Relation between psychophysics and electrophysiology of flicker

Summary Experiments are described measuring ERG's and occipital EEG's and de Lange curves under identical conditions. There is little correspondence between the responses and the psychophysical results. ERG responses as found by Gouras & Gunkel give second harmonics at about 10 cps. Curves are shown in which the h.f. attenuation is smaller for the ERG and EEG responses than for the de Lange curves. The EEG responses with large field illumination show a linear and highly variable character with different subjects between 9–15 cps. A sharp resonance at 10 cps is reported in one subject. Strong essential second harmonics are found in the EEG below 9 cps and with small fields and high intensities round 27 cps. Opposite phase stimulation cancels fundamental frequency responses and does not influence second harmonics. Also here little relation is found with psychophysical results.

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Zusammenfassung Es werden Experimente beschrieben, in denen ERG's, occipitale EEG's und de Lange Kurven unter identischen Bedingungen gemessen werden. Man fand nicht viel Übereinstimmung zwischen den elektrischen Reaktionen und den psychophysischen Ergebnissen. Gouras & Gunkel berichten über ERG Antworten um 10 Hz mit hervorragenden zweiten Obertönen. Kurven werden gezeigt, in denen ERG und EEG Reaktionen eine kleinere h.f. Abschwächung angeben als die de Lange Kurven.Die EEG Antworten mit Grossfeldbelichtung haben einen linearen Charakter zwischen 9 und 15 Hz und sind individuel unterschieden. In einer Person wird über eine scharfe Resonanz berichtet um 10 Hz, grosse zweite Obertöne wurden gefunden unter 9 Hz und mit kleinen und leuchtstarken Feldern um 27 Hz.Reizung mit Gegenphase für jedes Auge unterdrückt die Grundfrequenz, aber lässt die zweiten Obertöne ungeändert. Auch hier ist wenig Korrespondenz mit psychophysischen Ergebnissen.

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Résumé On décrit des expériences dans lesquelles l'ERG, l'EEG occipital et les courbes selon De Lange sont déterminées dans des conditions identiques. Il n'y a pas beaucoup de rapport entre les trois. Gouras & Gunkel ont trouvé des distortions doubles harmoniques dans l'ERG à une fréquence d'environ 10 cps. On montre des courbes dans lesquelles l'atténuation h.f. est moins pour l'ERG et l'EEG que pour les courbes subjectives.Les réponses de l'ERG avec les champs étendus entre 9–15 cps sont linéaires et montrent une variation considérable entre les sujets. Une résonance aiguë est trouvée chez une personne à 10 cps. Des doubles harmoniques essentielles dans l'EEG sont rapportées au-dessous de 9 cps et avec des champs petits et des intensités élevées environ 27 cps. La stimulation avec des phases opposées supprime la fréquence fundamentale, mais laisse les doubles harmoniques intactes. Aussi dans ce cas il n'y a pas beaucoup de rélation avec la perception de flicker.

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Part of this work was supported by Contract no N. 62558-2701 of the US Navy European Research Contracts Program.

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Laboratory of Medical Physics, University of Amsterdam.     

Retinal receptive fields under different adaptation levels studied with pattern-evoked ERG

The pattern-evoked electroretinogram (PERG) was studied in three normal subjects under different levels of adaptation using pattern onset-offset stimulation. The occurrence of a response maximum (spatial selectivity) in the onset response at a certain spatial frequency can be interpreted as reflecting the activity of neurons having antagonistic center-surround receptive fields and allows an estimation of receptive-field center sizes. The present data suggest that in the light-adapted state, the majority of receptive fields, dominating the response can be estimated to have center diameters of 6–13 min of arc. With increasing dark adaptation, the spatial selectivity shifts from high to low spatial frequencies over 1.3–2.4 octaves, indicating that large receptive fields are active in the dark and small fields in the light. The physiological mechanisms of these changes are discussed on the basis of findings obtained from single-unit studies.     

Helicoidal peripapillary chorioretinal degeneration: electrophysiology and psychophysics in 17 patients

AIMS—To characterise retinal function using electrophysiological and psychophysical tests in 17 patients with helicoidal peripapillary chorioretinal degeneration.
METHODS—The electroretinogram (ERG) was recorded using gold foil corneal electrodes. The electro-oculogram (EOG) was recorded using a standard protocol. Dark adaptometry was recorded with an SST-1 dark adaptometer and colour vision assessed with Ishihara plates and Farnsworth D-15.
RESULTS—All subjects had a recordable ERG. The amplitudes and implicit times of the a- and b-waves were within normal limits at all luminances in five subjects (age 21-70 years, mean 40 years). The ERG of six (age 26-55 years, mean 40.7 years) had subnormal amplitudes at all luminances, but normal implicit times, and six (age 38-81 years, mean 60.7 years) had abnormal ERGs with marked reduction of a- and b-waves, and delayed implicit times of the b-wave. The implicit times of the a-wave were normal in all subjects. A reduction in the b/a wave ratios was not found, nor was there selective loss of scotopic, mixed rod/cone, or cone responses. The light/dark ratio of the EOG was subnormal (150-185%) or abnormal (below 150%) in all but three subjects. Two patients with normal EOG showed normal ERGs in both eyes, but one had subnormal ERGs in both eyes. The scotopic sensitivity was normal in all subjects and dark adaptation showed a normal time course. Colour vision was normal in all patients.
CONCLUSION—The results suggest that in most cases the function of the retinal pigment epithelium is affected by this disease before any changes in the function of the sensory retina are detectable by our methods, and that retinal dysfunction is focal rather than diffuse.

