The Conscious Vision of the Blind

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 61-61 ◽  
Author(s):  
S Zeki
Keyword(s):  
Visual Cortex ◽  
Conscious Experience ◽  
Conscious State ◽  
Visual Signals ◽  
Visual World ◽  
Essential Information ◽  
Cortex Area ◽  
Visual Areas ◽  
Colour Form ◽  
The Brain

The most fundamental function of the visual brain is to acquire knowledge about the constant, essential properties of the visual world, in conditions in which the information reaching the brain is never constant from moment to moment. This requires the brain to undertake complex operations on the incoming visual signals, discounting all that is not essential for it to acquire knowledge about the world, selecting that which is important, and subjecting the latter to operations that make the brain independent of the continually changing and non-essential information reaching it. One strategy that the brain uses in undertaking this task is that of functional specialisation, through which different essential features, such as motion and colour, are extracted in specialised and geographically distinct visual areas lying outside the primary visual cortex area V1. Our recent psychophysical experiments show that, just as the processing systems for different attributes of vision are separate, so are the final perceptual systems, since different attributes of the visual scene such as colour, form, and motion are perceived at different times, with colour being ahead of motion by about 80 ms, thus leading to a perceptual asynchrony in terms of real time. The end-result of the operations in these individual areas is the acquisition of knowledge. But knowledge can only be acquired in the conscious state. A conscious awareness is therefore the corollary of activity in the specialised areas. Recent experiments using imaging and time resolution methods as well as patients blinded by lesions either in V1 or in more extensive parts of the visual cortex show that the activity in one or a small number of visual areas, without involvement of V1, can give rise to both conscious experience and a crude knowledge about the visual world. This leads us to the conclusion that consciousness itself may be modular.

scholarly journals Spatial modulation of visual signals arises in cortex with active navigation

2019 ◽  
Author(s):  
E. Mika Diamanti ◽  
Charu Bai Reddy ◽  
Sylvia Schröder ◽  
Tomaso Muzzu ◽  
Kenneth D. Harris ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Spatial Position ◽  
Visual Signals ◽  
Spatial Modulation ◽  
Visual Responses ◽  
Active Behavior ◽  
Visual Areas ◽  
Familiar Environment ◽  
Higher Visual Areas

During navigation, the visual responses of neurons in primary visual cortex (V1) are modulated by the animal’s spatial position. Here we show that this spatial modulation is similarly present across multiple higher visual areas but largely absent in the main thalamic pathway into V1. Similar to hippocampus, spatial modulation in visual cortex strengthens with experience and requires engagement in active behavior. Active navigation in a familiar environment, therefore, determines spatial modulation of visual signals starting in the cortex.

scholarly journals Linearly Additive Shape and Color Signals in Monkey Inferotemporal Cortex

2009 ◽  
Vol 101 (4) ◽  
pp. 1867-1875 ◽  
Author(s):  
David B. T. McMahon ◽  
Carl R. Olson
Keyword(s):  
Visual Cortex ◽  
Feature Binding ◽  
Neural Representation ◽  
Inferotemporal Cortex ◽  
Visual Areas ◽  
Color Signals ◽  
Color Combinations ◽  
The Brain ◽  
Effective Representation ◽  
Low Order

How does the brain represent a red circle? One possibility is that there is a specialized and possibly time-consuming process whereby the attributes of shape and color, carried by separate populations of neurons in low-order visual cortex, are bound together into a unitary neural representation. Another possibility is that neurons in high-order visual cortex are selective, by virtue of their bottom-up input from low-order visual areas, for particular conjunctions of shape and color. A third possibility is that they simply sum shape and color signals linearly. We tested these ideas by measuring the responses of inferotemporal cortex neurons to sets of stimuli in which two attributes—shape and color—varied independently. We find that a few neurons exhibit conjunction selectivity but that in most neurons the influences of shape and color sum linearly. Contrary to the idea of conjunction coding, few neurons respond selectively to a particular combination of shape and color. Contrary to the idea that binding requires time, conjunction signals, when present, occur as early as feature signals. We argue that neither conjunction selectivity nor a specialized feature binding process is necessary for the effective representation of shape–color combinations.

