Speed perception is affected by the Ebbinghaus-Titchener illusion

We examined whether the apparent extent of motion affects speed perception. On the first presentation of each trial, a light dot travelled horizontally across a central circle of one of the Ebbinghaus configurations (with either small or large inducing elements). On the second presentation, observers adjusted the speed of a dot moving within the central circle alone so as to match the speed perceived in the first presentation. For all stimulus speeds (1.3, 2.1, and 5.5 deg s-1), the matched speed with small inducing circles was systematically less than that with large inducing circles. The findings indicate that the perceived speed depends on the apparent extent of motion: the larger the apparent size of a frame, the slower the apparent speed. These results are consistent with the predictions of transposition effects in visual motion.     

Motion capture depends on signal strength

When flickering dots are superimposed onto a drifting grating, the dots appear to move coherently with the grating. In this study we examine: (i) how the perceived direction of a compound stimulus composed of superimposed grating and dots, moving in opposite directions with equal speeds, is influenced by the relative strength of the motion signals; (ii) how the perceived speed of a compound stimulus composed of superimposed grating and dots, moving in the same direction but at different speeds, is influenced by the relative strength of the motion signals; and (iii) whether this stimulus is discriminable from its metameric speed match. Dot signal strength was manipulated by using different proportions of signal dots in noise and different dot lifetimes. Both the perceived direction and speed of these compound stimuli depended upon the relative motion-signal strengths of the grating and the dots. Those compound stimuli that appeared coherent were not discriminable from the speed-matched metameric compound stimuli. When the signals were completely integrated into a coherent compound stimulus, the local motion signals were no longer perceptually available, though both contributed to the global percept. These data strongly support a weighted-combination model where the relative weights depend on signal strength, instead of a winner-takes-all model.     

Sensitivity to shearing and compressive motion in random dots

The sensitivity of the visual system to motion of differentially moving random dots was measured. Two kinds of one-dimensional motion were compared: standing-wave patterns where dot movement amplitude varied as a sinusoidal function of position along the axis of dot movement (longitudinal or compressional waves) and patterns of motion where dot movement amplitude varied as a sinusoidal function orthogonal to the axis of motion (transverse or shearing waves). Spatial frequency, temporal frequency, and orientation of the motion were varied. The major finding was a much larger threshold rise for shear than for compression when motion spatial frequency increased beyond 1 cycle deg-1. Control experiments ruled out the extraneous cues of local luminance or local dot density. No conspicuous low spatial-frequency rise in thresholds for any type of differential motion was seen at the lowest spatial frequencies tested, and no difference was seen between horizontal and vertical motion. The results suggest that at the motion threshold spatial integration is greatest in a direction orthogonal to the direction of motion, a view consistent with elongated receptive fields most sensitive to motion orthogonal to their major axis.     

The modulation of the flash-lag effect by voluntary attention

In the flash-lag effect (FLE), a flashing object appears to lag behind a moving object when both happen to be physically aligned to each other. According to an earlier account of the FLE (Baldo and Klein 1995 Nature 378 565-566), this perceptual phenomenon would result from differential delays in the perceptual processing of moving and flashing stimuli, presumably involving attentional mechanisms. Here, we have attempted to demonstrate in a more convincing way the participation of voluntary attention as a major component of the FLE. In experiment 1 the observer's attentional set was induced by the spatial probability structure of the visual stimulus. A flashing dot (relative to which the location of a moving dot should be judged) was presented, in separate blocks, at fixed, alternating, or randomly chosen locations. The two former conditions, providing a higher spatial predictability, yielded a smaller FLE than the latter condition, which provided a lower spatial predictability of the flashing dot. In experiment 2 we employed a standard cueing procedure, in which a participant was instructed to shift covertly his/her attentional focus according to a symbolic cue. The cue indicated, with a validity of 80%, the visual hemifield at which the flashing dot would be presented. As predicted by our conceptual model, the mean magnitude of the FLE in the valid trials was significantly smaller than that found in the invalid ones. Therefore, both experiments provided strong evidence supporting the participation of voluntary attention in the FLE. Attentional mechanisms should be seen not as the primary cause of the FLE, but rather as an important modulatory component of a broader process whose spatiotemporal dynamics engenders the FLE and possibly other related phenomena. Even though we elected an account based on the influence of attention on perceptual latencies, our empirical findings are compatible with other theoretical models embraced by the current flash-lag controversy and should be accommodated by every attempt to explain this perceptual phenomenon.     

