Non-cardinal color mechanism elicitation by stimulus shape: Bringing the S versus L+M color plane to the table.

Neurons in the cortex typically respond best to elongated stimuli, or gratings, whereas neurons in the lateral geniculate nucleus (LGN) typically prefer circular stimuli, or spots. Further, neural mechanisms specifically tuned for non-cardinal colors largely do not emerge until the cortex; therefore, the use of gratings should better reveal non-cardinal color mechanisms. This hypothesis has been tested in the isoluminant color plane in macaque monkeys (Stoughton, Lafer-Sousa, Gagin, & Conway, 2012) and in the L-M versus L+M color plane in human subjects (Gegenfurtner & Kiper, 1992). Here, this hypothesis was tested in the third color plane, S versus L+M, in human subjects in two experiments. Experiment 1 tested 10 subjects across four directions in this color plane; Experiment 2 tested three subjects in eight to twelve color directions. Consistent with data from the other two color planes, in both experiments in the S versus L+M color plane, gratings revealed the presence of non-cardinal mechanisms more strongly than did spots.

Poor peripheral binding depends in part on stimulus color.

We have compared two explanations for poor peripheral binding. Binding is the ability to assign the correct features (e.g., color, direction of motion, orientation) to objects. Wu, Kanai, and Shimojo (Nature, 429(6989), 262, 2004) showed that subjects performed poorly on binding dot color with direction of motion in the periphery. Suzuki, Wolfe, Horowitz, and Noguchi (Vision Research, 82, 58-65, 2013) similarly showed that subjects had trouble binding color with line orientation in the periphery. These authors concluded that performance in the periphery was poor because binding is poor in the periphery. However, both studies used red and green stimuli. We tested an alternative hypothesis, that poor peripheral binding is in part due to poor peripheral red/green color vision. Eccentricity-dependent changes in visual processing cause peripheral red/green vision to be worse than foveal vision. In contrast, blue/yellow vision remains centrifugally more stable. We tested 9 subjects in a replication and extension of Suzuki and colleagues' line orientation judgment, in red and green, and in blue and yellow. There were three central conditions: (1) red (or blue) all horizontal, green (or yellow) all vertical; (2) red (or blue) all vertical, green (or yellow) all horizontal; or (3) random pairing of color and orientation. In both the red/green and the blue/yellow color schemes, peripheral performance was influenced by central line orientation, replicating Suzuki and colleagues. However, the effect with blue/yellow lines was smaller, indicating that poor peripheral "binding," as hypothesized by both Wu and colleagues and Suzuki and colleagues, is due in part to their use of red and green stimuli.

Trombones Elicit Bitter More Strongly Than Do Clarinets: a Partial Replication of Three Studies of Crisinel and Spence.

We present a partial replication of the crossmodal pitch/taste correspondence of Crisinel and Spence. Male college students (n=46) were asked to judge the pitch (F1-C4 on trombone; F3-C6 on clarinet) that best corresponded with each of four tastants (unsweetened coffee, unsweetened chocolate, salt, and sugar). With trombone there was a significant effect of tastant [F(3,135)=7.574, p<0.001, η2=0.144] with unsweetened chocolate being associated with the lowest pitch and sugar with the highest. With clarinet we did not find a significant effect [F(3,135)=2.468, p=0.065, η2=0.052]. The average across instruments was significant [F(3,135)=4.269, p=0.006, η2=0.087]. When looking at the effect of taster status, we found a significant correlation [r(44)=0.389, p=0.007] with supertasters associating the bitterness of a PTC strip with higher pitches than did nontasters - this is in contrast with Crisinel and Spence's finding of no correlation with taster status. In light of the 'replication crisis' in psychology as found by the Open Science Collaboration, it is noteworthy that this crossmodal pitch/taste correspondence, at least for trombone, was replicated in a different lab.

Influence of stimulus size on revealing non-cardinal color mechanisms.