Keywords: chorioretinal degeneration; electroretinogram; dark adaptation; colour vision     

Retinal correspondence of monocular receptive fields in disparity-sensitive complex cells from area V1 in the awake monkey

PURPOSE: To explore the neural mechanisms underlying disparity sensitivity in complex cells of the macaque visual cortex, the relationship between interocular receptive field (RF) positional shift and disparity sensitivity was studied in area V1. METHODS: Single-unit recordings were made from area V1 of awake Macaca mulatta. Monocular RFs were mapped by means of a reverse cross-correlation technique, and their centers were determined after performing a bidimensional Gaussian function fitting. Interocular RF shifts were calculated for both bright and dark stimuli. Similarly, Gabor adjustments were obtained from disparity profiles to bright and dark dynamic random-dot stereograms (RDSs). RESULTS: Twenty-five complex cells were studied. The response profiles to disparity were similar for bright and dark RDSs. Interocular RF positional shift correlated significantly with both the peaks of Gabor fittings of disparity-sensitivity profiles and the peaks of the Gaussian envelopes of these Gabor fittings. Correlation between interocular RF positional shift and the peaks of the Gaussian envelopes was stronger than correlation between interocular RF positional shift and peaks of Gabor fittings. CONCLUSIONS: Interocular shift of monocular RFs is more related to the center of the range of disparities to which the cell is sensitive, than to the preferred disparity of the cell.     

Psychophysical receptive fields of edge detection mechanisms

Theories of edge detection generally assume a front-end linear stage involving some population of neural filters. Here we study these early mechanisms using psychophysical techniques, and evaluate a number of models for edge detection. We measured psychophysical efficiency for detection of noisy luminance edge stimuli over a range of stimulus sizes and shapes. The data suggest a diversity in receptive field shape and orientation bandwidth, consistent with physiological evidence, but inconsistent with standard multi-channel models of visual processing.     

Balanced interactions in ganglion-cell receptive fields.

Receptive fields of retinal ganglion cells in turtle have excitatory and inhibitory components that are balanced along the dimensions of wavelength, functional ON and OFF responses, and spatial assignments of center and surround. These components were analyzed by spectral light adaptations and by the glutamate agonist, 2-amino-4-phosphonobutyric acid (APB). Extracellular recordings to stationary and moving spots of light were used to map changes in receptive fields. ON spike counts minus OFF spike counts, derived from flashed stationary light spots, quantified functional shifts by calculating normalized mean response modulations. The data show that receptive fields are not static, but rather are dynamic arrangements which depend on linked, antagonistic balances among the three dimensions of wavelength, ON and OFF response functions, and center/surround areas.     

Estimating nonlinear receptive fields from natural images

The response of visual cells is a nonlinear function of their stimuli. In addition, an increasing amount of evidence shows that visual cells are optimized to process natural images. Hence, finding good nonlinear models to characterize visual cells using natural stimuli is important. The Volterra model is an appealing nonlinear model for visual cells. However, their large number of parameters and the limited size of physiological recordings have hindered its application. Recently, a substantiated hypothesis stating that the responses of each visual cell could depend on an especially low-dimensional subspace of the image space has been proposed. We use this low-dimensional subspace in the Volterra relevant-space technique to allow the estimation of high-order Volterra models. Most laboratories characterize the response of visual cells as a nonlinear function on the low-dimensional subspace. They estimate this nonlinear function using histograms and by fitting parametric functions to them. Here, we compare the Volterra model with these histogram-based techniques. We use simulated data from cortical simple cells as well as simulated and physiological data from cortical complex cells. Volterra models yield equal or superior predictive power in all conditions studied. Several methods have been proposed to estimate the low-dimensional subspace. In this article, we test projection pursuit regression (PPR), a nonlinear regression algorithm. We compare PPR with two popular models used in vision: spike-triggered average (STA) and spike-triggered covariance (STC). We observe that PPR has advantages over these alternative algorithms. Hence, we conclude that PPR is a viable algorithm to recover the relevant subspace from natural images and that the Volterra model, estimated through the Volterra relevant-space technique, is a compelling alternative to histogram-based techniques.     

