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At least 1,135 records · Page 63Linked to original sources
PubMed1981

Linear analysis of the responses of simple cells in the cat visual cortex.

Spatial response profiles to stationary and moving stimuli and spatial frequency tuning curves to drifting sinusoidal gratings were recorded from a series of cells in the simple family. The spatial response profiles were recorded both to stationary flashing bars and sinusoidal gratings as well as to light and dark bars and edges and gratings moving at the optimal velocity. On the assumption that cells in the simple family operate linearly, spatial response profiles recorded experimentally were compared with those predicted by inverse Fourier transformation of the spatial frequency tuning curves. Conversely, the spatial frequency tuning curves recorded experimentally were compared with those predicted from the response profiles to moving and stationary stimuli. As a result of these comparisons, it is clear that moving stimuli provide a more accurate estimate of the spatial organization of the receptive field than do stationary stimuli. Cells with the higher optimal spatial frequencies tended to have narrower bandwidths. The simple cell with the narrowest bandwidth (0.94 octave) had five, and possibly six, subregions in the spatial response profile to moving light and dark bars, the largest number of subregions we encountered.

Animals↗
PubMed1981

The dependence of response amplitude and variance of cat visual cortical neurones on stimulus contrast.

For neurones in the cat's striate cortex, we examined the dependence of response on the contrast of moving sinusoidal gratings. Most neurones showed a clear threshold contrast below which no response was elicited. Such thresholds presumably contribute to the animal's behavioural threshold, which should not be accounted for solely in terms of the detection of a signal in the presence of spontaneous "noise". Above threshold, the response amplitude usually increased linearly with contrast until it began to saturate at the highest contrasts. The variance of the response increased with its amplitude; this finding perhaps underlies the Weber-Fechner relation for psychophysical contrast discrimination.

Animals↗
PubMed1994

Arthrokinetic and vestibular information enhance smooth ocular tracking during linear (self-)motion.

We studied the gain of smooth ocular tracking for visual, vestibular and arthrokinetic cues, in combination as well as separately, in order to examine how these multisensory cues influence tracking performance. By use of motion along a linear track (besides the self-evident visual influence) evidence was found for arthrokinetic and vestibular enhancement of smooth ocular tracking. These results were in close correspondence with the results of our former study about arthrokinetic influence on linear self-motion perception. Therefore, we conclude that information from the limbs about linear (self-)movement has analogous characteristics and generates analogous responses to the information about angular (self-)movement.

Analysis of Variance↗
PubMed1988

The organization of receptive fields in area 18 neurones of the cat varies with the spatio-temporal characteristics of the visual stimulus.

The spatial frequency tuning curves of neurones of area 18 depend upon the velocity of the visual stimulus. The higher the velocity the lower the spatial frequencies to which the cell is tuned. Since in area 17 the size of the cell receptive field is inversely related with the optimal spatial frequency to which the cell responds, we have investigated whether the shift of the optimal spatial frequency with the velocity corresponds to a "change" in the receptive field size. We recorded extracellularly from neurones in area 18; for each cell we selected two gratings, one of high spatial frequency drifting at low velocity and another of low spatial frequency drifting at high velocity to which the cell gave comparable responses. The results show that the masking of the cells receptive field which abolishes the response to the high frequency low velocity grating does not prevent the cell from responding to the low frequency high velocity grating. We conclude that the size of the receptive field of neurones in area 18 depends upon the characteristics (spatial frequency and velocity) of the visual stimulus.

Animals↗
PubMed1988

Neurophysiological properties of the retinal ganglion cell classes of the Cuban treefrog, Hyla septentrionalis.

The properties of the retinal ganglion cell classes in the cuban treefrog Hyla septentrionalis were studied qualitatively and quantitatively. In the superficial layers of the optic tectum three main classes of afferent optic nerve fibers could be distinguished, class-1*, class-3 and class-4 neurons. Hyla displays a more "classical" organization of the receptive fields in class-1* neurons and a weaker inhibitory surround and lower thresholds with respect to velocity, size and contrast than in Bufo or ranid frogs. The functions for velocity, contrast, size of stimulus, neuronal adaptation and adaptation to background luminance level were evaluated. Experiments with monochromatic light spots are mentioned. The results are compared to those of other amphibia and the diversity of the retinal ganglion cell properties in the different species is stressed as an important factor in the processing of the various ganglion cell types at the tectal level.

Action Potentials↗
PubMed1990

Stimulus characteristics influence the gain of smooth pursuit eye movements in normal subjects.

