Masking by Uniform Field Flicker: Some Practical Problems

Abstract

The technique of uniform field flicker (UFF) masking has frequently been used to address issues concerning the relative performance of sustained and transient neural channels in the human visual system. Unfortunately there has been an artifact in the implementation of this method in most published experiments which has meant that the contrast of the target has been flickered in synchrony with the mean luminance. A study is reported in which the artifact was corrected and the effects of UFF masking on the contrast sensitivity function then examined. With this correction, masking was still restricted to low spatial frequencies but it was much weaker than reported originally. It is argued that the original evidence suggesting that UFF masking can be used to examine the functioning of transient and sustained channels has not been interpreted correctly and that the basis for such a claim is weak.

The effects of a luminanace-modulated background on the grating-evoked cortical potential in the cat

“…Although mean luminance is independent of contrast in grating patterns, contrast is dependent on mean luminance. As a result, the contrast of the target grating varies with the luminance modulation of the background when the two are superimposed (Badcock & Sevdalis, 1987). In the present experiment, because the modulation of the background and the presentation of the target were not synchronized, the contrast of the target varied randomly both within and between trials when it was added to the background.…”

Visual field effects in the discrimination of sine-wave gratings

“…Kitterle, Heilige, and Christman (1990) pointed out that this cou1d have arisen as a result of failures to control for changes in mean luminance that accompanied grating presentations (i.e., Grabowska et al, 1989;Sze1ag et al, 1987). Changes in mean 1uminance can have complex effects on the processing of spatial frequencies (Badcock& Sevdalis, 1987;Green, 1981;Kitterle, Corwin, & Berta, 1979). Fiorentini and Berardi (1984) controlled for changes in mean 1uminance and measured the minimum spatialfrequency difference that cou1d be detected from a base Apparstus and Stimuli The stimuli used in these experiments were vertically oriented sinewave gratings that were produced by means of a computer-eontrolled Picasso CRT Spatio-Temporal Image Synthesizer (Innisfree) and displayed on Tektronix 608 monitors (P-31 phosphor).…”

Using perceptual tasks to selectively measure magnocellular and parvocellular performance: Rationale and a user’s guide

“…For example, M-cell lesions dramatically impacted contrast sensitivity for stimuli at high-temporal and low-spatial frequencies, but did not affect sensitivities to stimuli at high spatial frequencies (Merigan, Byrne, et al, 1991a ). Note that a uniform screen, as used in critical-flicker-fusion thresholds, is defined by very low spatial frequencies, essentially 0 c/deg—this interplay between temporal and spatial frequencies has also been demonstrated in masking studies in humans (Badcock & Sevdalis, 1987 ; Yang, Qi, & Makous, 1995 ). These results are consistent with high spatial frequencies being selectively processed by P cells.…”