眼跳的双相调节理论的行为证据

为了研究眼跳的双相调节理论是否适用于人类的视觉系统,本研究测量了人类被试对分别呈现在三种眼跳时间段（基线、眼跳抑制和眼跳增强）内的光栅的朝向辨别准确率。研究发现：相对于光栅呈现在基线时间段内,被试对呈现在抑制（或增强）时间段内的光栅的朝向辨别准确率显著地更低（或更高）（实验1）;另外,只有使用低或中等空间频率光栅作为测试刺激时,才有这种双相调节作用（实验2）。这些结果表明：人类的视觉系统在眼跳过程中存在双相调节机制,并且这种双相调节机制具有刺激选择性。     

Variations in apparent spatial frequency with stimulus orientation: L Incidence of the effect in the general population

The human visual system is anisotropic not only for stimulus detection and discrimination but also for stimulus appearance. The apparent length of a stationary stimulus and the apparent velocity of a moving stimulus vary with orientation. These variations are predictable from a model assuming a compression of the horizontal spatial meridian relative to the vertical meridian. In this paper, the apparent spatial frequency of a suprathreshold grating is shown to depend on the grating orientation. Specifically, horizontal gratings appear coarser than vertical gratings of equivalent spatial frequency. Additional data collected from the same group of observers show that horizontal lines appear shorter than vertical lines of the same extent. The presence of the spatial frequency and length illusions, although both predictable from the compression model, were not found to be correlated within observers. Implications of these results for other data in the literature are discussed.     

Tactile learning is task specific but transfers between fingers

Practice-related improvement in visual perception is highly specific for properties of the stimulus used in training. We explored the specificity of such perceptual learning in the human tactile system, using gratings consisting of alternating ridges and grooves. Practice effects on grating discrimination showed limited transfer between grating sets defined by spatial variation in either groove width or ridge width, consistent with partially overlapping neural representations of these two spatial parameters. In contrast, substantial interdigital transfer of practice effects occurred for discrimination of gratings varying in either spatial parameter and also for spatial acuity-dependent discrimination of grating orientation. We conclude that tactile learning, although quite as task specific as in other sensory systems, generalizes with considerable facility across fingers, unlike visual learning, which is highly location specific.     

Binocular interaction of orientation and spatial frequency channels: Evoked potentials and observer sensitivity

The interaction between size and orientation feature processing in the human visual system was investigated. Both observer sensitivity (d’ss) and the visual evoked potential (VEP) to test gratings flashed to one eye were investigated as a function of the nature of a continuously presented suppressing grating viewed either by that same eye or the opposite eye. The test and suppressing gratings were varied both in bar width (9′ss vs. 36′ss) and orientation (vertical vs. horizontal). The continuous grating intra- and interocularly suppressed the monocular VEPs to the flashed grating, the specificity of the suppression depending on the latency at which VEP amplitude was measured. VEP amplitude measured at early latencies (100–125 msec) was suppressed primarily when the flashed and continuous gratings were the same orientation, regardless of size. Starting at about 200 msec, and thereafter, VEP amplitudes were suppressed when the continuous bars were either the same orientationor size as the flashed bars. Late latencies, starting at 220 msec, and thereafter, were suppressed primarily when the bars in the two gratings were the same orientation and size. The reduction in observer sensitivity (d′ss) paralleled the changes found in the late VEP measures. These effects were evident under both the intraocular and interocular suppressing conditions. This pattern of VEP suppression, measured across eight points in the VEP waveform, was interpreted as indicating the existence of a sequence of channels that are specific first to a particular grating orientation, then to either a particular grating spatial frequency or orientation, and finally to the conjunction of a particular orientation and spatial frequency. Both sequential and parallel feature processing appears to take place in the human visual cortex, with grating orientation being encoded earlier than grating size.     

Discriminative performance of the domestic hen in a visual acuity task

The performance of 6 domestic hens on a visual acuity task was studied using a spatial discrete-trial conditional discrimination procedure. Gray stimuli and vertical square-wave gratings, ranging in spatial frequency from 1 to 10 cycles per millimeter, were presented in a descending and ascending series of probes. On each trial, either a grating or gray stimulus was presented. Only one spatial frequency of grating was presented during each session. Between probe sessions, training continued at the coarsest grating value. Stimulus discriminability, measured as values of log d, changed with changes in grating spatial frequency for both probe series. Fitted lines described the linear portion of the psychometric functions. Thresholds estimated from the lines generally ranged from four to six cycles per degree, with slightly greater estimates from data from the descending probe series. There were no systematic changes in response bias as a function of grating spatial frequency.     

