How apparent motion affects mental rotation: Push or pull?

Subjects were timed as they judged whether a small bar perpendicular to one side of a clockhand would point left or right if the hand was pointing upward (i.e., at the 12:00 position). The clockhand was shown in two successive orientations 30°apart, so that it was perceived to jump from one to the other, but the bar was included at only one of the two orientations. Analysis of reaction times as a function of angular orientation showed that the subjects “mentally rotated” the clockhand to the upright position before making their decisions. When the bar appeared on the second presentation, the jump had no significant influence on mental rotation but when it appeared on the first presentation, the estimated orientation from which the clockhand was mentally rotated was “dragged” in the direction of the jump.     

Background stripes affect apparent speed of rotation

A gray line that rotated about its own center against a stationary background of vertical stripes appeared to double in perceptual speed as it rotated through the vertical position and thus momentarily aligned with the background. Four factors may contribute to this speed-up: (i) landmarks, in which the tip of the moving vertical line moves horizontally across the maximum number of stationary stripes; (ii) orientation repulsion of the moving line by the vertical stripes, which may distort the line's perceived position and hence its perceived speed; (iii) the orientation of an induced brightness pattern along the line; and (iv) the motion of the induced brightness pattern, which moves physically most rapidly along the line when the line is near vertical. To test these possibilities, an annulus display provided landmarks but no intersections, and this almost abolished the effect. A rotating-slit display provided an oriented, moving pattern that mimicked the induced brightness but had no landmarks, and this increased the effect. We conclude that the motion, but not the orientation, of the intersections [option (iv)] was responsible for the illusion. The fact that this motion along the length of the line affected the perceived speed of the line orthogonal to its own length indicates a failure on the part of the visual system to fully decouple tangential from radial motion.     

Nonlinearity in color space measured by apparent motion

We used an apparent motion technique to examine the intensity coding along the three cardinal axes of color space: achromatic (L + M + S), L-M cone, and S cone axes. Two horizontal bars of different colors were alternated to produce a vertical displacement. The color of the background was a mixture varied between the colors of the two bars. When the background color was close to either of the test colors, only the bar that was more salient appeared to jump. Observers adjusted the color of the background until they saw either the two bars moved equally frequently or both bars moved at once. If the color difference in a linear cone excitation space controls this apparent motion, the setting should be midway between the two colors. All of the three cardinal axes showed some deviation from linear behavior. The nonlinearity was less extreme than a logarithmic function for both the achromatic and S cone axes and could be attributed to a small compressive nonlinearity, possibly at the level of cone responses. However, the L-M stimuli showed a more extreme departure from linearity, which suggested a nonlinearity at an opponent site. A test of perceived contrast judgments did not show this nonlinearity for L-M axis, suggesting that it is specific to the L-M contribution to apparent motion.     

Seeing versus imagining movement in depth

Subjects judged the quality of rigid motion between pairs of three-dimensional drawings that differed by a rotation in depth. The figures were aligned with, and rotated around, either the vertical axis or an axis that was oblique with respect to the XYZ co-ordinate system. Rated quality of motion decreased with increasing angular disparity between the figures and with decreasing stimulus duration, regardless of whether the figures were vertical or oblique. The same subjects then participated in a mental rotation task using the same stimuli and angular disparities. An effect of principal axis emerged, such that subjects took longer to make decisions about obliquely aligned stimuli than about vertically aligned stimuli, especially if they received the oblique stimuli first. These data imply that perceived versus imagined movement through the same trajectory involves different processes. Whereas the apparent motion system performs its computations relatively automatically, the processes involved in mental rotation are more strategic in nature.     

Nonretinotopic processing is related to postdictive size modulation in apparent motion

The present study briefly examined how the perceived size of a leading flash would be modulated by trailing motion signals. Observers were presented with two vertical green bars that were followed by white bars with different lengths, which were presented at different locations from the green bars. The task of observers was to discriminate which of the green bars was shorter than the other (Experiment 1) or whether the lengths of the green bars were equal or not (Experiments 2 and 3). One green bar producing apparent motion with the following shorter white bar was reported to be shorter than the other green bar producing apparent motion with the following longer white bar, not only when motion correspondence was determined on the basis of retinal proximity (Experiments 1 and 2),but also when motion correspondence was determined on the basis of nonretinotopic information-that is, a relative location within each perceptual group of bars (Experiment 3). These results indicate that motion processing involving object updating or motion deblurring in the nonretinotopic frame of reference is related to postdictive size modulation.     

