Effect of luminance contrast on the motion aftereffect

The effects of luminance contrast and spatial frequency on the motion aftereffect were investigated. The point of subjective equality for velocity was measured as an index of the motion aftereffect. The largest effect was observed when a low contrast grating (5%) was presented as a test stimulus after adaptation to a high contrast grating (100%) in the low spatial frequency condition (0.8 cycle deg.-1). On the whole, the effect increased with increasing adapting contrast and with decreasing test contrast or spatial frequency. Small effects were observed at high test contrasts. These results were inconsistent with those of Keck, Palella, and Pantle in 1976. Analysis showed that there was no saturation on velocity of the motion aftereffect above 5% of the contrast although Keck, et al. (1976) found that the incremental increases of the effect above 3% adapting contrast were small.     

Effects of age and brightness contrast on perception of the Wundt-Hering illusion

Susceptibility to the Wundt-Hering illusion was studied as a function of age and contrast. Preschoolers, third-graders and college students were shown light-grey, medium-grey, and black Wundt-Hering figures on white ground. Pre-schoolers were most susceptible to the illusion, differing from third graders in the medium and high contrast conditions and from college students in all contrast conditions. Low contrast figures resulted in significantly less distortion than did high contrast figures for the preschoolers. The significant interaction of age and contrast effects highlights the importance of a developmental approach to the study of illusions.     

The development of contrast constancy

The mature visual system possesses mechanisms that enable invariant perception of the contrast of an object and its features as the object undergoes changes in distance. This phenomenon, which has been called contrast constancy, obtains at suprathreshold contrasts only. Some models of contrast constancy assume the presence of narrowband spatial-frequency channels. An implication of M.S. Banks, B.R. Stephens, and E.E. Hartmann (1985, Journal of Experimental Child Psychology, 40, 501-527) is that contrast constancy should not be observed at 6 weeks but may be observed at 12 weeks. We examined this implication by investigating the development of contrast constancy in 6- and 12-week-old infants. Two sine wave gratings, differing in spatial frequency by a factor of 3, were presented side-by-side. The contrast of one grating was varied in order to estimate the contrast at which preference for the two gratings was equal. The equal preference points for 6-week-olds were predictable from their contrast thresholds. The 12-week-olds' equal preference points for low-contrast stimuli were predictable from their contrast thresholds, but those for intermediate and high-contrast stimuli were not. Thus, if one accepts the assumption that equal preference in infants is analogous to apparent contrast matches in adults, these data imply that contrast constancy is observed at 12 weeks but not 6 weeks. The perceptual consequences of this developmental transition are discussed.     

Extraction of linguistically relevant pragmatic contrast through language learning

This study explores whether pragmatic contrast that is not expressed as relevant in the subjects' native language is extracted through language learning. Miniature artificial languages were used. In Experiment 1, a contrast was created such that four persons appeared together in each situation, with three persons performing the same activities and the fourth one performing a different target activity. Under this presentation condition pragmatic contrast was shown to be rather easily extracted. In Experiments 2 and 3, a single person appeared in each situation and contrast was created serially by changing the position in which the person performing the target activity was placed. Under these presentation conditions sufficient evidence for the extraction of pragmatic contrast was not found. Experiment 2 also examined the effect of different experience of instances on the extraction of pragmatic contrast. Results showed that although different experience did not produce a differential effect as expected, a definite conclusion was not drawn for a low level of performance. It was formulated that the two presentation conditions differed in the degree of transparency for a mapping relation between the linguistic structure and the pragmatic contrast. Implications of the findings were suggested in relation to a natural learning situation.Deep gratitude is due to Professor D. D. Steinberg for his reading of an earlier version of this paper.     

The role of albedo and contrast in a test of selective attention

The operation of a selective process was demonstrated under conditions that eliminated exploratory behavior, receptor adjustments, and that could not be construed as abstraction. Ss were given a choice reaction-time test to tachistoscopically exposed stimuli. There were three conditions of brightness and contrast. Four targets equally spaced in brightness units were presented either on a black, a medium gray, or a white background. If a selective process was found to operate, it was hoped to separate the effects of albedo and contrast as factors determining priority in selection. The results confirmed that Ss chose the stimuli of highest contrast, but in the event that contrast was equivalent for two stimuli, the target of highest albedo was chosen significantly more often.     

