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D C Burr

Publications and source records attributed to D C Burr.

15 recordsLinked to original sources
PubMed1992

Electro-physiological investigation of edge-selective mechanisms of human vision.

This study investigates the spatial and temporal characteristics of human visual mechanisms that respond selectively to the polarity of edges. The technique was to record steady-state visual evoked-potentials (VEPs) while visually stimulating with a sawtooth waveform (a series of edges of the same polarity) periodically reversing in contrast (and hence edge-polarity) at a suitable frequency. To ensure that phase-locked VEPs resulted from polarity reversal (rather than local luminance modulation) the stimuli were randomly jittered to a new position between each contrast reversal. The jittered stimulus elicited strong and reliable second-harmonic modulation, usually about one-fifth the amplitude of standard VEPs under similar conditions. The amplitude and extrapolated thresholds of polarity-specific VEPs (relative to standard VEPs) did not vary with eccentricity (up to 10 degrees) or with stimulus orientation. The dependency on spatial frequency was similar to that of standard VEPs, but the polarity-specific VEPs tended to peak at lower temporal frequencies. Perhaps the clearest difference in the two types of VEPs was in the estimated response latency, about 140 msec for the polarity VEPs, compared with 90 msec for standard VEPs.

Contrast Sensitivity↗
PubMed1992

The effects of aging on the pattern electroretinogram and visual evoked potential in humans.

We have recorded patterns electroretinograms (PERGs) and visual evoked potentials (VEPs) from 14 elderly subjects (mean age 72 yr) and 12 young subjects (mean age 21 yr) in response to stimulation by high contrast sinusoidal grating patterns of variable spatial frequency (at 9 Hz) and temporal frequency (at 1.7 c/deg). The major effect of aging on the PERG was an aspecific reduction in amplitude (of about 40%) at most spatial and temporal frequencies, together with a small but systematic phase lag. Control measurements suggest that senile miosis may be responsible for the phase lag, but not for the reduction in amplitude. The effects of aging on the VEP were more dramatic and depended on the spatial and temporal properties of the stimulus. VEP amplitudes (at 1.7 c/deg) were significantly lower for the aged at low temporal frequencies (below about 6 Hz), but were similar at high temporal frequencies. At 9 Hz, there was no effect of spatial frequency on VEP amplitude. At high temporal frequencies (above 10 Hz), the latencies of VEPs (estimated from the rate at which phase varied with temporal frequency) were similar for old and young (94 and 99 msec respectively). Below 10 Hz, however, the latencies of the old observers was much greater (153 compared with 108 msec). The second-harmonic phase of VEPs of the old but not the young decreased considerably with spatial frequency, by about 1.9 pi radians (52 msec) over the range from 0.5 to 11 c/deg. The selective reduction in amplitude at low temporal frequencies, the longer latencies at low temporal frequencies and the phase lag at high spatial frequencies are consistent with the hypothesis that mechanisms sensitive to high spatial and low temporal frequencies are selectively degraded by aging.

Adult↗
PubMed1991

Orientation discrimination depends on spatial frequency.

Thresholds were measured for discriminating the orientation of sinusoidal gratings of varying spatial frequency, and found to decrease monotonically with increasing spatial frequency. For discrimination of high-contrast (10 times threshold) near-vertical gratings, thresholds ranged from about 1 deg at 0.04 c/deg to 0.5 deg at 0.2 c/deg, after which there was little improvement. At lower contrasts and for discriminations around a mean of 45 deg, thresholds varied more so, and continued to improve until 1 c/deg. The variation of orientation discrimination thresholds with spatial frequency follows a similar trend to the variation in orientation bandwidth of visual units over the same range of spatial frequencies. Thus the present results are consistent with recent "opponent-process" models of orientation discrimination, that predict that thresholds to be limited (at least in part) by the maximum slope of orientation selectivity of visual detectors. That thresholds for high contrast vertical gratings did not improve for frequencies higher than 0.2 c/deg implies that orientation bandwidth and noisiness of oriented detectors may not be the sole factor limiting orientation discrimination, and suggests the existence of more central noise sources.

Contrast Sensitivity↗
PubMed1991

Development of visual inhibitory interactions in kittens.

This study was designed to monitor the development of inhibitory interactions elicited in the cat visual system by oriented visual stimuli. Steady-state visual-evoked potentials (VEPs) were recorded from the scalp of 11 behaving and alert kittens while they viewed contrast-reversed sinusoidal gratings. In adult cats, the form of VEP contrast-response curves (the amplitude of second harmonic modulation as a function of stimulus contrast) was modified by superimposing a mask grating on the test. Parallel masks displaced the curves to a higher contrast region (probably via contrast gain-control mechanisms), increasing contrast threshold without affecting the slope of the curve. Orthogonal gratings, on the other hand, decrease the slope of the curve without affecting threshold (so called cross-orientation inhibition: Morrone et al., 1981). These effects are similar to those previously reported in human VEPs (Morrone & Burr, 1986; Burr & Morrone, 1987) and single cortical cat cells (Morrone et al., 1982). For young kittens of 20 days, the orthogonal mask had no effect whatsoever on the response curves, and the effect of the parallel mask was much less than for adult cats. At about 40 days, the orthogonal mask began to attenuate responses multiplicatively, and by 50 days the amount of multiplicative attenuation had reached adult levels. The effect of the parallel mask (as indicated by the increase in threshold elevation) increased gradually from 20-50 days. The results are consistent with the existence of at least two types of inhibition in cat visual neurones that develop at different rates.

