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According to the sequential surface integration process hypothesis, the fine near-ground-surface representation and the homogeneous ground surface play a vital role in the representation of the ground surface. When an occluding box or opaque wall is placed between observers and targets, observers underestimate egocentric distance. However, in our daily life, many obstacles are perforated and cover the ground surface and targets simultaneously (e.g., fences). Humans see and observe through fences. The images of these fences and targets, projected onto observers’ retinas, overlap each other. This study aims to explore the effects of perforated obstacles (i.e., fences) on space perception. The results showed that observers underestimated the egocentric distances when there was a fence on the ground surface relative to the no-fence condition, and the effect of widely spaced thick wood fences was larger than that of narrowly spaced thin iron fences. We further demonstrated that this effect was quite robust when the target size had a visual angle of 1°, 2°, or 4° in three virtual reality experiments. This study may add support for the notion that the sequential surface integration process hypothesis is applicable even if the obstacle is perforated and covers the target.

The texture of an object’s surface influences its perceived spatial extent. For example, Hermann von Helmholtz reported that a square patch with black and white stripes appears elongated perpendicular to the stripes’ orientation. This time-honoured finding stands in contrast with more recent recommendations by interior-design experts who suggest that stripe wall patterns make rooms appear elongated in the direction parallel to the stripes’ orientation. In a series of four experiments, we presented stripe wall patterns and varied the orientation of the stripes (horizontal vs. vertical) and their density (number of stripes per degree of visual angle). Subjects estimated the width and height of stereoscopically presented interior spaces. Stripe patterns with higher densities made rooms appear both wider and higher than did stripe patterns with lower densities or plain walls. In contrast to both the predictions from the Helmholtz-square and the design guidelines, this effect was only weakly modulated by pattern orientation, in the sense that rooms appeared elongated in the direction parallel to the stripes’ orientation. We conclude that object-based texture effects cannot be generalised to interior space perception. For a room’s perceived spatial extent, pattern density is more important than pattern orientation.

We investigated artificial scotomas created when a moving object instantaneously crossed a gap, jumping ahead and continuing its otherwise smooth motion. Gaps of up to 5.1 degrees of visual angle, presented at 18° eccentricity, either closed completely or appeared much shorter than when the same gap was crossed by two-point apparent motion, or crossed more slowly, mimicking occlusion. Prolonged exposure to motion trajectories with a gap in most cases led to further shrinking of the gap. The same gap-shrinking effect has previously been observed in touch. In both sensory modalities, it implicates facilitation among codirectional local motion detectors and motion neurons with receptive fields larger than the gap. Unlike stimuli that simply deprive a receptor surface of input, suggesting it is insentient, our motion pattern skips a section in a manner that suggests a portion of the receptor surface has been excised, and the remaining portions stitched back together. This makes it a potentially useful tool in the experimental study of plasticity in sensory maps.

A number of virtual reality head-mounted displays (HMDs) with integrated eye trackers have recently become commercially available. If their eye tracking latency is low and reliable enough for gaze-contingent rendering, this may open up many interesting opportunities for researchers. We measured eye tracking latencies for the Fove-0, the Varjo VR-1, and the High Tech Computer Corporation (HTC) Vive Pro Eye using simultaneous electrooculography measurements. We determined the time from the occurrence of an eye position change to its availability as a data sample from the eye tracker (delay) and the time from an eye position change to the earliest possible change of the display content (latency). For each test and each device, participants performed 60 saccades between two targets 20° of visual angle apart. The targets were continuously visible in the HMD, and the saccades were instructed by an auditory cue. Data collection and eye tracking calibration were done using the recommended scripts for each device in Unity3D. The Vive Pro Eye was recorded twice, once using the SteamVR SDK and once using the Tobii XR SDK. Our results show clear differences between the HMDs. Delays ranged from 15 ms to 52 ms, and the latencies ranged from 45 ms to 81 ms. The Fove-0 appears to be the fastest device and best suited for gaze-contingent rendering.

Visual discomfort is predicted from a luminance map with a model based on the receptive field mechanism in the human eye. A centre-surround receptive field is described by a Difference of Gaussians. Eight commercially available office luminaires are assessed for visual discomfort in a paired comparison experiment. The correlation between the subjective data and the receptive field model is optimized for three factors: the centre Gaussian width, the surround Gaussian width and the centre-to-surround weighing factor (WF). A centre and surround visual angle of 0.53 and 2.19 min arc, respectively, and a WF of 0.87 result in a coefficient of determination of 0.77. The model is validated independently with magnitude estimation data obtaining a coefficient of determination of 0.82. Where the standard unified glare rating method fails (coefficient of determination of 0.45), the receptive field model ameliorates predictability for visual discomfort. The model based on receptive fields is promising to replace current standard glare metrics, specifically when non-uniform luminaires are to be evaluated.

This study explored whether the color of letters could influence letter discrimination task performances and whether this effect of color could be modulated by processing level (global vs. local) and attention level of color (color-attended vs. color-unattended). We used the Navon letters in red, green, or white as stimuli at a relatively small (Experiment 1) or large visual angle (Experiments 2, 3, and 4). Each experiment included two tasks: color-attended task in which participants were told to respond only to target letters in a designated color; color-unattended task in which color was task-irrelevant. Experiment 1 found that the responses to red stimuli were significantly faster than those to the other color stimuli in the color-attended task. In Experiment 2, the same pattern occurred only at the local level in the color-attended task. Experiments 3 and 4 further controlled the brightness and chroma of stimuli and the results replicated the enhancement effect of red at the local level in the color-attended task and demonstrated an interference effect of red and green in the color-unattended task. These results suggested that red facilitated letter discrimination at the local processing level, reflecting the effect of avoidance motivation evoked by red on cognition and behavior which was consistent with color-in-context model. Moreover, this study found that the effect of color was modulated by attention level of color, and the interference effect of color in the color-unattended task confirmed that the color effect might mainly arise from controlled processes but not automatic processes.