Multiple studies have shown that performance of subjects on a number of visual tasks is worse for non-cardinal than cardinal colors, especially in the red-green/luminance (RG/LUM) and tritan/luminance (TRIT/LUM) color planes. Inspired by neurophysiological evidence that suppressive surround input to receptive fields is particularly sensitive to luminance, we hypothesized that non-cardinal mechanisms in the RG/LUM and TRIT/LUM planes would be more sensitive to stimulus size than are isoluminant non-cardinal mechanisms. In Experiment 1 we tested 9-10 color-normal subjects in each of the three color planes (RG/TRIT, RG/LUM, and TRIT/LUM) on visual search at four bull's-eye dot sizes (0.5°/1°, 1°/2°, 2°/4°, and 3°/6° center/annulus dot diameter). This study yielded a significant main effect of dot size in each of the three color planes. In Experiment 2 we tested the same hypothesis using noise masking, at three stimulus sizes (3°, 6° and 9° diameter Gabors), again in all three color planes (5 subjects per color plane). This experiment yielded, in the RG/TRIT plane, a significant main effect of stimulus size; in the RG/LUM plane, significant evidence for non-cardinal mechanisms only for the 9° stimulus; but in the TRIT/LUM plane no evidence for non-cardinal mechanisms at any stimulus size. These results suggest that non-cardinal mechanisms, particularly in the RG/LUM color plane, are more sensitive to stimulus size than are non-cardinals in the RG/TRIT plane, supporting our hypothesis.

Non-cardinal color perception across the retina: easy for orange, hard for burgundy and sky blue.

Cardinal color performance (reddish, greenish, bluish, yellowish, black, and white) has been shown to decline in peripheral viewing. What about non-cardinal color performance (e.g., orange, burgundy, and sky blue)? In visual search, performance on non-cardinal colors matched that of the cardinal colors in the (L-M)/(S-(L+M)) (isoluminant) color plane (Experiment 1, n=10, to 30°; Experiment 2, n=3, to 50°). However, performance in the (L-M)/(L+M) and (S-(L+M))/(L+M) color planes was worse for non-cardinal colors, at all eccentricities, even in the fovea. The implications that these results have for the existence of non-cardinal mechanisms in each color plane are discussed.

Non-cardinal color mechanism strength differs across color planes but not across subjects.

This study tested two hypotheses: (1) that non-cardinal color mechanisms may be due to individual differences: some subjects have them (or have stronger ones), while other subjects do not; and (2) that non-cardinal mechanisms may be stronger in the isoluminant plane of color space than in the two planes with luminance. Five to six subjects per color plane were tested on three psychophysical paradigms: adaptation, noise masking, and plaid coherence. There were no consistent individual differences in non-cardinal mechanism strength across the three paradigms. In group-averaged data, non-cardinal mechanisms appear to be weaker in the two planes with luminance than in the isoluminant plane.

A tritan Waldo would be easier to detect in the periphery than a red/green one: evidence from visual search.

In a color naming task from 0° to 55° eccentricity, we found that red/green performance (n=10 subjects) declines around 40° eccentricity, 5° earlier than does tritan performance (main effect of color, p=0.009; eccentricity, p<0.001; interaction, p=0.005). In a feature visual search task (e.g., red target dot among green distractor dots; twelve 2.5° diameter dots; 0, 20, and 45° eccentricity; 12 subjects), performance was significantly more impaired for red/green than for tritan stimuli, especially in the periphery (main effect of color, p=0.007; eccentricity, p<0.001; interaction, p=0.003). This effect occurred even following a rod bleach. Our results are consistent with influences from both the retina (especially random rather than selective peripheral cone input to midget ganglion cells for red/green perception, and selective cone input to small bistratified cells for tritan perception) and the cortex (differential cortical magnification across the two chromatic axes).

The use of "non-fiction novels" in a sensation and perception course.

Scientific material can be difficult to relate to everyday knowledge. Textbook facts can be abstract. This Study of Teaching and Learning project examined the use of "non-fiction novels" (biographies and other books that read like novels but are true) in an undergraduate Sensation and Perception course in order to increase the concreteness of the reading material and to give the students a story on which to hang the facts learned in lecture. In Phase I (Fall 2009) non-fiction novels were used for half of the units and a standard textbook for the other half. In Phase II (Fall 2010) only non-fiction novels were used. The Fall 2009 class was very positive about the use of non-fiction novels, but exam scores did not mirror this enthusiasm, either on semester exam scores or on a four-month re-take of the cumulative final exam. In contrast, the Fall 2010 class missed having a textbook, but exam performance significantly improved over prior semesters, and performance on the four-month re-take of the cumulative final exam showed performance equivalent to the Fall 2009 class's four-month performance on questions from textbook units. In both semesters, the effectiveness of the instructor in stimulating student interest was significantly higher than in prior years where only the textbook was used. In addition, 68% of the students said that reading the non-fiction novels made them want to learn more about our sensory systems.

