Spatiotemporal frequency responses of cat retinal ganglion cells

Spatiotemporal frequency responses were measured at different levels of light adaptation for cat X and Y retinal ganglion cells. Stationary sinusoidal luminance gratings whose contrast was modulated sinusoidally in time or drifting gratings were used as stimuli. Under photopic illumination, when the spatial frequency was held constant at or above its optimum value, an X cell's responsivity was essentially constant as the temporal frequency was changed from 1.5 to 30 Hz. At lower temporal frequencies, responsivity rolled off gradually, and at higher ones it rolled off rapidly. In contrast, when the spatial frequency was held constant at a low value, an X cell's responsivity increased continuously with temporal frequency from a very low value at 0.1 Hz to substantial values at temporal frequencies higher than 30 Hz, from which responsivity rolled off again. Thus, 0 cycles X deg-1 became the optimal spatial frequency above 30 Hz. For Y cells under photopic illumination, the spatiotemporal interaction was even more complex. When the spatial frequency was held constant at or above its optimal value, the temporal frequency range over which responsivity was constant was shorter than that of X cells. At lower spatial frequencies, this range was not appreciably different. As for X cells, 0 cycles X deg-1 was the optimal spatial frequency above 30 Hz. Temporal resolution (defined as the high temporal frequency at which responsivity had fallen to 10 impulses X s-1) for a uniform field was approximately 95 Hz for X cells and approximately 120 Hz for Y cells under photopic illumination. Temporal resolution was lower at lower adaptation levels. The results were interpreted in terms of a Gaussian center-surround model. For X cells, the surround and center strengths were nearly equal at low and moderate temporal frequencies, but the surround strength exceeded the center strength above 30 Hz. Thus, the response to a spatially uniform stimulus at high temporal frequencies was dominated by the surround. In addition, at temporal frequencies above 30 Hz, the center radius increased.     

Visual acuity of the midland banded water snake estimated from evoked telencephalic potentials

The visual acuity of seven midland banded water snakes was measured by recording evoked responses from telencephalon to temporally modulated square wave grating patterns. Using conventional electrophysiological techniques and signal averaging, high contrast square wave gratings of different spatial frequencies were presented. Acuity was estimated by extrapolating relative response amplitude/log₁₀ spatial frequency functions which yielded an average acuity of 4.25 cycles/degree. Refractive state was also estimated by recording evoked potentials to intermediate spatial frequencies with different lenses in front of the eye. Polynomial fits indicated that under the experimental conditions the snakes were around 6.4 diopters hyperopic suggesting a corrected acuity of 4.89 cycles/degree. Reduction of grating luminance resulted in a reduction in evoked potential acuity measurements. These results indicate that the spatial resolution of midland banded water snakes is the equal of cat; about 20/120 in human clinical terms.     

Role of the Mouse Retinal Photoreceptor Ribbon Synapse in Visual Motion Processing for Optokinetic Responses

The ribbon synapse is a specialized synaptic structure in the retinal outer plexiform layer where visual signals are transmitted from photoreceptors to the bipolar and horizontal cells. This structure is considered important in high-efficiency signal transmission; however, its role in visual signal processing is unclear. In order to understand its role in visual processing, the present study utilized Pikachurin-null mutant mice that show improper formation of the photoreceptor ribbon synapse. We examined the initial and late phases of the optokinetic responses (OKRs). The initial phase was examined by measuring the open-loop eye velocity of the OKRs to sinusoidal grating patterns of various spatial frequencies moving at various temporal frequencies for 0.5 s. The mutant mice showed significant initial OKRs with a spatiotemporal frequency tuning (spatial frequency, 0.09 ± 0.01 cycles/°; temporal frequency, 1.87 ± 0.12 Hz) that was slightly different from the wild-type mice (spatial frequency, 0.11 ± 0.01 cycles/°; temporal frequency, 1.66 ± 0.12 Hz). The late phase of the OKRs was examined by measuring the slow phase eye velocity of the optokinetic nystagmus induced by the sinusoidal gratings of various spatiotemporal frequencies moving for 30 s. We found that the optimal spatial and temporal frequencies of the mutant mice (spatial frequency, 0.11 ± 0.02 cycles/°; temporal frequency, 0.81 ± 0.24 Hz) were both lower than those in the wild-type mice (spatial frequency, 0.15 ± 0.02 cycles/°; temporal frequency, 1.93 ± 0.62 Hz). These results suggest that the ribbon synapse modulates the spatiotemporal frequency tuning of visual processing along the ON pathway by which the late phase of OKRs is mediated.     

