Phase-reversal discrimination in one and two dimensions: Performance is limited by spatial repetition, not spatial frequency content (original) (raw)
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The effect of phase structures on spatial phase discrimination
Vision Research, 1984
This study was concerned with the discrimination of multifrequency gratings uhich diKered only in the relative phase of one sinewave component (the test frequency) relative to the other components (the background frequencies). The dependent variable was the contrast of the test frequency required to discriminate between the two gratings. This study found that increasing the test frequency's relative phase difference from IO to 90 deg significantly increased an observer's contrast sensitivity. However, no overall change in contrast thresholds was measured for test gratings having a relative phase difference between 90 to IS0 deg. Moreover. when the mean relative phase was changed from 0 to 45 deg, contrast thresholds did not change when discriminating between gratings having a 90 deg relative phase difference. The type of processing most likely to account for these results in discussed.
Discrimination of spatial phase in central and peripheral vision
Vision Research, 1989
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.
Vision Research, 1991
We examined the effects of contrast, spatial scale, and orientation, on phase discrimination thresholds. In expt I, the ratio of thresholds for 180 deg shifts in F + 2F gratings remained invariant across a wide range of fundamental contrasts. Experiment II demonstrated that random fluctuations in overall pattern contrast did not affect discrimination. Experiment III found that foveal, but not peripheral, thresholds were roughly independent of spatial scale; foveal-peripheral differences in phase sensitivity could not be eliminated by scaling stimulus size. Finally, expt IV found that thresholds for some phase shifts varied significantly with orientation in the periphery; in general, peripheral sensitivity was greatest for radially-oriented gratings. The implications of these findings for models of phase discrimination are discussed. Spatial phase Peripheral vision Discrimination Cortical magnification criminate O-180 deg, but not 90-270, phase shifts, so those models might predict lower peripheral thresholds for O-180 than for 90-270 phase shifts, as observed by Bennett and Banks (1987). Experiments I and II test this nonlinearity hypothesis. Methods Stimuli. The stimuli were vertical F + 2F compound sinewave gratings: L(x) = La_ [ 1 + C, cos(2nFx) + C,, cos(2n2Fx-19)] (1) where Lavg is the space-average luminance, C, and C,, are the Michelson contrasts of F and 2F, respectively, and 8 is the base phase of 2F. Pattern contrast was modulated horizontally and vertically by a Gaussian envelope with a radius (at half-amplitude) that equalled one period of F. Stimulus eccentricity was defined as the angle between the fixation point and the center of the Gaussian envelope. The waveforms were generated on a PDP-1 l/73 computer and passed through a 12-bit DAC and an adjustable step attenuator to a Joyce Electronics display with P4 phosphor. The frame rate was 83 Hz. Mean luminance was fixed at lOOcd/m*. All calibrations were done with a Pritchard spot photometer (model UDB) and care was taken to ensure that the display's response was linear at all contrasts used in these experiments. Observers. Observers P.J.B. and M.S.B. are emmetropic with normal visual acuity; J.C. is a corrected-to-normal myope. The visual fields of all observers are normal. Observers P.J.B. and M.S.B. are the authors; J.C. was naive with respect to the aims of these experiments. Observers P.J.B. and J.C. received extensive practice (i.e. >20,000 trials) distributed across all conditions. M.S.B. received less practice (approx. 1200 trials) in the peripheral conditions. Procedure. Discrimination thresholds for 180 deg relative phase shifts were measured by fixing the contrast of F at a suprathreshold value and then varying the contrast of 2F until the phase shift was just visible. Trials were started by the observer and consisted of two 250 msec intervals marked by tones and separated by 250 msec.
1991
Detection and discrimination of compound grating stimuli were examined in fovea1 and peripheral vision. At the fovea, stimuli containing two components (spatial frequencies F and 3F) can be discriminated on the basis of their relative spatial phase when the 3Fcomponent is at a contrast below its independent detection threshold. This is no longer the case at increasing retinal eccentricity, where phase discrimination thresholds fall off much more steeply than simple detection thresholds. This relative fall-off in discrimination performance is still present for stimuli scaled for the cortical magnification factor, and is not attributable to fading of peripheral images due to the Troxler effect. The results therefore must imply a qualitative change in the processing of phase information between fovea1 and peripheral vision.
Spatial phase or luminance profile discrimination?
Vision Research, 1984
The ability of human observers to discriminate diffrrences in the relative phase of the components of high contrast compound gratings has been investigated. It is found that differences of less than 10' in the phase angle of the higher harmonic can be detected reliably, if sufficient practice is given. However, examination of the mechanisms involved in making "phase" discriminations suggests that observers, in most studies of phase discrimination, may not code relative phase directly in making their judgements. Indeed, it appears that the most parsimonious explanation is that the observers detect differences in the contrast of local regions of the stimuli.