Electrophysiological and behavioral indicants of selective attention to multifeature gratings

The mechanisms underlying selective attention to gratings consisting of a particular conjunction of spatial frequency and orientation were investigated by means of both visual evoked potential (VEP) and behavioral measures. The effects of selective attention upon the VEP indicated two general types of selection processes: one which is specific to the features contained in the relevant gratings and is most pronounced approximately 225 msec post-stimulation, and another which is specific to the conjunction of features defining the relevant grating and is most pronounced 250–375 msec following the presentation of the stimulus. The behavioral responses primarily reflected this latter, or grating-specific, attentional process. The results are discussed in terms of the role of sensory feature channels in mediating selective attention to visual stimuli and are related to various information processing models of visual pattern selection.     

Apparent contrast of suprathreshold gratings varies with stimulus orientation

Human contrast sensitivity is known to vary with both stimulus spatial frequency and orientation. Previous research has indicated, however, that the apparent contrast of a sinusoidal grating is independent of spatial frequency at suprathreshold levels. We have found that the apparent contrast of suprathreshold gratings is not independent of its orientation. Observers adjusted the apparent contrasts of vertical and oblique gratings to match a 40% standard. Contrast match deviations were found at a number of spatial frequencies, indicating a lack of contrast constancy with stimulus orientation. The apparent contrast of gratings in different orientations could not be predicted in any simple fashion from either contrast threshold differences or ratios.     

Effects of spatial-frequency specific adaptation and target duration on visual persistence

Two experiments investigated the properties of visual persistence as functions of spatial frequency, stimulus duration, and pattern-specific adaptation. In Experiment 1, increasing the duration of high spatial-frequency gratings from 50 to 500 msec decreased the duration of visual persistence produced by that grating to an asymptotic level. However, low-frequency gratings produced a constant estimate of visual persistence independent of presentation time. Also, spatial-frequency specific adaptation reduced the persistence of the high-frequency gratings to this asymptotic level, but the lower frequency persistence estimates already at this level were unaffected (Experiment 2). These findings are related to possible temporal properties of the sustained and transient visual systems.     

Out of mind, but not out of sight: Intentional control of visual memory

Does visual information enjoy automatic, obligatory entry into memory, or, after such information has been seen, can it still be actively excluded? To characterize the process by which visual information could be excluded from memory, we used Sternberg’s (1966, 1975) recognition paradigm, measuring visual episodic memory for compound grating stimuli. Because recognition declines as additional study items enter memory, episodic recognition performance provides a sensitive index of memory’s contents. Three experiments showed that an item occupying a fixed serial position in a series of study items could be intentionally excluded from memory. In addition, exclusion does not depend on lowlevel information, such as the stimulus’s spatial location, orientation, or spatial frequency, and does not depend on the precise timing of irrelevant information, which suggests that the exclusion process is triggered by some event during a trial. The results, interpreted within the framework of a summed similarity model for visual recognition, suggest that exclusion operates after considerable visual processing of the to-be-excluded item.     

The Relationship Between Visual Illusion and Aesthetic Preference – an Attempt to Unify Experimental Phenomenology and Empirical Aesthetics

Experimental phenomenology has demonstrated that perception is much richer than stimulus. As is seen in color perception, one and the same stimulus provides more than several modes of appearance or perceptual dimensions. Similarly, there are various perceptual dimensions in form perception. Even a simple geometrical figure inducing visual illusion gives not only perceptual impressions of size, shape, slant, depth, and orientation, but also affective or aesthetic impressions. The present study reviews our experimental phenomenological work on visual illusion and experimental aesthetics, and examines how aesthetic preference is influenced by stimulus factors determining visual illusions including anomalous surface and transparency as well as geometrical illusion. Along with line figures producing geometrical illusions, illusory surface figures inducing neon color spreading and transparency effects were used as test patterns. Participants made both of psychophysical judgments and of aesthetic judgments for the same test pattern. Both of geometrical illusions and aesthetic preferences were found to change similarly as a function of stimulus variables such as the number of filling lines and the size ratio of the inner and outer figural components. Also, following specific stimulus variables such as lightness contrast ratio and spatial interval between inducing figural elements (so called ``packmen''), strong effects of color spreading and transparency were accompanied with strong preferences. It seems that the paradigm to investigate aesthetic phenomena along with perceptual dimensions is useful to bridge the gap between experimental phenomenology and experimental aesthetics.     

