Visual Responses

2017 ◽  
pp. 214-226
Author(s):  
Riitta Hari ◽  
Aina Puce
Keyword(s):  
Visual Stimulus ◽  
Visual Angle ◽  
Visual Stimulation ◽  
Evoked Responses ◽  
Visual Responses ◽  
Visual Evoked Responses ◽  
Steady State Responses ◽  
Entire Visual Field ◽  
State Responses ◽  
Light Flashes

This chapter introduces visual evoked responses. Transient VEPs are maximal across the posterior scalp and consist of three main deflections—N75, P100, and N135. Magnetic VEFs also show a prominent occipital response peaking at around 100 ms. Visual stimulation can include light flashes, pattern onset/offsets, pattern reversals and natural images. The extent and eccentricity of the visual stimulus can selectively encompass foveal or extrafoveal regions, or include quadrants, hemifield or the entire visual field. Stimulus attributes such as visual angle, spatial frequency, luminance and contrast greatly affect VEF and VEP amplitudes and latencies. Selective responses in the dorsal and ventral visual streams can be elicited with carefully chosen stimuli. Steady-state responses to periodically varying visual stimuli can be used to frequency-tag different aspects of the visual stimulus.

Two-Channel Polarization Analyzer in the Sustaining Fiber-Dimming Fiber Ensemble of Crayfish Visual System

1998 ◽  
Vol 80 (5) ◽  
pp. 2571-2583 ◽  
Author(s):  
Raymon M. Glantz ◽  
Andy McIsaac
Keyword(s):  
Visual System ◽  
Polarized Light ◽  
Polarization Sensitivity ◽  
Visual Responses ◽  
Polarization Analyzer ◽  
Peripheral Neurons ◽  
Steady State Responses ◽  
Vector Orientation ◽  
Channel Polarization ◽  
State Responses

Glantz, Raymon M. and Andy McIsaac. Two-channel polarization analyzer in the sustaining fiber-dimming fiber ensemble of crayfish visual system. J. Neurophysiol. 80: 2571–2583, 1998. Polarization sensitivity (PS) was examined in two classes of neurons, sustaining fibers and dimming fibers, in the medulla externa (second optic neuropile) of the crayfish, Pacifasticus leniusculus. Visual responses were recorded intracellularly and extracellularly. The influence of e-vector orientation (θ) was probed in steady-state responses, with brief flashes and with a rotating polarizer. The results indicate that the entire sustaining fiber population appears to be maximally sensitive to vertically polarized light. Although the evidence is less complete for dimming fibers, they appear to be maximally inhibited by vertically polarized light and excited by horizontally polarized light. Thus the sustaining fibers and dimming fibers form a two-channel polarization analyzer that captures the main features of the polarization system established in photoreceptors and lamina monopolar cells. The available evidence suggests that this two-channel system has the same characteristics across most or all of the retinula. Lateral inhibition in sustaining fibers is differentially sensitive to θ. Inhibition is substantial at θ = 90° (horizontal) and essentially absent at θ = 0°. The details of the sustaining fiber polarization response closely follow features established in more peripheral neurons, including the magnitude of PS, enhanced responsiveness to a changing e-vector, and modest directionality to a changing e-vector in∼40% of the cells.

scholarly journals Audio-visual synchrony and spatial attention enhance processing of dynamic visual stimulation independently and in parallel: a frequency-tagging study

2017 ◽  
Author(s):  
Amra Covic ◽  
Christian Keitel ◽  
Emanuele Porcu ◽  
Erich Schröger ◽  
Matthias M Müller
Keyword(s):  
Spatial Attention ◽  
Visual Stimulus ◽  
Visual Processing ◽  
Visual Stimulation ◽  
Visual Fields ◽  
Tone Presentation ◽  
Neural Processing ◽  
Brain Responses ◽  
Neural Processes ◽  
Steady State Responses

