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PubMed2000

Color constancy in goldfish: the limits.

Color constancy was investigated in behavioral training experiments on colors ranging from blue to yellow, located in the color space close to Planck's locus representing the main changes in natural skylight. Two individual goldfish were trained to peck at a test field of medium hue out of a series of 13-15 yellowish and bluish test fields presented simultaneously on a black background. During training the tank in which the fish were swimming freely was illuminated with white light. Correct choices were rewarded with food. During the tests differently saturated yellow or blue illumination was used. The degree of color constancy was inferred from the choice behavior under these illuminations. Perfect color constancy was found up to a certain degree of saturation of the colored light. Beyond this level test fields other than the training test field were chosen, indicating imperfect color constancy. Color constancy was quantified by applying color metrics on the basis of the goldfish cone sensitivity functions.

Animals↗

PubMed2005

Evaluation of polymerization-dependent changes in color and translucency of resin composites using two formulae.

The aim of this study was to evaluate polymerization-dependent changes in the color and translucency parameter (TP) of resin composites and to compare results obtained using two color-difference metric formulae, CIELAB and CIEDE 2000. Twenty-eight shades of commercial resin composites were analyzed. Specimens (n = 5) were made as discs, 11 mm in diameter and 2-mm thick, using cylindrical molds. Data were collected before and after composite polymerization, using a spectrophotometer. In regard to in vitro color changes of composites (DeltaE*) a DeltaE76 of 3.7 or greater was considered to be an unacceptable color change. Data were analyzed by analysis of variance, and Fisher's protected least significant difference (PLSD) intervals for comparison of means were calculated at the 0.05 level of significance. Mean polymerization-dependent differences in color were DeltaE00 = 4.48 (2.11) and DeltaE76 = 5.51 (2.68). The DeltaTP00 range was 2.57, while the DeltaTP76 range was 2.89. Mean polymerization-dependent differences in translucency were DeltaTP00 = 0.84 (0.77) and DeltaTP76 = 0.87 (0.76). Analysis of variance showed significant differences among composites, shades, and their interactions (P < 0.0001; power = 1.0). Regression equations and r values for the two color-difference formulae and all evaluated TP values showed very strong correlation. In conclusion, within the limitations of this study, polymerization-dependent changes in color and translucency were highly varied. The majority of shades showed polymerization-dependent differences in color higher than the DeltaE76 = 3.7. The TP generally increased after light polymerization by light activation. The very strong correlation (r > 0.97) between the two color-difference formulae indicates that the limitations of the CIELAB system do not appear to be a problem when evaluating composites; however, recorded differences between DeltaE76 and DeltaE00 values stress the importance of data conversion.

Algorithms↗

PubMed1995

Echo Doppler evaluation of patients with acute mitral regurgitation: superiority of transesophageal echocardiography with color flow imaging.

Acute mitral regurgitation is a medical emergency that requires prompt, accurate diagnosis and urgent therapy. Although the use of echo Doppler imaging has been described in these patients, preliminary observations have suggested that color flow Doppler performed from the standard transthoracic windows may underestimate the severity of mitral insufficiency in this setting. The aim of this study was to compare transesophageal color Doppler quantitation of regurgitation with results obtained from standard transthoracic windows in patients with acute, severe mitral regurgitation. Two-dimensional echocardiography with pulsed, continuous, and color flow Doppler was performed by both transthoracic and transesophageal methods in 16 consecutive patients who were documented to have acute severe mitral insufficiency by catheterization. Transthoracic and transesophageal scans were reviewed by two blinded observers and assessed for the detection of mitral regurgitation by transthoracic pulsed wave (81%), continuous wave (100%), and color flow Doppler (81%) compared with transesophageal color flow imaging (100%; p = NS). Severity of mitral regurgitation was graded as none, mild, moderate, or severe on the basis of existing transthoracic pulsed wave and color flow criteria and compared with transesophageal color flow grading. At first examination patients were critically ill, with elevated pulmonary wedge pressures (mean 27 +/- 7 mm Hg) and V waves (mean 45 +/- 10 mm Hg). Fifteen of the patients underwent emergency surgery, and the overall hospital mortality rate was 12%. Maximal color flow jet areas were significantly greater on transesophageal scanning (mean 10.5 cm2) compared with transthoracic color jets (mean 2.3 cm2).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

PubMed1987

Intraoperative Doppler color flow mapping for assessment of valve repair for mitral regurgitation.