The influence of visual experience on spatial imagery is still not fully understood. Although numerous experiments have been interpreted as showing considerable limitations in the functioning of imagery processes in people who are totally blind, especially those who were born blind or had early onset of blindness, there are studies suggesting that no significant differences in this area can be detected between blindfolded sighted and nonsighted individuals. There are claims that in some cases persons deprived of visual experience perform better than blindfolded sighted individuals (for a review, see Cattaneo et al., 2008). The differences in the results of the experiments reported in this and in other sources seem to follow from the specificity of the imagery task rather than from the imagery operation (mental imagery activity) being tested (see, for example, Cornoldi & Vecchi, 2003). Testing imagery scaling operations may serve as an example. Mental scaling transformation is an operation that involves changing the size of an image found, for example, when sighted persons compare objects (Larsen & Bundesen, 1978). The reaction time increased with the size ratio of objects (see also Bennett & Warren, 2002; Craddock & Lawson, 2009). Some research suggests that adults without prior visual experience do not understand that the size of an object imagined to be moving away must be reduced in accordance with the principle of perspective (Arditi, Holtzman, & Kosslyn, 1988; Vanlierde & Wanet-Defalque, 2005). There is, however, research providing evidence that it is unlikely that these difficulties result from an inability to perform the operation of mental scaling (Kennedy, 1993; Wnuczko & Kennedy, 2014). For clarity of argumentation, it is important to distinguish between linear size (which can, for example, be measured in centimeters), and angular size. The linear size of a particular object is an objective property that does not change over time. The ability to evaluate the linear size can therefore be treated as an indication of conceptual knowledge related to typical sizes of objects encountered in the real world. These sizes may change only in fantasy (for example, in Alice in Wonderland). In visual perception, the angular size--that is, the angle at which the observed object subtends at the eye--changes with the distance between the object and the observer. Angular size is usually measured in degrees of the arc, although in some research it was shown by pointing to the ends of the imagined object. In those cases the pointing span indicated the angular size (see, for example, Arditi et al., 1988). In visual perception, identical objects placed at different distances from the observer create images on the retina that differ in size. It is also possible to determine the changing pointing span for these objects. The size differences are reflected in verbal descriptions: a lake observed from an airplane may be compared to a puddle, and a dog observed from a distance may seem as small as an ant. We get this impression despite being aware that the linear size of these objects does not change (this is the mechanism of size constancy). Visual angular size has its analogy in imagery. Kosslyn (1978) defines angular size as the visual angle of the mind's eye, and provides empirical evidence that sighted persons imagine objects as being a certain distance away from the mind's eye. Sighted persons first experience size constancy in infancy (Slater, Mattock, & Brown, 1990). This constancy, functioning as automatic inference, makes it possible to assess the linear size of an object on the basis of its optical size and the distance. The accuracy of the inference involved in the process of visual perception improves gradually, and at early school age is not yet fully developed (Granrud & Schmechel, 2006). Developmental progress in understanding the relationship between angular and linear size can be observed in drawings made by sighted children. …

Theories of lightness, like theories of perception in general, can be categorized as high-level, low-level, and mid-level. However, I will argue that in practice there are only two categories: one-stage mid-level theories, and two-stage low-high theories. Low-level theories usually include a high-level component and high-level theories include a low-level component, the distinction being mainly one of emphasis. Two-stage theories are the modern incarnation of the persistent sensation/perception dichotomy according to which an early experience of raw sensations, faithful to the proximal stimulus, is followed by a process of cognitive interpretation, typically based on past experience. Like phlogiston or the ether, raw sensations seem like they must exist, but there is no clear evidence for them. Proximal stimulus matches are postperceptual, not read off an early sensory stage. Visual angle matches are achieved by a cognitive process of flattening the visual world. Likewise, brightness (luminance) matches depend on a cognitive process of flattening the illumination. Brightness is not the input to lightness; brightness is slower than lightness. Evidence for an early (< 200 ms) mosaic stage is shaky. As for cognitive influences on perception, the many claims tend to fall apart upon close inspection of the evidence. Much of the evidence for the current revival of the ‘new look’ is probably better explained by (1) a natural desire of (some) subjects to please the experimenter, and (2) the ease of intuiting an experimental hypothesis. High-level theories of lightness are overkill. The visual system does not need to know the amount of illumination, merely which surfaces share the same illumination. This leaves mid-level theories derived from the gestalt school. Here the debate seems to revolve around layer models and framework models. Layer models fit our visual experience of a pattern of illumination projected onto a pattern of reflectance, while framework models provide a better account of illusions and failures of constancy. Evidence for and against these approaches is reviewed.

One major limitation of existing microscopic traffic simulation models is the lack of data about vehicle interactions during the lane-changing process in congested merging areas. The interactions between vehicles during lane changing in the congested weaving sections are quantified. A series of acceleration-deceleration models was developed for the merging vehicle, its putative leader (PL), and its putative follower (PF). After US-101 data were analyzed, the yielding behavior of the merging vehicle's PL for merging cooperation and the lateral separation between vehicles in the weaving section (features largely ignored in previous research) were introduced into the proposed acceleration-deceleration models, and visual angle data were used as the stimuli to reflect the influence of longitudinal and lateral vehicle movements. Car-following behavior was incorporated into the model (e.g., the PF gradually changed its car-following leader from the PL to the merging vehicle, dependent on relative vehicle locatio...

Rear-end collisions account for about one-third of all traffic crashes on a yearly basis. It has been apparent for some time that the key to perceiving a slower vehicle ahead of us as an imminent hazard, i.e., one requiring immediate action, is a sufficient rate of change of the visual angle of the lead vehicle. This is known as the “looming threshold”, among other things. A number of laboratory researchers have reported values of the looming threshold to be in the range of 0.003 radian/sec. Forensic practitioners routinely use elevated values of the looming threshold, e.g., 0.005-0.008, to account for the complexity of real-world driving tasks. However, only one source has used data from actual vehicle accidents to arrive at a looming threshold – and that value, 0.0275 rad/sec, is an order of magnitude larger than that derived from laboratory studies. In this study, we examine a much broader range of real-world accident data to obtain an estimate of the reasonable upper end of the looming threshold. The results show a range of 0.0397 to 0.0117 rad/sec, for presumed perception-reaction times (PRTs) of 0.75 and 2.0 seconds, respectively. We discuss the implications for forensic human factors analysis of rear-end crashes.