The effect of a moving dot transversal on the Poggendorff illusion

In attempting to derive the minimal component of the Poggendorff figure which would still produce an illusion, responses to three types of transversal were measured. One was the customary solid line type; a second type presented the two segments sequentially, alternating between them; and the third consisted of a moving dot which traveled the transversal path. Each transversal was shown with and without verticals, for a total of six conditions. Ten subjects in each condition adjusted the luminous transversal until the segments appeared to be collinear. Figures with verticals present showed a greater magnitude of illusion than those without, and discrepancies for moving dot transversals were greater than those for comparable solid line figures. Since alternating transversals were not significantly larger than solid line figures, it was concluded that the magnitude of the moving dot effect could not be attributed to temporal sequence. An eyemovement hypothesis was suggested instead.     

The whole moves less than the spin of its parts

When individually moving elements in the visual scene are perceptually grouped together into a coherently moving object, they can appear to slow down. In the present article, we show that the perceived speed of a particular global-motion percept is not dictated completely by the speed of the local moving elements. We investigated a stimulus that leads to bistable percepts, in which local and global motion may be perceived in an alternating fashion. Four rotating dot pairs, when arranged into a square-like configuration, may be perceived either locally, as independently rotating dot pairs, or globally, as two large squares translating along overlapping circular trajectories. Using a modified version of this stimulus, we found that the perceptually grouped squares appeared to move more slowly than the locally perceived rotating dot pairs, suggesting that perceived motion magnitude is computed following a global analysis of form. Supplemental demos related to this article can be downloaded from app.psychonomic-journals.org/content/supplemental.     

The relationship between space and time in the perception of stimuli moving behind a slit

When a shape defined by a set of dots plotted along its contour is presented in a sequence of frames within the boundaries of a slit, and in each frame only one dot (featureless frame) or two dots (feature frame) are displayed, a whole moving dotted shape is perceived. Masking techniques and psychophysical measures have been used to show that a dynamic random-dot mask interferes with shape identification, provided the interframe interval is greater than about 15 ms, and there are no stimulus features for recognition in individual frames. A similar pattern of results was obtained when the observer had only to detect the movement of a single dot or a pair of dots against a dynamic-noise background. It is concluded that the visual system can resolve the correspondence problem in both apparent movement (one moving dot) and aperture viewing (featureless-frame condition) by extracting motion before the extraction of features in each frame. However, the results also show that where feature identification in each frame is possible, it can also be used to identify the moving targets.     

Comparing the sensitivity of manual pursuit and perceptual judgments to pictorial depth effects

Abstract - We examined whether a pictorial depth illusion influences the manual pursuit of a moving dot to the same extent that it influences the dot's apparent displacement. Fourteen subjects performed two tasks. In one case, they used their unseen hand to track a dot that moved on an elliptical path. In the other, they first watched the dot move on the same path, and then set an ellipse to match the shape of the dot's path. The illusion influenced the two tasks to the same extent, suggesting that the visual information processing is the same for the two tasks.     

