Detectability of several ideal spatial patterns.
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Form Perception↗
Biomedical subjects
A M Derrington
Publications and source records attributed to A M Derrington.
The influence of temporal frequency and adaptation level on receptive field organization of retinal ganglion cells in cat.
1. The discharges of single X and Y ganglion cells (distinguished by a test of linearity of spatial summation) were recorded in the optic tract of anaesthetized, paralysed cats.2. Fourier techniques were used to analyse the distribution of amplitudes of several component temporal frequencies in the maintained discharge. X and Y cells were distinguished by their mean rates, but not by the amplitude or variability of other component frequencies.3. Sensitivities to moving sinusoidal gratings were measured by an automatic procedure in which stimulus contrast was adjusted to give the smallest modulation of discharge that reliably exceeded that of the relevant component frequency in the maintained discharge.4. Spatial contrast sensitivity curves of X cells and of on-centre Y cells could be described by a model of the receptive field as two concentric Gaussian sensitivity profiles representing the centre and the antagonistic surround.5. Changes in temporal frequency altered the shapes of the spatial contrast sensitivity curves of most units. For X cells sensitivity at the optimum spatial frequency was greater at a temporal frequency of 10.4 Hz than at lower or higher temporal frequencies. The relative sensitivity to low spatial frequencies improved as temporal frequency was raised from 0.16 to 20.8 Hz. The shapes of the contrast sensitivity functions of Y cells were less affected by changes in temporal frequency: at all spatial frequencies sensitivity was greater at 2.6 Hz than at lower or higher frequencies.6. The effect of temporal frequency upon the shape of the spatial contrast sensitivity curve could be explained by assuming that the centre and surround changed their sensitivities without changing their characteristic radii. A simple model, using a temporal R-C filter in the surround pathway, predicted qualitatively similar changes in the shape of contrast sensitivity curves but failed to provide acceptable fits to the observations. A second model, which assumed that surround signals are delayed by a fixed amount before being combined with those from the centre, fitted the observations of most, but not all, X cells.7. Dark adaptation produced changes in the shape of the spatial contrast sensitivity curve consistent with a reduction in the relative sensitivity of the surround, but did not bring about systematic changes in the space constants of the best-fitting theoretical curves.8. The effects of adaptation level upon contrast sensitivity were expressed as plots of increment-threshold against mean illumination. The shallowest of these curves, obtained for the optimum spatial stimulus moving at about 10 Hz, had slopes averaging 0.77. Decreases in spatial or temporal frequency increased the slopes of the curves.
Action Potentials↗
Pattern discrimination with flickering stimuli.
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Differential Threshold↗
Spatial and temporal properties of cat geniculate neurones after prolonged deprivation.
1. Extracellular recordings were made from the dorsal lateral geniculate nucleus of monocularly deprived, dark-reared and normal cats. The spatial and temporal properties of the neurones were studied. 2. The mean acuity of X-cells with receptive fields 3 degrees of the area centralis was 3.9 c/degree for deprived eye cells from monocularly deprived cats, compared was 3.8 c/degree for normal cells. 3. The mean activity of X-cells with receptive fields within 4 degrees of the area centralis was 4.3 c/degree for a dark-reared cat compared with 4.0 c/degree for a normal cat. 4. The peak response rates of X-cells to their best spatial frequency were determined. The mean values for the normal, monocularly deprived and dark-reared populations were all similar. 5 Measurement of the temporal frequency tuning of a number of cells was made. The mean peak temporal frequency for the dark-reared X-cells was lower than for monocularly deprived or normal X-cells. 6. The results are discussed with reference to the location of the primary neural deficit induced by visual deprivation.
Action Potentials↗
The development of spatial-frequency selectivity in kitten striate cortex.
1. Single units were recorded in the striate cortex of kittens aged between 2 and 12 weeks. Contrast sensitivity measurements made using moving sinusoidal gratings were used to construct spatial-frequency tuning curves. 2. In young kittens cells had low sensitivities, responded only to low spatial frequencies and were unselective for spatial frequency. In addition 30% of the cells recorded in the youngest kittens were unresponsive to visual stimuli. 3. Sensitivity improved to near-adult values within 5-6 weeks. 4. Best spatial frequency improved more gradually, so that even in the oldest kittens best spatial frequencies were lower than adult values. 5. Selectivity for spatial frequency, considered both in terms of the numbers of selective cells and the narrowness of their tuning curves, improved rapidly, and reached adult values within the first 6 weeks. 6. These results are discussed in relation to other developmental studies.
Age Factors↗
The mechanism of peripherally evoked responses in retinal ganglion cells.