Illusions of familiarity caused by cohort activation

Subjects took part in an auditory lexical decision task followed by an auditory test of recognition memory for words presented in this task. Subjects categorized their recognition judgments as based on either recollection (“remember” responses) or familiarity (“know” responses). Distractor items in the recognition test included the base words from which the nonwords used in the lexical decision task were derived. Consistent with the findings of Wallace, Stewart, Sherman, and Mellor (1995), more false alarms were made to “late” base words (where the corresponding nonwords were created by changing a phoneme near the end of the word) than to “early” base words (corresponding nonwords were created by changing a phoneme at the beginning of the word). However, this effect was found in “know” responses but not in “remember” responses. The findings are attributed to enhanced fluency with which the base words are processed following their implicit activation at encoding.     

Cues reduce direction uncertainty and enhance motion detection

Previous work has shown that detectability of motion is better when the observer knows ahead of time the direction of that motion (“certainty”) than when he does not know the direction (“uncertainty”). We now report attempts to reduce this performance decrement associated with direction uncertainty. In these experiments, a briefly flashed, oriented line cued the observer to the direction of motion that might occur. When the cue appeared before the moving target, detectability increased; when the cue appeared after the moving target, performance dropped below that for no cue at all. In addition, we examined the effect of cue reliability, varying the relation between cue orientation and actual direction of target motion. The more accurate the cue is, the larger the performance increment. When the cue indicated a direction more than 90 deg from the actual target direction, performance was worse than when there was no cue. Results are discussed with regard to the feasibility of reducing uncertainty in real-world situations.     

Visual masking effects on duration,size, and form discrimination

In duration, size, and form discrimination tasks, a visual noise mask was presented at variable delays after stimulus offset in order to interrupt processing and control the extent of processing time. Previous work (Thomas & Cantor, 1975) had suggested that both perceived duration and perceived nontemporal “information” might be expected to increase as processing time was extended. As predicted, accuracy in the discrimination of size of circles and form of non-sense figures was found to vary directly with stimulus duration (20, 50 msec) and mask delay interval (0, 30, 70, 110 msec). Differences in perceived duration between filled (forms or circles) and unfilled (blank) intervals were found to increase monotonically with increases in the mask delay interval, when non-sense forms, but not circles, were presented. Two hypotheses of visual masking (“integration” and “interruption”) are discussed. Within the context of the “integration” hypothesis, a model is proposed which predicts processing time as a function of stimulus duration, mask delay interval, and the interval between onset of the mask and termination of processing.     

Catching oriented objects

We have investigated how participants match the orientation of a line, which moves on a vertical screen towards the subject. On its path to the participant, the line could disappear at several positions. Participants were instructed to put a bar on a predefined interception point on the screen, such that the bar touched the screen with the same orientation as the moving line at the very moment when the line passed through the interception point or (in case of line disappearance) when the hidden line would pass through the interception point (like in catching). Participants made significant errors for oblique orientations, but not for vertical and horizontal orientations of the moving line. These errors were small or absent when the moving line was visible all the way along its path on the screen. However, these errors became larger when the line disappeared farther away from the interception point. In the second experiment we tested whether these errors could be related to errors in visual perception of line orientation. The results demonstrate that errors in matching of the bar do not correspond to the last perceived orientation of the line, but rather to the perceived orientation of the moving line near the beginning of the movement path. This corresponds to earlier observations that participants shortly track a moving target and then make a saccadic eye movement to the interception point.     

Dual adaptation of apparent concomitant motion contingent on head rotation frequency

Perceived movement of a stationary visual stimulus during head motion was measured before and after adaptation intervals during which participants performed voluntary head oscillations while viewing a moving spot. During these intervals, participants viewed the spot stimulus moving alternately in the same direction as the head was moving during either .25- or 2.0-Hz oscillations, and then in the opposite direction as the head at the other of the two frequencies. Postadaptation measures indicated that the visual stimuli were perceived as stationary only if traveling in the same direction as that viewed during adaptation at the same frequency of head motion. Thus, opposite directions of spot motion were perceived as stationary following adaptation depending on head movement frequency. The results provide an example of the ability to establish dual (or “context-specific”) adaptations to altered visual—vestibular feedback.     

Experience-guided attention: Uniform and implicit

Frequently finding a visual search target in one region of space induces a spatial attentional bias toward that region. Past studies on this effect typically tested fewer than 20 participants. The small sample prevents an investigation of two properties of learning: visual field uniformity and role of explicit awareness. Pooling data from multiple studies, here we examined location probability learning from ~120,000 visual search trials across 420 participants. Participants performed a serial search task. Unbeknownst to them, the target was disproportionately likely to appear in one visual quadrant. Location probability learning (LPL) was measured as the difference in reaction time to targets in the high-probability “rich” quadrant and the low-probability “sparse” quadrants. Results showed a lack of visual field effect. LPL was equivalent for “rich” quadrant in the upper left, upper right, lower left, and lower right. Learning did not induce a hotspot diagonal to the “rich” quadrant. To the contrary, RT was the longest in the diagonal quadrant. Recognition rate of the “rich” quadrant was above chance. However, recognition accuracy was unrelated to the size of LPL. Implicit learning induces visual-field-independent changes in spatial attention.     