The ability of color Doppler flow mapping to provide intraoperative information about mitral regurgitation (MR) severity and to evaluate adequacy of mitral valve repair was assessed by performing color Doppler echocardiography immediately before and after cardiopulmonary bypass, with the transducer placed directly on the epicardium. In 56 patients, the degree of MR by intraoperative color Doppler correlated well with left ventricular angiography (kappa = 0.80) and with closed-chest preoperative color Doppler (kappa = 0.84) and had good interobserver reproducibility (kappa = 0.88). Good correlation was also seen between closed-chest color Doppler and angiography (kappa = 0.75). After mitral valve repair in 18 patients (15 ischemic MR, 3 cleft valves), color Doppler was used to assess severity of residual MR intraoperatively and postoperatively. Intraoperative color Doppler identified satisfactory repair (MR less than or equal to 2+) in 15 patients and failure (MR greater than or equal to 3+) in 3, whereas conventional surgical assessment of MR by fluid filling of the arrested ventricle failed to provide reliable differentiation. MR severity on subsequent closed-chest color Doppler follow-up did not change significantly compared with intraoperative evaluation after repair. Intraoperative color Doppler provides accurate grading of MR severity, offers instantaneous evaluation of the adequacy of mitral valve repair before chest closure, and appears to predict the degree of postoperative MR seen on subsequent closed-chest follow-up studies.

Blood Flow Velocity↗

PubMed1984

The neon color effect in the Ehrenstein pattern. Dependence on wavelength and illuminance.

The neon color effect can be described as an illusory spread of color surrounding colored lines embedded in certain line gaps. The effect is seen in the Ehrenstein pattern if colored crosses are added to the central gaps so as to connect the inner tips of the pattern. Experiments were conducted to explore the dependence of this neon color effect on the wavelength and retinal illuminance of the inducing lines. The following results were obtained: neon color effects are strong when the wavelength of the crosses is in the short- (less than 480 nm) or long-wave part of the spectrum (greater than 620 nm) and the wavelength of the Ehrenstein pattern is in the middle-wave part (500-580 nm). Effects are weak or absent when the crosses and the pattern have similar wavelengths. The neon color effect is just detectable when the ratio between the retinal illuminances of the Ehrenstein pattern and the crosses ranges from 0.1 to 0.8. The neon color effect is maximal at illuminance ratios ranging from 0.8 to 8. The strength of the neon color effect is independent of the illuminance level of the crosses if the illuminance ratio to the Ehrenstein pattern is maintained.

Color Perception↗

PubMed1992

The Bezold-Brücke effect in the color vision system of the honeybee.

Evidence is presented that intensity dependent color shifts (Bezold-Brücke effect) occur in the color vision system of the honeybee. The evidence comes from a fit between the choices of monochromatic lights in training experiments (Menzel, R., 1981; Journal of Comparative Physiology A, 141, 389-393) and the choice percentages derived now from recently presented quantitative predictions from the color opponent coding (COC) model for the bee (Backhaus, W., 1991; Vision Research, 31, 1381-1397) for the Bezold-Brücke effect. The only open parameter in the simulations of the training experiments is an experiment type dependent factor describing the weighting of color differences (judgement values) in the choice behavior. The results show (1) that the Bezold-Brücke effect exists in the bee. The results (2) confirm the color opponent coding (COC) model which was developed to describe the physiological components of the color vision system in the bee, (3) the general psychophysical assumptions about the structure of the color space, (4) the color difference formula, and (5) the general psychophysical assumptions about the (triadic) structure of judgements as tested in color similarity experiments.

Animals↗

PubMed1993

Color enhances Mach bands detection threshold and perceived brightness.

We have previously argued that unless color and luminance are shown to be processed independently, using isoluminant stimuli may not reveal the full contribution of color to visual functioning. Here we study the interaction of color and luminance in a task, Mach bands detection and perceived brightness, where color by itself is not effective at all. Subjects viewed luminance or color/luminance ramps and had to determine in either case the luminance contrast necessary for detecting Mach bands and, in another experiment, to compare the brightness of the bands in the luminance and in the combined displays. Isoluminant color displays did not generate any Mach bands, but the addition of color to the luminance display lowered Mach bands detection thresholds and enhanced their perceived brightness. It is thus concluded that the failure to perceive Mach bands in an isoluminant display is not indicative of the lack of color contribution to spatial vision but rather indicates that the strong effect that color has on contrast enhancement mechanisms can be revealed if color and luminance are allowed to interact.