Recording eye motions in surgical environments is challenging. This study describes the authors’ experiences with performing eye-tracking for improving surgery training, both in the laboratory and in the operating room (OR). Three different eye-trackers were used, each with different capabilities and requirements. For monitoring eye gaze shifts over the room scene in a simulated OR, a head-mounted system was used. The number of surgeons’ eye glances on the monitor displaying patient vital signs was successfully captured by this system. The resolution of the head-mounted eye-tracker was not sufficient to obtain the gaze coordinates in detail on the surgical display monitor. The authors then selected a high-resolution eye-tracker built in to a 17-inch computer monitor that is capable of recording gaze differences with resolution of 1° of visual angle. This system enables one to investigate surgeons’ eye–hand coordination on the surgical monitor in the laboratory environment. However, the limited effective tracking distance restricts the use of this system in the dynamic environment in the real OR. Another eye-tracker system was found with equally high level of resolution but with more flexibility on the tracking distance, as the eye-tracker camera was detached from the monitor. With this system, the surgeon’s gaze during 11 laparoscopic procedures in the OR was recorded successfully. There were many logistical challenges with unobtrusively integrating the eye-tracking equipment into the regular OR workflow and data processing issues in the form of image compatibility and data validation. The experiences and solutions to these challenges are discussed.

The ACT-R cognitive architecture only deals with a single display interface, which needs to be expanded and improved so as to describe the real environment that needs more than a single display. Therefore, this paper proposes a method to describe human performance in a multi-display environment by developing the head module because the behavior of searching the object beyond the preferred visual angle of ± 15° could not be modeled with the visual module in ACT-R. The result shows that ACT-R model with the head module should be necessary when performing tasks in a multi-display environment. In addition, a separate ACT-R model was also developed when a different head movement pattern was involved such as a peripheral vision.

Car-following theory is of significance in microscopic traffic flow theory. The key assumption of current car-following theory is that vehicles travel in the middle of a single lane. However, this assumption is unrealistic and cannot describe driving behavior in a complex traffic environment. When the lateral separation characteristics between the follower and the leader are taken into account, the time-to-collision equation is modified with visual angle information and introduced into the General Motors model. A non-lane-based model of car following was developed; it uses time to collision and is based on the stimulus–response framework. The proposed model was investigated with simulations conducted under several driving scenarios. The model could describe local and asymptotic stabilities, lateral movement, and the effect of neighboring vehicles. Results implied that this staggered car-following model incorporating lateral separation greatly enhanced the realism of car-following behavior.

With the advent of increasing advances in visual display technology, MIL-STD-1472F, Design Criteria Standard for Human Engineering, was designated for an upgrade to capture how new technologies may have impacted its display standards. Large-Screen Displays (LSDs) were subject to review and, henceforth, the following study emerged. Six variables were chosen for inclusion in the present experiment: display type (monitor v. projector), ambient lighting (light v. dark), viewing distance (8 ft, 16 ft, 32 ft), viewing offset (0°, 25°), object type (letter, number, symbol), and object size (in terms of visual angle, i.e., 6 min, 8 min, 10 min). The variables chosen were expected to impact operator performance in terms of response time and accuracy based on stimulus legibility. The results did not support any reductions in current minimum text size, but new recommendations for preferred text size, symbol size, viewing distance, and viewing offset were established.

Two theories regarding the role of a texture gradient in the perception of the relative size of objects are compared. Relational theory states that relative size is directly specified by the projective ratio of the numbers of texture elements spanned by objects. Distance calibration theory assumes that relative size is a product of visual angle and distance, once the distance is specified by the texture. Experiment 1 involved three variables: background (no texture, texture gradient patterns), the ratio of heights of the comparison stimulus to a standard (three levels), and angular vertical separation of the standard stimulus below the horizon (two levels). The effect of the retinal length of the comparison stimulus was examined in experiment 2. In both experiments, participants judged both the apparent size and distance of a comparison stimulus relative to a standard stimulus. Results suggest that the cues selected by observers to judge relative size were to some degree different from those used to judge relative distance. Relative size was strongly affected by a texture gradient and the retinal length of a comparison stimulus whereas relative distance perception was affected by relative height. When dominant cues that specify size are different from those which specify distance, relational theory might provide a better account of relative size perception than distance calibration theory.

Visual symptoms are the most common complaints associated with prolonged computer use. We investigated effects of accommodation and vergence demands specified by the computer monitor viewing distance on the development of visual symptoms and visual function changes. Ten 18–35 year-old subjects performed a two-hour, visually demanding, text-viewing task at three viewing distances over three days. The visual angle of the character size was held constant. We measured changes in several static and dynamic properties of accommodation and binocular vision before and for 90 minutes after the viewing task. The 100 cm viewing distance induced less lead effect for accommodation to a distant target and less lag retention for accommodation to a near target. On the other hand, the viewing distance of 33 cm introduced less eye irritation or tearing symptoms and a higher overall dynamic convergence response compared to longer viewing distances. There were weak associations between changes in binocular functions and visual symptoms. While the symptoms were influenced by the viewing distance, they cannot be fully explained by the changes in the visual functions measured here.

Terrestrial-passage theory proposes that the ‘moon’ and ‘sky’ illusions occur because observers learn to expect an elevation-dependent transformation of visual angle. The transformation accompanies daily movement through ordinary environments of fixed-altitude objects. Celestial objects display the same visual angle at all elevations, and hence are necessarily non-conforming with the ordinary transformation. On hypothesis, observers should target angular sizes to appear greater at elevation than at horizon. However, in a sample of forty-eight observers there was no significant difference between the perceived angular size of a constellation of stars at horizon and that predicted for a specific elevation. Occurrence of the illusion was not restricted to those observers who expected angular expansion. These findings fail to support the terrestrial-passage theory of the illusion.