Visual signals in an optomotor reflex: systems and information theoretic analysis

Compensatory optomotor reflexes were examined in crayfish (Procambarus clarkii) with oscillating sine wave gratings and step displacements of a single stripe. A capacitance transducer was used to measure the rotation of the eyestalk about its longitudinal axis. System studies reveal a spatial frequency response independent of velocity and stimulus amplitude and linear contrast sensitivity similar to that of neurons in the visual pathway. The reflex operates at low temporal frequencies (<0.002 Hz to 0.5 Hz) and exhibits a low-pass temporal frequency response with cut-off frequency of 0.1 Hz. Eyestalk rotation increases as a saturable function of the angular stimulus displacement. When compared to the oscillatory response, transient responses are faster, and they exhibit a lower gain for large stimulus displacements. These differences may reflect system nonlinearity and/or the presence of at least two classes of afferents in the visual pathway. Our metric for information transmission is the Kullback-Leibler (K-L) distance, which is inversely proportional to the probability of an error in distinguishing two stimuli. K-L distances are related to differences in responsiveness for variations in spatial frequency, contrast, and angular displacement. The results are interpreted in terms of the neural filters that shape the system response and the constraints that the K-L distances place on information transmission in the afferent visual pathway.     

Spatial frequency characteristics of receptive fields of neurons in the lateral suprasylvian area of the cat cortex

Two-dimensional spatial frequency characteristics of receptive fields of 46 neurons in the lateral suprasylvian area of the cat cortex were obtained. These receptive fields possessed orientation anisotropy. Peak frequencies lay in the frequency region below 1.5 cycles/deg. The transmission band width was measured during optimal orientation of test gratings in 21 neurons. It averaged 1.47±0.6 octave. In the remaining neurons the lower boundary frequency was shifted into the region of spatial frequencies below the range used. During nonoptimal orientation of test gratings, inhibition of the discharge was observed in 17 neurons. The inhibitory spatial frequency characteristics of six neurons were of the narrow band type, and averaged 1.1±0.6 octave.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 608–614, November–December, 1982.     

Spatio-temporal organization of receptive fields of the cat striate cortex

The responses of cortical cells to gratings and bars were compared. The excitatory and inhibitory on-and off-zones of a simple cell are composed of on- and off-subfields of CGL. Any zone is formed by an opponent pair of subfields one of which gives an excitatory effect, the other — inhibitory. Such organization assumes the linear properties of a simple field. The deviations from linearity are due to spatial dis-placements of the subfields, heterogeneity of subfields, or the absence of one subfield in the opponent pair. Subfields may be both phasic and tonic, even in the same RF. Analysis of the most common type of a complex cell with modulated responses against unmodulated background shows that a mask eliminating stimulation of any half of the RF causes (according to the theory of filtres) increasing the bandwidth due to the increase or the appearance of responses to side low and high frequencies. The modulated components of the responses from both halves of the RF are out of phase. Analysis of this fact and the responses to thin bars suggests that a complex field is formed by linear and nonlinear subsystems converging onto output neuron. Other types of complex fields are organized by different combinations of subsystems. Limited in area by masking the RF responds to much higher spatial frequencies than the whole RF. The optimal frequency in two-dimensional spatial frequency characteristics of the RF does not change with orientation. Simple RFs and a part of complex RF calculate the amplitude and the phase of the stimulus, the other part of complex RFs (with unmodulated response) calculate only amplitude. Given all this, the RFs are grating filters of spatial frequency.     