An assessment of decision-making as a possible factor in the age-related loss of contrast sensitivity

The possibility that changes in decision-making may contribute to the age-related decline in contrast sensitivity has been investigated in nineteen young subjects (ages 21-38 years) and twenty-seven old subjects (ages 55-92 years). A signal detection paradigm was employed in which the detection of stationary sinusoidal grating patterns was measured at 3 and 15 cycles deg-1 for a range of contrasts which were psychophysically equivalent for each subject. A decline in contrast sensitivity with age at the spatial frequencies studied was confirmed for contrast thresholds obtained both by the ascending method and from the 50% hit rate for detection of the grating pattern. The criterion adopted for decision-making, expressed as both beta and percentage bias, did not change significantly between young and old subjects at 15 cycles deg-1. At 3 cycles deg-1, criterion beta did not change significantly at X0.8, X1.0, or X1.2 contrast threshold, but at contrast giving 50% hit rate there was a significant increase with age. The percentage bias increased significantly at contrast threshold but not at 50% hit rate. It is inferred from the results that the loss of contrast sensitivity was not accountable in terms of the adoption of a more conservative criterion by older subjects. Hence visual loss in ageing is attributed to changes within the visual pathway rather than within higher decision-making centres.     

Local contrast in multiple schedules: the effect of stimulus discriminability.

A three-ply multiple schedule assessed responding in a standard component as a function of the just-preceding schedule. The principal experimental condition was the difference among the wavelengths signaling the schedule components. Only the pigeons working in a narrow wavelength range showed persistent positive local contrast; that is, response rate during the standard component was higher when that component followed extinction than when it followed itself. Birds in both narrow- and medium-range groups showed persistent negative local contrast; that is, rate was lower following a relatively rich component. The dissipation of positive contrast appeared to be most clearly related to the establishment of differential responding. Negative contrast was inversely related to wavelength differences. Theories pertaining to contrast must account for the role of discrimination in both positive and negative types.     

Contrast and spatial frequency components in visual preferences of newborns

A preferential-looking procedure was used to investigate newborns' responses to square-wave gratings varying in spatial frequency and contrast. A preliminary study confirmed that the gratings used in the experiment were suprathreshold. In the experiment newborns' preference for a grating of 0.1 cycle deg-1 within the peak contrast sensitivity range was examined. Reduction in the contrast of this grating led to a transfer of the preference to a high-contrast grating of the same space-averaged luminance with a spatial frequency outside this range (0.42 cycle deg-1). The findings are discussed with reference to the role of the contrast sensitivity function in pattern preferences of newborns: it is suggested that contrast and spatial frequency interact in determining pattern preferences.     

Discriminative stimulus location as a determinant of positive and negative behavioral contrast in the pigeon

Four pigeons were exposed to a series of two-component multiple schedules of reinforcement that ordinarily yield positive and negative behavioral contrast. The stimuli that signalled the component schedules were sometimes located on the response key and sometimes off. Positive behavioral contrast was observed only when the stimuli were on the key. Negative contrast was observed independent of stimulus location. These data suggest that positive and negative contrast may be causally unrelated, and support an account of contrast in terms of the summation of key pecks that are separately controlled by response-reinforcer and stimulus-reinforcer dependencies.     

Contrast gain control in psychophysical contrast discrimination

Contrast masking may in part reflect the operation of contrast gain control mechanisms in the visual system. Four experiments were conducted in order to examine contrast discrimination under conditions in which the base contrast was interrupted with various maskers. Interrupting the base contrast grating at 8 Hz—with a uniform field, with a randomly phase-shifted version of the same grating, or with a higher contrast version of the same grating—interfered with contrast discrimination. These effects occurred only when the background contrast was above its own threshold. These results may be explained by assuming that the networks responsible for contrast gain control operate by temporally averaging contrast over a period greater than 62.5 msec. When this time-averaged contrast is different from the base contrast, contrast discrimination suffers.     