Two experiments investigated the effect of perceptual depth as a cue to highlight unexpected or changing stimuli. We used a new display technology known as a Multi-Layered Display (MLD). The results of the first experiment showed a significant effect of depth on the detection of an unexpected event when it is located in the front layer regardless of the depth plane in which the distracters were located. Detection was three times higher when the unexpected event was located less than 20 degrees of visual angle from the focus of attention. The second experiment indicated that the depth cue, although slower than the colour transient, presented the highest accuracy. The results suggested that depth may not always be the best transient to highlight changes, however, in cases where colour and flashing are no longer appropriate, the use of depth is a viable alternative.

Visual search in an important aspect of many tasks, but it not well understood how layout design affects visual search. This research uses reaction time data, eye movement data, and computational cognitive modeling to investigate the effect of local density on the visual search of structured layouts of words. Layouts were all-sparse, all-dense, or mixed. Participants found targets in sparse groups faster, and searched sparse groups before dense groups. Participants made slightly more fixations per word in sparse groups, but these were much shorter fixations. The modeling suggests that participants may have attempted to process words within a consistent visual angle regardless of density, but that they were more likely to miss the target if the target was in a dense group. Furthermore, it was found that the participants tended to search sparse groups before dense groups. When combining densities in a layout, it may be beneficial to place important information in sparse groups.

The current study was designed to examine whether increasing foveal task complexity would cause the functional field to shrink as a result of a visual funneling effect. Using 8 male participants, the study examined whether the effects of foveal task complexity on peripheral performance was most pronounced at the far periphery. The response time to an addition task using foveal vision tended to increase with the increase of the visual angle. The percentage correct, however, did not differ among 3 levels of task complexity or among 4 levels of visual angle. The miss rate in the peripheral vision task tended to increase with the increase in not only the complexity of the foveal task but also the visual angle. This is indicative of visual funneling. However, greater funneling was not necessarily observed for response time. In this study, response time was not a sensitive measure of visual funneling. Actual or potential applications of this research include safe driving and other vigilance tasks.

An important task during driving is the maintenance of headway during car following. The visual information available to a driver for successful car following was examined. A model of car following that used the visual angle and change in visual angle of a lead vehicle was developed. The study examined whether information from the surrounding scene (e.g., the roadway and buildings) influenced car-following performance. Licensed drivers were presented with a car-following task in a driving simulator. The simulator display consisted of a roadway scene with a lead vehicle that varied speed according to a sine wave. To evaluate the role of scene information, car-following performance was examined when the surrounding scene was present or absent. Two frequencies and three amplitudes of speed variation were also examined. The results indicated that control gain was greater when the scene was absent, with near unity gain when the scene was present. These findings indicated more accurate control during car following when the surrounding scene information was present. These results suggest that drivers also use other sources of information (e.g., absolute distance information from height in the visual field relative to the horizon and edge rate information specifying observer speed) to maintain headway. The implications of this research to nighttime accident rates and intelligent highway systems are discussed.

Cognitive tunneling occurs when the pilot's attention becomes locked on non-conformal, superimposed head-up display (HUD) symbology, while neglecting to scan the out-the-window scene, as a result of locating the HUD symbology near (in visual angle) the outside scene information (Foyle, McCann, Sanford & Schwirzke, 1993). Previous studies have shown that cognitive tunneling could be eliminated by placing the HUD symbology at least 8 deg from the out-the-window path being tracked. Limitations to previous research have included experimental designs that tested participants in multiple HUD information locations without fostering an efficient eyescan strategy for any one HUD location. Experiment 1 dedicates a participant to a single HUD location with blocked presentation. The results indicate that cognitive tunneling is not only eliminated by placing HUD symbology greater than 8 deg, but path tracking performance improves with symbology placed in an upper location on the HUD. Experiment 2 shows that the resulting performance decrement when information is overlaying the path (0 deg) may be associated with symbology compellingness, regardless of symbology relevance to the task.

This paper describes an investigation into the effect of reduced field of view and target size in transparent stereo augmented reality systems. Six subjects were asked to identify the maximum disparity limit of correct 3D perception for a random dot target of different sizes, viewed through a transparent scene with a varying field of view (FOV). The results showed that the maximum disparity limit increased linearly up to 25 degrees FOV after which it showed no significant increase for increasing FOV. There was no significant difference in the maximum disparity values obtained using a 4, 8, or 10 degree target. The maximum disparity limit of 5.9 ±1 (mean ± SD) degrees visual angle was used in an equation to predict the range in which correct depth perception occurs for transparent AR in a binocular surgical microscope. We suggest that the optimum image position to give the greatest range for correct 3D depth perception is 25cm when viewing transparent targets behind a transparent real scene.

Joint visual attention is defined as looking where someone else is looking. The purpose of this study was to examine the conditions for establishing joint visual attention in autistic children who have no functional speech. An experimenter, sitting facing the child, looked at one of six pictures near the child. Analysis showed that joint visual attention to stimuli behind the child and therefore outside of the visual field occurred at a higher rate when the visual angle between the stimuli was about 60°. Spontaneous pointing at the target object increased with training which included feedback and physical guidance. These results are discussed in terms of the effects of environmental variables and perceptual mechanisms on the emergence of joint visual attention in autistic children. The possibility of using an adult's social cues and expanding the child's visual field as a remedial procedure is also addressed.

