Electrophysiological and Psychophysical Responses to Modulation of Contrast of a Grating Pattern

Bódis-Wollner, Iván; Hendley, Charles D.; Kulikowski, JJ

doi:10.1068/p010341

Cited by 61 publications

(28 citation statements)

References 19 publications

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“…The major contribution to the evoked potential amplitude comes from post-synaptic changes in pyramidal cells with long apical dendrites (Pollen, 1969), although it is certain that other types of neurones exert at least a modulating influence. Changes in the human visual evoked response with contrast modulation suggest that both components of the contrast modulated grating contribute to the evoked potential (Bodis-Wollner et al 1972). Pattern adaptation affects only slightly the amplitude to contrast modulation, but it does change the evoked potential phase and waveform (Bodis-Wollner & Hendley, 1978).…”

Section: Discussionmentioning

confidence: 99%

“…Temporal factors must also be considered. Later psychophysical experiments (Keesey, 1972; Bodis-Wollner, Hendley & Kulikowski, 1972;Kulikowski & Tolhurst, 1973) also implied that two broadly tuned mechanisms with different spatial and temporal frequency optima are responsible for these differences in grating detection. While these observations did imply the existence of independent mechanisms responding to pattern and flicker, they were also compatible with the concept that the sensitivity of each individual spatial mechanism depends on temporal factors.…”

Section: Introductionmentioning

confidence: 99%

“…The contrast of grating patterns was modulated in time, and the observer's task was to detect a time-varying change of the contrast at various spatial frequencies. We call this stimulus a contrast-modulated grating (Bodis-Wollner et al 1972;BodisWollner, Hendley & Tajfel, 1973 (b) Spatial contrast of a steady grating is the difference of maximum (L..) and minimum (Lmin) luminance over their sum.…”

Section: Introductionmentioning

confidence: 99%

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On the separability of two mechanisms involved in the detection of grating patterns in humans.

Bódis-Wollner¹,

Hendley²

1979

The Journal of Physiology

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SU1MMARY1. The delectability of contrast modulation (M) of sinusoidal gratings was explored at the rate of 8 Hz. The luminance profile of a contrast modulated sinusoidal grating is L = L(1 + C cos 27rFx). This stimulus may also be regarded as the sum of a steady grating pattern and counterphase flicker of the same spatial frequency.2. Contrast modulation sensitivity (1/M) was established in five observers at several levels of contrast and over a range of spatial frequencies, where M = AC/C of AC is the just detectable contrast change and C is the mean contrast of the grating. The slope of a modulation sensitivity function (C/AC v8. C) is 1 (i.e. AC = constant) near threshold contrast at each spatial frequency, but in the suprathreshold contrast range the slope flattens from close to 1 at 1.5 c/deg to almost 0 (AC/C = constant) at 12 c/deg.3. Adaptation to a high contrast steady grating of the same spatial frequency as the contrast modulated test gratings shifts each modulation sensitivity function to the right at low contrasts, but not at high. As a result the adapted curves cross their corresponding unadapted ones. At each spatial frequency the modulation sensitivity function is now fitted by a straight line of slope 1. While AC needs to be higher than half the detection threshold of the same grating at spatial frequencies above 3 c/deg, in the adapted condition the values are nearly equal at each frequency. Thus pattern adaptation unmasks the threshold of the counterphase component of the contrast modulated grating near threshold contrast as well as above it. The phase of the steady adapting grating, relative to the steady component of the test grating, does not make any difference.4. Apparently contrast modulation reveals differences beyond threshold sensitivity between spatial frequencies adjacent to the peak of the contract sensitivity curve. For each spatial frequency channel there must be different neural coupling between steady and modulated inputs. Electrophysiological studies using -contrast modulated gratings would be useful in the exploration of individual and ensemble properties of neurones of the visual cortex.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the separability of two mechanisms involved in the detection of grating patterns in humans.

Bódis-Wollner¹,

Hendley²

1979

The Journal of Physiology

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“…The effect of average contrast on the response to modulated contrast has also been 422 CONTRAST GAIN CONTROL IN HUMAN VISION studied using electrophysiological recordings of visual evoked potentials (VEP) in humans (Bodis-Wollner, Hendley & Kulikowski, 1972). The stimulus was a sinusoidal grating with a spatial frequency of 6 cycles/deg of visual angle, which is near the peak of the contrast sensitivity function (Campbell & Green, 1965).…”

Section: Introductionmentioning

confidence: 99%

Cortical contrast gain control in human spatial vision.