Animals↗
PubMed1991

Effects of monocular deprivation on the development of visual inhibitory interactions in kittens.

A visual-evoked-potential (VEP) masking technique was used to assess the effects of short- and long-term monocular deprivation on the development of visual inhibitory interactions in kittens. VEP contrast-response curves were recorded in response to contrast-reversed sinusoidal gratings, both with and without superimposed high-contrast masks. The contrast-response curves measured from the nondeprived eye were similar to those of normal cats: with no mask VEP amplitudes increase with contrast up to saturation at about 10% contrast; parallel masks shift the curves to the right, decreasing thresholds; and orthogonal masks decrease the slope of the contrast-response curves without affecting thresholds. After monocular deprivation (either brief or extensive), the contrast-response curves without mask did not show the typical response saturation, and neither parallel nor orthogonal mask had any effect on the contrast-response curves. The masking effects did not return after 100 days of normal vision, although contrast sensitivity and acuity recovered to about half of the normal levels during that period. The results indicate that the inhibitory intracortical circuitry that mediates the orientation-dependent masking effects are highly vulnerable to visual experience.

Animals↗
PubMed1991

Spatial summation properties of directionally selective mechanisms in human vision.

Our goal in this paper was to measure psychophysically the receptive-field size of motion units in human vision. To this aim, length and width spatial summation functions were measured for drifting (8-Hz) sinusoidal gratings of spatial frequencies 0.1, 1.0, and 10.0 cycles per degree (c/deg) with two threshold criteria: direction discrimination and simple detection. For each spatial frequency, contrast sensitivity for detection of the direction of drift increased with increasing stimulus size (length or width), at first rapidly (slope greater than or equal to 1.0) and then more gradually (slope 0.29). For most stimuli, the detection and direction-discrimination contrast thresholds were nearly the same. However, for stimuli severely curtailed in width, significantly more contrast was required for direction discrimination than for detection. These results were predicted with a summation model, which incorporated three-dimensional (space-space-time) linear input filters, and probability summation over space and among different filter types. The fit of the model gave an estimate of both the receptive-field length and width of motion-detector units in human vision. At each spatial frequency, the estimates of receptive-field width and length were similar, indicating that the receptive fields of motion-detector units are as long as they are wide at all spatial scales. Receptive-field size varied from approximately 0.12 cycle at 0.1 c/deg to 0.52 cycle at 10.0 c/deg.

Adult↗
PubMed1991

Two-dimensional spatial and spatial-frequency selectivity of motion-sensitive mechanisms in human vision.

Thresholds for detecting the direction of motion of drifting (8-Hz) vertical gratings [of spatial frequencies 0.1, 1.0, and 10.0 cycles per degree (c/deg)] were measured in the presence of masks that varied in both spatial frequency and orientation. Masks with different temporal properties were used. The specificity of masking was also measured for a stationary test grating of spatial frequency 3.0 c/deg. After suitable scaling and transformation, the masking data gave an estimate of the two-dimensional spatial-frequency tuning surface of cortical detector units in human vision. With the assumption of small-signal linearity and zero phase, the tuning surfaces were inverse Fourier transformed to give an indication of the size and structure of the psychophysical receptive fields of detector units. The results obtained with drifting test gratings and jittering (random phase) mask gratings indicate that motion-detector receptive fields increase in size (in cycles) with increasing spatial frequency but, at all spatial scales, have a length-width ratio of 1. These results are in close agreement with the summation results reported in J. Opt. Soc. Am. A 8, 1330 (1991). Using the same jittering mask stimuli and stationary test gratings, we confirm reports by Daugman [Vision Res. 24, 891 (1984)] and Harvey and Doan [J. Opt. Soc. Am. A 7, 116 (1990)] that motion-independent units have elongated receptive fields with a length-width ratio near 1.8. We conclude that the receptive fields of motion-dependent and -independent mechanisms in human vision are fundamentally different. The possibility that the orientation selectivity of a motion unit is sharpened by its selectivity for direction of motion is discussed.

Contrast Sensitivity↗
PubMed1990

Development of contrast sensitivity and acuity of the infant colour system.