环境条件和兴趣对大学生妥协决策的影响

研究旨在考察个体在选择职业时是否会为了更好的环境条件(组织、城市)而降低对兴趣的要求。对63名大学生被试开展了两个实验,采用在环境条件和兴趣水平上有不同程度差异的职位配对来模拟两难决策。结果发现:(1)对不同组织声望和兴趣水平的职位的选择无性别差异;(2)组织声望差距、组织声望差距与兴趣差距的交互作用能显著预测职位的选择;(3)对不同城市级别和兴趣水平的职位的选择有性别差异,男生比女生更少放弃兴趣;(4)兴趣差距、城市级别差距与兴趣差距的交互作用能预测男生的选择,只有兴趣差距能预测女生的选择。结论:个体会为了更好的环境而或多或少在兴趣方面妥协。     

Distortions of temporal integration and perceived order caused by the interplay between stimulus contrast and duration

Stimulus contrast and duration effects on visual temporal integration and order judgment were examined in a unified paradigm. Stimulus onset asynchrony was governed by the duration of the first stimulus in Experiment 1, and by the interstimulus interval in Experiment 2. In Experiment 1, integration and order uncertainty increased when a low contrast stimulus followed a high contrast stimulus, but only when the second stimulus was 20 or 30 ms. At 10 ms duration of the second stimulus, integration and uncertainty decreased. Temporal order judgments at all durations of the second stimulus were better for a low contrast stimulus following a high contrast one. By contrast, in Experiment 2, a low contrast stimulus following a high contrast stimulus consistently produced higher integration rates, order uncertainty, and lower order accuracy. Contrast and duration thus interacted, breaking correspondence between integration and order perception. The results are interpreted in a tentative conceptual framework.     

The effect of spatial frequency and contrast on visual persistence

The visual persistence of sinusoidal gratings of varying spatial frequency and contrast was measured. It was found that the persistence of low-contrast gratings was longer than that of high-contrast stimuli for all spatial frequencies investigated. At higher contrast levels of 1 and 4 cycles deg-1 gratings, a tendency for persistence to be independent of contrast was observed. For 12 cycles deg-1 gratings, however, persistence continued to decrease with increasing contrast. These results are compared with recently published data on other temporal responses, and are discussed in terms of the different properties of sustained and transient channels.     

The effect of contrast randomisation on the discrimination of changes in the slopes of the amplitude spectra of natural scenes

It has been suggested (Tadmor and Tolhurst, 1994 Vision Research 34 541-554) that the psychophysical task of discriminating changes in the slope of the amplitude spectrum of a complex image may be similar to detecting differences in the degree of blur. It has also been suggested that human observers may perform this discrimination by detecting changes in the effective contrast within single narrow spatial-frequency bands, rather than by detecting changes in the slope per se which would involve the use of contrast information across many different frequency bands. To distinguish between these two possibilities, we have developed an experiment where observers were asked to discriminate changes in the spectral slope while different amounts of random contrast variation were introduced, with the purpose of disrupting their performance. This disruptive effect was designed to be particularly manifest if the observer really was performing a single-frequency-band contrast discrimination but to be unnoticeable if the observer was discriminating the change of slope per se. Our results imply that the observers do not usually detect changes in contrast in just one narrow spatial-frequency band when they discriminate changes in the slope of the amplitude spectrum. Rather, they must compare contrast between bands or, at least, they use contrast information from more than one band. However, for edge-enhanced (whitened) pictures, there is some evidence to suggest that observers rely on contrast changes in only a limited low-spatial-frequency band.     

Adaptation of suprathreshold contrast and luminance stimuli

The temporal and spatial properties of the difference in perceived contrast and brightness of two suprathreshold stimuli presented successively in different retinal locations were determined. Stimulus onset asynchrony (SOA) was varied and the perceived contrast or brightness of the first stimulus (S1) was measured as a function of SOA by matching the contrast or luminance of the second stimulus (S2) to that of S1. The two stimuli overlapped in time for 200 ms to allow the comparison to be made. The adjusted values for S2 could well be fitted with an exponential decay function of SOA. For luminance increments and decrements the time constant for this function was 253 ms; for checkerboards with checks of size 16 min square the time constant was 164 ms. The difference in perceived contrast was dependent on initial contrast in a nonlinear fashion. It increased with increasing check size and was independent of the mean luminance and spatial proximity of the two stimuli. The phenomenon was observed with different pattern types and with dichoptic presentation, but could only be seen when direct comparison of the two stimuli was possible.     