Inhibition of return (IOR) refers to the finding that response times (RTs) are typically slower for targets at previously attended (cued) locations than for targets at novel (uncued) locations. Although previous research has indicated that IOR may spread beyond a cued location, the present study is the first to examine the spatial distribution of IOR with high spatial resolution over a large portion of the central visual field. This was done by using a typical IOR procedure (cue, delay, target) with 4 cue locations and 441 target locations (each separated by 1° of visual angle). The results indicate that IOR spreads beyond the cued location to affect the cued hemifield. However, the cues also produced a gradient of RTs throughout the visual field, with inhibition in the cued hemifield gradually giving way to facilitation in the hemifield opposite the cue.

This paper reports the operation of robust attentional bias to the top and right during perception of small, single geometric forms. Same/different judgements of successively presented standard and comparison forms are faster when local differences are located at top and right rather than in other regions of the forms. The bias persists when form size is reduced to approximately one degree of visual angle, and it is unaffected by saccadic eye movements and by instructions to attend to other reliably differentiating regions of the forms. Results lend support in various degrees to two of the possible explanations of the bias: (1) a static, skewed distribution of attentional resources around eye fixation; and (2) biased, covert scanning that commences invariably at the top and right of stim ulus forms. Origins of the bias in terms of possible left-hemispheric capacity for constructing representations of visual stimuli from parts, as well as in terms of reading experience and prevailing optic flow during locomotion through space are considered. Recent investigations of conditions under which the bias can be maintained or reduced are mentioned.

The visual angle subtended by the frame seems to be an important determinant of the contribution of orientation contrast and illusion of self-tilt (ie vection) to the rod-and-frame effect. Indeed, the visuovestibular factor (which produces vection) seems to be predominant in large displays and the contrast effect in small displays. To determine how these two phenomena are combined to account for the rod-and-frame effect, independent estimates of the magnitude of each component in relation to the angular size subtended by the display were examined. Thirty-five observers were exposed to three sets of experimental situations: body-adjustment test (illusion of self-tilt only), the tilt illusion (contrast only) and the rod-and-frame test, each display subtending 7, 12, 28, and 45 deg of visual angle. Results showed that errors recorded in the three situations increased linearly with the angular size. Whatever the size of the frame, both mechanisms, contrast effect (tilt illusion) and illusory effect on self-orientation (body-adjustment test), are always present. However, rod-and-frame errors became greater at a faster rate than the other two effects as the size of the stimuli became larger. Neither one nor the other independent phenomen, nor the combined effect could fully account for the rod-and-frame effect whatever the angular size of the apparatus.

A brief advance of the presentation of distant nontargets has previously been shown to secure them an analysis, suggesting that even stimuli beyond the putative ‘spotlight’ of attention are analysed. In the present experiment nontargets were presented near to fixation or peripherally (at 0.6 or 1.9 deg of visual angle) for a duration of 17, 33, or 67 ms before being masked. After a subsequent period (SOA) of 0, 20, 40, 60, or 80 ms the target was presented at fixation. The results from the shortest nontarget duration show a time lag in the development of the effect of far nontargets on response to the target. At durations of 33 and 67 ms the identity of far nontargets has been established before masking takes place, since their effect is observable at zero SOA. However, while this effect remains relatively constant over SOAs of 20 to 80 ms it increases wth SOA in the near condition, suggesting that, although both near and far nontargets have been identified, it is only the near nontargets which are subject to further processing during the interval between nontarget and target presentations. The results favour a model of attention in which stimuli are passively selected and subject to additional processing on the basis of their spatial location rather than that the location or representation of distractor items are actively suppressed.

The helmet-mounted display (HMD) affords continuous availability of critical flight information independent of head orientation. With appropriate information presented on a HMD, aircraft control can be maintained regardless of where the pilot is looking. This research addresses the development of an empirically based HMD symbol set. Three attitude formats and three altitude formats were evaluated within a composite fixed-wing HMD symbology layout. The attitude formats varied in basic form and symbol compression ratio. Symbol compression ratio is the ratio of the angle represented by the symbol to the symbol's subtended visual angle. High symbol compression results in symbols which represent large angles, and therefore have slow rate-of-motion relative to their uncompressed counterparts. The altitude symbologies were formed of both vertical scale and dial formats and included vertical velocity indicators. Subjects performed a flight-path maintenance task within sessions of differing “real” horizon presence and orientation. The formats were evaluated under a task which was designed to require high-accuracy flight-path maintenance. This type of task is traditionally thought to require less symbol compression. The results showed that performance was influenced by the manipulation of the attitude symbology formats. The results also suggest that symbol compression may be advantageous.

The approach of an object can be monitored from its optic flow. More specifically, it has been postulated that time-to-collision at constant velocity is perceived by relating visual angle θ to its rate of change θ̇, time-to-collision being θ/θ̇. This hypothesis is reappraised, and an alternative based on the parameters θ̇ and angular acceleration θ̈ is proposed. The expression 2 θ̇/θ̈ also specifies time-to-collision, with the benefits that it removes reliance on θ and permits time-to-collision to be determined from even momentary perception of an approaching point. This is supported by tests in which subjects responded to computer simulations of approaching objects. A further benefit is that if the object is accelerating rather than at constant velocity, time-to-collision is adjusted by 2 θ̇/θ̈, but not by θ/θ̇. As time-to-collision increases, however, its cognitive derivation should transfer from optic flow to separate perceptions of distance and speed. It is proposed that when drivers of road vehicles are in potential collision with pedestrians their perception of distance is based primarily on familiar size, resulting in overestimation of size and therefore of time-to-collision with child pedestrians. This is supported by further computer simulations and is corroborated by predicting the effect of that overestimation on certain types of accidents, then testing from national accident statistics. These analyses indicate that drivers' misperception of time-to-collision has a dramatic effect on the accident rate of child pedestrians. It is proposed that this could be greatly reduced by the provision of remedial measures.