Aberrant visual population receptive fields in human albinism

Retinotopic organization is a fundamental feature of visual cortex thought to play a vital role in encoding spatial information. One important aspect of normal retinotopy is the representation of the right and left hemifields in contralateral visual cortex. However, in human albinism, many temporal retinal afferents decussate aberrantly at the optic chiasm resulting in partially superimposed representations of opposite hemifields in each hemisphere of visual cortex. Previous functional magnetic resonance imaging (fMRI) studies in human albinism suggest that the right and left hemifield representations are superimposed in a mirror-symmetric manner. This should produce imaging voxels which respond to two separate locations mirrored across the vertical meridian. However, it is not yet clear how retino-cortical miswiring in albinism manifests at the level of single voxel population receptive fields (pRFs). Here, we used pRF modeling to fit both single and dual pRF models to the visual responses of voxels in visual areas V1 to V3 of five subjects with albinism. We found that subjects with albinism (but not controls) have sizable clusters of voxels with unequivocal dual pRFs consistently corresponding to, but not fully coextensive with, regions of hemifield overlap. These dual pRFs were typically positioned at locations roughly mirrored across the vertical meridian and were uniquely clustered within a portion of the visual field for each subject.     

The unresponsive regions of visual cortical receptive fields

We have recorded from simple and complex cells in area 17 of the cat cortex. Around the classical receptive field (regions within which a moving or flashing bar can elicit a response from a cell) there are large regions which dramatically influence the cell's responsiveness. In some cells these regions are facilitatory, in others, inhibitory. Since these regions do not respond in isolation to moving or flashing bars, we called them unresponsive regions of the receptive field. Both the inhibitory and facilitatory unresponsive regions show spatial-frequency selectivity. All the facilitatory unresponsive regions show orientation selectivity, while most of the inhibitory unresponsive regions are not orientation selective. Both the facilitatory and the inhibitory unresponsive regions contribute to the size-selectivity of the cell. The facilitatory unresponsive regions show a great influence on the orientation selectivity of the cell, in that they sharpen the orientation channel of the cell. The inhibitory unresponsive regions, on the contrary, have not such an effect.     

Bimodal receptive fields of cat retinal ganglion cells

Receptive fields of cat retinal ganglion cells were stimulated by a drifting, sinusoidal luminance pattern of fixed contrast. The amplitudes and phases of the harmonic components in the response were determined as a function of spatial frequency. For most cells, the graphs of response vs spatial frequency (when plotted on linear scales) were unimodal and skewed towards zero frequency for all stimulus orientations. However, some cells had bimodal frequency response functions when the stimulus was in the non-preferred orientation. These unusual cells also exhibited a sudden phase-reversal of π radians which occurred at the frequency of the changeover between the two modes. Calculations based on the experimental data predicted two distinctly separate regions of high sensitivity within the receptive centres of such cells. A narrow bar stimulus was used to confirm that the receptive fields had, in effect, double centres.     

Double color-opponent receptive fields of carp bipolar cells

Bipolar cells with double color-opponent receptive fields were found in the carp retina. They were classified into two types depending on their response polarity. In the receptive field center, type I cells showed hyperpolarization to a long wavelength spot (R-) and depolarization to a short wavelength spot (G+), while in the surround they showed R+, G- responses. Type II cells showed responses of opposite polarities to those of type I cells, namely R+ G- in the center, and R- G+ in the surround. From their spectral sensitivity, R components were identified as coming from red-sensitive cones, and G components from green-sensitive cones. These bipolar cells are thought to be the origin of double color-opponent receptive fields of retinal ganglion cells.     

The dynamic receptive fields of retinal ganglion cells

Retinal ganglion cells (RGCs) were one of the first classes of sensory neurons to be described in terms of a receptive field (RF). Over the last six decades, our understanding of the diversity of RGC types and the nuances of their response properties has grown exponentially. We will review the current understanding of RGC RFs mostly from studies in mammals, but including work from other vertebrates as well. We will argue for a new paradigm that embraces the fluidity of RGC RFs with an eye toward the neuroethology of vision. Specifically, we will focus on (1) different methods for measuring RGC RFs, (2) RF models, (3) feature selectivity and the distinction between fluid and stable RF properties, and (4) ideas about the future of understanding RGC RFs.     

Expansion of visual receptive fields in experimental glaucoma

Glaucoma is a major cause of blindness and is characterized by death of retinal ganglion cells. In a rat model of glaucoma in which intraocular pressure is raised by cautery of episcleral veins, the somata and dendritic arbors of surviving retinal ganglion cells expand. To assess physiological consequences of this change, we have measured visual receptive-field size in a primary retinal target, the superior colliculus. Using multiunit recording, receptive-field sizes were measured for glaucomatous eyes and compared to both those measured for contralateral control eyes and to homolateral eyes of unoperated animals. Episcleral vein occlusion increased intraocular pressure. This was accompanied by a significant increase in receptive-field size across the superior colliculus. The expansion of receptive fields was proportional to both degree and duration of the increase of intraocular pressure. We suggest that this increase in the size of receptive fields of glaucomatous eyes may be related to the increase in the size of dendritic arbors of the surviving ganglion cells in retina.