scholarly journals Fixation Induced Blindness

2020 ◽  
Author(s):  
Ahmad Yousef
Keyword(s):  
Receptive Field ◽  
Visual Awareness ◽  
Visual Space ◽  
Saccadic Eye Movements ◽  
Retinal Photoreceptors ◽  
Invariance Hypothesis ◽  
Respective Field ◽  
The Brain ◽  
Emmert’S Law

This article reports how fixation could convey visual stimuli to the invisibility region whether the stimuli are presented centrally or peripherally regardless the textures of the background. It also reports the impossibility of conveying visual stimulus to the invisibility region when the stimulus is not fixated, namely, when the stimulus is in motion. We started in discussing how visual fixation could convey a centrally presented stimulus (pink horse) into the invisibility region under certain conditions, and why breaking the aforementioned invisibility by an intentional saccade away from the fixational point allows the stimulus to exert a ghostly horse but with complementary colours. Scientists had been hypothesizing that image aftereffect is caused by neural adaptation. In another word, the retinal photoreceptors & its corresponding neurological pathways to the visual awareness might be being idle, namely, the visual respective field might be idle. Idle visual receptive field seems to be the best explanation of the present illusion, namely, we see the light grayish background turned to greenish in the aforementioned desensitized receptive field. Important to mention, fixation greatly inhibits the spontaneous saccadic eye movements, and thus, it reduces the rooms of the receptive field remapping. Namely, every visual space will be possibly have unchangeable visual map in the brain. To arrest the aforementioned statements, we built a running stimulus to disallow the overlapping of the image and its aftereffect, and we found that the image cannot disappear. In another word, the visual awareness of the aforementioned stimulus would have ghostly & cloudy green balls in between the original materials (purple balls). The previously mentioned finding confirms the role of the spontaneous saccadic movement in promoting visibility & preventing the blindness, also see reference 1. We ended this research with asserting whether the claims against Emmert's law which raised doubts about the accurate compliance of the aforementioned law and size–distance invariance hypothesis. Weirdly enough, the claims are correct as if the image aftereffect projected against distant wall is following the dynamical visual angle but not the static one.

The Role of Brain Oscillations in the Temporal Limits of Attention

2014 ◽  
Author(s):  
Kimron Shapiro ◽  
Simon Hanslmayr
Keyword(s):  
Frequency Band ◽  
Visual Space ◽  
Visual Input ◽  
Brain Oscillations ◽  
Approaches To Studying ◽  
Alpha Frequency ◽  
Alpha Frequency Band ◽  
Long Time ◽  
The Brain

Attention is the ubiquitous construct referring to the ability of the brain to focus resources on a subset of perceptual input which it is trying to process for a response. Attention has for a long time been studied with reference to its distribution across space where, for example, visual input from an attentionally monitored location is given preference over non-monitored (i.e. attended) locations. More recently, attention has been studied for its ability to select targets from among rapidly, sequentially presented non-targets at a fixed location, e.g. in visual space. The present chapter explores this latter function of attention for its relevance to behaviour. In so doing, it highlights what is becoming one of the most popular approaches to studying communication across the brain—oscillations—at various frequency ranges. In particular the authors discuss the alpha frequency band (8–12 Hz), where recent evidence points to an important role in the switching between processing external vs. internal events.

scholarly journals Illusory Snakes Might Be Due to Asynchronized Respective Field Remapping

2019 ◽  
Author(s):  
Ahmad Yousef
Keyword(s):  
Visual Perception ◽  
Apparent Motion ◽  
Peripheral Vision ◽  
Visual Awareness ◽  
Visual Space ◽  
Peripheral Retina ◽  
Conscious Perception ◽  
Illusory Motion ◽  
Central Retina ◽  
Respective Field