Rapid volitional control of apparent motion during percept generation

How rapidly can one voluntarily influence percept generation? The time course of voluntary visual–spatial attention is well studied, but the time course of intentional control over percept generation is relatively unknown. We investigated the latter question using “one-shot” apparent motion. When a vertical or horizontal pair of squares is replaced by its 90º-rotated version, the bottom-up signal is ambiguous. From this ambiguous signal, it is known that people can intentionally generate a percept of rotation in a desired direction (clockwise or counterclockwise). To determine the time course of this intentional control, we instructed participants to voluntarily induce rotation in a precued direction (clockwise rotation when a high-pitched tone was heard, and counterclockwise rotation when a low-pitched tone was heard), and then to report the direction of rotation that was actually perceived. We varied the delay between the instructional cue and the rotated frame (cue-lead time) from 0 to 1,067 ms. Intentional control became more effective with longer cue-lead times (asymptotically effective at 533 ms). Notably, intentional control was reliable even with a zero cue-lead time; control experiments ruled out response bias and the development of an auditory–visual association as explanations. This demonstrates that people can interpret an auditory cue and intentionally generate a desired motion percept surprisingly rapidly, entirely within the subjectively instantaneous moment in which the visual system constructs a percept of apparent motion.     

Effects of circular motion on judgment of rotation direction and depth order in visual motion

Abstract:  The rotation direction and depth order of a rotating sphere consisting of random dots often reverses while it is viewed under orthographic projection. However, if a short viewing distance is simulated under perspective projection, the correct rotation direction can be perceived. There are two motion cues for the rotation direction and depth order. One is the speed cue; points with higher velocities are closer to the observer. The other is the vertical motion cue; vertical motion is induced when the dots recede from or approach the observer. It was examined whether circular motion, which does not have any depth information but induces vertical velocities, masks the vertical motion cue. In Experiment 1, the effects of circular motion on the judgment of the rotation direction of a rotating sphere were examined. The magnitude of the two cues (the speed cue and the vertical velocity cue) as well as the angular speed of circular motion was varied. It was found that the performance improved as the vertical velocity increased and that the speed cue had slight effects on the judgment of the rotation direction. It was also found that the performance worsened as the angular speed of the circular motion was increased. In Experiment 2, the effects of circular motion on depth judgment of a rotating half sphere were investigated. The performance worsened as the angular speed of the circular motion increased, as in Experiment 1. These results suggest that the visual system cannot compensate perfectly for circular motion for the judgment of the rotation direction and depth order.     

Time-till-breakdown and scalp electrical potential maps of long-range apparent motion

A series of psychophysical and electrophysiological experiments is reported using the apparent motion (AM) breakdown effect. Breakdown describes an effect in AM in which, during continuous viewing, the percept of smooth motion of a single stimulus alternates with the percept of two discrete alternating stimuli. Visual evoked potentials (VEPs) were recorded during periods of motion or breakdown (“nonmotion”) in horizontal and vertical displays. VEPs were compared with synthetic VEPs (“composite-flash”) produced by adding VEPs to each element of the display recorded in isolation. Subtraction of VEPs was used in an attempt to compare the electrical responses with the processing of information relating to the form of the stimulus, subthreshold motion processing, and suprathreshold motion processing. The results, presented as scalp electrical potential distribution maps, were interpreted as consistent with a central adaptation process underlying the breakdown effect. The results also indicated that the hemispheric asymmetries in AM VEPs described by Manning, Finlay, and Fenelon (1988) were most likely due to the position of the stimuli in the visual field, rather than as a lateralization of motion processes per se. The results also provided evidence that the subthreshold and suprathreshold motion responses to the display were the product of different populations of motion units.     