1. Responses to stimulation of retinal regions remote from the classical receptive field were recorded from optic tract fibres in lightly anaesthetized cats. 2. X- and Y-cells gave reliably different responses to the sudden reversal of the phase of a high contrast grating that fell on the retina more than 15 deg from the centre of the receptive field. 3. The mechanism that generates these responses ('shift effect' or 'periphery effect') in Y-cells is insensitive to the spatial phase of the stimulating grating. It can resolve gratings of higher spatial frequency than can be resolved by the classical receptive field mechanisms of Y-cells but its temporal resolution is poorer. 4. Signals that contribute to peripherally evoked responses are accumulated over a region that extends to at least 35 deg from the centre of the receptive field. Although this region is not uniformly sensitive, regions in the periphery of the visual field are as effective as regions around the area centralis in eliciting the responses, and do not require coarser gratings. 5. In some Y-cells the response to peripheral stimulation was amplified by increasing (on-centre units) or decreasing (off-centre units) the steady illumination of the centre of the receptive field. This confirms Krüger & Fisher (1973), but the effect is only found in a proportion of cells. 6. The mechanism that generates peripherally evoked responses is tentatively identified with the 'rectifying subunits' postulated by Hochstein & Shapley (1976b) to account for the spatial non-linearity in the receptive fields of Y-cells. Transient (bistratified) amacrine cells are known to have many of the properties attributed to these mechanisms (Chan & Naka, 1976).
Animals↗
Spatial and temporal properties of X and Y cells in the cat lateral geniculate nucleus.
1. Extracellular recordings were obtained from units in the dorsal lateral geniculate nucleus of anaesthetized cats. 2. Of sixty-nine units, sixty-three could be unambiguously identified as either X (n = 33) or Y (n = 30) by testing the presence of a null response to stationary sine wave gratings presented in different spatial phases. 3. In response to stationary gratings flashed on and off, Y cells exhibited bigger, more transient responses than X cells. 4. All Y cells but few X cells exhibited a shift effect (modulated periphery effect). 5. In response to drifting sine wave gratings of different spatial frequencies, X cells preferred higher spatial frequencies and showed smaller peak contrast sensitivities and somewhat narrower tuning curves than Y cells. 6. In response to a sine wave grafting of optimal spatial frequency drifting at different velocities, X and Y cells had similar temporal tuning curves. However, Y cells, largely because they preferred lower spatial frequencies, preferred higher drift velocities than X cells. 7. Our data suggest that X and Y cells can be differentiated objectively on the basis of a number of discharge parameters. These parameters are compared with similar data collected by others from neurones in the visual cortex.
Action Potentials↗
Development of selectivity in kitten striate cortex [proceedings].
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Aging↗
Spatial and temporal frequency tuning in cat lateral geniculate nucleus [proceedings].
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Action Potentials↗
The effects of remote retinal stimulation on the responses of cat retinal ganglion cells.
1. Action potentials were recorded from optic nerve fibres of lightly anaesthetized cats while parts of the retina remote from the receptive field were stimulated by a shifting grating. 2. Vigorous responses can be obtained under these conditions, confirming McIlwain (1966), Krüger & Fischer (1973), and others. 3. These 'shift responses' are not caused by fluctuations of stray light because (a) they cannot be reduced by deliberately increasing or decreasing the light falling on the receptive field synchronously with the shifting grating; (b) a steady adapting light applied to the receptive field does not raise the threshold for the responses, whereas adapting light on the peripheral retina does, and (c) the threshold for the responses is elevated more following bleaching adaptation of the periphery than following bleaching adaptation of the centre. 4. Shift responses are strong, of short latency, and brief in duration in brisk-transient (Y-type) neurones. With few exceptions they are weak but long-lasting in brisk-sustained (X-type) neurones. 5. Shift responses are unlike responses from the main receptive field in having a distinct threshold; the magnitude of the response to weak gratings is not simply proportional to contrast, as is the case with weak stimuli applied to the receptive field. 6. It is thought that the excitatory pathway may involve amacrine cells, and that this mechanism may be concerned with the detection of the shifts of the image that occur with saccadic eye movements.
Action Potentials↗
Detecting and discriminating the direction of motion of luminance and colour gratings.
Human observers were required to discriminate the direction of motion of vertically moving, 1 c/deg luminance and colour gratings. The gratings had different contrasts and moved at temporal frequencies between 0.5 and 32 Hz. Sensitivity [the reciprocal of the contrast at which performance reached 75% correct in a temporal two-alternative forced-choice (2 AFC) discrimination task] was a band-pass function of temporal frequency for luminance gratings, and a low-pass function of temporal frequency for colour gratings. Further, when colour contrast was expressed in terms of the modulation in cone excitation produced by the stimulus, sensitivity to colour gratings was greater than sensitivity to luminance gratings at frequencies below 2 Hz. On the other hand, at temporal frequencies above 4 Hz, sensitivity to colour gratings was comparable with sensitivity to luminance gratings of double the temporal frequency. Detection sensitivity was measured for luminance and colour gratings of 1, 4 and 16 Hz. With either colour or luminance gratings, detection thresholds were very similar to those for direction-of-motion discrimination. This result confirms findings of Mullen and Boulton [(1992) Vision Research, 32, 483-488] and Cavanagh and Anstis [(1991) Vision Research, 31, 2109-2148], but is different from that reported by Lindsey and Teller [(1990) Vision Research, 30, 1751-1761] who used a smaller stimulus seen in a parafoveal region and found that motion discrimination thresholds were higher than detection threshold for colour gratings. We repeated our threshold measurements using parafoveal viewing conditions similar to those used by Lindsey and Teller (1990). We found that, although for luminance gratings detection thresholds were very close to direction-discrimination thresholds, for colour gratings, they were lower. The result is in qualitative agreement with Lindsey and Teller (1990). Our results suggest that low-level, or "first-order" motion mechanisms are not as sensitive to chromatic gratings as are colour-detection mechanisms.