Color Perception↗

PubMed1989

One-dimensional color order system for dental shade guides.

The purpose of this study was to re-arrange the master Bioform shade guide into a long-range one-dimensional color system based upon color difference. Although most shade guides may show local order when arranged according to hue, long-range order has not been established. However, shade guide arrangement according to a logical color order would be an advantage to the user. The first step in determining the color order was to measure the color of the shade guide teeth. A methodology was developed for measuring the color by use of a reflectance spectrophotometer. The precision of measurement was determined to be equal to CIE L*a*b* delta E of 0.5. Spectra were obtained and converted into CIE L*a*b* and Munsell notation. The measured colors of the Bioform shades ranged from a Munsell hue of 0.9 Y to 3.5 Y; a value of 6.6 to 7.8; and a chroma of 1.9 to 4.1. The teeth were then arranged visually from light to dark. The correlation coefficient between the visual ranking and color difference was 0.95. There was an inverse correlation between visual ranking and Munsell value, with a correlation coefficient of 0.90. Therefore, the sequence according to color difference provided the better agreement with visual perception.

Color↗

PubMed1975

Identification and differentiation between colored pencils.

With pencils of any color, the first step certainly involves visual examination to distinguish between the color tints and to study the quality of the stroke itself. In many instances by this step alone, 2 pencils can be distinguished if they are the product of 2 different manufacturers. In other words, the most useful of all tests is the visual examination. In the case of red pencils, infrared luminescence reveals significant information and should be resorted to in those instances where two questioned strokes are extremely similar. Study under ultraviolet radiation may also help to establish similarities or differences which are not readily discernible by visual examination. However, reflected infrared examination and study with dichroic filters have no particular value when dealing with red pencil although chemical spot testing may be of some assistance. In the case of blue pencils, a number of brands absorbs infrared radiation to a different extent and some give off distinctive infrared luminescence, so that these 2 tests can assist in distinguishing between certain similar colors or tints. Also, study through dichroic filters has value. Thus, the combination of these 3 tests can be of some advantage, but in most instances, particularly with dark blues, examination under ultraviolet radiation is not particularly helpful. Chemical spot testing has some limited advantages but generally only in combination with all other tests. In the case of green pencils, the same pattern of testing may be used as with blues. Many of the greens absorb infrared rays and some have bright infrared luminescence. Ultraviolet radiation can cause certain greens to fluoresce in a distinctive way. Thus, with each color studied, differences can be revealed and similarities established. Colored pencils are a distinct group of writing instruments. Within any color classification, there is a variety of shades or tints. Although it is not psosible to determine the make of pencil used in any particular writing, it is possible under many circumstances to distinguish between the work of different makes and grades of red, blue and green pencils, as well as other colors which have not been covered by this paper. While visual examination will separate the many different makes, other tests are described which will further assist in grouping or separating colored writing strokes. For a number of reasons, and particularly because of manufacturing procedures of different companies, not every make of pencil is distinctive, but there has been found to be a definite variety within each color group, and many makes are distinguishable.

Coloring Agents↗

PubMed1993

Comparison of various agents in contrast enhancement of color Doppler flow images: an in vitro study.

The commercially manufactured contrast agents, Echovist and Albunex, were compared with sonicated conventional agents, indocyanine green, 29% renografin-60, 0.9% normal saline and 25% mannitol in their ability to enhance color Doppler flow signals. In a pneumatically regulated pulsatile flow system, a glycerine, saline (0.9%) and sand (5 microns particle size) solution was imaged using a 2.5 MHz phased-array transducer. Four different flow velocities (0.40, 0.35, 0.30 and 0.25 m/s) as measured by color Doppler guided pulse Doppler were utilized. All color Doppler settings were kept constant throughout the study. Utilizing a power injector, four different volumes (1.0, 1.5, 2.0 and 2.5 mL) of each contrast agent were injected into the flow medium at various transducer angles (20, 30, 40 and 60 degrees) and various distances from the transducer (3.38, 5.5, 6.76 cm). For Echovist and Albunex, several concentrations varying from 2% to 100% were used. Keeping instrument settings constant, color flow areas obtained before and after each contrast injection were planimeterized and the percent increase in the color flow area computed and compared. At full (100%) concentration, 20 degrees transducer angle and a flow velocity of 0.40 m/s, the maximum increase in the color flow area was 568%, 251%, 180%, 110%, 71%, and 38% for Echovist, Albunex, sonicated indocyanine green, renografin, normal saline and mannitol, respectively. However, a significant reduction in the degree of color flow enhancement was observed, with decreases in the concentration of these agents, and increases in the Doppler beam incident angle or distance from the transducer. Increasing the flow velocity of the medium into which contrast was injected did not produce significant changes in the contrast enhancement effect for all agents except Echovist. Increasing the injection volume significantly increased the color flow area for sonicated agents but not for Echovist or Albunex. This preliminary in vitro study shows that the commercially manufactured contrast agents, Echovist and Albunex, are much superior to sonicated conventional contrast agents in the enhancement of color Doppler flow signals. Of the sonicated agents, indocyanine green had the best enhancement capability.

