Vernier acuity as affected by target length and separation

Vernier acuity was measured for vertical lines of different lengths; the threshold (about 4 sec of arc) was almost as good for the shortest stimuli (1 min 20 sec squares) as for the longest (21 min 20 sec × 1 min 20 sec rectangles) and did not change when two round dots were shown in positions corresponding to the squares. The threshold for the two dots measured in terms of minimum detectable lateral offset increased when the vertical separation between the dots increased, but, when replotted in terms of the angle of tilt between them with respect to vertical, the threshold improved with dot separation; moreover, at asymptote, the threshold was comparable to that obtained for detecting that an actual line was tilted out of vertical. Our data suggest that, in performing the vernier task, Ss do not extrapolate the edges of the vernier elements; instead, they judge the deviation of the inner ends of the stimuli from verticality. This hypothesis explains the effect of increasing separation between vernier elements and also accounts for other types of acuity, such as the detection of curvature.     

The misperception of rotary motion

Two principles for predicting the relative frequency of illusory reversals of rotating plane objects were derived and tested empirically. Ten objects, variously’ combining valid and confounding depth cues, were used. Predictions based on the principles were confirmed in every case. The results are offered as an improved explanation of the Ames trapezoid illusion and other illusions of rotary motion.     

Perceived direction of rotary motion

The starring point for this study was the rotating trapezoidal window. The aim was to reanalyze the problem of information about direction of rotation that is available in simplified proximal stimulations and to study empirically if the Ss utilized the possibilities demonstrated in the theoretical analyses. These analyses showed that a distal poin t moving in a horizontal circular path gives different proximal stimulations when moving clockwise and counterclockwise Further, a distal vertical line moving with its midpoint in the same path has a proximal change of length with different phase relations with the horizontal back-and-forth motion for the two directions. The proximal stimulation is ambiguous, however, unless some restrictions or “decoding principles” are introduced. In the first two experiments it was shown that the Ss could not report “correct” direction of motion of the point but were able to do so about the vertical line. In a third experiment a second vertical line was introduced. This necessitates a determination of relative distance to the two lines. It was shown that the proximally shorter line was usually perceived further away than the proximally longer one. The results are discussed with reference to the trapezoidal window. and some hypotheses are stated.     

Illusory motion produced by dichoptic stimuli during saccades

A new motion illusion is reported in which saccadic eye movements can produce a perceived jump of a static stimulus presented dichoptically. In three experiments, observers made saccades while viewing a stationary stimulus consisting of a disk and random dots presented separately to the two eyes. In experiments 1 and 2, by measuring the strength of the perceived motion and the velocity of binocular eye movements, we found that (a) motion ratings were high for the stimulus that contained a large interocular difference in luminance, and (b) the saccadic strategy of the observer was virtually identical across different stimulus conditions. In experiment 3, by measuring the detectability of a short temporal gap introduced into the stimulus around saccades, we found that saccadic suppression was normal in the dichoptic presentation. We discuss possible mechanisms underlying the illusory motion.     

Delayed offset of distracters masks a local target

Object substitution masking (OSM) is observed when a brief target surrounded with a mask is presented among distracter stimuli and cannot be identified when it and the distracters disappear but the mask remains in view. We probed whether OSM also occurs without a local mask object when the distracters remain after target offset. We also varied the congruence between the local target and the global search display and the grouping properties of the delayed offset distracters. A target was briefly presented in a global object configuration of distracters that had delayed offset. Results showed that OSM could be observed with delayed offset of distracters grouped into a global mask shape. Congruence of the shapes of the global and local objects did not affect OSM, suggesting that a generalized abstract visual pattern representation of the global object may not be involved in OSM nor did the grouping properties of the delayed offset distracters influence OSM.     

Simple rotary motion is integrated across fixations

Participants were shown a line rotating at a constant angular velocity and were asked to judge whether motion was continuous or whether the line jumped (i.e., moved either forward or backward in the rotary cycle). In two experiments, the participants were significantly better than chance in detecting these jumps in simple rotary motion even when the jumps occurred during a saccade. Moreover, in Experiment 2, when the jump occurred during a saccade followed by a masking flash, perception of the jump was at least as good as when it occurred during a fixation followed by a masking flash. These results complement and extend the findings of Verfaillie and co-workers, who found that perceptions of some changes in biological motion were as good across fixations as when they occurred during a fixation. These findings are in contrast to the common finding, in the reading literature, that people are consciously "blind" to many changes in the text and to those, in the scene perception literature, in which detection of static changes across fixations is above chance but plausibly well below the level that would be expected if the change occurred during a fixation.     

Minimal conditions for the perception of rotary motion

Abstract.— The necessity of simultaneous length and direction changes for the perception of rotary motion in depth was studied using patterns of one to four segments of a horizontal line. The patterns changed in length only, according to one of four waveforms: A sinusoidal waveform, with both the left and right half of the pattern changing at the same rate (simulating a parallel projection of rotary motion); a sinusoidal waveform, with asymmetric left-right changes (simulating a polar projection of rotary motion); a linear waveform, the same for both the left and right halves (a simple expansion and contraction); and a linear waveform on which the asymmetries of a polar projection were superimposed. Most reports described rotary motion in depth. Both the linearity and the right-left symmetry of the waveforms affected the proportion of rotary motion responses, with the proportions greater for the sinusoidal waveforms and for the asymmetrical waveforms.     