Comparison at a distance

The visual system is known to contain hard-wired mechanisms that compare the values of a given stimulus attribute at adjacent positions in the visual field; but how are comparisons performed when the stimuli are not adjacent? We ask empirically how well a human observer can compare two stimuli that are separated in the visual field. For the stimulus attributes of spatial frequency, contrast, and orientation, we have measured discrimination thresholds as a function of the spatial separation of the discriminanda. The three attributes were studied in separate experiments, but in all cases the target stimuli were briefly presented Gabor patches. The Gabor patches lay on an imaginary circle, which was centred on the fixation point and had a radius of 5 deg of visual angle. Our psychophysical procedures were designed to ensure that the subject actively compared the two stimuli on each presentation, rather than referring just one stimulus to a stored template or criterion. For the cases of spatial frequency and contrast, there was no systematic effect of spatial separation up to 10 deg. We conclude that the subject's judgment does not depend on discontinuity detectors in the early visual system but on more central codes that represent the two stimuli individually. In the case of orientation discrimination, two naive subjects performed as in the cases of spatial frequency and contrast; but two highly trained subjects showed a systematic increase of threshold with spatial separation, suggesting that they were exploiting a distal mechanism designed to detect the parallelism or non-parallelism of contours.     

Binocular rivalry and surface-boundary processing

Theoretical and empirical studies show that the visual system relies on boundary contours and surface features (e.g. textures) to represent 3-D surfaces. When the surface to be represented has little texture information, or has a periodic texture pattern (grating), the boundary contour information assumes a larger weight in representing the surface. Adopting the premise that the mechanisms of 3-D surface representation also determine binocular rivalry perception, the current paper focuses on whether boundary contours have a similar role in binocular rivalry. In experiment 1, we tested the prediction that the visual system prefers selecting an image/figure defined by boundary contours for rivalry dominance. We designed a binocular rivalry stimulus wherein one half-image has a boundary contour defined by a grating disk on a background with an orthogonal grating orientation. The other half-image consists solely of the (same orientation) grating background without the grating disk, ie no boundary contour. Confirming our prediction, the predominance for the half-image with the grating disk is approximately 90%, despite the fact that the grating disk corresponds to an area with orthogonal grating in the fellow eye. The advantage of the grating disk is dramatically reduced to about 50% predominance when a boundary contour is added to the background-only half-image at the location corresponding to the grating disk. We attribute this reduced advantage to the formation of a corresponding binocular boundary contour. In experiment 2 the grating background was substituted by a random-dot background in a similar stimulus design. We found that the perceptual salience of the corresponding binocular boundary contours extracted by the interocular matching process is an important factor in determining the dynamics of binocular rivalry. Experiment 3 showed that vertical lines with uneven thickness and spacing as the background reduce the contribution of the monocular boundary contour of the grating disk in binocular rivalry, possibly through the formation of binocular boundary contours between the local edges (vertical components) of the vertical lines and the corresponding grating disk.     

Weak stimulus generalization using sinusoidal gratings: A cautionary note in animal psychophysics

Psychophysical techniques involving operant and classical conditioning are used commonly to determine the visual thresholds of nonverbal subjects. Typically, subjects are conditioned to respond to a particular stimulus, and once trained sufficiently, the subject’s sensitivity to this and similar stimuli can be determined by decreasing the stimulus intensity until the animal no longer responds. However, this assumes that the animal’s tendency to respond correlates with its sensory abilities. Stimulus generalization to sinusoidal gratings of different spatial frequencies was examined in goldfish. Subjects were classically conditioned to suppress respiration upon presentation of a sinusoidal grating. Animals’ learning curves to each spatial frequency grating were compared in order to determine whether the animals generalized across stimuli. Results indicate that fish show weak stimulus generalization across spatial frequencies. Also, the shape of the contrast sensitivity function, a common measure of the animal’s visual capabilities, is distorted by insufficient training. We conclude that when the goal is to obtain accurate data on visual capabilities, either subjects should be trained to each stimulus to be tested or their generalization gradients should be measured.     

Hemispheric differences are found in the identification,but not the detection,of low versus high spatial frequencies

The processing of sine-wave gratings presented to the left and right visual fields was examined in four experiments. Subjects were required either to detect the presence of a grating (Experiments 1 and 2) or to identify the spatial frequency of a grating (Experiments 3 and 4). Orthogonally to this, the stimuli were presented either at threshold levels of contrast (Experiments 1 and 3) or at suprathreshold levels (Experiments 2 and 4). Visual field and spatial frequency interacted when the task required identification of spatial frequency, but not when it required only stimulus detection. Regardless of contrast level (threshold, suprathreshold), high-frequency gratings were identified more readily in the right visual field (left hemisphere), whereas low-frequency gratings showed no visual field difference (Experiment 3) or were identified more readily in the left visual field (right hemisphere) (Experiment 4). Thus, hemispheric asymmetries in the processing of spatial frequencies depend on the task. These results support Sergent’s (1982) spatial frequency hypothesis, but only when the computational demands of the task exceed those required for the simple detection of the stimuli.     