ABSTRACTThe neural processing of a visual stimulus can be facilitated by attending to its position or by a co-occurring auditory tone. Using frequency-tagging we investigated whether facilitation by spatial attention and audio-visual synchrony rely on similar neural processes. Participants attended to one of two flickering Gabor patches (14.17 and 17 Hz) located in opposite lower visual fields. Gabor patches further “pulsed” (i.e. showed smooth spatial frequency variations) at distinct rates (3.14 and 3.63 Hz). Frequency-modulating an auditory stimulus at the pulse-rate of one of the visual stimuli established audio-visual synchrony. Flicker and pulsed stimulation elicited stimulus-locked rhythmic electrophysiological brain responses that allowed tracking the neural processing of simultaneously presented stimuli. These steady-state responses (SSRs) were quantified in the spectral domain to examine visual stimulus processing under conditions of synchronous vs. asynchronous tone presentation and when respective stimulus positions were attended vs. unattended. Strikingly, unique patterns of effects on pulse- and flicker driven SSRs indicated that spatial attention and audiovisual synchrony facilitated early visual processing in parallel and via different cortical processes. We found attention effects to resemble the classical top-down gain effect facilitating both, flicker and pulse-driven SSRs. Audio-visual synchrony, in turn, only amplified synchrony-producing stimulus aspects (i.e. pulse-driven SSRs) possibly highlighting the role of temporally co-occurring sights and sounds in bottom-up multisensory integration.

Effects of norepinephrine on the activity of visual neurons in the superior colliculus of the hamster

1999 ◽  
Vol 16 (3) ◽  
pp. 541-555 ◽  
Author(s):  
YI ZHANG ◽  
RICHARD D. MOONEY ◽  
ROBERT W. RHOADES
Keyword(s):  
Electrical Stimulation ◽  
Visual Cortex ◽  
Superior Colliculus ◽  
Visual Stimulation ◽  
Optic Chiasm ◽  
Evoked Responses ◽  
Visual Responses ◽  
Signal To Noise ◽  
Direct Stimulation ◽  
Stimulation Of

Single-unit recording and micropressure ejection techniques were used to test the effects of norepinephrine (NE) on the responses of neurons in the superficial layers (the stratum griseum superficiale and stratum opticum) of the hamster's superior colliculus (SC). Application of NE suppressed visually evoked responses by ≥30% in 75% of 40 neurons tested and produced ≥30% augmentation of responses in only 5%. The decrement in response strength was mimicked by application of the α2 adrenoceptor agonist, p-aminoclonidine, the nonspecific β agonist, isoproterenol, and the β1 agonist, dobutamine. These agents had similar effects on responses evoked by electrical stimulation of the optic chiasm and visual cortex. The α1 agonist, methoxamine, augmented the light-evoked responses of 53% of 49 SC cells by ≥30%, but had little effect on responses evoked by electrical stimulation of optic chiasm or visual cortex. The effects of adrenergic agonists upon the glutamate-evoked responses of SC cells that were synaptically “isolated” by concurrent application of Mg2+ were similar to those obtained during visual stimulation. Analysis of effects of NE on visually evoked and background activity indicated that application of this amine did not significantly enhance signal-to-noise ratios for most superficial layer SC neurons, and signal-to-noise ratios were in some cases reduced. These results indicate that NE acts primarily through α2 and β1 receptors to suppress the visual responses of SC neurons. Activation of either of these receptors reduces the responses of SC neurons to either of their two major visual inputs as well as to direct stimulation by glutamate, and it would thus appear that these effects are primarily postsynaptic.

An electroencephalograph study of classical conditioning

1962 ◽  
Vol 203 (1) ◽  
pp. 173-184 ◽  
Author(s):  
Robert Galambos ◽  
Guy C. Sheatz
Keyword(s):  
Visual Stimulus ◽  
Limbic System ◽  
Auditory Pathway ◽  
Evoked Responses ◽  
Conditioning Procedure ◽  
Wave Shape ◽  
Sensory Pathways ◽  
Evoked Activity ◽  
Relationship Of ◽  
Light Flashes

Unanesthetized monkeys and cats bearing indwelling electrodes show electrical activity evoked by clicks and light flashes in regions such as caudate nucleus, hypothalamus, and limbic system as well as in the classically defined sensory pathways. Amplitude and duration of the evoked responses, which display a similar triphasic form wherever recorded, vary spontaneously but can be experimentally enhanced by reinforcement or reduced by extinction in a simple Pavlovian conditioning procedure. When an animal displaying large responses to click stimuli appears to attend to a simultaneous visual stimulus (distraction) the click-evoked activity is remarkably reduced. Both wave shape and lability of the responses are preserved despite paralysis produced by a curare-like drug and (at auditory cortex) cutting the auditory pathway bilaterally at the midbrain level. Relevance of these results to some previous studies on learning is discussed, along with the possible relationship of these data to the neurophysiological findings reported on anesthetized preparations.