In this proposal, we try to virtually navigate inside the human brain to understand the neural mechanism of the perception of illusory snakes. To achieve this mission, we have to imagine the neural network of the visual motion perception during spontaneous saccadic eye movements; and digging into clear distinction between the foveal versus the peripheral visual receptive field remapping. We had previously discussed that conscious perception generated by the central retina has very different attributes than the visual awareness generated by the peripheral retina. It was clear that the central retina triggers visual perception which decelerates the apparent motion of the cyclic elements, and enlarge the size of these elements, see reference 2. The peripheral retina , however, not only accelerates the apparent motion, but it generates illusory motion reversals, see reference 19. Since there are clear discrepancies in the spatiotemporal characteristics between the central and the peripheral retina in the visual awareness, we hypothesized that the illusory rotating snakes might be due to asynchronized respective field remapping; namely, a rivalrous remapping processes of the central versus the peripheral retinal images. In another word, the respective field remapping process triggered by the central retina has different spatial and temporal feeds to the visual awareness than the retinal peripheries. Interestingly, it had been found that deactivating the retinal peripheries through significant reduction against the contrast of the stimulus (that may stop the retinal peripheries from signaling the brain) eliminates the rotating snakes illusion. Elimination that might evidence the role of active retinal peripheries in creating the perception of illusory snakes. Collectively, we think that illusory snakes is due to a rivalry between the central and the peripheral retina; and their corresponding conscious brains; and the saccades are nothing but to convey parts of the retinal image from the center to the peripheries, and vice versa. Namely, the illusory snakes is generated by a spontaneous saccadic rivalry between the fovea & its corresponding conscious brain competing with the peripheral retina & its corresponding conscious brain. Similarly, peripheral drift illusion that requires peripheral vision to be perceived, may not be generated without the aforementioned saccadic rivalry; namely, we think that the perception of that illusion may not be occurred without spontaneous saccade away from the fixational peripheral visual space, see also reference 1 and 5. That saccade is mostly due to spatial attention which conveys the retinal image from the retinal peripheries (the fixational visual space) to the central retina (the attentional visual space). Namely, we think that without the aforementioned conveyance, the perceived illusion may not be generated because the aforementioned spatiotemporal discrepancies will be terminated. Importantly, we investigated the contribution of the human medial temporal complex in producing the illusory motion conscious perception with three different mechanisms: Cognitive control, deep breathing, and the arrangements of the patterns of the building blocks. The aforementioned processes are found to alter the visual perception of rotating snakes stimulus. Inclusively, we distinguished between two distinct visual awareness, namely, the central versus the peripheral vision and we show how active vision which requires cognitive control but not passive vision can ultimately control the perception of the rotating snakes stimulus, namely, alternation between real and illusory visual awareness!

What Delay Fields Tell Us About Striate Cortex

2007 ◽  
Vol 98 (2) ◽  
pp. 559-576 ◽  
Author(s):  
Edward J. Tehovnik ◽  
Warren M. Slocum
Keyword(s):  
Striate Cortex ◽  
Visual Space ◽  
Saccadic Eye Movements ◽  
Visual Signal ◽  
Delay Effect ◽  
Electrical Microstimulation ◽  
Cortex Area ◽  
Motor Signal ◽  
The Brain ◽  
Stimulation Of

It is well known that electrical activation of striate cortex (area V1) can disrupt visual behavior. Based on this knowledge, we discovered that electrical microstimulation of V1 in macaque monkeys delays saccadic eye movements when made to visual targets located in the receptive field of the stimulated neurons. This review discusses the following issues. First, the parameters that affect the delay of saccades by microstimulation of V1 are reviewed. Second, the excitability properties of the V1 elements mediating the delay are discussed. Third, the properties that determine the size and shape of the region of visual space affected by stimulation of V1 are described. This region is called a delay field. Fourth, whether the delay effect is mainly due to a disruption of the visual signal transmitted through V1 or whether it is a disturbance of the motor signal transmitted between V1 and the brain stem saccade generator is investigated. Fifth, the properties of delay fields are used to estimate the number of elements activated directly by electrical microstimulation of macaque V1. Sixth, these properties are used to make inferences about the characteristics of visual percepts induced by such stimulation. Seventh, the disruptive effects of V1 stimulation in monkeys and humans are compared. Eighth, a cortical mechanism to account for the disruptive effects of V1 stimulation is proposed. Finally, these effects are related to normal vision.

scholarly journals Effects of Focal Inactivation of Dorsal or Ventral Layers of the Lateral Geniculate Nucleus on Cats' Ability to See and Fixate Small Targets

1998 ◽  
Vol 80 (4) ◽  
pp. 2206-2209 ◽  
Author(s):  
Andrew K. Tate ◽  
Joseph G. Malpeli
Keyword(s):  
Lateral Geniculate Nucleus ◽  
Visual Space ◽  
Saccadic Eye Movements ◽  
Velocity Amplitude ◽  
Visuomotor Behavior ◽  
Lateral Geniculate ◽  
Saccade Velocity ◽  
Areas 17 And 18 ◽  
Small Targets

Tate, Andrew K. and Joseph G. Malpeli. Effects of focal inactivation of dorsal or ventral layers of the lateral geniculate nucleus on cats' ability to see and fixate small targets. J. Neurophysiol. 80: 2206–2209, 1998. To reveal contributions of different subdivisions of the lateral geniculate nucleus (LGN) to visuomotor behavior, segments of either layer A or the C layers were inactivated with microinjections of γ-aminobutyric acid while cats made saccades to retinally stabilized spots of light placed either in affected regions of visual space or mirror-symmetric locations in the opposite hemifield. Inactivating layer A reduced the success rate for saccades to targets presented in affected locations from 82.4 to 26.8% while having no effect on saccades to the control hemifield. Saccades to affected sites had reduced accuracy and longer initiation latency and tended to be hypometric. In contrast, inactivating C layers did not affect performance. Data from all conditions fell along the same saccade velocity/amplitude function (“main sequence”), suggesting that LGN inactivations cause localization deficits, but do not interfere with saccade dynamics. Cerebral cortex is the only target of the A layers, so behavioral decrements caused by inactivating layer A must be related to changes in cortical activity. Inactivating layer A substantially reduces the activity of large subsets of corticotectal cells in areas 17 and 18, whereas few corticotectal cells depend on C layers for visually driven activity. The parallels between these behavioral and electrophysiological data along with the central role of the superior colliculus in saccadic eye movements suggests that the corticotectal pathway is involved in both deficits and remaining capacities resulting from blockade of layer A.

