Poster Session II: Luminance and chromaticity discrimination sensitivities following a sudden decrease in background luminance
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When we enter a dark place like a tunnel from a bright exterior, our visual sensitivities take some time to adapt to the lower light level. However, there have been few reports about how quickly our sensitivities of luminance and chromaticity discrimination recover in this situation. This study aimed to quantify the time course of discrimination sensitivity for luminance and chromaticity directions after an abrupt decrease in background luminance. In each trial, the background luminance dropped from 100 cd/m² to 1 cd/m². Then, one target and three reference stimuli with different colors were presented under four stimulus onset asynchrony (SOA) conditions. The observer was asked to discriminate the target stimulus from the reference stimuli. The results showed that discrimination sensitivity was lowest right after the background luminance change and gradually improved with SOAs. However, sensitivity recovery differed across color directions, with the most improvement in luminance, followed by S, and negligible change in L-M. There was a statistically significant difference between +S and ±(L-M) sensitivities, indicating that the sensitivity recovery after the sudden background luminance change differed between chromaticity directions. Based on the comparison with previous studies, we speculate that both adaptation and masking may contribute to the temporal change of discrimination sensitivities.Keywords:
Chromaticity
Stimulus (psychology)
Stimulus onset asynchrony
Backward masking
In order to judge whether a surface that one is looking at is white or grey, one needs to consider the intensity of the illumination. We here show that people do not simply use the maximal luminance in the light from the scene as a measure for the intensity of the illumination but also consider how luminance and chromaticity are associated. We suggest that they take into account that there are physical limitations to the luminance that reflecting surfaces can achieve at high chromatic saturation. These limitations arise because chromaticity is the result of surfaces selectively reflecting light of different wavelengths, so that the luminance of the illumination must be higher than that of the brightest patch in the scene if that patch is not white.
Chromaticity
Intensity
Spectral color
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Age differences in central perceptual processing were investigated using young (mean age 19.5 years) and old (mean age 64.2 years) subjects in a backward masking paradigm known to produce central interference. Subjects were presented with symmetrical, straight-lined letters as target stimuli (TS). The masking stimulus (MS) was a pattern of line segments of the same width as the strokes of the letters spaced evenly over the part of the visual field occupied by the letters. The TS was presented to the right eye and followed by the MS to the left eye. A robust masking effect was found for both young and old across conditions in which TS energy was much greater than MS energy. The asynchrony between TS and MS onset (SOA) was found to be the variable describing escape from masking for both age groups. However, the older group required 24% longer SOAs than the young to escape masking, suggesting a slowing with age in central perceptual processing.
Backward masking
Stimulus onset asynchrony
Stimulus (psychology)
Visual masking
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In general, when two or more stimuli are simultaneously presented to the eye, the phenomenon referred to as "contrast" results. This contrast will be produced by differences between the stimuli, in either luminance or chromaticity, or both.Making use of the fact that veiling luminance, commonly called "glare," destroys contrast, the authors propose the use of veiling luminance as a means for specifying the equivalence between chromaticity differences and luminance differences. The results of measurements on a large number of samples are presented, together with a practical application of the proposed method to the problem of determining how much chromaticity differences contribute to the judgment of graininess in photographic materials.
Chromaticity
Contrast ratio
GLARE
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Visual search times were measured as a function of chromaticity and luminance differences between a target and distractor stimuli. Results showed that mean search time increased linearly with the number of distractors if the luminance difference between target and distractors was small but was roughly constant if the luminance difference was large. Similar results were previously found for chromaticity differences. With the number of distractor stimuli held constant, the mean search time decreased with increases in the difference between target and distractors, up to some critical difference. Further increases in target-distractor difference had little effect. Results were similar for targets defined by luminance and chromaticity. There was some advantage to combining luminance differences with chromaticity differences when the target was dimmer than the distractors. Generally there was no advantage for combining a chromaticity difference with a luminance difference when the target was brighter than the distractors.
Chromaticity
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Four experiments are reported investigating recognition of emotional expressions in very briefly presented facial stimulus. The faces were backwardly masked by neutral facial displays and recognition of facial expressions was analyzed as a function of the manipulation of different parameters in the masking procedure. The main conclusion was that stimulus onset asynchrony between target and mask proved to be the principal factor influencing recognition of the masked expressions. In general, confident recognitions of facial expressions required about 100–150 msec, with shorter time for happy than for angry expressions. The manipulation of the duration of both the target and the mask, by itself, had only minimal effects.
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Stimulus onset asynchrony
Stimulus (psychology)
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Backward masking
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Backward masking
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ABSTRACT In backward masking, psychophysical performance varies as a function of the interval between target and mask (stimulus onset asynchrony—SOA). Early studies of averaged evoked responses (AERs) and backward masking suggested a close, monotonic relationship, i.e., increasing psychophysical performance accompanied by increasingly larger AERs as a function of SOA. We asked what would happen to AERs if the perceptual task were designed to produce a U‐shaped performance function, i.e., one in which performance initially decreased and then increased as a function of SOA? In two experiments U‐shaped psychophysical performance was accompanied by monotonic AER functions. In a third experiment, comparing backward and forward masking at comparable SOAs, disparate psychophysical performances were obtained from the same subjects accompanied by similar AERs. Target AERs do not necessarily correlate with a subject's behavioral performance.
Stimulus onset asynchrony
Backward masking
Stimulus (psychology)
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Spatial and figural characteristics of backward masking were studied, with two collinear arcs presented end-to-end and serving as target and mask, respectively. Stimulus onset asynchrony was 50 ms while interstimulus interval was 0 ms. Mask exposure duration required for masking was determined as a function of target length with mask length as a parameter. The exposure duration of the mask required for complete masking varied directly with target length, but inversely with mask length. The fact that masking strength increased with mask duration while all other parameters were kept constant suggests that masking depended on stimulus termination asynchrony. Maximal masking occurred for target arcs as long as 5.0 deg of visual angle, exceeding previously reported distances. Misaligned or differently shaped stimuli produced less masking, suggesting that figural factors play a role in long-range backward masking.
Backward masking
Stimulus onset asynchrony
Stimulus (psychology)
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