Bobak

Bódis-Wollner

Marx

1988

The Journal of Physiology

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SUMMARY1. We evaluated human visual cortical contrast gain using visual evoked potential (VEP) measurements. The steady-state VEP was elicited by 7-5 Hz contrast modulation of a 6 cycles/deg sinusoidal grating. The stimulus may be regarded as the sum of a'steady grating (C) and a counterphase grating of the same spatial frequency (AC). The counterphase grating is modulated sinusoidally in time.2. The VEP was measured to combinations of different modulation contrasts (AC) and different mean levels of grating contrast (C) which produced stimuli with contrast modulation depths (AC/C) ranging from 00625 to 1-0 ('on-off').3. The VEP signals were Fourier analysed and the amplitude and phase of the first (7 5 Hz) and second (15 Hz) harmonic frequency components were examined. The monocular VEP to a contrast-modulated grating contains significant first and second harmonic frequency components.4. The amplitude and phase of the monocular VEP was plotted as a function of AC for each mean level of contrast explored. The amplitudes of both the first and second harmonic frequency components grow with increasing AC. However, the slope of each function depends on the mean contrast (C): with higher levels of C, the slope of the function is more shallow. Furthermore, at each level of C the amplitude of the first harmonic frequency saturates at a lower AC than does the second harmonic frequency component. VEP amplitude is therefore not determined by the absolute contrast change (AC) alone. The VEP phase of the first harmonic frequency shows less dependence on either modulation or on mean contrast; the phase of the second harmonic frequency component is strongly dependent on mean contrast (C) but not on AC. P. BOBAK, I. BODIS-WOLLNER AND M. S. MARXgratings to opposite eyes. The dichoptic VEP, in distinction to the monocular VEP, contains only a second harmonic frequency component. The amplitude of the second harmonic frequency component grows with increasing AC, similar to the function seen for the monocular VEP. The phase of the dichoptic VEP shows a dependence on the mean contrast (C) of the grating presented to the other eye, although the amount of phase change in the second harmonic frequency component of the VEP is less pronounced than that seen in the second harmonic frequency component of the monocular VEP.7. The monocular vs. dichoptic data suggest that the origin of the first harmonic frequency component of the VEP (which occurs only with monocular stimulation) must arise at some point in the monocular pathway. The similarities between the second harmonic frequency component of the monocular and dichoptic VEP suggest, but do not establish, that the second harmonic frequency component of the monocular VEP is of cortical origin.8. These data demonstrate that spatial contrast controls the gain of both the monocular and dichoptic visual evoked potential in the human.

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“…1), with the temporal pattern of contrast modulations of the components being either identical (i.e., synchronized) or uncorrelated (i.e., unsynchronized). Physiological work (16)(17)(18) shows that fluctuations in contrast amplitude over time will evoke corresponding temporal modulations in neural activity. Therefore, discrimination of synchronized from unsynchronized contrast modulations of the two components would depend on information contained in the temporal patterning of activity within the separate populations of neurons responsive to those components.…”

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confidence: 99%

Spatial and temporal coherence in perceptual binding

Blake

Yang

1997

Proc. Natl. Acad. Sci. U.S.A.

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Component visual features of objects are registered by distributed patterns of activity among neurons comprising multiple pathways and visual areas. How these distributed patterns of activity give rise to unified representations of objects remains unresolved, although one recent, controversial view posits temporal coherence of neural activity as a binding agent. Motivated by the possible role of temporal coherence in feature binding, we devised a novel psychophysical task that requires the detection of temporal coherence among features comprising complex visual images. Results show that human observers can more easily detect synchronized patterns of temporal contrast modulation within hybrid visual images composed of two components when those components are drawn from the same original picture. Evidently, time-varying changes within spatially coherent features produce more salient neural signals.Early vision entails local feature analyses of the retinal image carried out in parallel over the entire visual field. By virtue of the receptive-field properties of the neurons performing this analysis, visual information is registered at multiple spatial scales, ranging from coarse to fine, for different contour orientations (1-3). Moreover, different qualitative aspects of the visual scene engage populations of neurons distributed among numerous, distinct visual areas (4, 5). Yet we perceive objects whose constituent features are, at least metaphorically speaking, bound together coherently. One popular but controversial hypothesis posits as a binding agent temporal synchronization of neural activity among cortical cells registering object features (6-11). In experiments reported here, we have discovered that synchronized modulations over time in the contrast of separate components of complex images are easier to detect when those components form a meaningful object. These findings are compatible with the notion that temporal and spatial coherence are involved in the promotion of perceptual binding.Several recent experiments have tried to assess whether patterns of neural activity coincident in time promote perceptual grouping, by determining whether visual features flickering in temporal synchrony more readily promote figure͞ ground segregation. Results from those experiments, however, have led to contradictory conclusions (12-14). To pursue this question of figural binding from a complementary perspective, we tested for enhanced detectability of temporal synchrony among spatial features that define a visual object. To understand the rationale for our study, imagine a picture composed of two components each selected to activate separate populations of visual neurons. Suppose further that the contrast of each component can be independently varied over time (Fig. 1), with the temporal pattern of contrast modulations of the components being either identical (i.e., synchronized) or uncorrelated (i.e., unsynchronized). Physiological work (16)(17)(18) shows that fluctuations in contrast amplitude over time will evo...

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Electrophysiological and Psychophysical Responses to Modulation of Contrast of a Grating Pattern

Cited by 61 publications

References 19 publications

On the separability of two mechanisms involved in the detection of grating patterns in humans.

On the separability of two mechanisms involved in the detection of grating patterns in humans.

Cortical contrast gain control in human spatial vision.

Spatial and temporal coherence in perceptual binding

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