Avoiding Electromagnetic Artifacts When Recording Auditory Steady-State Responses

2004 ◽  
Vol 15 (08) ◽  
pp. 541-554 ◽  
Author(s):  
Terence W. Picton ◽  
Sasha M. John
Keyword(s):  
Steady State ◽  
High Intensity ◽  
Sensory Level ◽  
Evoked Responses ◽  
Frequency Spectra ◽  
Conversion Rates ◽  
Low Pass ◽  
Steady State Responses ◽  
Auditory Steady State Responses ◽  
State Responses

Electromagnetic artifacts can occur when recording multiple auditory steady-state responses evoked by sinusoidally amplitude modulated (SAM) stimuli. High-intensity air-conducted stimuli evoked responses even when hearing was prevented by masking. Additionally, high-intensity bone-conducted stimuli evoked responses that were completely different from those evoked by air-conducted stimuli of similar sensory level. These artifacts were caused by aliasing since they did not occur when recordings used high analog-digital (AD) conversion rates or when high frequencies in the electroencephalographic (EEG) signal were attenuated by steep-slope low-pass filtering. Two possible techniques can displace aliased energy away from the response frequencies: (1) using an AD rate that is not an integer submultiple of the carrier frequencies and (2) using stimuli with frequency spectra that do not alias back to the response frequencies, such as beats or "alternating SAM" tones. Alternating SAM tones evoke responses similar to conventional SAM tones, whereas beats produce significantly smaller responses.

scholarly journals Optogenetic suppression of corticogeniculate feedback in anesthetized ferrets is overridden by visual stimulation

2021 ◽  
Author(s):  
Silei Zhu ◽  
J. Michael Hasse ◽  
Farran Briggs
Keyword(s):  
Visual Stimulus ◽  
Visual Stimulation ◽  
Dorsal Lateral Geniculate Nucleus ◽  
Visual Responses ◽  
Neuronal Responses ◽  
Floor Effect ◽  
Slow Oscillations ◽  
V1 Neurons ◽  
Stimulation Parameters ◽  
Dorsal Lateral Geniculate

The feedforward projection from the retina shapes the spatial receptive field properties of neurons in the dorsal lateral geniculate nucleus of the thalamus (LGN). Corticogeniculate feedback from the visual cortex appears to exert a more subtle, modulatory influence on LGN responses. Studies involving manipulations of corticogeniculate feedback have yielded inconsistent findings, but the reasons for these inconsistencies are not known. To examine the functional contributions of corticogeniculate feedback, and to resolve past inconsistencies, we examined the effects of selective optogenetic suppression of corticogeniculate neurons in anesthetized ferrets. In particular, we examined the responses of LGN and V1 neurons during optogenetic suppression of corticogeniculate feedback in the presence and absence of visual stimulation and across conditions in which the frequency of LED illumination varied. Optogenetic suppression of corticogeniculate feedback decreased activity among LGN neurons in the absence of visual stimulation, dispelling the notion that anesthesia causes a floor effect. In contrast, suppressing corticogeniculate feedback did not affect the visual responses of LGN neurons, suggesting that feedforward visual stimulus drive overrides weak corticogeniculate influence. Optogenetic effects on LGN and V1 neuronal responses depended on the frequency of LED illumination, with higher frequency illumination inducing slow oscillations in V1, dis-inhibiting V1 neurons locally, and producing more suppression among LGN neurons. These results demonstrate that corticogeniculate influence depends on stimulation parameters including visual stimulus conditions and frequency of inactivation. Furthermore, weak corticogeniculate influence is overridden by strong feedforward visual stimulus drive; this attribute is the most likely source of inconsistencies in past studies.

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