Seeing objects in motion

This paper reports estimates of the conjoint spatiotemporal tuning functions of the neural mechanisms of the human vision system which detect image motion. The functions were derived from measurements of the minimum contrast necessary to detect the direction of drift of a sinusoidal grating, in the presence of phase-reversed masking gratings of various spatial and temporal frequencies. A mask of similar spatial and temporal frequencies to the test grating reduces sensitivity considerably, whereas one differing greatly in spatial or temporal frequency has little or no effect. The results show that for test gratings drifting at 8 Hz, the tuning function is bandpass in both space and time, peaked at the temporal and spatial frequency (SF) of the test (SFs were 0.1, 1 or 5 c deg-1; c represents cycles throughout). For a grating of 5 c deg-1 drifting at 0.3 Hz, the function is bandpass in space but lowpass in time. Fourier transform of the frequency results yields a function in space-time which we term the 'spatiotemporal receptive field'. For movement detectors (bandpass in space and time) the fields comprise alternating ridges of opposing polarity, elongated in space-time along the preferred velocity axis of the detector. We suggest that this organization explains how detectors analyse form and motion concurrently and accounts, at least in part, for a variety of perceptual phenomena, including summation, reduction of motion smear, metacontrast, stroboscopic motion and spatiotemporal interpolation.     

Are receptive fields of the visual cortex detectors or spatial frequency filters?

Besides its principal maximum, the spatial frequency characteristic curve of the complex visual cortical receptive field of curarized cats also has additional maxima and also negative regions, as predicted by the theory of piecewise Fourier analysis. Comparison of responses of the complex receptive field to sinusoidal gratings completely and incompletely contained in the field and comparison of responses to sinusoidal and square-wave gratings indicate that the receptive field, as a spatial frequency filter, has linear properties. The response of the complex receptive field rises with an increase in the number of periods of the sinusoidal grating. Several periods of optimal frequency match the complex field. Receptive fields tuned to a broad band of spatial frequencies were found in neuron columns. The results confirm the view that complex receptive fields are spatial frequency filters and not detectors.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 403–411, September–October, 1979.     

The Spatial Properties of L- and M-Cone Inputs to Electroretinograms That Reflect Different Types of Post-Receptoral Processing

We studied the spatial arrangement of L- and M-cone driven electroretinograms (ERGs) reflecting the activity of magno- and parvocellular pathways. L- and M-cone isolating sine wave stimuli were created with a four primary LED stimulator using triple silent substitution paradigms. Temporal frequencies were 8 and 12 Hz, to reflect cone opponent activity, and 30, 36 and 48 Hz to reflect luminance activity. The responses were measured for full-field stimuli and for different circular and annular stimuli. The ERG data confirm the presence of two different mechanisms at intermediate and high temporal frequencies. The responses measured at high temporal frequencies strongly depended upon spatial stimulus configuration. In the full-field conditions, the L-cone driven responses were substantially larger than the full-field M-cone driven responses and also than the L-cone driven responses with smaller stimuli. The M-cone driven responses at full-field and with 70° diameter stimuli displayed similar amplitudes. The L- and M-cone driven responses measured at 8 and 12 Hz were of similar amplitude and approximately in counter-phase. The amplitudes were constant for most stimulus configurations. The results indicate that, when the ERG reflects luminance activity, it is positively correlated with stimulus size. Beyond 35° retinal eccentricity, the retina mainly contains L-cones. Small stimuli are sufficient to obtain maximal ERGs at low temporal frequencies where the ERGs are also sensitive to cone-opponent processing.     

Spatial properties of goldfish ganglion cells

We systematically classified goldfish ganglion cells according to their spatial summation properties using the same techniques and criteria used in cat and monkey research. Results show that goldfish ganglion cells can be classified as X-, Y-, or W-like based on their responses to contrast-reversal gratings. Like cat X cells, goldfish X-like cells display linear spatial summation. Goldfish Y-like cells, like cat Y cells, respond with frequency doubling at all spatial positions when the contrast-reversal grating consists of high spatial frequencies. There is also a third class of neurons, which is neither X- nor Y-like; many of these cells' properties are similar to those of the "not-X" cells found in the eel retina. Spatial filtering characteristics were obtained for each cell by drifting sinusoidal gratings of various spatial frequencies and contrasts across the receptive field of the cell at a constant temporal rate. The spatial tuning curves of the cell depend on the temporal parameters of the stimulus; at high drift rates, the tuning curves lose their low spatial frequency attenuation. To explore this phenomenon, temporal contrast response functions were derived from the cells' responses to a spatially uniform field whose luminance varied sinusoidally in time. These functions were obtained for the center, the surround, and the entire receptive field. The results suggest that differences in the cells' spatial filtering across stimulus drift rate are due to changes in the interaction of the center and surround mechanisms; at low temporal frequencies, the center and surround responses are out-of-phase and mutually antagonistic, but at higher temporal rates their responses are in-phase and their interaction actually enhances the cell's responsiveness.     