Blood Flow Velocity↗

PubMed2006

Color tissue Doppler myocardial velocities consistently underestimate spectral tissue Doppler velocities: impact on calculation peak transmitral pulsed Doppler velocity/early diastolic tissue Doppler velocity (E/Ea).

BACKGROUND: Color tissue Doppler (TD) measures mean myocardial velocities, whereas spectral TD measures peak velocities. Given that most data on left ventricular (LV) diastolic function used spectral TD, we investigated whether the differences in myocardial velocities between these modalities resulted in discrepancies in calculated E/Ea. METHODS: Patients were imaged using an ultrasound machine. The systolic (Sa), early diastolic (Ea), and late diastolic (Aa) myocardial velocities by color and spectral TD were measured at basal and midsegments of the LV septal, lateral, inferior, and anterior walls in the apical views. The average of basal septal and lateral Ea was combined with the early transmitral diastolic velocity (E) to obtain E/Ea. RESULTS: In all, 31 patients were imaged, with a mean LV ejection fraction of 47.7% +/- 19.9. There were significant correlations between Sa, Ea, and Aa by color and spectral TD at all sites (R = 0.92, P < .001 for Ea at basal lateral wall) and between spectral and color E/Ea (R = 0.85, P < .001). Sa, Ea, and Aa were significantly lower by color TD than by spectral TD (basal septal color Ea = 3.0 +/- 2.0 cm/s vs 5.6 +/- 2.5 cm/s for spectral Ea, P < .001). Consequently, E/Ea by color TD was significantly higher than by spectral TD (22.3 +/- 15.3 vs 13.6 +/- 7.8, P < .001). CONCLUSIONS: Although significant correlations exist, myocardial velocities measured using color TD significantly underestimate velocities by spectral TD. Consequently, E/Ea by color TD significantly overestimates E/Ea using spectral TD, which could lead to errors in assessment of LV diastolic function.

Artifacts↗

PubMed2006

Contrast affects the strength of synesthetic colors.

Grapheme-color synesthesia is an automatic, involuntary experience of seeing colors when viewing numbers, letters or words on a printed page. Previous research has demonstrated that synesthesia is a genuine perceptual phenomenon, but crucially, all of these experiments have used high-contrast letters and numbers. Our synesthete, JC, anecdotally reported that the strength of his synesthetic colors varied depending on whether the graphemes were presented in high or low contrast. To test this, we asked JC to rate the strength of his experiences to letters of different contrasts on three different dates. JC's ratings of the strength of his synesthetic colors consistently declined monotonically with contrast, suggesting that his synesthetic colors were reduced or absent at low contrasts. To more precisely quantify the impact of this, we then tested JC on modified versions of our embedded figures task (Ramachandran and Hubbard, 2001a) and crowding task (Ramachandran and Hubbard, 2001b) by presenting displays with varying contrast between the graphemes and the background. Behavioral data in the contrast variant of our embedded figures task showed that JC performed significantly better than controls at high contrast, replicating our previous findings. However, at low contrast this advantage was eliminated, consistent with his reports of weaker or absent colors. A similar, but weaker pattern of results was found in the modified version of our crowding task. These results suggest that JC's synesthetic colors may be elicited at contrast dependent stages of visual processing. We propose that regions of the fusiform gyrus specialized for letter and number grapheme recognition that have been shown to respond in a contrast dependent manner mediate JC's synesthetic colors. However, whether this is true for all grapheme-color synesthetes or is only true of the group we refer to as lower synesthetes, remains to be seen.

Adult↗

PubMed1986

Visual half-field presentations of incongruent color words: effects of gender and handedness.

