid the development of rehabilitation methods. In this rare case of a Rhesus macaque (monkey S), likely born without V1, the animal’s in-group behaviour was unremarkabl...
Preprint
Full-text available
Lesions of primate primary visual cortex (V1) lead to loss of conscious visual perception, and are often devastating to those affected. Understanding the neural consequences of such damage may aid the development of rehabilitation methods. In this rare case of a Rhesus macaque (monkey S), likely born without V1, we investigated the brain structures...
Chapter
Stereoscopic vision describes the ability to perceive three-dimensional information from visual inputs. This article provides an overview of the history of scientific discoveries about binocular stereoscopic depth and gives an insight into our current understanding of how the primary cue for stereoscopic depth perception, called binocular disparity...
Article
Zusammenfassung Die neurowissenschaftliche Forschung hat enorme Fortschritte in der Entschlüsselung der neuronalen Codes unserer Sinneswahrnehmung erzielt. Von Einzelzellen in der Sehrinde des Affen bis zu Aktivitätsmustern in neuronalen Schaltkreisen korreliert elektrische Aktivität über verschiedene Ebenen mit Wahrnehmung. Der Schlüssel zum Verst...
Article
Neuroscientific research has made tremendous progress towards unravelling the neuronal codes that underlie our rich sensory perception and experience. From single neurons in primates’ visual brain that predict perceptual choices to activity patterns in defined neuronal circuits, electrical activity across different levels correlates with perception...
Preprint
Full-text available
Animals with forward-facing eyes exploit slight differences between the images in the two eyes to determine binocular depth using stereopsis. Evidence for an organized structure in human visual cortex for the representation of stereoscopic depth has proved elusive. Using 7-tesla functional MRI, with gradient-echo echo-planar imaging at 0.75 mm isot...
Article
Full-text available
Combined fMRI-MRS is a novel method to non-invasively investigate functional activation in the human brain using simultaneous acquisition of hemodynamic and neurochemical measures. The aim of the current study was to quantify neural activity using combined fMRI-MRS at 7 T. BOLD-fMRI and semi-LASER localization MRS data were acquired from the visual...
Article
Full-text available
Vision is a new open-access journal covering all aspects of experimental vision research and clinical science. We particularly want to create a forum for the development of a dialogue between fundamental laboratory-based research and clinical research practice [...].
Article
Full-text available
Extrastriate visual area V5/MT in primates is defined both structurally by myeloarchitecture and functionally by distinct responses to visual motion. Myelination is directly identifiable from postmortem histology but also indirectly by image contrast with structural magnetic resonance imaging (sMRI). First, we compared the identification of V5/MT u...
Article
Full-text available
In the primate visual cortex, neurons signal differences in the appearance of objects with high precision. However, not all activated neurons contribute directly to perception. We defined the perceptual pool in extrastriate visual area V5/MT for a stereo-motion task, based on trial-by-trial co-variation between perceptual decisions and neuronal fir...
Article
Full-text available
Many aspects of our perceptual experience are dominated by the fact that our two eyes point forward. Whilst the location of our eyes leaves the environment behind our head inaccessible to vision, co-ordinated use of our two eyes gives us direct access to the three-dimensional structure of the scene in front of us, through the mechanism of stereosco...
Article
Full-text available
Stereoscopic vision delivers a sense of depth based on binocular information but additionally acts as a mechanism for achieving correspondence between patterns arriving at the left and right eyes. We analyse quantitatively the cortical architecture for stereoscopic vision in two areas of macaque visual cortex. For primary visual cortex V1, the resu...
Data
Large and small reward conditions do not differ in the proportion of microstimulated trials, nor in the distribution of stimulus disparities. The nature of the reward contingencies in this experiment meant that the reward size for any particular trial was dictated by the monkey's accumulated performance on the previous trials. Therefore, the distri...
Article
Full-text available
An important advance in the study of visual attention has been the identification of a non-spatial component of attention that enhances the response to similar features or objects across the visual field. Here we test whether this non-spatial component can co-select individual features that are perceptually bound into a coherent object. We combined...
Article
Full-text available
Magnetoencephalography (MEG) allows the physiological recording of human brain activity at high temporal resolution. However, spatial localization of the source of the MEG signal is an ill-posed problem as the signal alone cannot constrain a unique solution and additional prior assumptions must be enforced. An adequate source reconstruction method...
Article
Full-text available
The power and significance of artwork in shaping human cognition is self-evident. The starting point for our empirical investigations is the view that the task of neuroscience is to integrate itself with other forms of knowledge, rather than to seek to supplant them. In our recent work, we examined a particular aspect of the appreciation of artwork...
Article
Full-text available
Perceiving binocular depth relies on the ability of our visual system to precisely match corresponding features in the left and right eyes. Yet how the human brain extracts interocular disparity correlation is poorly understood. We used functional magnetic resonance imaging (fMRI) to characterize brain regions involved in processing interocular dis...
Article
Full-text available
The study of sensory signaling in the visual cortex has been greatly advanced by the recording of neural activity simultaneously with the performance of a specific psychophysical task. Individual nerve cells may also increase their firing leading up to the particular choice or decision made on a single psychophysical trial. Understanding these sign...