Nucleotide polymorphisms upstream of the X-chromosome opsin gene array tune L:M cone ratio.

In support of the long-held idea that cone ratio is genetically determined by variation linked to the X-chromosome opsin gene locus, the present study identified nucleotide differences in DNA segments containing regulatory regions of the L and M opsin genes that are associated with significant differences in the relative number of L versus M cones. Specific haplotypes (combinations of genetic differences) were identified that correlated with high versus low L:M cone ratio. These findings are consistent with the biological principle that DNA sequence variations affect binding affinities for protein components of complexes that influence the relative probability that an L versus M opsin gene will be silenced during development, and in turn, produce variation in the proportion of L to M cones.

Adaptive optics retinal imaging reveals S-cone dystrophy in tritan color-vision deficiency.

Tritan color-vision deficiency is an autosomal dominant disorder associated with mutations in the short-wavelength-sensitive- (S-) cone-pigment gene. An unexplained feature of the disorder is that individuals with the same mutation manifest different degrees of deficiency. To date, it has not been possible to examine whether any loss of S-cone function is accompanied by physical disruption in the cone mosaic. Two related tritan subjects with the same novel mutation in their S-cone-opsin gene, but different degrees of deficiency, were examined. Adaptive optics was used to obtain high-resolution retinal images, which revealed distinctly different S-cone mosaics consistent with their discrepant phenotypes. In addition, a significant disruption in the regularity of the overall cone mosaic was observed in the subject completely lacking S-cone function. These results taken together with other recent findings from molecular genetics indicate that, with rare exceptions, tritan deficiency is progressive in nature.

A novel mutation in the short-wavelength-sensitive cone pigment gene associated with a tritan color vision defect.

Inherited tritan color vision deficiency is caused by defects in the function of the short-wavelength-sensitive (S) cones. This heterozygous group of disorders has an autosomal dominant pattern of inheritance. Amino acid variations of the S cone opsin are rare and all that have been identified thus far are associated with inherited tritan color vision defects. Here we report the identification of a 30-year-old male who made errors on standard color vision tests consistent with the presence of a mild tritan color vision deficiency. We tested the hypothesis that his color vision impairment was due to a mutation in the S cone photopigment gene. He was found to be heterozygous for a mutation that caused the amino acid proline to be substituted in place of a highly conserved leucine at amino acid position 56 in the S cone opsin. This mutation was absent in 564 S cone photopigment genes from 282 subjects who did not make tritan errors. Thus, we conclude that this mutation disrupts the normal function of S cones.

Induction effects for heterochromatic brightness matching, heterochromatic flicker photometry, and minimally distinct border: implications for the neural mechanisms underlying induction.

Brightness induction refers to the finding that the apparent brightness of a stimulus changes when surrounded by a black versus a white stimulus. In the current study, we investigated the effects of black/white surrounding stimuli on settings made between red and green stimuli on three different tasks: heterochromatic brightness matching (HBM), heterochromatic flicker photometry (HFP), and minimally distinct border (MDB). For HBM, subjects varied the relative luminance between the red and green stimuli so that the brightness of the two colors appeared equal. For the two other tasks, matches were made based on minimizing red/green flicker (HFP) or the saliency of a red/green border (MDB). For all three tasks, the presence of black/white surrounding stimuli significantly altered red/green settings, demonstrating the existence of induction effects. These results are discussed in terms of which underlying color pathways (L+ M versus L-M) may contribute to induction effects for the different tasks.

Independence of mechanisms tuned along cardinal and non-cardinal axes of color space: evidence from factor analysis.