Measuring the search image: expectation,detection, and recognition in pigeon visual search

Pigeons searched computer screens for a grating target that varied in spatial frequency and orientation. In Experiment 1, a pretrial cue signaled that a particular target would appear. The cue speeded response to this primed target and to targets of the same orientation and similar spatial frequency to the primed target. However, the cue slowed search for targets differing from the primed target in orientation. In Experiment 2, pecks to a single target were reinforced. Responding generalized somewhat to targets of spatial frequency similar to the primed target and to targets of either orientation. Thus, stimulus aspects that affect detection may differ from those that affect recognition; if a common representation serves both, it functions differently in the 2 cases.     

两维特征图形的客体和空间工作记忆存储研究

研究采用单探测变化检测范式,考察了两维特征图形在视觉客体和视觉空间工作记忆中的存储机制,并对其容量进行测定。40名被试(平均年龄20.56±1.73岁)随机分为两个等组,分别完成实验一和实验二。实验一的刺激图形由颜色和形状两基本特征组成,实验二的刺激为由不同颜色和开口朝向组成的兰道环。两个实验结果均显示:(1)特征交换变化条件下的记忆成绩与单特征变化条件下最差的记忆成绩差异不显著;(2)空间工作记忆任务的成绩显著优于客体工作记忆任务;(3)被试在视觉工作记忆中能存储2~3个客体和3~4个空间位置。这表明,由两种不同维度特征组成的图形在视觉客体和视觉空间工作记忆中均以整合方式进行存储,空间工作记忆的容量大于客体工作记忆。     

Variations in apparent spatial frequency with stimulus orientation: IL Matching data collected under normal and interferometric viewing conditions

Using an adjustment procedure, human observers matched the apparent spatial frequencies of sinusoidal gratings presented in different orientations (0, 45, 90, and 135 deg). Matches were made between all possible pairwise orientation combinations. Significant match deviations indicated that the apparent frequency of a grating depends on its orientation. The most consistent deviations were found between horizontal and vertical gratings, with horizontal gratings appearing to be of a lower spatial frequency than vertical gratings. These effects were relatively independent of stimulus contrast and persisted when the optics of the eye were bypassed with laser interferometry. A neurophysiological explanation of these effects is proposed.     

The directional tuning of the barber-pole illusion.

In order to study the integration of local motion signals in the human visual system, we measured directional tuning curves for the barber-pole illusion by varying two crucial aspects of the stimulus layout independently across a wide a range in the same experiment. These were the orientation of the grating presented behind the rectangular aperture and the aspect ratio of the aperture, which in combination determine the relative contributions of local motion signals perpendicular to the gratings and parallel to the aperture borders, respectively. The strength of the illusion, ie the tendency to perceive motion along the major axis of the aperture, obviously depends on the spatial layout of the aperture, but also on grating orientation. Subjects were asked which direction they perceived and how compelling their motion percept was, revealing different strategies of the visual system to deal with the barber-pole stimulus. Some individuals respond strongly to the unambiguous motion information at the boundaries, leading to multistable percepts and multimodal distributions of responses. Others tend to report intermediate directions, apparently being less influenced by the actual boundaries. The general pattern of deviations from the motion direction perpendicular to grating orientation--a decrease with aspect ratio approaching unity (ie square-shaped apertures) and with gratings approaching parallel orientation to the shorter aperture boundary--is discussed in the context of simple phenomenological models of motion integration. The best fit between model predictions and experimental data is found for an interaction between two stimulus parameters: (i) cycle ratio, which is the sine-wave gratings equivalent of the terminator ratio for line gratings, describing the effects from the aperture boundaries, and (ii) the grating orientation, responsible for perpendicular motion components, which describes the influence of motion signals from inside the aperture. This suggests that the most simple cycle (terminator) ratio explanation cannot fully account for the quantitative properties of the barber-pole illusion.     

The effects of spatial frequency and temporal waveform on three measures of temporal processing

The effects of spatial frequency and temporal transition of sine-wave grating onset and offset were assessed using measures of reaction time, visual persistence, and temporal order judgements. The stimuli were lateralized fields, separated by 1 degree of visual angle. Slow temporal transition resulted in significantly poorer performance than did abrupt onset and offset, but spatial frequency had a minimal effect. Thus, the latency, temporal resolution, and temporal ordering of events are mediated by a mechanism that is sensitive to abrupt temporal transients. The stimulus conditions employed did not result in a shift in the point of subjective simultaneity.