China
Africa
Explore chapters and articles related to this topic
The Biological Bases of Photoreception in the Process of Image Vision
Published in Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe, Visual and Non-Visual Effects of Light, 2020
Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe
In this way, visual information is transmitted to the lateral geniculate nucleus of the thalamus (a gate controlling passage of information to the primary visual cortex in the occipital lobe). In this nucleus, color-sensitive projection neurons have the same receptive field organization as those found in ganglion cells. At the level of the cortex, color-sensitive neurons and the organization of their receptive fields differ from the previously described mechanisms. Color opponency appears within the center and surround of the receptive field and also between the center and surround (double-opponent color-sensitive cells). Some cortical neurons are orientation-selective and motion-sensitive. The primary visual cortex carries out an analysis of the visual field for a variety of aspects of visual stimuli, such as orientation, direction of movement, and object color [Matthews 1998]. Further, visual information is transmitted to higher-order cortical areas – anterior to the primary visual cortex – for the processing of specialized information. Such functions as the processing of object form, color, or motion project to more specialized areas in a more anterior part of the occipital lobe and the posterior part of the temporal lobe cortex [Matthews 1998].
Driver Behavior
Published in Motoyuki Akamatsu, Handbook of Automotive Human Factors, 2019
The initial stage of visual information processing in the brain (visual cortex) involves neurons that respond to basic visual features, such as brightness, color, and the orientation of line segments. These neurons have a relatively narrow receptive field. Each neuron responds to a stimulus only when the stimulus is given within the receptive field of vision. Also, neurons of the visual cortex in their early stages have a structure in which adjacent neurons have receptive fields at similar visual field. Consequently, locations of visual fields and locations of neurons on the visual cortex almost perfectly match on a one-on-one basis (retinotopy). As such, neurons of the visual system in their early stage play a role of coding both features and locations of visual stimuli. In attentional models, features of the visual system are expressed in terms of feature maps. The forms of feature maps differ depending on the models used. In general, models that extract basic visual features, such as brightness, color and the orientation of edges, are commonly used.
Restoration: Nanotechnology in Tissue Replacement and Prosthetics
Published in Harry F. Tibbals, Medical Nanotechnology and Nanomedicine, 2017
Retinal degeneration or detachment is one of the main causes of vision loss. Therefore, most efforts to develop a visual neuroprosthesis have attempted to stimulate the ganglia cell layer behind the retina, as the simplest strategy to interface to the visual signal processing that is in place on the optical nerve path. Some prostheses have been designed and tested that stimulate the visual cortex directly, producing a low-resolution pattern of visual sensation, and some have mapped digitized imaging onto touch sensors in the back or other skin areas, in a kind of transposed Braille that delivers images rather than encoded letters.
Brain–Computer Interface Games Based on Consumer-Grade EEG Devices: A Systematic Literature Review
Published in International Journal of Human–Computer Interaction, 2020
Gabriel Alves Mendes Vasiljevic, Leonardo Cunha de Miranda
Visual stimulations are processed in the visual cortex, located at the occipital lobe. There are specific signal modulations that occur in the visual cortex when certain visual stimuli are perceived, and these modulations, known as VEP (Visually Evoked Potentials), are easily detected, especially as the stimuli moves closer to the visual field, as the VEP amplitude increases. SSVEP (Steady-State VEP) is a particular type of VEP that is elicited when the visual stimulus changes at a frequency higher than 6 Hz (Baseler, Sutter, Klein, & Carney, 1994; Liu et al., 2012). This stimulus can be either a pattern or a flashing light or image. In the case of a BCI, a SSVEP can be used as a control signal by means of the eye-gaze, in which the user can select one among many targets by focusing his/her gaze at the corresponding visual stimulus (Zhu, Bieger, Molina, & Aarts, 2010). Other forms of evoked potentials are possible, such as AEP (Auditory-Evoked Potentials) and SEP (Somatosensory-Evoked Potentials), with their corresponding SSAEP (Steady-State AEP) (Punsawad & Wongsawat, 2017) and SSSEP (Steady-State SEP) (Ahn, Kim, & Jun, 2016).
Towards enhanced information transfer rate: a comparative study based on classification techniques
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2020
SSVEP is defined as the presence of steady-state harmonics in the EEG signal recorded over the visual cortex after the subject is subjected to flickering objects of predefined frequencies (Regan 1989). The visual cortex is located over the occipital region, located at the back of the human scalp. This region is identified by locating 10% of the total distance value between Nasion and Inion with reference at Inion. The SSVEP appears in the form of 1st, 2nd and 3rd harmonics of the fundamental flickering frequencies within the EEG with respect to the flickering stimulus (Müller-Putz et al. 2005; Combaz and Van Hulle 2015). In a stereotypical SSVEP paradigm based BCI, the subjects fixed their gaze on one of the multiple decision targets presented on a computer screen, such that each target has a unique flickering frequency. When the subject is focusing on one of the targets, the SSVEP response over that object’s frequency is most significant. Thus the determination of the decision target under consideration can be done by finding the 1st harmonic frequency which has maximum power. Yet another way of eliciting SSVEP is the checker-board paradigm which produces a stronger SSVEP activity (Lalor et al. 2005; Trejo et al. 2006; Martinez et al. 2007). Like P300, SSVEP requires little or no training but it might be annoying for some subjects and might cause seizures in some subjects. However, the numbers of decisions in an SSVEP paradigm which are uniquely represented by different frequencies are limited due to the bandwidth of the frequencies that can elicit SSVEP in a subject. Hence other techniques like phase coding or resorting to hybrid paradigms based on SSVEP are considered for developing and improvement of ADs.