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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.
Functional Magnetic Resonance Imaging of the Human Motor Cortex
Published in Alexa Riehle, Eilon Vaadia, Motor Cortex in Voluntary Movements, 2004
Andreas Kleinschmidt, Ivan Toni
the clear-cut demonstration of somatotopy was improved by directly contrasting different finger movements performed in alternating blocks. One of the reasons for this may be that spatially less specific effects — for instance, in the locally draining vasculature or from partial-volume effects in single voxels — arise when contrasting against rest. In that sense, this approach resembled those used in the visual system for retinotopic mapping where there is continuous visual stimulation that slowly changes its position in the visual field.49 Alternatively, this may also reflect the fact that similar types of proximal coinnervation for stabilization were recruited for both the experimental and the control task, and that nonspecific activations were thus canceled out. Because we found no segregation but only relative predominance, we proposed to think of the contribution of somatatopy to functional organization of Ml as a "gradient." In other words, movements of different fingers are associated with extensive neural activations throughout the entire hand representation (and beyond), but the peaks for different fingers are in systematic accord with the homunculus cartoon. We believe that such a description presents a safeguard not only against overinterpreting the historical homunculus cartoons, but also against seeing more segregation in contemporary fractured or mosaic patterns obtained in nonhuman primates than the methods applied in those studies can positively affirm.
High Resolution Diffuse Optical Tomography of the Human Brain
Published in Francesco S. Pavone, Shy Shoham, Handbook of Neurophotonics, 2020
Muriah D. Wheelock, Adam T. Eggebrecht
In the same year, a second research study utilized a retinotopy paradigm during separate HD-DOT and fMRI sessions in healthy adults. A rotating, flickering, checkerboard wedge was displayed on the screen in a phase-encoded paradigm. The location of activation during each quadrant of the checkerboard presentation was mapped to the visual cortex. Single-subject and group average data demonstrated that fMRI and HD-DOT retinotopic mapping boasted a high degree of correspondence in the visual cortex (Figure 17.8B) (Eggebrecht et al., 2012).
Beyond the neural correlates of consciousness: using brain stimulation to elucidate causal mechanisms underlying conscious states and contents
Published in Journal of the Royal Society of New Zealand, 2021
Corinne A. Bareham, Matt Oxner, Tim Gastrell, David Carmel
Stimulation of visual cortex is known to trigger phosphenes, brief visual sensations that do not correspond to any visual input (Marg and Rudiak 1994). Above a certain threshold strength, single TMS pulses to early visual cortex evoke stationery phosphenes, whereas pulses to the part of retinotopic cortex that processes motion, area V5 (which is located laterally to early visual cortex), evoke moving phosphenes. Moving phosphenes are abolished, though, when a supra-threshold V5 pulse is followed 20-40 ms later by a sub-threshold pulse to early visual cortex (Pascual-Leone and Walsh 2001), and a moving phosphene is evoked when a sub-threshold pulse to V5 is followed by a supra-threshold pulse to early visual cortex (Silvanto et al. 2005). These manipulations of the relative timing of paired TMS pulses reveal that conscious experiences may depend on feedback projections to early visual cortex.
A unified dynamic neural field model of goal directed eye movements
Published in Connection Science, 2018
While a heterogeneous field of view (e.g. characterising the retina with a central macula and fovea) could be viewed as a complicating factor for the above issues, it is actually a solution to the problem when one considers the generation of eye movements. Foveating a target indeed facilitates its pursuit by increasing the neural resources for processing the motion signals, and at the same time hinder and make unnecessary the learning of stimuli dynamics for all locations of the visual field. Learning to foveate the target and keep it in the central visual field will reduce the problem to processing the motion signals and characterise the dynamics of the input stimulus. Also pointing in such direction, a model of target position encoding in the superior colliculus has been recently proposed in Taouali et al. (2015), demonstrating that apparently complex foveation performance can be accounted for by dynamical properties of neural field and retinotopic stimulation (using a log-polar representation of the visual field).