视觉诱发电位(VEP)方位效应与刺激位置的关系

以人视觉诱发电位(VEP)反应为指标,在视野的不同位置测定了VEP对四个方位的闪烁方波光栅刺激(时间频率2.9Hz,空间频率1.4c/deg,对比度0.94)的反应幅度。在距中央凹20°视角同心圆的八个刺激位置上,VEP反应幅度对与向心线垂直方位的光栅刺激(同心圆的切线方向),有统计意义上的优势。这一规律在垂直、水平向心线上尤为明显。从总体上未发现VEP反应幅度与刺激光栅方位有着明显的关系。这说明在人视野周边区,VEP反应幅度与光栅方位和向心线的夹角(偏向角)相关,而与光栅的绝对方位无关。在相同的刺激条件下,中央区的VEP反应幅度与刺激光栅方位之间也未发现明显关系。     

Normal variability of the amplitude and phase of steady-state VEPs

The present study quantifies the amplitude and phase variability of steady-state VEPs (S-VEPs) and compares this variability between subjects and between individual runs. The S-VEPs were recorded repeatedly in 14 normal subjects with varying spatial and temporal frequencies of sinusoidal gratings; 6 spatial frequencies (range 0.5–8.0 c/deg) with 3 temporal frequencies (4, 6 and 8 Hz) were used. A total of 75 responses were averaged and analyzed by the Fourier method. Four recordings were obtained in each spatio-temporal combination.In general, the phase data showed small inter- and intrasubject variability. As anticipated, the amplitude data showed a large degree of intersubject variability, although the intrasubject variability was very small. In addition, in some stimulus conditions the inter- and intrasubject variability increased, which thus suggested the existence of an optimal spatio-temporal combination. Therefore, these stimulus parameters should be taken into consideration when S-VEPs are applied in clinical practice.     

Receptive field mechanisms of cat X and Y retinal ganglion cells

We investigated receptive field properties of cat retinal ganglion cells with visual stimuli which were sinusoidal spatial gratings amplitude modulated in time by a sum of sinusoids. Neural responses were analyzed into the Fourier components at the input frequencies and the components at sum and difference frequencies. The first-order frequency response of X cells had a marked spatial phase and spatial frequency dependence which could be explained in terms of linear interactions between center and surround mechanisms in the receptive field. The second-order frequency response of X cells was much smaller than the first-order frequency response at all spatial frequencies. The spatial phase and spatial frequency dependence of the first-order frequency response in Y cells in some ways resembled that of X cells. However, the Y first-order response declined to zero at a much lower spatial frequency than in X cells. Furthermore, the second-order frequency response was larger in Y cells; the second-order frequency components became the dominant part of the response for patterns of high spatial frequency. This implies that the receptive field center and surround mechanisms are physiologically quite different in Y cells from those in X cells, and that the Y cells also receive excitatory drive from an additional nonlinear receptive field mechanism.     