scholarly journals Spatial modulation of visual responses arises in cortex with active navigation

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
E Mika Diamanti ◽  
Charu Bai Reddy ◽  
Sylvia Schröder ◽  
Tomaso Muzzu ◽  
Kenneth D Harris ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Spatial Position ◽  
Visual Signals ◽  
Spatial Modulation ◽  
Visual Responses ◽  
Active Behavior ◽  
Visual Areas ◽  
Familiar Environment ◽  
Higher Visual Areas

During navigation, the visual responses of neurons in mouse primary visual cortex (V1) are modulated by the animal’s spatial position. Here we show that this spatial modulation is similarly present across multiple higher visual areas but negligible in the main thalamic pathway into V1. Similar to hippocampus, spatial modulation in visual cortex strengthens with experience and with active behavior. Active navigation in a familiar environment, therefore, enhances the spatial modulation of visual signals starting in the cortex.

scholarly journals Saccade-based termination responses in macaque V1 and visual perception

2018 ◽  
Vol 35 ◽  
Author(s):  
JAMES E. NIEMEYER ◽  
MICHAEL A. PARADISO
Keyword(s):  
Visual Cortex ◽  
Visual Perception ◽  
Firing Rate ◽  
Visual Stimulation ◽  
Saccadic Eye Movement ◽  
Perceptual Sensitivity ◽  
Neural Correlate ◽  
Visual Areas ◽  
Natural Situation ◽  
The Brain

AbstractNeurons in visual areas of the brain are generally characterized by the increase in firing rate that occurs when a stimulus is flashed on in the receptive field (RF). However, neurons also increase their firing rate when a stimulus is turned off. These “termination responses” or “after-discharges” that occur with flashed stimuli have been observed in area V1 and they may be important for vision as stimulus terminations have been shown to influence visual perception. The goal of the present study was to determine the strength of termination responses in the more natural situation in which eye movements move a stimulus out of an RF. We find that termination responses do occur in macaque V1 when termination results from a saccadic eye movement, but they are smaller in amplitude compared to flashed-off stimuli. Furthermore, there are termination responses even in the absence of visual stimulation. These findings demonstrate that termination responses are a component of naturalistic vision. They appear to be based on both visual and nonvisual signals in visual cortex. We speculate that the weakening of termination responses might be a neural correlate of saccadic suppression, the loss of perceptual sensitivity around the time of saccades.

scholarly journals The Visual Cortex in Context

2019 ◽  
Vol 5 (1) ◽  
pp. 317-339 ◽  
Author(s):  
Emmanouil Froudarakis ◽  
Paul G. Fahey ◽  
Jacob Reimer ◽  
Stelios M. Smirnakis ◽  
Edward J. Tehovnik ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Visual Processing ◽  
Hierarchical Models ◽  
Sensorimotor Integration ◽  
Brain Areas ◽  
Cortex Area ◽  
Brain Circuitry ◽  
Open Question ◽  
The Brain

In this article, we review the anatomical inputs and outputs to the mouse primary visual cortex, area V1. Our survey of data from the Allen Institute Mouse Connectivity project indicates that mouse V1 is highly interconnected with both cortical and subcortical brain areas. This pattern of innervation allows for computations that depend on the state of the animal and on behavioral goals, which contrasts with simple feedforward, hierarchical models of visual processing. Thus, to have an accurate description of the function of V1 during mouse behavior, its involvement with the rest of the brain circuitry has to be considered. Finally, it remains an open question whether the primary visual cortex of higher mammals displays the same degree of sensorimotor integration in the early visual system.