Right-handed (dextral) and left-handed (sinistral) males and females (N = 15) were compared for language lateralization in a visual half-field (VHF) incongruent color-words paradigm. The paradigm consists of repeated brief (less than 200 msec) presentations of color-words written in an incongruent color. Presentations are either to the right or to the left of center fixation. The task of the subject is to report the color the word is written in on each trial, ignoring the color-word. Color-bars and congruent color-words were used as control stimuli. Vocal reaction time (VRT) and error frequency were used as dependent measures. The logic behind the paradigm is that incongruent color-words should lead to a greater cognitive conflict when presented in the half-field contralateral to the dominant hemisphere. The results showed significantly longer VRTs in the right half-field for the dextral subjects. Furthermore, significantly more errors were observed in the male dextral group when the incongruent stimuli were presented in the right half-field. There was a similar trend in the data for the sinistral males. No differences between half-fields were observed for the female groups. It is concluded that the present results strengthen previous findings from our laboratory (Hugdahl and Franzon, 1985) that the incongruent color-words paradigm is a useful non-invasive technique for the study of lateralization in the intact brain.

Adolescent↗

PubMed2002

Color removal from cotton textile industry wastewater in an activated sludge system with various additives.

The low biodegradability of many dyes and textile chemicals indicates that biological treatment is not always successful in the treatment of cotton textile wastewater, in terms of color removal. In this study, a specific organic flocculant (Marwichem DEC), powdered activated carbon (PAC), bentonite, activated clay and commercial synthetic inorganic clay (Macrosorb) were directly added into the activated sludge laboratory pilot plant model. Before dosage, the optimum sludge retention time and hydraulic retention time were determined as 30 days and 1.6 days, respectively. The Monod kinetic constants were determined as Y = 0.76 kg MLSS/kg COD, Kd = 0.026 l/day, K(S) = 113.3 mg/L, k = 0.42 l/day and mu(max) = 0.32 kg MLSS/kg COD day. Under these conditions the average COD removal was 94% and color removal was 36%. The addition of these materials did not change COD removal significantly. The most effective materials were found to be DEC and PAC for color removal. While the color removal efficiency for 120 mg/L DEC addition was 78%, it was 65% for 100 mg/L, 77% for 200 mg/L and 86% for 400 mg/L PAC addition. The advantage of DEC compared to PAC was the lower sludge production. Statistical analyses using multiple linear regression indicate that there is no relationship between the effluent color with the influent color and total suspended solids (TSS) for DEC and PAC addition. On the other hand, when only bentonite, activated clay and Macrosorb were added, the effluent color was primarily dependent on the influent color and the TSS concentration had little effect. When the data is examined by using Kruskal-Wallis H and Mann-Whitney U tests and it was found that there was a significant difference between the color data groups.

Adsorption↗

PubMed2004

'Double-blindsight' revealed through the processing of color and luminance contrast defined motion signals.

Background perturbation techniques using both static and dynamic luminance contrast and chromatic contrast noise have been employed to investigate the interaction between luminance and chromatic contrast signals. A number of experiments involving contrast detection thresholds for static stimuli, simple reaction times, and pupil color responses yield evidence for independent processing of luminance and color signals. One exception is the perception of color-defined coherent motion of randomly distributed checks when dynamic, luminance-defined, motion signals can disrupt completely the perception of coherent motion. When the moving stimulus contains color-defined, recognizable features that are spatially distinct from background noise, the perception of coherent motion is restored and becomes completely independent of dynamic luminance contrast noise. Feature-tracking mechanisms must therefore play a major part in the detection of color-defined motion. Other findings reveal the existence of a motion channel that receives exclusively achromatic inputs and a separate channel that extracts and combines luminance contrast and color-defined motion signals. Further studies carried out to investigate the interaction between luminance and chromatic signals show that color-defined, position-change thresholds are mediated by motion detection mechanisms and are, therefore, also disrupted by dynamic luminance contrast noise. In spite of the perceived uncertainty of spatial location, other experiments show that accurate, color-defined position information is preserved and available for use in other tasks. For example, accurate position information can be used to detect the vertical misalignment of color-defined checks, independently of luminance contrast noise, even when position-change thresholds are severely impaired. The analogy with 'blindsight' is obvious and irresistible. 'Blindsight' describes the ability to make accurate use of visual information in the absence of conscious visual perception. The findings that have emerged from this investigation reveal the ability of normal subjects to discard misleading, consciously perceived visual signals. The ability to override perception and to make good use of accurate visual information, in spite of misleading percepts, can best be described as 'Double-blindsight'.

Awareness↗

PubMed2002

Standardized color-coded scales for anterior and posterior elevation maps of scanning slit corneal topography.