Color Perception↗
Long-range interactions in the lateral geniculate nucleus of the New-World monkey, Callithrix jacchus.
Visual stimulation of zones extending beyond the classical receptive field can modulate the contrast gain of neurons in the lateral geniculate nucleus (LGN) of cats, but little is known about the effect of extra-classical visual stimulation on the LGN of primates. Hence, we compare the effect of long-range interactions in parvocellular and magnocellular LGN layers of the marmoset monkey Callithrix jacchus using optimal, incremental spots flashed on the classical receptive field either alone or simultaneously with the shift of a grating (98% contrast; 0.1 cycles/deg) confined to a peripheral annulus (radii: 5-15 deg). The contrast required to drive the response halfway to saturation (c50) of most LGN neurons was raised by remote pattern shifts. The c50 ratio [(shift+spot)/spot] in OFF-center magnocellular neurons was significantly higher than in OFF-center parvocellular neurons. OFF-center magnocellular neurons closer to the fovea (<10 deg eccentricity) tended to have a higher c50 ratio than in more peripheral neurons. A significant drop in visual sensitivity to 25% contrast spots was observed during remote motion: d' fell from 1.8 to 1.4 in parvocellular neurons and from 2.2 to 1.7 in magnocellular neurons. Such long-range interactions produce a reduction in visual sensitivity by changing the gain of the geniculate relay and point to an inhibitory, motion-sensitive extra-classical receptive field in both parvocellular and magnocellular pathways, which may be involved in saccadic suppression and attentional mechanisms in early vision.
Animals↗
Peripheral shift reduces visual sensitivity in cat geniculate neurones.
The sudden displacement of the retinal image during a saccade raises the visual threshold of human observers to foveal stimuli. The fall in visual sensitivity observed during this phenomenon, known as saccadic suppression, seems to occur very early in the visual processing chain. The lateral geniculate nucleus (LGN) is a likely locus for the multiple retinal and extraretinal interactions occurring during saccadic eye movements, therefore we used the responses of relay cells of adult cats to simulate a psychophysical experiment. We first measured the responses of X and Y relay cells (27 X and 13 Y) to central spots of optimal size and different contrasts. The spots were presented either alone or time locked with the rapid movement of a large, high-contrast peripheral pattern, referred to as shift. We measured the percentage of trials on which the relay cell fired more spikes when the spot (contrast: 0.03-1.0) was present than when it was absent. In experiments with human observers the task was to indicate, by a keypress, which of two otherwise identical temporal intervals contained the spot. The shift reduces the sensitivity (raises the contrast threshold) of neurones in the cat relay cells to brief, stationary targets presented to the receptive-field center. The suppression of visual sensitivity is significantly greater in Y cells than in X cells (average sensitivity ratios 5.6 +/- 5.4 in Y cells, 1.59 +/- 0.9 in X cells: P < 0.001, U test). The shift also reduces the sensitivity of human observers to the same target. This suggests that the LGN is a potential locus for the modulation of visual responses that leads to saccadic suppression.
Animals↗
Long-range interactions modulate the contrast gain in the lateral geniculate nucleus of cats.
In previous work, we have shown that sudden image displacements well outside the classical receptive field modulate the visual sensitivity of LGN relay cells. Here we report the effect of image displacements on the response versus contrast function. The stimuli consisted of a central spot of optimal size and polarity (contrast range: 3-98%), flashed alone or in the presence of a peripheral annulus (radii: 5-15 deg) containing a low spatial-frequency grating displaced at saccade-like velocities (shift). The most consistent effect of the shift on the response to a central spot was to reduce the responsiveness of Y relay cells and, to a lesser extent, of X relay cells. The reduction in responsiveness was primarily a divisive rather than a subtractive effect and could be modelled by assuming that a greater contrast was required to produce a given excitatory response. In the absence of a central spot, remote motion had inhibitory effects on the firing rates of the majority of relay cells, but its effect on retinal ganglion cells was mainly excitatory. When the shifting grating covered the classical receptive field and its periphery, facilitatory effects or suppressive effects, depending on the spatial phase of the pattern, were observed in both retinal and geniculate cells. Remote motion strongly suppresses the responsiveness of relay cells to stimuli within the classical receptive field. This suppressive effect involves intrageniculate processing and is primarily associated with a reduction in contrast gain. It is likely that shift suppression contributes to the loss of visual sensitivity observed in saccadic suppression.
Animals↗