scholarly journals Compressive Temporal Summation in Human Visual Cortex

2017 ◽  
Author(s):  
Jingyang Zhou ◽  
Noah C. Benson ◽  
Kendrick Kay ◽  
Jonathan Winawer
Keyword(s):  
Visual Cortex ◽  
Visual System ◽  
Temporal Summation ◽  
Neural Response ◽  
Visual World ◽  
Sensory Inputs ◽  
Space And Time ◽  
Visual Areas ◽  
Invariant Representations ◽  
Over Time

AbstractCombining sensory inputs over space and time is fundamental to vision. Population receptive field models have been successful in characterizing spatial encoding throughout the human visual pathways. A parallel question—how visual areas in the human brain process information distributed over time—has received less attention. One challenge is that the most widely used neuroimaging method—fMRI—has coarse temporal resolution compared to the time-scale of neural dynamics. Here, via carefully controlled temporally modulated stimuli, we show that information about temporal processing can be readily derived from fMRI signal amplitudes in male and female subjects. We find that all visual areas exhibit sub-additive summation, whereby responses to longer stimuli are less than the linear prediction from briefer stimuli. We also find fMRI evidence that the neural response to two stimuli is reduced for brief interstimulus intervals (indicating adaptation). These effects are more pronounced in visual areas anterior to V1-V3. Finally, we develop a general model that shows how these effects can be captured with two simple operations: temporal summation followed by a compressive nonlinearity. This model operates for arbitrary temporal stimulation patterns and provides a simple and interpretable set of computations that can be used to characterize neural response properties across the visual hierarchy. Importantly, compressive temporal summation directly parallels earlier findings of compressive spatial summation in visual cortex describing responses to stimuli distributed across space. This indicates that for space and time, cortex uses a similar processing strategy to achieve higher-level and increasingly invariant representations of the visual world.Significance statementCombining sensory inputs over time is fundamental to seeing. Two important temporal phenomena are summation, the accumulation of sensory inputs over time, and adaptation, a response reduction for repeated or sustained stimuli. We investigated these phenomena in the human visual system using fMRI. We built predictive models that operate on arbitrary temporal patterns of stimulation using two simple computations: temporal summation followed by a compressive nonlinearity. Our new temporal compressive summation model captures (1) subadditive temporal summation, and (2) adaptation. We show that the model accounts for systematic differences in these phenomena across visual areas. Finally, we show that for space and time, the visual system uses a similar strategy to achieve increasingly invariant representations of the visual world.

scholarly journals Functional ultrasound imaging of deep visual cortex in awake non-human primates

2019 ◽  
Author(s):  
Blaize Kévin ◽  
Gesnik Marc ◽  
Arcizet Fabrice ◽  
Ahnine Harry ◽  
Ferrari Ulisse ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Ocular Dominance ◽  
Functional Responses ◽  
Spatiotemporal Resolution ◽  
Retinotopic Maps ◽  
Visual Areas ◽  
Deep Layers ◽  
Fixation Task ◽  
Passive Fixation ◽  
The Brain

SummaryDeep regions of the brain are not easily accessible to investigation at the mesoscale level in awake animals or humans. We have recently developed functional Ultrasound (fUS) imaging fUS imaging technique to uncover deep hemodynamic functional responses. Applying fUS imaging on two awake non-human primates performing a passive fixation task, we reconstructed their retinotopic maps down to the deep calcarine and lunate sulci on visual areas (V1, V2 and V3). These maps were acquired in a single hour session with very few stimuli presentation. The spatial resolution of the technology is illustrated by mapping of Ocular Dominance (OD) columns within superficial and deep layers of the primary visual cortex. These acquisitions showed that OD selectivity is mostly present in layer IV but with evidence also in layers II/III and V. The fUS imaging technology therefore provides a new mesoscale approach to map brain activities at high spatiotemporal resolution in awake subjects within the whole depth of the cortex.