PURPOSE: To find the most appropriate color-coded scales for the anterior and posterior elevation maps of scanning slit topography in the screening of abnormal corneas such as keratoconus. DESIGN: Retrospective case-control study. PARTICIPANTS: Eighty eyes of 40 normal subjects and 175 eyes of 95 patients with keratoconus. INTERVENTION: Anterior and posterior corneal elevations were assessed using Orbscan 2. Best-fit sphere maps were drawn with several color-coded scales: 2-, 5-, 10-, and 20-microm height per each color interval. MAIN OUTCOME MEASURES: The maps were judged to be abnormal when more than three colors (discriminant number) were found within the central 3-mm area. For each color-coded scale, sensitivity, specificity, positive predictive value, negative predictive value, and sensitivity + specificity were calculated. After determining the most appropriate color-coded scales for the anterior and posterior elevation maps, validity of the discriminant number was assessed. By varying the discriminant number from two to eight, receiver operator characteristic (ROC) curves were created using the sensitivity and specificity for each threshold number. RESULTS: The highest sensitivity + specificity values and highly balanced predictive values were obtained with the 10- and 20-microm scales for the anterior and posterior elevation maps, respectively. The ROC curve analyses showed that the best discriminant color number is three, indicating that maps with four or more colors within the central 3-mm area are judged abnormal in screening. CONCLUSIONS: The 10- and 20-microm interval color scales are most appropriate for the anterior and posterior elevation maps of the scanning slit topography, respectively.

Adolescent↗

PubMed1998

Temporal variability of vena contracta and jet areas with color Doppler in aortic regurgitation: a chronic animal model study.

OBJECTIVE: The purpose of our study was to determine the temporal variability of regurgitant color Doppler jet areas and the width of the color Doppler imaged vena contracta for evaluating the severity of aortic regurgitation. METHODS: Twenty-nine hemodynamically different states were obtained pharmacologically in 8 sheep 20 weeks after surgery to produce aortic regurgitation. Aortic regurgitation was quantified by peak and mean regurgitant flow rates, regurgitant stroke volumes, and regurgitant fractions determined using pulmonary and aortic electromagnetic flow probes and meters balanced against each other. The regurgitant jet areas and the widths of color Doppler imaged vena contracta were measured at 4 different times during diastole to determine the temporal variability of this parameter. RESULTS: When measured at 4 different temporal points in diastole, a significant change was observed in the size of the color Doppler imaged regurgitant jet (percent of difference: from 31.1% to 904%; 233% +/- 245%). Simple linear regression analysis between each color jet area at 4 different periods in diastole and flow meter-based severity of the aortic regurgitation showed only weak correlation (0.23 < r < 0.49). In contrast, for most conditions only a slight change was observed in the width of the color Doppler imaged vena contracta during the diastolic regurgitant period (percent of difference, vena contracta: from 2.4% to 12.9%, 5.8% +/- 3.2%). In addition, for each period the width of the color Doppler imaged vena contracta at the 4 different time periods in diastole correlated quite strongly with volumetric measures of the severity of aortic regurgitation (0.81 < r < 0.90) and with the instantaneous flow rate for the corresponding period (0.85 < r < 0.87). CONCLUSIONS: Color Doppler imaged vena contracta may provide a simple, practical, and accurate method for quantifying aortic regurgitation, even when using a single frame color Doppler flow mapping image.

Animals↗

PubMed1999

Unconscious letter discrimination is enhanced by association with conscious color perception in visual form agnosia.

Adaptive behavior guided by unconscious visual cues occurs in patients with various kinds of brain damage as well as in normal observers, all of whom can process visual information of which they are fully unaware [1] [2] [3] [4] [5] [6] [7] [8]. Little is known on the possibility that unconscious vision is influenced by visual cues that have access to consciousness [9]. Here we report a 'blind' letter discrimination induced through a semantic interaction with conscious color processing in a patient who is agnosic for visual shapes, but has normal color vision and visual imagery. In seeing the initial letters of color names printed in different colors, it is normally easier to name the print color when it is congruent with the initial letter of the color name than when it is not [10]. The patient could discriminate the initial letters of the words 'red' and 'green' printed in the corresponding colors significantly above chance but without any conscious accompaniment, whereas he performed at chance with the reverse color-letter mapping as well as in standard tests of letter reading. We suggest that the consciously perceived colors activated a representation of the corresponding word names and their component letters, which in turn brought out a partially successful, unconscious processing of visual inputs corresponding to the activated letter representations.

Adult↗