scholarly journals Using the Change Manager Model for the Hippocampal System to Predict Connectivity and Neurophysiological Parameters in the Perirhinal Cortex

2016 ◽  
Vol 2016 ◽  
pp. 1-13
Author(s):  
L. Andrew Coward ◽  
Tamas D. Gedeon
Keyword(s):  
Receptive Field ◽  
Memory Retrieval ◽  
Focal Point ◽  
Receptive Fields ◽  
Perirhinal Cortex ◽  
Prior Learning ◽  
Episodic Memories ◽  
Cortical Receptive Fields ◽  
The Brain

Theoretical arguments demonstrate that practical considerations, including the needs to limit physiological resources and to learn without interference with prior learning, severely constrain the anatomical architecture of the brain. These arguments identify the hippocampal system as the change manager for the cortex, with the role of selecting the most appropriate locations for cortical receptive field changes at each point in time and driving those changes. This role results in the hippocampal system recording the identities of groups of cortical receptive fields that changed at the same time. These types of records can also be used to reactivate the receptive fields active during individual unique past events, providing mechanisms for episodic memory retrieval. Our theoretical arguments identify the perirhinal cortex as one important focal point both for driving changes and for recording and retrieving episodic memories. The retrieval of episodic memories must not drive unnecessary receptive field changes, and this consideration places strong constraints on neuron properties and connectivity within and between the perirhinal cortex and regular cortex. Hence the model predicts a number of such properties and connectivity. Experimental test of these falsifiable predictions would clarify how change is managed in the cortex and how episodic memories are retrieved.

The Role of Mitochondria in the Genesis of Neuroaxonal Dystrophy in the Brains of Aging Mice

1975 ◽  
Vol 33 ◽  
pp. 372-373
Author(s):  
J.E. Johnson
Keyword(s):  
Electron Microscopy ◽  
Present Report ◽  
Light And Electron Microscopy ◽  
Dorsal Column ◽  
Neuroaxonal Dystrophy ◽  
Nucleus Gracilis ◽  
Dystrophic Axons ◽  
The Brain ◽  
Nucleus Cuneatus

Although neuroaxonal dystrophy (NAD) has been examined by light and electron microscopy for years, the nature of the components in the dystrophic axons is not well understood. The present report examines nucleus gracilis and cuneatus (the dorsal column nuclei) in the brain stem of aging mice.Mice (C57BL/6J) were sacrificed by aldehyde perfusion at ages ranging from 3 months to 23 months. Several brain areas and parts of other organs were processed for electron microscopy.At 3 months of age, very little evidence of NAD can be discerned by light microscopy. At the EM level, a few axons are found to contain dystrophic material. By 23 months of age, the entire nucleus gracilis is filled with dystrophic axons. Much less NAD is seen in nucleus cuneatus by comparison. The most recurrent pattern of NAD is an enlarged profile, in the center of which is a mass of reticulated material (reticulated portion; or RP).

Fibrinolytic Activity of Cerebro-Spinal Fluid and the Development of Artificial Cerebral Haematomas in Dogs

1969 ◽  
Vol 21 (02) ◽  
pp. 294-303 ◽  
Author(s):  
H Mihara ◽  
T Fujii ◽  
S Okamoto
Keyword(s):  
Cerebrospinal Fluid ◽  
Carboxylic Acid ◽  
Fibrinolytic Activity ◽  
Clinical Implications ◽  
Trans Form ◽  
Plate Method ◽  
Blood Samples ◽  
Fibrin Plate ◽  
The Brain

SummaryBlood was injected into the brains of dogs to produce artificial haematomas, and paraffin injected to produce intracerebral paraffin masses. Cerebrospinal fluid (CSF) and peripheral blood samples were withdrawn at regular intervals and their fibrinolytic activities estimated by the fibrin plate method. Trans-form aminomethylcyclohexane-carboxylic acid (t-AMCHA) was administered to some individuals. Genera] relationships were found between changes in CSF fibrinolytic activity, area of tissue damage and survival time. t-AMCHA was clearly beneficial to those animals given a programme of administration. Tissue activator was extracted from the brain tissue after death or sacrifice for haematoma examination. The possible role of tissue activator in relation to haematoma development, and clinical implications of the results, are discussed.

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