The relationship between temporal phase discrimination ability and the frequency doubling illusion
Journal of Vision, 2007
The frequency doubling illusion (FDI) occurs when a low spatial frequency sinusoidal grating is modulated at high temporal frequenciesVits apparent spatial frequency increases. A recent study suggests that this illusion is perceived due to a frequency-dependent loss of temporal phase encoding ability. We sought to elucidate the relationship between temporal phase encoding and the FDI by exploring the spatiotemporal characteristics of temporal phase discrimination (TPD) thresholds using a novel stimulus comprising three grating patches presented simultaneously in a triangular pattern. A reference grating was presented superiorly, and six degrees below two gratings (one a copy of the reference) were each randomly presented in one of two fixed positions. The odd grating had abutting regions of spatial half-cycles with alternate half-cycles locked in temporal phase. The temporal phase difference between adjoining half-cycles was varied between 0and 180-via QUEST staircaseVsubjects had to identify which lower stimulus appeared different from the reference grating. TPD thresholds were measured for 0.25, 0.50, and 2.20 cpd stimulus at six temporal frequencies (1 to 28 Hz) at 2Â, 4Â, and 8Â orientation identification contrast thresholds. For all subjects, thresholds were variable at low contrasts. At higher contrasts, TPD thresholds increase for 0.25 and 0.50 cpd gratings with increasing flicker rate. These data support the idea that frequency-dependent loss of temporal phase encoding ability could possibly underlie the FDI.
Spatial-frequency spectrum of patterns changes the visibility of spatial-phase differences
Journal of the Optical Society of America A, 1985
This study showed that spatial-frequency components over a 4-octave range affected the visibility of spatial-phase differences. Contrast thresholds were measured for discrimination between two (+45-and-45-deg) spatial phases of a sinusoidal test grating added to a background grating. The background could contain one or several sinusoidal components, all in 0-deg phase. Phase differences between the test and the background were visible at lower constrasts (1) when test and background frequencies were harmonically related than when they were not, (2) when test and background frequencies were within 1 octave than when they were farther apart, (3) when the fundamental frequency of the background was low than when it was high, and (4) for some discriminations more than for others, after practice. The visibility of phase differences was not affected by additional components in the background if the fundamental and difference frequencies of the background remained unchanged. Observers' reports of their strategies gave information about the types of attentive processing that were used to discriminate phase differences. Attentive processing facilitated phase discrimination for multifrequency gratings spanning a much wider range of spatial frequencies than would be possible by using only local preattentive processing. These results were consistent with the visibility of phase differences being processed by some combination of even-and odd-symmetric simple cells tuned to a wide range of different spatial frequencies.
Temporal limits of long-range phase discrimination across the visual field
2007
When two flickering sources are far enough apart to avoid low-level motion signals, phase judgment relies on the temporal individuation of the light and dark phases of each source. The highest rate at which the individuation can be maintained has been referred to as Gestalt flicker fusion [Van de Grind, W. A., Grü sser, O. -J., & Lunkenheimer, H. U. (1973). Temporal transfer properties of the afferent visual system. Psychophysical, neurophysiological and theoretical investigations. In R. Jung (Ed.), Handbook of sensory physiology (Vol. VII/3, pp. 431-573). Berlin: Springer, Chapter 7] and this has been taken as a measure of the temporal resolution of attention [Verstraten, F. A., Cavanagh, P., & Labianca, A. T. (2000). Limits of attentive tracking reveal temporal properties of attention. Vision Research, 40, 3651-3664; Battelli, L., Cavanagh, P., Intriligator, J., Tramo, M. J., Henaff, M. A., Michel, F., et al. (2001). Unilateral right parietal damage leads to bilateral deficit for high-level motion. Neuron, 32, 985-995].
Temporal phase discrimination depends critically on separation
Vision Research, 2002
Temporal phase discrimination was measured as a function of spatial separation of the stimulus components. In contrast to many previous studies, phase discrimination thresholds were measured directly, rather than inferred from the ability to discriminate synchronous from antiphase stimuli, or from segregation or shape tasks. For abutting bars, relative phase thresholds were closely proportional to temporal frequency. The proportionality corresponded to a threshold temporal offset of 2.5-9.5 ms, across subjects. Introduction of a small gap (0.125°or greater) led to a dramatic (3-to 7-fold) increase in thresholds for temporal phase discrimination, and thresholds were no longer proportional to temporal frequency. Insertion of a third bar filling the gap resulted in a recovery of the low thresholds, provided that its modulation was consistent with apparent motion across the three bars. Below 8 Hz, phase discrimination thresholds across three bars were equivalent to thresholds for two abutting bars. Above 8 Hz, phase discrimination thresholds for the three bar combination were lower than thresholds for two adjacent bars, implying that phase information was integrated across all three bars.
Detection and discrimination of relative spatial phase by V1 neurons
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2002
Edge-like and line-like features result from spatial phase congruence, the local phase agreement between harmonic components of a spatial waveform. Psychophysical observations and models of early visual processing suggest that human visual feature detectors are specialized for edge-like and line-like phase congruence. To test whether primary visual cortex (V1) neurons account for such specificity, we made tetrode recordings in anesthetized macaque monkeys. Stimuli were drifting equal-energy compound gratings composed of four sinusoidal components. Eight congruence phases (one-dimensional features) were tested, including line-like and edge-like waveforms. Many of the 137 single V1 neurons (recorded at 45 sites) could reliably signal phase congruence by any of several response measures. Across neurons, the preferred spatial feature had only a modest bias for line-like waveforms. Information-theoretic analysis showed that congruence phase was temporally encoded in the frequency band pr...