Impaired smooth pursuit eye movements are commonly believed to indicate a lesion of the central nervous system. Smooth pursuit performance, however, is strongly dependent on non-specific variables like cooperation, arousal and attentiveness. Therefore, disturbed smooth pursuit can be attributed either to lesions of the smooth pursuit system per se, or to the influence of non-controlled variables (non-structural disturbances). This renders the evaluation of smooth pursuit uncertain. In the present study we attempted to design a stimulus that yields smooth pursuit eye movements, which are not influenced by uncontrolled variations of state and input, for a better separation of structural lesions of the pursuit system and the effect of nonspecific variables. Our results suggest that a stimulus that leads to a centrally generated representation (percept) of motion is most suitable to elicit high gains of smooth pursuit (sigma pursuit), but only if attentiveness is optimal. Beta-motion (motion elicited by discrete steps of the target) or real target motion are capable to render the smooth pursuit performance optimal, even with low attentiveness, when the fixation point and its wider surroundings or enough discrete points in the neighbourhood move in the same direction in space.

Adolescent↗
PubMed1994

Vector reconstruction from firing rates.

In a number of systems including wind detection in the cricket, visual motion perception and coding of arm movement direction in the monkey and place cell response to position in the rat hippocampus, firing rates in a population of tuned neurons are correlated with a vector quantity. We examine and compare several methods that allow the coded vector to be reconstructed from measured firing rates. In cases where the neuronal tuning curves resemble cosines, linear reconstruction methods work as well as more complex statistical methods requiring more detailed information about the responses of the coding neurons. We present a new linear method, the optimal linear estimator (OLE), that on average provides the best possible linear reconstruction. This method is compared with the more familiar vector method and shown to produce more accurate reconstructions using far fewer recorded neurons.

Animals↗
PubMedDate not supplied

Responses to visual stimuli in thalamic neurons of the turtle Emys orbicularis.

The responses to movement of shaped stimuli and diffuse illumination were studied for 300 neurons in three thalamic regions of the bog turtle Emys orbicularis L.' characteristics of their receptive fields (RF) were also studied. According to their responses to stimuli of various sizes, neurons were divided into two types. Neurons of Type I (85%) were activated by stimuli of any size and has large, small or medium RF. Weak or medium adaptive changes were found more often (63%) than strong changes (37%). Some of the neurons (33%) did not react to diffuse light; the remainder gave responses of various types. 57% of the neurons exhibited spontaneous activity, and 9% of the units were direction sensitive. Neurons of Type II (15%) responded only to presentation of stimuli of large sizes and were characterized by large RF, strong adaptation (89%) and weak reactivity to diffuse light (46%). 35% of the neurons exhibited spontaneous activity, and 20% were direction sensitive.

Animals↗
PubMedDate not supplied

Neuronal level of organization of the visual analyzer in frog tectum.

A study of neuronal responses of frog tectum to diffuse light and a moving visual stimulus, in which paired microelectrodes were used, disclosed the excitation-inhibition constructions originating in the midbrain tectum in response to various forms of visual stimulation. It was demonstrated that the dimensions of the excitation zones of these constructions are 100-200 mu in cross section, and are separated by inhibition zones. The dimensions of the excitatory tectal constructions resulting from various kinds of visual stimulation correlated with the width of the branching zones and locations of terminals of the afferents and intratectal fibers.

Animals↗
PubMed1981

Response properties of visual units in the anterior dorsolateral thalamus of the chick (Gallus domesticus).

Receptive fields of neurons in the anterior dorsolateral thalamus (DLA) of the chick were plotted and their response properties analyzed. The average size was 18 degrees X 13 degrees but there were some wide-field units. DLA cells were classified as detectors of 1. general movement (uniform-field), 22%; 2. general movement (centre-periphery), 22%; 3. moving dark objects, 29%; 4. direction, 8%; and 5. illumination, 19%.

Animals↗
PubMed2002

Role of visual input in nonlinear postural control system.

Stabilometry signals involve irregular and unpredictable components. The purpose of the present study was to investigate these signals with a nonlinear technique to examine how the complexity of the postural control system breaks down under altered visual conditions. We evaluated the dynamical similarities of the postural control system when the eyes were open or closed, or when there was optokinetic stimulation (OKS). A similarity index was calculated by the cross-correlation integral between the two dynamics: eyes open and eyes closed, or eyes open with OKS. Using this technique, dynamical changes were not observed between eyes-open and eyes-closed conditions. This result suggests that the nonvision condition does not produce any striking effect on the postural control system; instead, the eyes-open condition causes a decrease in the stochastic activity of the postural control system, which may originate mainly from the stiffness of the musculoskeletal systems. In contrast, the visual input of OKS affected the dynamics of the postural control system in nearly half of the subjects (group 2) despite showing no significant differences between the eyes-open condition and the other conditions for area as the conventional parameter. However, the other half of the subjects (group 1) did not experience any influence of OKS on their postural dynamics, despite showing significant differences between eyes-open and the other conditions for all traditional parameters. From the results for group 2, we hypothesize that OKS may induce the striking effect on dynamics properties of the multilink network system involving visual and vestibular cortex related to self-motion perception, which acts to decrease the stochastic activity in order to correct disturbed posture.