The effects of initial movement dynamics on human responses to postural perturbations

Falls are a major cause of injury, and often occur while turning, reaching, or bending. Yet, we have little understanding of how an ongoing feet-in place activity at the onset of imbalance, and its associated cognitive and biomechanical demands, influence our ability to recover balance. In the current study, we used an ankle-rocking paradigm to determine how the nature of the baseline task influences the balance recovery response to a backward support surface translation. Fourteen participants were instructed to “recover balance without stepping” and were perturbed at vertical while standing quietly (“S”), while ankle rocking and moving forward (“A_f”), or while ankle rocking and moving backward (“A_b”). The results showed that changes in rocking velocity at the time of the perturbation elicited changes in the incidence of stepping, magnitude of trunk angular displacements (p < .01), and the onset latencies of distal muscles (gastrocnemius and soleus, both p < .01) used to recover balance. In addition, plots of onset latencies across all muscles showed that onset latencies appeared to occur earlier in many muscles when participants held a static position compared to when they performed a dynamic task at the onset of the perturbation. The results suggest that muscle activities used to recover balance are tailored to the nature of the perturbation and the ongoing task, and that onset latencies are later when participants are performing a dynamic as opposed to static task at the time of a perturbation. These findings support previous research suggesting that automatic postural responses are highly adaptable to environmental, situational, and task demands.     

The safety and conspicuity of pedestrian crossing at roundabouts: The effect of median refuge island and zebra markings

Roundabouts are one of the most used road intersections because, compared to signalized ones, they reduce conflict points between traffic flows and moderate driving speed. Great attention should also be paid to vulnerable road users at roundabouts. According to accident statistics, in fact, accessibility of pedestrians and cyclists is not always ensured.This paper has evaluated the effects on the visibility of pedestrian crossing before and after the displacement of zebra markings, moved before intersections, and the introduction of media refuge islands and “Yield here to pedestrians” vertical signs. The above effects have been assessed by before-after analysis of speed and visual behaviour of drivers approaching the crosswalk.Moreover, the analysis of the drivers’ eye movements has highlighted the most salient elements of the pedestrian crossing. The relation between the drivers’ visual behaviour and the vehicle speed have also been calculated. Results have confirmed that the intervention carried out has increased both visibility and safety of the studied pedestrian crosswalks.Zebra markings and the median refuge island have turned out to be the most glanced elements, respectively seen by 93.75% and 56.25% of the drivers, followed by the “Yield here to pedestrians” vertical sign. The mean distance of first fixation of the crosswalk increased from 21.98 m before the intervention, to 40.69 m after it. The drivers perceived the pedestrian crossings from a longer distance after the intervention, and they continued to glance at the crosswalk while approaching it, enhancing their visual attention.     

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.     

Male Bar Drinkers' Perspective on Female Bar Drinkers

Five focus group discussions were conducted with 34 male bar drinkers to obtain their perception of the character and risks for aggression among women they observe in bars. The majority of the men were European American (61.8%), 29.4% were African American, and 8.8% were from other ethnic groups. Their impressions of women were based on appearance, type and speed of alcohol being consumed, and behavior. Every group suggested that women who dress in a sexually provocative manner or get drunk are more likely to be perceived as “loose” or sexually “easy” by men in general. These findings are consistent with stereotypes of women drinkers as sexually promiscuous and highlight the societal double standards for men and women who drink. The men described a woman calling attention to herself, being alone, out late, or having contact with many men in the bar as vulnerable. These findings are similar to those found during focus group discussions with women bar drinkers (K. A. Parks, B. A. Miller, R. L. Collins, & L. M. Zetes-Zanatta, 1998).     

Perceptual completion in rhesus monkeys (Macaca mulatta) and pigeons (Columba livia)

In a two-dimensional drawing, when the narrow edge of a bar appears to touch the edge of a large rectangle, humans overestimate the length of the bar (Kanizsa, 1979). Kanizsa has suggested that this illusion occurs because humans perceive the bar as continuing behind the rectangle and complete the “occluded” portion of the bar. Rhesus monkeys and pigeons were trained to classify black target bars with a variety of lengths as “long” or “short.” In training, the bar was always located at the same distance from a gray box. After learning this discrimination, the subjects were tested on novel stimuli, in which the bar was located at three new locations. Monkeys showed a consistent response bias for “long” when the bar touched the box, but pigeons did not. Monkeys appear to have completed the “occluded” part like humans, whereas pigeons failed to do so. Because this procedure does not require animals to complete the “occluded” part with any particular form, their failure suggests that pigeons do not even perceive the target bar as continuing behind the “occluding” figure. The failure of pigeons may be due to difficulty in perceiving depth from two-dimensional drawings.     

The relationship between visual persistence and event perception in bistable motion display

Observers viewed two alternating frames, each consisting of three rectangular bars displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three bars moving as a whole (group motion), and at short IFIs the overlapping elements in the two frames appeared stationary, while the third element appeared to move from one end of the display to the other (element motion). The upper temporal limit for perceiving element motion was reduced when bars with blurred edges were used and when either frame duration or bar size was increased. However, when inner and outer elements had different sizes, the element motion percept was dominant up to 230 ms IFI. These findings may be interpreted in terms of spatial tuning of motion mechanisms involved in the perception of bistable apparent motion.