多目标追踪的任务难度对不同类型非目标选择性抑制的影响

采用多目标追踪（MOT）与点探测刺激觉察任务相结合的实验范式,分别通过改变运动与静止非目标数量,考察追踪难度变化对不同类型非目标选择性抑制的影响。实验一通过改变运动非目标数量为4、5、6,发现当运动非目标数量为6时,追踪难度显著增加,静止非目标上的抑制量也显著增加,而运动非目标上的抑制量则不随追踪难度的变化而变化;实验二改变静止非目标数量为4、5、6,同样发现当静止非目标数量为6时,追踪难度显著增加,静止非目标上的抑制量也显著增加,而运动非目标上的抑制量仍不随追踪难度的变化而变化,且当静止非目标数量为6时,静止非目标上的抑制量显著大于运动非目标,出现了反转现象,其原因可能是视野范围内总的对象数量超出了视觉索引容量,被试改变了对静止与运动非目标的抑制策略。综合实验结果表明,静止非目标上的抑制程度随追踪难度的提高而增加;而运动非目标上的抑制程度对追踪难度的变化不敏感,在不同难度水平上保持相对稳定。     

非预想刺激的运动速率对无意视盲的影响

无意视盲是指由于对某些事物的专注而导致的眼前对象被忽视的现象。它受到诸如非预想刺激的位置、大小、颜色; 非预想刺激与注意刺激之间的关系; 被试的年龄、专业知识、加工能力等诸多因素的影响。本文通过改进的MR范式考察了“等时”和“等距”条件下非预想刺激的运动速率对无意视盲的影响。实验结果显示: (1)非预想刺激的运动速率和其呈现时间对无意视盲的比率有显著影响; (2)在一定的呈现时间范围内, 视盲率随运动速率的升高而降低, 但当维持相等的运动距离时, 视盲率没有显著变化; (3)当呈现时间超出一定范围时, 运动速率对无意视盲的影响急剧减小, 即呈现时间制约着运动速率对无意视盲的影响, 两者间呈倒U型曲线关系。文末就实验结果进行了详细分析和讨论。     

Effects of agency on movement interference during observation of a moving dot stimulus

Human movement performance is subject to interference if the performer simultaneously observes an incongruent action. It has been proposed that this phenomenon is due to motor contagion during simultaneous movement performance-observation, with coactivation of shared action performance and action observation circuitry in the premotor cortex. The present experiments compared the interference effect during observation of a moving person with observation of moving dot stimuli: The dot display followed either a biologically plausible or implausible velocity profile. Interference effects due to dot observation were present for both biological and nonbiological velocity profiles when the participants were informed that they were observing prerecorded human movement and were absent when the dot motion was described as computer generated. These results suggest that the observer's belief regarding the origin of the dot motion (human-computer generated) modulates the processing of the dot movement stimuli on their later integration within the motor system, such that the belief regarding their biological origin is a more important determinant of interference effects than the stimulus kinematics.     

The pigeon's discrimination of movement patterns (Lissajous figures) and contour-dependent rotational invariance

The ability of pigeons to discriminate complex motion patterns was investigated with the aid of moving Lissajous figures. The pigeons successfully learned to differentiate two successively presented cyclic trajectories of a single moving dot. This suggests that they can recognize a movement Gestalt when information about shape is minimal. They also quickly learned a new discrimination between moving-outline stimuli with repetitively changing contour patterns. Contrasting results were obtained when the dot or outline stimuli were axis-rotated through 90 degrees. Rotational invariance of pattern discrimination was clearly demonstrated only when moving contours were visible. Nevertheless, pigeons could discriminate the axis-orientation of a moving-dot or moving-outline pattern when trained to do so. Discrimination did not seem to depend on single parameters of motion but rather on the recognition of a temporally integrated movement Gestalt. The visual system of pigeons, as well as that of humans, may be well adapted to recognize the types of oscillatory movements that represent components of the motor behaviour shown by many living organisms.     