Two spatio-temporal filters in human vision

1. We have studied visual detection of a circular target moving across a spatially and/or temporally modulated background. Illumination, I _t , for threshold detection of the target has been measured as a function of background modulation frequency and changes in I _t associated with background modulation provide a means of determining the frequency response characteristics of visual channels. 2. Temporal frequency responses obtained with temporally modulated, spatially uniform backgrounds have pass-band characteristics and the temporal frequency for peak response increases with increase in mean background illumination. These temporal frequency responses resemble those of the de Lange (1954) filter, but the latter incorporates the incremental thresholds for steady backgrounds. 3. The amplitude of this temporal response saturates at low (40%) background modulation, decreases to zero as the target velocity falls to zero, and is maximum for a circular target of diameter 2°. 4. The spatial characteristics of this temporal filter were measured with a background field consisting of alternate steady and flickering bars. The resulting spatial frequency curve peaks at 1 cycle deg^-1 for all background illuminations and is independent of the background grating orientation. This spatial response differs significantly from the IMG spatial functions observed with a background grating (Barbur and Ruddock, 1980). 5. The spatial and temporal responses reviewed above exhibit similar parametric variations and we therefore associate them with a single spatiotemporal filter, ST2. 6. A second temporal response, with low-pass frequency characteristics, was observed with a background field consisting of two matched gratings, presented in spatial and temporal antiphase. This response has parametric properties similar to those of the IMG spatial response described previously by Barbur and Ruddock (1980), thus we associated the two sets of data with a single spatio-temporal filter, ST1. 7. We show that the ST2 responses can be obtained by combining ST1 responses, and we present a network incorporating the two filters. 8. We review other psychophysical studies which imply the activity of two spatio-temporal filters with properties of the kind revealed in our studies. We argue that filter ST1 has properties equivalent to those of X-type and filter ST2 has properties equivalent to those of Y-type electrophysiological mechanisms.     

Simulated bipolar cells in fovea of human retina

Fourier analysis is used to study resolution of images processed by the matrix of simulated red-center (BCR) and green-center (BCG) bipolar cells (BC) of the human central fovea. Simulated achromatic and chromatic sine and square waves, and a two-bar stimulus are used to activate the BCs. Due to the "honeycomb" packing of the cones and BC matrices Fourier transforms are computed row by row using a one-dimensional FFT. Resolution computed by the Fourier transform is compared with the resolution index (RI), which is a method for determining resolution based on two-point discrimination in the space domain. In general the harmonic with the maximum amplitude gives the best correlation with RI for the three stimuli. Amplitudes at all spatial frequencies are enhanced by increasing the number of cycles in the sine and square wave gratings. Results with simulated BCs compare favorably with human and macaque psychophysics measuring contrast sensitivity. Square wave gratings are better than sine wave greetings for studying resolution.     

Visual sensitivity of ground squirrels to spatial and temporal luminance variations

Summary We have investigated the visual sensitivity of the California ground squirrel (Speromphilus beecheyi) to spatial and temporal luminance patterns. Spatial contrast sensitivity functions were determined in behavioral discrimination experiments in which the stimuli were sinusoidally-modulated luminance gratings. These squirrels were found to be maximally sensitive to spatial frequencies of about 0.7 cycles/ degree (c/d), and they are unable to discriminate gratings whose frequencies exceed 4 c/d. Similar results were obtained in electrophysiological experiments when the visually evoked cortical potential (VECP) was recorded from anesthetized squirrels. A third experiment involved tests of the ability of ground squirrels to discriminate square-wave gratings of much higher luminance (340 cd/m²). The finest gratings which were discriminable at this luminance level did not exceed 3.9–4.3 c/d and, thus, we conclude that the maximal spatial resolution of the California ground squirrel is about 4 c/d (corresponding to a bar separation of 7.5). In another behavioral experiment the abilities of ground squirrels to discriminate sinusoidally flickering lights (mean luminance = 3.4 cd/m²) was measured. The results show that ground squirrels are maximally sensitive to lights flickering at a rate of about 18 Hz, and that the highest rates that are still discriminable are slightly above 60 Hz.Abbreviations c/d cycles/degree - CFF critical flicker frequency - VECP visually evoked cortical potential This research was supported by Grant EY 00105 from the National Eye Institute. We thank David Birch who participated in some preliminary behavioral experiments and Kenneth Long who provided the histological material from which measurements of receptor spacing were made.     