Many previous studies employing paradigms such as adaptation, masking and summation-near-threshold have demonstrated the existence of separate mechanisms underlying the detection of the three cardinal axes of color space: L+M, L-M and S-(L+M). In addition, some studies have demonstrated the existence of higher-order mechanisms tuned to non-cardinal axes (which are made up of combinations of the cardinal axes). In order to address the issue of separate and independent color mechanisms further, here we applied factor analysis to contrast threshold data obtained from 41 subjects for nine different axes in color space (the three cardinal axes and the six non-cardinal axes midway between). In line with previous studies, the results of a three-factor analysis performed on contrast thresholds for the cardinal axes revealed independence across the three. However, in some of our factor analyses (for example, when a two-factor analysis was performed on the cardinal axes), intercorrelation was observed between L-M and S-(L+M) stimuli. With regard to higher-order mechanisms, our factor analyses revealed mechanisms selective for non-cardinal axes within the (L-M)/(L+M) and (S-(L+M))/(L+M) color planes, but not the (L-M)/(S-(L+M)) color plane. To ensure that the intercorrelation observed between L-M and S-(L+M) cardinal axes was not due to the particular stimulus parameters or testing measures employed, in three of our subjects we performed a "summation-near-threshold" experiment using experimental conditions nearly identical to those in the factor analysis experiments. In accordance with previous findings [Vision Research 39 (1999) 733], L-M and S-(L+M) stimuli were found to be separable in this analysis. This seeming discrepancy between the results of our factor analysis and those obtained from paradigms such as summation-near-threshold can be resolved by proposing that the mechanisms underlying detection of L-M and S-(L+M) stimuli are separable (as defined by the ability to isolate activity within each mechanism using select stimuli), yet nonetheless intercorrelated. Such intercorrelation could arise if these two mechanisms are limited by the same source of variability and/or subject to the same gain control.

Individual differences in chromatic (red/green) contrast sensitivity are constrained by the relative number of L- versus M-cones in the eye.

Many previous studies have shown that the relative number of long-wavelength-selective (L) versus medium-wavelength-selective (M) cones in the eye influences spectral sensitivity revealed perceptually. Here, we hypothesize that the L:M cone ratio should also influence red/green chromatic contrast sensitivity. To test this, in each subject we derived an estimate of L:M ratio based on her red/green equiluminance settings (obtained with heterochromatic flicker photometry), and measured both red/green chromatic and luminance contrast sensitivity at different spatial and temporal frequencies. Factor analysis was applied to the data in order to reveal covariance between conditions. As expected, chromatic and luminance contrast sensitivity were found to be independent of one another, and no relationship was observed between L:M ratio and luminance contrast sensitivity. However, a significant relationship was observed between L:M ratio and chromatic contrast sensitivity, wherein subjects possessing the most symmetrical L:M cone ratios (i.e., near 1:1) appear to possess the relatively greatest chromatic contrast sensitivity. This relationship can be accounted for by a simple model based on the notion of random L- and M-cone inputs to the center and surround receptive fields of chromatic (L-M) mechanisms.

Surfactant replacement for ventilator-associated pneumonia: a preliminary report.

BACKGROUND: Surfactant abnormalities have been described in bacterial pneumonia. OBJECTIVE: To determine the safety and effect of exogenous surfactant replacement in patients with ventilator-associated pneumonia (VAP). METHODS: Patients with VAP were randomized in a double-blind study to receive either an artificial surfactant (Exosurf) consisting mostly of disaturated phospholipids (DSPL) or saline via a continuous nebulizer system for 5 days. Patients underwent bronchoscopy and bronchoalveolar lavage (BAL) prior to and after 4 days of therapy. RESULTS: Twenty-two patients were randomized, with 8 receiving Exosurf. There was no detected difference in outcome between the saline- and Exosurf-treated patients in terms of days on ventilator, 30-day or hospital mortality. At the follow-up lavage, the patients treated with Exosurf had a significant rise in the level of DSPL (p < 0.05), while the saline group did not, suggesting delivery of drug. Also at the follow-up lavage, the percentage of neutrophils in the BAL fell in the Exosurf patients (p < 0.01), but not in the saline group. CONCLUSION: Exogenous surfactant replacement given to patients with VAP increased the amount of DSPL retrieved by BAL. This treatment was associated with a fall in the neutrophil response to pneumonia.