Interactions between simultaneous contrast and adaptation to gradual change of luminance

Following adaptation to a field of light which was modulated by a rising ramp so that it repetitively grows gradually brighter, a steady test field of light appears to be gradually growing dimmer. In this study, if a small grey spot of constant luminance was centered in the brightening field, it appeared to be growing gradually dimmer by simultaneous contrast. This apparent dimming led to a brightening aftereffect in the spot. It was shown that this spot aftereffect had two independent components: the apparent dimming of the adapting spot produced its own aftereffect (contrast produced an aftereffect) and also the dimming aftereffect in the surround field spatially induced an aftereffect into the spot during the test period (aftereffect produced simultaneous contrast). Thus simultaneous contrast can both precede and follow successive contrast in the visual system.     

Human taste contrast and self-reported measures of anxiety.

Successive negative taste contrast in humans was demonstrated with a common taste stimulus, i.e., cherry-flavored Kool-Aid. A total of 31 male and female college-aged participants rated a 7% sucrose solution which was cherry-flavored as less sweet when it was preceded by a 28% rather than a 7% sucrose solution which was cherry-flavored. Because drugs such as the benzodiazepines affect taste contrast in rats and act as anxiolytics in humans, the present experiment also examined whether several self-reported measures of anxiety were related to taste contrast in humans. Neither scores on Taylor's Manifest Anxiety Survey nor those on the State-Trait Anxiety Inventory were related to "sweetness" ratings or contrast effects.     

Behavioral contrast for key pecking as a function of component duration when only one component varies

Pigeons pecked keys for food reinforcers delivered by multiple variable-interval 2-min variable-interval 2-min schedules. Positive behavioral contrast was created by changing one component to extinction; negative contrast was achieved by changing one component to a variable-interval 15-s schedule. The duration of each component was varied independently of the other from 5 to 960 s. The size of positive contrast was greatest when the extinction component was 30 or 60 s long. It did not change significantly with changes in the duration of the variable-interval 2-min component. The absolute size of negative contrast decreased with increases in the duration of the variable-interval 2-min component. It did not change significantly with changes in the duration of the variable-interval 15-s component. These results show that the size of contrast is determined primarily by the duration of the component that provides the less favorable conditions of reinforcement. These results are not predicted by current theories.     

Behavior of Maudsley reactive and nonreactive rats (Rattus norvegicus) in three consummatory contrast paradigms

Maudsley reactive (MR/Har) and nonreactive (MNRA/Har) rats (Rattus norvegicus) were tested in successive, simultaneous, and anticipatory contrast procedures. The MR/Har rats showed smaller successive negative contrast effects than the MNRA/Har rats when shifted from 32% to 4% sucrose, and the degree of contrast was smaller in animals of both strains than that typically obtained with unselected Sprague-Dawley derived rats. Chlordiazepoxide (4 and 8 mg/kg), which typically reduces contrast, did not influence degree of contrast in rats of either strain. Animals of both strains showed positive and negative contrast in the simultaneous contrast procedure, but degree of contrast in both cases was smaller in rats of the MR/Har strain. Animals of both strains also showed anticipatory contrast when a 0.15% saccharin solution preceded 32% sucrose in once-per-day pairings. In terms of latency to initiate licking, the MNRA/Har rats showed a contrast effect, but the MR/Har rats showed a "reinforcement" effect--shorter latency when saccharin preceded sucrose than when saccharin preceded saccharin. Open-field tests showed typical strain differences: The MNRA/Har rats ambulated more, reared more, defecated less, and showed less thigmotaxis than the MR/Har rats.     

Some determinants of behavioral contrast in pigeons and rats

In Expt. 1, pigeons trained on a multiple variable interval, extinction schedule, showed a positive contrast effect by comparison with control groups trained with S+ only, provided that the interval between stimulus presentations was short (10 sec), but not when it was long (60 sec). Positive contrast also occurred more readily with an easier discrimination, and its appearance was highly correlated with the temporary appearance of transient contrast effects. Although a longer interval between trials produced an overall increase in rate of responding in subjects trained only with S+, it was suggested that this at best represented a different type of contrast effect. In Expt. 2, rats showed positive contrast to S+ when S− was correlated with a lower frequency of reinforcement, but not when it was correlated with a reduced magnitude of reinforcement. The results were discussed in terms of frustration theory.