When we read, our eyes do not move smoothly across the page of text as our phenomenological im pressions imply. Rather, we make a series of eye movements (referred to as saccades) separated by periods of time when the eyes are relatively still (fixations). Eye movements are nec essary during reading because of acuity limitations in the visual sys tem. A line of text extending around the point of fixation can be divided into three regions: foveal, parafoveal, and peripheral. The foveal region is the center of vision (extending 1? of visual angle to the left and right of fixation), where acu ity is sharpest, enabling us to resolve the letters in the text easily. In the parafoveal region (extending out to 5? of visual angle on either side of fixation) and the peripheral region (everything on the line beyond the parafoveal region), acuity drops off markedly so that our ability to iden tify letters is not very good even in the near parafovea. The purpose of eye movements in reading is there fore to place the foveal region on that part of the text we wish to pro cess next. The basic facts about eye move ments during reading have been known for some time. The typical saccade is about eight to nine letter spaces; this value is not affected by the size of the print as long as it is not too small or too large. The ap propriate metric to use when dis cussing eye movements during read ing is therefore letter spaces, and not visual angle; generally, three to four letter spaces is equivalent to 1? of visual angle. Because of the high ve locity of the saccade, no useful in formation is acquired while the eyes are moving; readers acquire infor mation from the text during fixa tions. The average fixation duration is about a quarter of a second (250 ms). The other primary characteristic of eye movements during reading is that about 10% to 15% of the time, we move our eyes back in the text (regressions) to look at material that we have already read. It is also important to note that as text difficulty increases, fixation du ration increases, saccade length de creases, and regression frequency increases. More important, the val ues just presented are averages, and there is considerable variability in the measures, both between and within readers. Thus, although the average fixation duration for a given reader might be 250 ms, for others it could be on the order of 200, 235, 280, or 300 ms. The average sac cade length and regression fre quency also vary across readers. As far as within-subject variability is concerned, although a reader's av erage fixation duration might be 250 ms, the range could be from under 100 ms to over 500 ms within a pas sage of text. Likewise, although the average saccade length for a given reader might be 8 letter spaces, the range could be from 1 letter to over 15 (though such long saccades typi cally follow regressions). A great deal of recent research has docu mented that the variability in these measures is related to the ease or dif ficulty associated with processing the text. Since the mid-1970s, there has been a resurgence of interest in us ing eye movement data to study the reading process.1 Researchers have typically been interested in eye movements during reading for two reasons: (1) to describe the charac teristics of the eye movements per se and (2) to use eye movement data to infer something about perceptual and cognitive processes during read ing. Because most of the work in my laboratory has focused on the latter issue, the major focus of this article is on processing during reading.

A series of studies was performed to explore the hypothesis that employees in windowless offices compensate for the lack of windows. In Experiment 1, students rated the degree to which they perceived various office features to be substitutes for windows. Analyses revealed four general categories of potential window substitutes: other apertures (e.g., skylights), paintings/art, living things (e.g., plants), and panels (e.g., light panels). Experiment 2 supported the external validity of the data in Experiment 1 in that full-time office workers produced virtually identical ratings of window substitutability. Experiment 3 was a field study of 173 offices. Measurements were made of the number and size of windows, number and size of all potential window substitutes, and size of wall space available for pictures. Size was measured in degrees of visual angle from the office workers' chairs. No evidence was obtained to indicate that any of the features measured were more prevalent or larger in offices without windows. Furthermore, power analyses indicated that the study had sufficient power to find such effects. Experiment 4 was designed to investigate other potential reasons for the use of the items that were examined in Experiment 3. Several reasons, such as space personalization, were found to be perceived by office occupants as more important than the desire to compensate for lack of windows.

Some statistics of rear-end crashes are given and their characteristics are described. The perceptual factors related to discerning closure, headway change and visual angle change and rate of change of visual angle, are described by prior research and analysis, and threshold values for them are given.

The classical thumb rule of visual angle was reexamined. Hence, the visual angle was measured as a function of a thumb's width and the distance between eye and thumb. The measurement of a thumb's width when held at arm's length was taken on 67 second-year students of psychology. The visual angle was about 2° as R. P. O'Shea confirmed in 1991. Also, we confirmed a linear relationship between the size of a thumb's width at arm's length and the visual angle.

Summary.-We report a phenomenon that seems to have potential to elucidate a role of eye movement in motion perception. When tracking a target controlled by a triangular wave, the viewer perceives movement of the target like a ball bouncing in between two walls. We measured eye movement with electrooculograms (EOGs) when the subject was tracking a target controlled by a triangular wave. Eye movement after passing the turning point and rapidly returning to the target with saccadic movement and then smoothly tracking the target was recorded for all 4 adults. It was considered that extraretinal information on eye position during saccade may mainly contribute to this illusion. Little attention has been paid to the role of eye movement in motion perception (Koga, 1991). We noticed recently a phenomenon that seems to have potential to elucidate the role eye movement plays in motion perception. In most studies of eye movement while tracking a moving target, the movement of a target has been controlled by a sine wave, not a triangular wave. When tracking a target controlled by a triangular wave, movement of the target is perceived as a ball bouncing between two walls. Although the target moves actually with uniform velocity from the left to the right side and in the reverse direction repeatedly, the target is perceived to move rapidly near the turning points and slowly in the central part of the course of the moving target. While the head was fixed, we measured each of four subjects' eye movements with electrooculograms (EOGs) during tracking a target controlled by a personal computer (NEC PC-9821) and presented on a CRT (NEC PC-KM151). Electrodes were placed at the lateral canthi and the supra- and suborbital ridges of one eye to record horizontal and vertical eye movements. EOGs were measured by a DC amplifier (NEC-Sanei 1169) and stored in a data recorder (TEAC RD-135T). The target was a yellow diamond at approximately .5O of visual angle and moving horizontally from the left to the right side and in the reverse direction repeatedly at approximately 40° of visual angle and with uniform velocity (approximately 22O/sec.). Its movement was equivalent to that while controlled by triangular wave. EOGs were A-D converted (sampling interval = 10 msec.) by a personal computer (NEC PC-9821).