Auditory clicks distort perceived velocity but only when the system has to rely on extraretinal signals

Previous work has found that repetitive auditory stimulation (click trains) increases the subjective velocity of subsequently presented moving stimuli. We ask whether the effect of click trains is stronger for retinal velocity signals (produced when the target moves across the retina) or for extraretinal velocity signals (produced during smooth pursuit eye movements, when target motion across the retina is limited). In Experiment 1, participants viewed leftward or rightward moving single dot targets, travelling at speeds from 7.5 to 17.5 deg/s. They estimated velocity at the end of each trial. Prior presentation of auditory click trains increased estimated velocity, but only in the pursuit condition, where estimates were based on extraretinal velocity signals. Experiment 2 generalized this result to vertical motion. Experiment 3 found that the effect of clicks during pursuit disappeared when participants tracked across a visually textured background that provided strong local motion cues. Together these results suggest that auditory click trains selectively affect extraretinal velocity signals. This novel finding suggests that the cross-modal integration required for auditory click trains to influence subjective velocity operates at later stages of processing.     

The influence of goals on sense of control

We examined the influence of goals on sense of control relative to that experienced when taking action randomly. In the experimental task, participants controlled the direction of a moving dot by pressing the left and right keys at will without a specific goal (the control condition), directed the moving dot to a destination as often as possible (the strong goal condition), or kept the moving dot in the central area of the screen (the weak goal condition) for as long as possible. The results showed that the strong goal impaired the sense of control, but the weak goal did not exert an influence. We concluded that the goal-based expectation influenced sense of control, but the goal-directed action selection did not. Furthermore, we proposed a modified comparator model of the sense of control, offering a promising approach to integration of the predictive and postdictive processes involved in the sense of control.     

Resource demands of object tracking and differential allocation of the resource

The attentional processes for tracking moving objects may be largely hemisphere-specific. Indeed, in our first two experiments the maximum object speed (speed limit) for tracking targets in one visual hemifield (left or right) was not significantly affected by a requirement to track additional targets in the other hemifield. When the additional targets instead occupied the same hemifield as the original targets, the speed limit was reduced. At slow target speeds, however, adding a second target to the same hemifield had little effect. At high target speeds, the cost of adding a same-hemifield second target was approximately as large as would occur if observers could only track one of the targets. This shows that performance with a fast-moving target is very sensitive to the amount of resource allocated. In a third experiment, we investigated whether the resources for tracking can be distributed unequally between two targets. The speed limit for a given target was higher if the second target was slow rather than fast, suggesting that more resource was allocated to the faster of the two targets. This finding was statistically significant only for targets presented in the same hemifield, consistent with the theory of independent resources in the two hemifields. Some limited evidence was also found for resource sharing across hemifields, suggesting that attentional tracking resources may not be entirely hemifield-specific. Together, these experiments indicate that the largely hemisphere-specific tracking resource can be differentially allocated to faster targets.     

Discrimination of intentional and random motion paths by pigeons

Twelve pigeons (Columba livia) were trained on a go/no-go schedule to discriminate between two kinds of movement patterns of dots, which to human observers appear to be "intentional" and "non-intentional" movements. In experiment 1, the intentional motion stimulus contained one dot (a "wolf") that moved systematically towards another dot as though stalking it, and three distractors ("sheep"). The non-intentional motion stimulus consisted of four distractors but no stalker. Birds showed some improvement of discrimination as the sessions progressed, but high levels of discrimination were not reached. In experiment 2, the same birds were tested with different stimuli. The same parameters were used but the number of intentionally moving dots in the intentional motion stimulus was altered, so that three wolves stalked one sheep. Despite the enhanced difference of movement patterns, the birds did not show any further improvement in discrimination. However, birds for which the non-intentional stimulus was associated with reward showed a decline in discrimination. These results indicated that pigeons can discriminate between stimuli that do and do not contain an element that human observer see as moving intentionally. However, as no feature-positive effect was found in experiment 1, it is assumed that pigeons did not perceive or discriminate these stimuli on the basis that the intentional stimuli contained a feature that the non-intentional stimuli lacked, though the convergence seen in experiment 2 may have been an effective feature for the pigeons. Pigeons seem to be able to recognise some form of multiple simultaneously goal-directed motions, compared to random motions, as a distinctive feature, but do not seem to use simple "intentional" motion paths of two geometrical figures, embedded in random motions, as a feature whose presence or absence differentiates motion displays. Electronic Publication     