scholarly journals Visual category-driven differences in memory

2021 ◽  
Author(s):  
Adam Steel ◽  
Edward Silson
Keyword(s):  
Visual Cortex ◽  
Human Memory ◽  
Memory Systems ◽  
Neural Mechanisms ◽  
Neural Responses ◽  
Cortical Areas ◽  
Visual Areas ◽  
High Level ◽  
Human Categorization ◽  
The Brain

Categorizing classes of stimuli in the real-world is thought to underlie features of general intelligence, including our ability to infer identities of new objects, environments, and people never encountered before. Our understanding of human categorization, and the neural mechanisms that underlie this ability, was initially described in the context of visual perception. It is now broadly accepted that a network of high-level visual areas on the ventral and lateral surfaces of the brain exhibit some level of ‘domain (or category)-selective’ activity: preferential neural responses to visual stimuli of one category more than another (e.g., larger responses to faces compared to scenes or manipulable objects). Inspired by this robust and intuitive organization, recent studies have begun investigating the extent to which human memory systems also exhibit a category-selective organization. Surprisingly, this work has revealed strong evidence for the existence of category-selective areas in swaths of cortex previously considered to be domain-general. These results suggest that category-selectivity is a general organizing principle not only of visual cortex, but also for higher-level cortical areas involved in memory. In this chapter we review the evidence for the manifestation of visual category preferences in memory systems, and how this relates to the well-established category-selectivity exhibited within visual cortex.

scholarly journals A massively asynchronous, parallel brain

2015 ◽  
Vol 370 (1668) ◽  
pp. 20140174 ◽  
Author(s):  
Semir Zeki
Keyword(s):  
Parallel Processing ◽  
Time Windows ◽  
Stimulus Onset ◽  
Visual Scene ◽  
Visual Signals ◽  
Visual Attributes ◽  
Visual Areas ◽  
New Generation ◽  
Perceptual Systems ◽  
The Brain

Whether the visual brain uses a parallel or a serial, hierarchical, strategy to process visual signals, the end result appears to be that different attributes of the visual scene are perceived asynchronously—with colour leading form (orientation) by 40 ms and direction of motion by about 80 ms. Whatever the neural root of this asynchrony, it creates a problem that has not been properly addressed, namely how visual attributes that are perceived asynchronously over brief time windows after stimulus onset are bound together in the longer term to give us a unified experience of the visual world, in which all attributes are apparently seen in perfect registration. In this review, I suggest that there is no central neural clock in the (visual) brain that synchronizes the activity of different processing systems. More likely, activity in each of the parallel processing-perceptual systems of the visual brain is reset independently, making of the brain a massively asynchronous organ, just like the new generation of more efficient computers promise to be. Given the asynchronous operations of the brain, it is likely that the results of activities in the different processing-perceptual systems are not bound by physiological interactions between cells in the specialized visual areas, but post-perceptually, outside the visual brain.

Consciousness

2018 ◽  
Author(s):  
Anil K. Seth
Keyword(s):  
Conscious Experience ◽  
Real Problem ◽  
Active Inference ◽  
Biological Mechanisms ◽  
Specific Content ◽  
Brain Responses ◽  
Biomimetic Approach ◽  
Multiple Levels ◽  
In Virtue Of ◽  
The Brain

Consciousness is perhaps the most familiar aspect of our existence, yet we still do not know its biological basis. This chapter outlines a biomimetic approach to consciousness science, identifying three principles linking properties of conscious experience to potential biological mechanisms. First, conscious experiences generate large quantities of information in virtue of being simultaneously integrated and differentiated. Second, the brain continuously generates predictions about the world and self, which account for the specific content of conscious scenes. Third, the conscious self depends on active inference of self-related signals at multiple levels. Research following these principles helps move from establishing correlations between brain responses and consciousness towards explanations which account for phenomenological properties—addressing what can be called the “real problem” of consciousness. The picture that emerges is one in which consciousness, mind, and life, are tightly bound together—with implications for any possible future “conscious machines.”

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