The legibility of displayed letters depends upon their size, or more accurately, their subtended visual angle at any viewing distance. Current design standards recommend letter heights in the range from 0.003 to 0.007 rad (10 to 24 mill of arc) for good viewing conditions, with 0.0015 rad (5 min) considered a lower limit based on normal visual acuity. A field study involving some 2000 measures for over 300 printed displays found a mean letter height of 0.0019 rad (7 min) at the limit of legibility, with over 90% legibility at 0.003 rad and virtually 100% at 0.007 radians.

Television viewing distances, visual angles, and viewing angles were calculated for 217 children and 119 adults from 78 families. The data were obtained from time-lapse videotapes automatically recorded in the families' homes over 10 day periods. Viewing distance increases with age and visual angle decreases with age. Viewers aged 17 years and younger viewed at an average distance of 225.3 cm, at an average visual angle of 12.3 deg., and at an average viewing angle of 23.7 deg. Adult viewers watched TV at an average distance of 336.8 cm, an average visual angle of 6.6 deg., and at an average viewing angle of 23.3 deg. The best predictors of viewing location were percent of time the viewer watched TV from furniture, room area, and screen width.

The relation of the increase in distance to narrowing of the visual angle was investigated with 20 subjects in high and low anxiety states. Stimuli were introduced from the periphery, and readings were taken at the limits of sharp perception of figures. The investigation partially confirmed that increase in distance resulted in narrowing of the visual field for the group low in anxiety. However, the visual angles were greater for the group high in anxiety.

If a few parallel horizontal rows of dots are set diagonally, like steps, across the visual field, the inner rows appear not to be horizontal but sloping up to one side; the effect holds as long as the vertical distances between the rows do not exceed a given visual angle. This illusion, described by Vicario in 1978, was never explained. An experiment is reported in which the illusion was still visible at row separations well in excess of the spatial limits originally considered, provided the stimulus elements were enlarged. The maximum illusion was obtained for length ratios (interrow distance to size of dots) identical to those which have been shown to produce the largest effects in a number of illusions of area and length. This suggests that Vicario's illusion is similar to other illusions of extent, and that it can be explained by a neural extent-coding model.

Contrast sensitivity functions of thirty-one young adults were determined using two recently developed chart systems. Resulting data were compared to data previously obtained with video display systems. Results indicate that the chart system can provide contrast sensitivity data similar to that obtained with microprocessor systems. Analysis of data from an additional license plate reading task produced significant Pearson product moment correlations between contrast sensitivities at 18 cycles per degree of visual angle and mean reading distance (r=.53, p

Summary.-Discrimination performance of two classes of patterns (histoforms and polygons) was determined as a function of the size of the forms at three levels of complexity (4, 6, and 8 columns or angles). The visual angle subtense of the stimulus forms was varied over a range of sizes from near threshold (1.88 min.) to well above it (16.56 min.). The important finding is that below a visual angle of 8 min. discrimination of the form is essentially identical in terms of both accuracy and speed of identification. At angular sizes above 8 rnin. consistent differences in the rate of processing the two classes of forms emerged. The results were interpreted as indicating that identification performance depends on "emergent features" of the forms as they increase in size. The concept of "emergence" has often been used to account for various perceptual phenomena. Emergence is said to occur when changes in perceptual performance appear as constituent parts are added together to form wholes. The process may be due to the configuration of the whole but it is not easily assigned to its component parts. The present study was undertaken to determine if accuracy and speed of identification of complex visual forms depend upon some "emergent properties," i.e., perception of the forms as wholes. In order to provide changes in forms that would permit the emergence of different properties, histoforms and polygons were increased from sizes so small that identification performance was no better than chance (threshold) to relatively large sizes. One of the prime considerations of the study was how small the forms should be in order to assure that they were near or below threshold. The literature concerning visual acuity functions provides little information relating to the visual angle subtense required of complex forms for accurate identification. Most of the research conducted on these acuity functions has employed Landolt sings and parallel bar gratings. Previous studies of visual acuity indicate that the critical detail of a form which differentiates it from other forms must have a visual subtense of at least 1 min. under ideal conditions. This is a general statement, however, and its application is made difficult by the lack of technique for quantifying the critical detail of a form which can be used to differentiate it from a class of other forms. Clinical measures of visual acuity, e.g., the Snellen acuity chart, indicate that with normal vision an individual is just able to recognize letters of the alphabet which subtend an over-all visual angle of 5 min. However, letters of the alphabet are over-learned, and for the most part it is not difficult to dis'This research was su ported in part by the Army Research Office under Army THEMIS Contract DA H~19-&-~-0009, "Studies of Performance Assessment and Enhancement." The authors wish to thank G. Abel, J. D. Repko, and K. E. Rothrock for technical assistance.

Eighteen participants each proofread 12 three-page articles. Each article was printed at six sizes (or scales) and in two different character sets. Reading distance was constant (52 cm). The lines of characters on the pages subtended 6.7, 10.6, 16.0, 24.3, 36.4, and 53.4 deg at a participant's eye. Proofreading speed and accuracy were reduced at the extreme visual angles. Within a range of at least 16 to 36 deg, proofreading speed and accuracy were unaffected. The significance of these findings is that people's reading efficiency is invariant over a large range of normal viewing. Most printed text and text shown on computer terminal screens form visual angles within this range. Therefore, differences in visual angle probably do not account for the slower reading speed found when people read from CRT displays than from paper (Gould and Grischkowsky, 1984).

The accuracy with which human observers can determine the spatial location of a shape boundary was measured by vernier alignment. The vernier targets were presented as random-dot stereograms, with varying amounts of camouflage in the monocular image. Camouflage decreased vernier acuity, but when the camouflage was broken by stereoscopic disparity, acuity was improved. In the limiting case when the shape boundaries were defined by disparity information alone, vernier thresholds (75% correct, binary forced-choice) were in the region of 40 s visual angle. This is poor acuity in comparison to vernier thresholds with monocular contour, but if the limited resolution acuity for stereopsis is taken into account, cyclopean and monocular positional acuities can be considered quite similar in relation to their respective resolution limits.