Unimodal and crossmodal effects of endogenous attention to visual and auditory motion

Three experiments were conducted examining unimodal and crossmodal effects of attention to motion. Horizontally moving sounds and dot patterns were presented and participants’ task was to discriminate their motion speed or whether they were presented with a brief gap. In Experiments 1 and 2, stimuli of one modality and of one direction were presented with a higher probability ( p = .7) than other stimuli. Sounds and dot patterns moving in the expected direction were discriminated faster than stimuli moving in the unexpected direction. In Experiment 3, participants had to respond only to stimuli moving in one direction within the primary modality, but to all stimuli regardless of their direction within the rarer secondary modality. Stimuli of the secondary modality moving in the attended direction were discriminated faster than were oppositely moving stimuli. Results suggest that attending to the direction of motion affects perception within vision and audition, but also across modalities.     

Displacement of the path of perceived movement by intersection with static contours

Observation of a moving dot gives rise to a perceived movement path, which has properties similar to those of real contours. If the dot crosses a line inclined to a horizontal direction of movement, it appears to undergo a vertical displacement. This displacement was found to be greatest for a line orientation of around 15° with respect to the movement. At other relative orientations, the size of the perceived displacement varied in the same manner as the perceived expansion of angles formed by intersection between static contours. Movement path distortions were measured with background fields like those that produce the Hering and Zöllner illusions with continuous lines. Illusory displacements of perceived movement were found to be equivalent to the static forms. The subjective contour formed by observation of movement can therefore give rise to illusions similar to those obtained with real lines.     

Shape discrimination for motion-defined and contrast-defined form: squareness in special.

Shape discrimination was measured for: (i) two-dimensional rectangular targets that were perfectly camouflaged within a stationary pattern of random dots and rendered visible by relative motion of the dots, and (ii) similar dotted rectangles that were rendered visible by luminance contrast. Shape discrimination was disconfounded from size discrimination by requiring subjects to discriminate the aspect ratios of rectangles whose areas were altered independently of aspect ratio. When dot speed and contrast were both high, the aspect-ratio discrimination threshold was as acute for motion-defined (MD) rectangles as for contrast-defined (CD) rectangles and, at 2-3%, corresponded to a change of side length of about 24 s arc compared to a mean dot separation of 360 s arc. Discrimination of MD rectangles collapsed at low dot speeds and could not be measured at speeds less than about 0.03-0.08 deg s-1, but discrimination of CD rectangles was almost unaffected by dot speed. The aspect-ratio discrimination threshold was lowest for a square and progressively increased as the rectangle became more asymmetric. It is suggested that the visual system contains a mechanism that compares the separations of pairs of contours along different azimuths, and that, during visual development, this shape-discrimination processing of MD and CD targets is driven by the same environmental and behavioural pressures towards a common end point. The human equivalent of a pathway that includes the cortical area MT is thought to be important for shape discrimination of MD forms.     

Pictures of you: Dot stimuli cause motor contagion in presence of a still human form

In this study, we investigate which visual cues induce participants to encode a non-human motion stimulus in their motor system. Participants performed reach-to-grasp actions to a target after observing a dot moving in a direct or higher-arcing path across a screen. Dot motion occurred in the presence of a meaningless (scrambled human model) stimulus, a still human model, or a human model performing a direct or exaggeratedly curved reach to a target. Our results show that observing the dot displacement causes motor contagion (changes in the height of the observer’s hand trajectory) when a human form was visually present in the background (either moving or still). No contagion was evident, however, when this human context was absent (i.e., human image scrambled and not identifiable). This indicates that visual cues suggestive of human agency can determine whether or not moving stimuli are encoded in the motor system.