Structure of a complex receptive field in the cat visual cortex

The most common type of complex receptive field, whose response to the passage of sinusoidal gratings across it consisted of modulated and unmodulated components, was analyzed. The use of a mask to cover half the field, according to the filter theory, led to widening of the transmission band of the field as a spatial frequency filter, due to the appearance or enhancement of the response at lateral low and high frequencies. Modulated components of responses from the left and right halves of the field were out of phase. Analysis of this fact, and also of responses of the field to thin light and dark bars enabled the field structure to be described. It consists of linear and nonlinear subsystems, converging on the output neuron of the complex field. The former is composed of several pairs of on- and off-subfields of the lateral geniculate body. The on- and off-subfields in the pair overlap spatially and converge on the output neuron of the linear subsystem with opposite signs. The nonlinear subsystem is composed of either on- or off-subfields. Other types of complex fields may include different combinations of subsystems. The results indicate that complex fields are spatiotemporal grating filters.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 19–25, January–February, 1982.     

Effects of temperature on the properties of primary auditory fibres of the spectacled caiman,Caiman crocodilus (L.)

Summary The effect of temperature on the response properties of primary auditory fibres in caiman was studied. The head temperature was varied over the range of 10–35 ° C while the body was kept at a standard temperature of 27 °C (T_s). The temperature effects observed on auditory afferents were fully reversible. Below 11 °C the neural firing ceased.The mean spontaneous firing rate increased nearly linearly with temperature. The slopes in different fibres ranged from 0.2–3.5 imp s^–1 °C^–1. A bimodal distribution of mean spontaneous firing rate was found (<20 imp s^–1 and >20 imp s^–1 at T_s) at all temperatures.The frequency-intensity response area of the primary fibres shifted uniformly with temperature. The characteristic frequency (CF) increased nearly linearly with temperature. The slopes in different fibres ranged from 3–90 Hz °C^–1. Expressed in octaves the CF-change varied in each fibre from about O.14oct °C^–1 at 15 °C to about 0.06 oct °C^–1 at 30 °C, irrespective of the fibre's CF at T_s. Thresholds were lowest near T_s. Below T_s the thresholds decreased on average by 2dB°C^–1, above T_s the thresholds rose rapidly with temperature. The sharpness of tuning (Q_10db) showed no major change in the temperature range tested.Comparison of these findings with those from other lower vertebrates and from mammals shows that only mammalian auditory afferents do not shift their CF with temperature, suggesting that a fundamental difference in mammalian and submammalian tuning mechanisms exists. This does not necessarily imply that there is a single unifying tuning mechanism for all mammals and another one for non-mammals.Abbreviations BF best frequency: frequency of maximal response at an intensity 10 dB above the CF-threshold - CF characteristic frequency - FTC frequency threshold curve, tuning curve - T _s standard temperature of 27 °C     

Complex Cell Response depends on Interslit Spacing

PSYCHOPHYSICAL studies have established that the human central visual system contains a large number of independent channels each of which responds maximally to a selectively oriented sine wave grating of a given spatial frequency and hardly at all to gratings of spatial frequencies differing by a factor of two^1–4. Electrophysiological studies with moving sinusoidally modulated grating patterns have demonstrated that there exists a class of neurones in the striate cortex of cats⁵ and monkeys⁶ each member of which is maximally selective to a given spatial frequency and orientation.     

On the variety of spatial frequency selectivities shown by neurons in area 17 of the cat

The amplitudes of the responses of over 300 neurons in area 17 of the cat were examined as a function of the spatial frequency of moving sinusoidal gratings. The optimal spatial frequency and the bandwidth of the tuning curves were determined. The bandwidth varied considerably from neuron to neuron. Neurons optimally responsive to high spatial frequencies tended to have narrower tuning curves than those responsive to lower frequencies. Neurons with narrow spatial frequency tuning curves also tended to have narrow orientation tuning curves. These observations suggest that linear spatial summation tends to occur over a relatively constant area of visual field despite marked differences in each neuron's optimal spatial frequency, a prediction of one model of visual analysis. There was little difference in either the optimal spatial frequencies or the bandwidths of tuning for different functional classes of neuron. Neurons with broad tuning curves tended to be restricted to lamina IV and its environs, being concentrated in the deep part of lamina II-III and the upper part of lamina IV ab. Neurons with very low optimal spatial frequencies were uncommon and tended to be found either at the border of laminae II-III and IV or in lamina V. These laminar distributions are discussed with respect to the laminar differences in the projection of l.g.m. X- and Y-cells to the visual cortex.