We have monitored the development of infant colour vision by measuring chromatic contrast sensitivity and acuity in eight young infants over a period of 6 months. Steady-state visual evoked potentials (VEPS) were recorded in response to both chromatic (red-green) and luminance (red-black or green-black) patterns that were reversed in contrast over time. For most infants, no response could be obtained to chromatic stimuli of any size or contrast before 5 weeks of age, although luminance stimuli of 20% contrast gave reliable responses at that age. When responses to chromatic stimuli first appeared, they could be obtained only with stimuli of very low spatial frequency, 20 times lower than the acuity for luminance stimuli. Both contrast sensitivity and acuity for chromatic stimuli increased steadily, more rapidly than for luminance stimuli. As the spectral selectivities of infant cones are similar to those of adults, the difference in rate of development of luminance and chromatic contrast sensitivity and acuity stimuli probably reflects neural development of the infant colour system.

Age Factors↗
PubMed1989

Evidence for edge and bar detectors in human vision.

The structure of receptive fields of human visual detectors was investigated by studying their phase response. Observers were required to discriminate between pairs of periodic stimuli that differed in phase by 180 degrees (reversed in contrast). The stimuli comprised 256 harmonics, smoothly filtered in amplitude, and congruent in phase at the origin. Reversal discrimination thresholds were measured as a function of the phase of the harmonics. Thresholds were slightly higher for phases around 45 degrees, consistent with the idea that all discriminations were mediated by independent detectors with 0 or 90 degrees phase response (assuming probability summation between them). Discrimination thresholds were also measured with a pedestal stimulus, of phase complementary to that of the test gratings. For discriminations between 0 and 180 degrees (cosine phase), or 90 and 270 degrees (sine phase), the complementary pedestal had little effect, implying independence of detectors in sine and cosine phase. However, for discrimination between 45 and 225 degrees (stimuli containing both sine and cosine components) the complementary pedestal, which also contained both sine and cosine components, facilitated greatly discrimination thresholds. The results suggest that there exist two classes of detectors, one with a Fourier phase spectrum of 0, the other with a Fourier phase spectrum of 90 degrees. This implies that the receptive fields are symmetric, one class having even-symmetry (line-detectors), the other odd-symmetry (edge-detectors).

Differential Threshold↗
PubMed1989

Discrimination of spatial phase in central and peripheral vision.

Sensitivity to relative phase was measured for central and peripheral vision using stimuli comprising 256 harmonics, smoothly filtered in amplitude. With these stimuli, peripheral phase sensitivity was much higher than that previously reported with two-harmonic stimuli. Sensitivity did not depend on the average phase of the stimuli, nor on their second-order statistics, irrespective of the spatial frequency of the stimulus or the position in the visual field. After scaling for size, peripheral sensitivity was as high as central sensitivity. The scaling factor required to equate phase sensitivity was the same as that required to equate contrast sensitivity and grating acuity. These results suggest that phase sensitivity decreases with eccentricity at a similar rate as contrast sensitivity and grating acuity, much more slowly than the positional acuities. This is consistent with the suggestion that phase discrimination is mediated by discriminating the amplitude of the response of quasi-linear filters, and does not require mechanisms that evaluate position. It is suggested that previous measurements on peripheral phase sensitivity may reflect positional uncertainty in the periphery, rather than a deficit in phase sensitivity per se.

Differential Threshold↗
PubMed1989

The conditions under which Mach bands are visible.

In this paper we challenge the classical explanation of Mach bands--that they result from lateral inhibitory mechanism operating in the visual system--and present an alternative explanation based on a recent local energy model of feature detection (Morrone & Burr, 1988). A series of experiments was conducted to establish the range of parameters under which Mach bands appear on periodic waveforms of the trapezoid family. The model predicts successfully the conditions under which Mach bands appear, and the contrast necessary to see them. Other models, including those based on lateral inhibition and band-pass filtering fail to do so.

Contrast Sensitivity↗
PubMed1989

Receptive field properties of human motion detector units inferred from spatial frequency masking.

This study was designed to investigate the spatial frequency selectivity and spatial structure of receptive fields of motion sensitive mechanisms in human vision. Spatial frequency selectivity was inferred from masking measurements, using dynamic test and mask stimuli. For test frequencies between 0.025 and 15.0 c/deg, maximal masking occurred when the mask frequency matched that of the test, suggesting that the test was detected by mechanisms tuned to (or near to) that frequency. For tests below 0.025 c/deg or above 15.0 c/deg, maximal masking occurred at 0.025 and 15.0 c/deg, respectively, suggesting that there exist no mechanisms selective to frequencies outside these limits. A masking model, suitable for interpreting results obtained with drifting test stimuli, was developed and used to calculate spatial frequency selectivity functions from masking data. Assuming small signal linearity, and a constant phase spectrum, the selectivity functions were inverse-Fourier transformed to yield estimates of the extent and structure of receptive fields. Field width was found to vary with test spatial frequency from 5.8 deg at 0.03 c/deg to 0.05 deg at 10.0 c/deg. These estimates were compared with width estimates previously obtained by a summation technique (Anderson & Burr, 1987), and found to be similar over a wide range of spatial frequencies (2.5 log units). Gabor functions provided a reasonable fit to the calculated field profiles at high spatial frequencies (above 1.0 c/deg), but not at low frequencies.

Fourier Analysis↗
PubMed1986

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.

Differential Threshold↗