In this study, 24 subjects with 20/20 correctible vision participated in a 3 − 3 − 2 visual estimation experiment. The stimulus was a dot or “ball” bouncing clockwise around a 12° visual angle square according to laws of ideal physics. At the end of the first collision, the ball disappeared, and subjects were then required to estimate where on each wall the ball would subsequently impact. The ball was presented at speeds of 3.5°, 6.7°, 10.0° visual angle/sec. Results indicated that there was a linear relationship in the times required to estimate the positions of the ball after 1, 2, and 3 bounces; however, the positional accuracy deteriorated rapidly after 3 bounces and about 8 seconds. Results also suggested that the speed at which the moving stimulus is observed also influences the speed at which one later imagines the moving object. We believe there is a “default” speed at which subjects optimally prefer to imagine moving objects, and that speed is around 5° to 8° of visual angle/sec. We suggest that simple motion presented on CRT displays might be accurately projected ahead by the subject when it is presented at this default speed.

The accuracy and speed of proofreading was unaffected by a wide range of visual angle (at least 16–36 deg). Text on most computer displays and on 8–1/2 × 11 in. paper subtend visual angles within this range—even with typical variations in reading distance.

Existing evidence indicates that there are differences between children and adults in size constancy when observation distances are large. Findings are reported which suggest that this phenomenon is based on a difference in the accessing of proximal stimulus information, which, in the case of size, refers to visual angle subtended. Age differences were found when a traditional size constancy task was used, but these differences disappeared when all the comparison objects subtended the same visual angle. Since this finding demonstrates that young children can make accurate size matches, it is suggested that the underconstancy previously reported is not necessarily the result of childrens' inability to use fully certain cues to distance. Rather, the findings suggest that children access proximal stimulus information more spontaneously than do adults.

Television viewing distances, visual angles, and viewing angles were calculated for 217 children and 149 adults from 78 families. The data were obtained from time-lapse videotapes automatically recorded in the families' homes over 10-day periods. Viewing distance increases with age, and visual angle decreases with age. Viewers aged 17 years and younger viewed at an average distance of 225.3 em, at an average visual angle of 12.3 deg, and at an average viewing angle of 23.7 deg. Adult viewers watched TV at an average distance of 336.8 cm, an average visual angle of 6.6 deg, and at an average viewing angle of 23.3 deg. The best predictors of viewing location were (1) percentage of time the viewer watched TV from furniture, (2) room area, and (3) screen width.

The interpolation of stereoscopic depth given only sparse disparity information was investigated. The basic stimulus was a rectangle with zero disparity at one edge, and 20 or 30 min visual angle disparity at the other. The depth assigned to the ambiguous intervening locations was measured by means of a small briefly-flashed binocular comparison spot. For a stimulus consisting of a uniform rectangle presented on a background of random dots with zero disparity, interpolated depth was greater for a high mean contrast between rectangle and background than for a low mean contrast. Relative to a linear interpolation between the edges, a larger difference in edge disparity resulted in poorer depth interpolation. Depth interpolation based on rivalrous information was examined by filling the stimulus rectangle with narrow-band filtered noise which was uncorrelated between the two eyes. Four different passbands which were matched in apparent contrast were investigated. The results demonstrate that the rivalrous low-spatial-frequency content was resistant to interpolation; rivalrous high spatial frequencies did not interfere with depth interpolation. High-spatial-frequency stimuli yielded a percept similar to the uniform-field condition, whereas low-spatial-frequency stimuli lay in a depth plane near or even behind the background. In the latter case a transparent plane was perceived which was linearly interpolated between the two edges, and which floated above the rivalrous noise.

A paradigm has been proposed to test the hypothesis that binocular fusion results in simple summation, S, of monocular photopic luminances: S = Δ LBM( L)/Δ LB(2 L) = 1, where Δ LBM and Δ LB are threshold luminances for a monocular and a binocular increment, appearing on a fused background of luminance L or 2 L, respectively. This prediction was tested psychophysically, with background size as parameter. Thresholds were measured for a brief (20 ms) foveal flash centered on a luminous disk encircled by a massive black annulus serving as a fusion lock. The flash was presented binocularly, or monocularly, at 30 and 60 cd m−2 background luminances. The diameter of the disk was varied from 3 min to 40 min visual angle. The size of the flash was constant (6 min diameter), except for the smallest disk (3 min diameter). All thresholds varied as a function of background size (the known ‘sensitization effect’). The summation index S did not vary with background size. A mean value S = 0.9 was found; this is consistent with the notion that summation of the order of 90% occurs during binocular fusion. We surmise that even a weak monocular test flash makes fusion less than perfect.

The effects of background luminance, contrast, and background wavelength on the perceived size of small line figures were studied at mesopic levels of light adaptation. Perceived size diminished at low levels of background luminance. The effect disappeared at high levels of luminance. Perceived size of luminous circles increased as a logarithmic function of background luminance when the background intensity did not exceed 25 td(1). The strength of the size effect decreased as a function of circle diameter from 0·125 to 2 deg of visual angle(2). Perceived size of small luminous circles, subtending less than 0·5 deg, also increased as a function of contrast at low values of contrast but at very high values of contrast there was a decrease in perceived size. Background luminance had the same effect on the perceived size of circles as on the perceived size of spatial cycles in gratings. Control experiments led to the conclusion that dark adaptation is the primary source of the size effects. The main evidence for this conclusion was obtained from a demonstration that the same background luminance produced either an increase or a decrease in perceived size, depending on the adaptational state of the eye. It was also found that a shift from cone vision to rod vision contributes to the effects, for a stimulus looked smaller on a short-wavelength background than on a long-wavelength background. The size effects can be predicted from the changes of receptive-field properties of single neurones under corresponding conditions of stimulation, if it is assumed that the perception of size is mediated by size-specific channels formed of single neurones. Stimulation that leads to an activation of small receptive fields appears to indicate to the brain the presence of small retinal images. If small receptive fields are experimentally made responsive to larger retinal images, an underestimation of size results.