Flash-induced forward and reverse illusory line motion in offset bars

Illusory line motion (ILM) refers to perception of motion in a bar that onsets or offsets all at once. When the bar onsets or offsets between two boxes after one of the boxes flashes, the bar appears to shoot out of the flashed box (_flashILM). If the bar offsets during the flash, it appears to contract into the flashed box (reverse ILM; rILM). Onset bars do not show rILM. Moreover, rILM and _flashILM are not correlated, indicating they are two different illusions. To date, rILM has only been studied using a 50-ms flash where the bar offsets 16.7 ms after flash onset. It is not clear if rILM is due to the 16.7-ms flash-bar-removal stimulus onset asynchrony (SOA) or due to the flash offsetting after the bar. The current studies explore these parameters to better understand the conditions that lead to rILM. The results suggest that _flashILM is sensitive to the temporal interval between flash onset and bar offset, while rILM appears to arise when the flash offsets after the bar has been removed regardless of the temporal interval between flash onset and bar removal. These results are consistent with _flashILM reflecting visual exogenous attention while rILM may reflect the low-level spreading of subthreshold activation radiating from the flashed box. The findings are incorporated into the recent work that suggests that the literature concerning ILM is possibly conflating a number of different illusions of line motion, including polarized gamma motion (PGM), transformational apparent motion (TAM), and exogenous attention induced motion (_flashILM).     

Perceived rotary motion from changes in a straight line

The problem dealth with was how perception of a three-dimensional space is related to the corresponding two-dimensional retinal image. The stimulation used was a straight line changing length and direction. For this stimulation a geometrical model was developed. The basic decoding principle in this model is that the changes in the two-dimensional figure will be perceived as three-dimensional motions of an object with constant shape and size. This principle was approximately verified for the majority of the data. The main deviation from the model was that there was generally less perceived depth than predicted. Also a second decoding principle was generally verified: rotary, but not translator motion is perceived from this kind of stimulation. A third unexpected decoding principle was found in the data: the line is perceived in a frontal-parallel direction when it has its maximal extention.     

Linear perspective as a cue in misperceived rotary motion

Pairs of luminous lines of differing length ratios, rotated about an axis perpendicular to the line of sight, resulted in misperceptions of the direction of rotation. The illusions are similiar to the Ames trapezoid illusion. The results help to clarify the role ofdepth cues in visual perception of motion.     

Infant perception of causal motion produced by humans and inanimate objects

Both the movements of people and inanimate objects are intimately bound up with physical causality. Furthermore, in contrast to object movements, causal relationships between limb movements controlled by humans and their body displacements uniquely reflect agency and goal-directed actions in support of social causality. To investigate the development of sensitivity to causal movements, we examined the looking behavior of infants between 9 and 18 months of age when viewing movements of humans and objects. We also investigated whether individual differences in gender and gross motor functions may impact the development of the visual preferences for causal movements. In Experiment 1, infants were presented with walking stimuli showing either normal body translation or a “moonwalk” that reversed the horizontal motion of body translations. In Experiment 2, infants were presented with unperformable actions beyond infants’ gross motor functions (i.e., long jump) either with or without ecologically valid body displacement. In Experiment 3, infants were presented with rolling movements of inanimate objects that either complied with or violated physical causality. We found that female infants showed longer looking times to normal walking stimuli than to moonwalk stimuli, but did not differ in their looking time to movements of inanimate objects and unperformable actions. In contrast, male infants did not show sensitivity to causal movement for either category. Additionally, female infants looked longer at social stimuli of human actions than male infants. Under the tested circumstances, our findings indicate that female infants have developed a sensitivity to causal consistency between limb movements and body translations of biological motion, only for actions with previous visual and motor exposures, and demonstrate a preference toward social information.     

Onset but not offset of irrelevant motion disrupts inhibition of return

In seven experiments, subjects were slower to detect targets in cued static objects than in uncued static objects, revealing inhibition of return (IOR). This occurred regardless of the presence or absence of continuous motion of other, task-irrelevant objects in the display. However, if the motion of the irrelevant objects began during the interval between cue and target, the amount of IOR was considerably reduced. Offset of motion during the cue-target interval had no effect. Implications for IOR, object perception, and attentional capture are discussed.     

Static and dynamic factors in the perception of rotary motion

Direction of rotation and static slant judgments were collected for a series of outline plane forms in four experiments with 106 subjects. Direction was judged more accurately for forms displaying the same perspective gradients as trapezoids, but with right-angled contours, than for trapezoids. There were no consistent differences among these forms in judged slant. Direction of rotation judgments were affected by a static false interposition cue, with interposition increasing the proportion of veridical judgments when placed in conflict with a relative size gradient and decreasing this proportion when a size gradient was absent. Both a dynamic factor (contour angle change) and a static factor (misperceived relative distance of the vertical sides) were found to affect perceived direction of rotation, with direction judgments based primarily on the dynamic factor.     

A three-dimensional motion aftereffect produced by prolonged adaptation to a rotation simulation

After adaptation to a perspective simulation of a square plane rotating in depth, an ambiguous rotation simulation (ie one containing no perspective information) appears to rotate in the direction opposite that of adaptation. The strength of this three-dimensional motion aftereffect (MAE) is proportional to the amount of perspective available in the adaptation display and, in the dark, decays to about 75% of its initial strength within about 546 s. The nature of the testing situation and a control experiment suggest that the three-dimensional MAE is not caused by retinal adaptation of two-dimensional directionally selective mechanisms.