What covariance mechanisms underlie green/red equiluminance, luminance contrast sensitivity and chromatic (green/red) contrast sensitivity?

Abstract

In order to investigate the mechanisms underlying green/red equiluminance matches in human observers and their relationship to mechanisms subserving luminance and/or chromatic (green/red) contrast sensitivity, we tested 21 human subjects along these dimensions at 16 different spatial and temporal frequencies (spatial frequency, 0.25-2 c/deg; temporal frequency, 2-16 Hz) and applied factor analysis to extract mechanisms underlying the data set. The results from our factor analysis revealed separate sources of variability for green/red equiluminance, luminance sensitivity and chromatic sensitivity, thus suggesting separate mechanisms underlying each of the three main conditions. When factor analysis was applied separately to green/red equiluminance data, two temporally-tuned factors were revealed (factor 1, 2-4 Hz; factor 2, 8-16 Hz), suggesting the existence of separate mechanisms underlying equiluminance settings at low versus high temporal frequencies. In addition, although the three main conditions remained separate in our factor analysis of the entire data set, our correlation matrix nonetheless revealed systematic correlations between equiluminance settings and luminance sensitivity at high temporal frequencies, and between equiluminance settings and chromatic sensitivity at low temporal frequencies. Taken together, these data suggest that the high temporal frequency factor underlying green/red equiluminance is governed predominantly by luminance mechanisms, while the low temporal frequency factor receives contribution from chromatic mechanisms.

How to use individual differences to isolate functional organization, biology, and utility of visual functions; with illustrative proposals for stereopsis

“…Several other researchers have used latent variable modeling techniques to isolate contrast sensitivity mechanisms (Dobkins et al, 2000;Billock & Harding, 1996;Mayer et al, 1995;Sekuler et al, 1984). Such methods have also contributed to our knowledge of the functional organization of color vision (Bimler, Kirkland & Jameson, 2004;Gunther & Dobkins, 2003;Burt, 1949;Jones, 1948) and motion perception (Morrone et al, 1999).…”

A multistream model of visual word recognition

“…Peterzell and Teller (2000) examined correlations between contrast sensitivity thresholds across seven levels of spatial frequency (0.27-2.16 cpd of visual angle) of gratings that were yellow-black (i.e., monochromatic or luminance modulated) and seven levels of spatial frequency of gratings that were red-green (i.e., chromatic modulated). Using principal components analysis with a varimax rotation on the 14 threshold variables, Peterzell and Teller interpreted three principal components as representing a lower spatial-frequency monochrome channel, a higher spatial-frequency monochrome channel, and a chromatic channel (see also Dobkins, Gunther, & Peterzell, 2000). These channels plausibly correspond to the MD, ID, and BD channels, respectively, of the model of visual processing of Van Essen and Anderson (1995).…”

Constructing isoluminant stimuli for word recognition research: A precautionary study

“…Two flicker rates were used: 16 Hz and 20 Hz. These rates were chosen for their suitability for magnocellular processing (see, e.g., Dobkins et al, 2000) and on the basis of a pilot study in which participants found performing the HFP task to be straightforward when these rates were used. The chromatic and luminance characteristics of the display screen were measured using a Cambridge Research Systems ColorCAL colorimeter.…”

“…The most straightforward approach is to match the onscreen luminance of the different components so they have the same physical luminance, as measured by a photometer (see, e.g., Chase et al, 2003;Knoblauch et al, 1991;Lehky, 2000;Ojanpää & Näsänen, 2003;Travis et al, 1990; see also Allen et al, 2002). Unfortunately, onscreen isoluminance does not guarantee that stimuli are isoluminant in either retinal images or postretinal neural responses (see, e.g., Bilodeau & Faubert, 1997; see also Cavanagh, MacLeod, & Anstis, 1987;Dobkins, Gunther, & Peterzell, 2000;Livingstone & Hubel, 1987;Metha & Mullen, 1996;von Berg, Ziebell, & Stiehl, 2002), and luminance differences may therefore be readily perceived by the observer. Consequently, an alternative approach to suppressing the processing of luminance contrasts in word recognition experiments is required.…”

“…However, the HFP task requires careful implementation if it is to be used effectively for studies of word recognition. In particular, evidence from psychophysical research using gratings suggests that the luminance values required for isoluminance in the HFP task may be affected by the physical properties of the stimuli used (see, e.g., Cavanagh et al, 1987;Dobkins et al, 2000;Metha & Mullen, 1996). As a consequence, if the stimuli used in the HFP task to determine isoluminance differ substantially from the (word) stimuli being used in the experiment proper, the experiment proper may not constitute a valid investigation of the effects of isoluminance on word recognition.…”