Adult↗
PubMed2000

Visual and non-visual cues in the perception of linear self-motion.

Surprisingly little is known of the perceptual consequences of visual or vestibular stimulation in updating our perceived position in space as we move around. We assessed the roles of visual and vestibular cues in determining the perceived distance of passive, linear self motion. Subjects were given cues to constant-acceleration motion: either optic flow presented in a virtual reality display, physical motion in the dark or combinations of visual and physical motions. Subjects indicated when they perceived they had traversed a distance that had been previously given to them either visually or physically. The perceived distance of motion evoked by optic flow was accurate relative to a previously presented visual target but was perceptually equivalent to about half the physical motion. The perceived distance of physical motion in the dark was accurate relative to a previously presented physical motion but was perceptually equivalent to a much longer visually presented distance. The perceived distance of self motion when both visual and physical cues were present was more closely perceptually equivalent to the physical motion experienced rather than the simultaneous visual motion, even when the target was presented visually. We discuss this dominance of the physical cues in determining the perceived distance of self motion in terms of capture by non-visual cues. These findings are related to emerging studies that show the importance of vestibular input to neural mechanisms that process self motion.

Acoustic Stimulation↗
PubMed2004

Identification of the head-neck complex in response to trunk horizontal vibration.

A method is proposed for identifying the head-neck complex (HNC) in the seated human body when it is exposed to the trunk horizontal (fore-and-aft) vibration. It is assumed that the HNC only has the anteroposterior (flexion/extension) motion in the sagittal plane. An electrohydraulic vibrator is used as a source of vibration. To generate the trunk horizontal vibration, the trunk of the seated subject is fixed to the seatback. The subjects are exposed to the random vibration at a magnitude of 1.60 ms(-2) rms (root-mean-square) for 50 s. The coherence and frequency response function are then obtained in the frequency range 0.5-3 Hz. The results show that the HNC behavior is quasilinear with a resonance frequency between 1 and 1.4 Hz. Accordingly, a two-dimensional single-inverted pendulum is considered as a model for the HNC. The frequency domain identification method is then used to estimate the unknown parameters, including the HNC viscoelastic and inertia parameters. The model is examined in a time domain using the random vibration. Good agreement is obtained between experimental and simulation results, indicating the reliability of the proposed method.

Acceleration↗
PubMed1981

Temporal and spatial response characteristics of the cat superior colliculus.

We have examined the responses of 72 cells of the cat superior colliculus to drifting gratings of sinusoidal luminance profile as a function of spatial frequency velocity and contrast. Of 72 cells, 66 responded to gratings either by change in mean firing rate only (58/72) or in a temporally modulated pattern in addition to the change in mean firing rate (8/72). The remaining 6 showed no change in discharge rate in response to any of the gratings tested. Many cells (24/72) were inhibited or excited by particular combinations of spatial and temporal frequencies. Some (8/72) demonstrated selective inhibition or excitation to a particular temporal frequency independent of spatial frequency and velocity and could therefore be said to be tuned specifically to temporal frequency. No cells were tuned only to a constant spatial frequency or a constant velocity. (24/72) cells displayed maximum inhibition or excitation only at a particular combination of spatial and temporal frequencies. Some cells (8/72) demonstrated a temporal modulation synchronous with the drifting grating in addition to an elevated mean discharge rate. The change in discharge rates evoked by gratings are generally less than those evoked by presentation of moving small slits or spots of light. Collicular cells often demonstrate a center-surround organization in their response to gratings. The center and surround often differ in their spatial frequency and velocity preferences. Compared to cortical and retinal ganglion cells, individual collicular cells are extremely non-linear. On a cell population basis, however, a linear Fourier analysis on grating response predicts the collicular cells' preference for movement of small objects.

Animals↗
PubMed1983

White noise analysis of cortical directional selectivity in cat.

We studied spatiotemporal interactions in cat cortical receptive fields by presenting a stimulus composed of 16 narrow bars whose luminances were randomly modulated. Conventional stimuli were also presented to classify receptive field properties. A white noise estimate of the cell's response to a stepwise moving bar stimulus was calculated from responses to the spatiotemporal random stimulus. The white noise estimate captured the most important feature of the receptive field demonstrated by conventional stimuli, i.e. directional selectivity. In addition, the white noise analysis; (1) made visible inhibitory response phases that are usually below threshold; (2) subdivided the response into its linear and non-linear estimates; (3) further subdivided the non-linear estimate into spatial and temporal interactions; and (4) allowed estimation of responses to stimuli that were never explicitly presented.

Animals↗