Data
Illustration of the type of stimulus used in this study. Consistent with an orthographic projection of a three-dimensional cylinder, the peak velocity of the stimulus dots was at the midline of cylinder image; i.e., the dot velocity increased as they approached the midline and then decreased as they moved toward the lateral edges of the cylinder. T...
Article
Full-text available
Judgments about the perceptual appearance of visual objects require the combination of multiple parameters, like location, direction, color, speed, and depth. Our understanding of perceptual judgments has been greatly informed by studies of ambiguous figures, which take on different appearances depending upon the brain state of the observer. Here w...
Conference Paper
The human visual system has an impressive ability to extract tiny differences from the left and right retinal images to produce the perception of depth. Moreover, the perception of depth is robust to a considerable amount of noise between the two images. Both these features of human vision contribute to the effectiveness of 3D imaging systems. Rece...
Article
INTRODUCTION. Binocular disparity signals are small spatial differences between the left and right eyes and create the perception of three-dimensional depth. Electrophysiology and optical imaging in primates have associated disparity processing with the thick stripes of the secondary visual cortex (V2). However, imaging at this scale in the human d...
Article
Full-text available
In this short communication, we respond to Westlund's critique of the NC3Rs Working Group report on refinement of the use of food and fluid control as motivational tools for macaques used in behavioural neuroscience research. The suggestions Westlund makes – in particular, the use of conditioned reinforcers and variable ratio schedules – were consi...
Article
Full-text available
Judgments of visual depth rely crucially on the relative binocular disparity between two visual features. While areas of ventral visual cortex contain neurons that signal the relative disparity between spatially adjacent visual features, the same tests in dorsal visual areas yield little evidence for relative disparity selectivity. We investigated...
Article
Full-text available
The expertise of others is a major social influence on our everyday decisions and actions. Many viewers of art, whether expert or naïve, are convinced that the full esthetic appreciation of an artwork depends upon the assurance that the work is genuine rather than fake. Rembrandt portraits provide an interesting image set for testing this idea, as...
Conference Paper
Full-text available
Perceiving solid objects involves extracting information about their 3D structure, often using a combination of motion and binocular cues. Little is known about how visual attention affects these processes. fMRI-studies suggest that objects can be selected as a unit of spatial attention [1] and that attending to features within objects can change r...
Article
We examined the ability of disparity-selective neurons (recorded from V1 of awake fixating macaques) to support depth judgements over the range of visible disparities. A selected population of 180 neurons with strong disparity selectivity (eccentricities 1 to 5 degrees) was used. To allow comparison between neurons that respond over different range...
Conference Paper
Variations in firing of single neurons in MT(V5) of awake, behaving macaques correlate highly with perceptual choice for the rotation of an ambiguous zero disparity cylinder (choice probability 0.67). Neuronal responses in MT(V5) are also correlated with direction discrimination in a random motion stimulus, but this choice probability is considerab...
Article
Interocular differences in orientation (orientation disparities) occur during binocular viewing of a surface slanted in depth. These orientation disparities could be exploited by the visual system to provide information about surface slant, but gradients of positional disparity provide an equally effective means to the same end. Both psychophysical...
Article
Full-text available
This report provides practical guidance on refinement of the use of food and fluid control as motivational tools for macaques used in behavioural neuroscience research. The guidance is based on consideration of the scientific literature and, where data are lacking, expert opinion and professional experience, including that of the members of a Worki...
Article
Current models of binocular simple cells assume that input from left and right eyes is initially combined linearly. Model cells of this type underlie the successful energy model of disparity-tuned complex cells (Ohzawa et al., 1990, Science 249:1037). An alternative hypothesis is that input from each eye is passed through a threshold non-linearity...
Article
Early visual areas can be defined using fMRI on the basis of their retinotopic organisation. Recently, very high-resolution images of the human brain in vivo have identified areas of myelination within the grey matter, corresponding to the striate cortex (Barbier et al. 2002; Clare et al. 2002). This myelination has traditionally been understood to...
Conference Paper
In the awake macaque, MT neuronal firing to ambiguously rotating cylinders is correlated with the reported direction of rotation when the stimulus is closely matched to the neuronal receptive field. We recently reported the existence of strong choice-related firing in MT, even when the orientation of the cylinder is sub-optimal for the neuron (Curn...
Article
Full-text available
In a traditional Ames room, perception of size is distorted by the observer's assumptions about parallel and perpendicular lines. For the illusion to be convincing, the room must be viewed from one vantage point. Using an immersive virtual reality system, we generated a dynamic version of the Ames room illusion. Subjects were free to move around an...
Data
Full-text available
Psychophysics data from Expt 1.1. (0.45 MB PDF)
Data
Psychophysics data from Expts 1.3, 2 and 3.1. (0.32 MB PDF)
Data
Full-text available
Note on fitting psychometric functions. (0.20 MB PDF)
Article
Full-text available
Both dorsal and ventral cortical visual streams contain neurons sensitive to binocular disparities, but the two streams may underlie different aspects of stereoscopic vision. Here we investigate stereopsis in the neurological patient D.F., whose ventral stream, specifically lateral occipital cortex, has been damaged bilaterally, causing profound vi...